OPEN ACCESS Asian Journal of Plant Sciences

ISSN 1682-3974DOI: 10.3923/ajps.2017.109.131

Review ArticleImpact of Crop Production Inputs on Soil Health: A Review

Yayeh Bitew and Melkamu Alemayehu

Department of Plant Science, College of Agriculture and Environmental Sciences, Bahir Dar University, P.O. Box 5501, Bahir Dar, Ethiopia

AbstractExternal crop production inputs such as mineral fertilizers, organic amendments, microbial inoculants and pesticides are applied with theultimate goal of maximizing productivity and economic returns, while side effects on soil health are often neglected. This studysummarized the current understanding of how crop production inputs affect soil health (soil physical, chemical and biological properties).Mineral fertilizers have limited direct (such as soil physical property) effects but their application can enhance soil biological activity viaincreases in system productivity, crop residue return and soil organic matter. Another important indirect effect such as N fertilization issoil acidification, with considerable negative effects on soil health such as on amount, activity and diversity of organisms. Organicamendments such as manure, compost, biosolids and humic substances provide a direct source of C for soil organisms as well as anindirect C source via increased plant growth and plant residue returns. Non-target effects of microbial inoculants appear to be small andtransient. Among the pesticides, herbicides have few significant effects on soil health, whereas negative effects of insecticides andfungicides are more common and their application warrants strict regulation. The sound management of crop production inputs mustattempt to ensure both an enhanced and safeguarded environment; therefore, an Integrated Pest and Nutrient Management (IPNM)strategy that combines the use of chemical, organic crop production inputs together with cultural practices must be developed andevaluated as suggested by Integrated Pest and Nutrient Management Protocols (IPNMP).

Key words: Soil health, input, pest, fertilizer, pesticide, crop, production, biosolids

Received: January 09, 2017 Accepted: May 05, 2017 Published: June 15, 2017

Citation: Yayeh Bitew and Melkamu Alemayehu, 2017. Impact of crop production inputs on soil health-a review. Asian J. Plant Sci., 16: 109-131.

Corresponding Author: Yayeh Bitew, Department of Plant Science, College of Agriculture and Environmental Sciences, Bahir Dar University, P.O. Box 5501,Bahir Dar, Ethiopia Tel: +251922608234

Copyright: © 2017 Yayeh Bitew and Melkamu Alemayehu. This is an open access article distributed under the terms of the creative commons attributionLicense, which permits unrestricted use, distribution and reproduction in any medium, provided the original author and source are credited.

Competing Interest: The authors have declared that no competing interest exists.

Data Availability: All relevant data are within the paper and its supporting information files.

Asian J. Plant Sci., 16 (3): 109-131, 2017

INTRODUCTION

Currently, increase in food production is the one of theprimary objective of all countries as world population isexpected to grow to nearly 9-10 billion by 20501. Indeveloping countries the population growth rate is 3% yearG1.Demand for food increases1 by 3.8% yearG1. However, foodproduction is increasing by only 1.2% yearG1. World foodproduction needs to increase by 70%, in order to keep pacewith the demand of growing population2. However, increasein food production is faced with the ever-growing challengesespecially the new area that can be increased for cultivationpurposes is very limited3. Moreover, the soil fertility ofdeveloping countries has become deteriorated4 andoccurrence of various pest infestations increased5. Theincreasing world population coupled with other challengeshas therefore put a tremendous amount of pressure on theexisting agricultural system so that food needs can be metfrom the same current resources like land, water etc.6. In theprocess of increasing crop production, crop production inputs(fertilizers and pesticides) are now being used in higherquantities than in the past with proper or improperapplication system4,7.

Crop production inputs to crop production systemsinclude mineral fertilizers such as urea, ammonium nitrate,sulfates and phosphates8; organic fertilizers such as animalmanures, composts and biosolids; various other organicproducts such as humic acids and microbial inoculants6,9 andpesticides including herbicides, insecticides, nematicides,fungicides and soil fumigants8. All these products are appliedwith the ultimate goal of maximizing crop productivity andeconomic returns9.

Mineral fertilizers are a major physical input into worldagricultural production. The global total nutrient capacity(N+P2O5+K2O) was 284 million tons in 2014, out of which thetotal supply was 240 million tons10. During 2015, the totalcapacity was increase by 2.9% and supplies were grown by1.6%. Based on the production process, it can be roughlycategorized into three types: chemical, organic and biofertilizer. Each type of fertilizer has its advantages anddisadvantages. Common types of mineral fertilizers as used inthis review are ammonium nitrate, ammonium sulfate, calciumnitrate, diammonium phosphate, elemental sulfur, phosphaterock, sodium dihydrogen phosphate, superphosphate, triplesuperphosphate and urea. Though, there is lack ofinformation on organic fertilizer consumption globally,Organic agriculture using organic fertilizer is now practiced inmore than 130 countries with a total area of 30.4 million ha in0.7 million number of organic farms11,12. It is clear that early

many long-term studies have shown that combinations ofboth organic and inorganic nutrient sources lead to enhancednutrient availability and synchronization of nutrient releaseand uptake by crops and positive effects on soil properties6.

Pesticides are a diverse group of inorganic and organicchemicals13. Now it become an integral part of our modern lifeand are used to protect agricultural land, stored grain, flowergardens as well as to eradicate the pests transmittingdangerous infectious diseases mainly in developingcountries14. It has been estimated that globally nearly $38billion are spent on pesticides each year15. Manufacturers andresearchers are designing new formulations of pesticides tomeet the global demand. Ideally, the applied pesticidesshould only be toxic to the target organisms and unwantedplants, should be biodegradable and eco-friendly to someextent to the soil health. Unfortunately, this is rarely the caseas most of the pesticides are non-specific and may kill theorganisms that are harmless or useful to the ecosystem. Ingeneral, it has been estimated that only about 0.1% of thepesticides reach the target organisms and the remainingcontaminates the surrounding environment16. On account ofthis behavior then, they can best be described as biocides(capable of killing all forms of life)17. Researches showed thatpesticides have not only entered into the food chain and havebio-accumulated in the higher tropic level but also morerecently causing several human acute and chronic illnesses7,18.The repeated uses of persistent and non-biodegradablepesticides and herbicides have polluted various componentsof water, air and soil ecosystem17. Pesticides and herbicidesaffect various properties of soil such as, soil physical andchemical properties and mainly soil microorganisms7,19.

This study summarized the current understanding ofthe effects of crop production inputs on soil health. Theunderlying concept is that these inputs can affect soil healththrough direct or indirect effects. Schreck et al.6 andBunemann et al.8 summarized this effect in to twocategories: (1) Direct effects (example: Increased amountand/or activity after removal of nutrient limitations anddecreased activity due to high nutrient availability anddecreased amount and/or activity due to toxicity) and(2) Indirect effects [Example: change in pH, change in soilphysical properties (aggregation, porosity), change inproductivity, residue inputs and soil organic matter levels].Due to difficulty to distinguished the above classification,existing data are presented for the different amendmentsseparately but the effects are discussed together. Note that,this study did not focused on the direct uptake of nutrientsand its effect on crop productivity rather mainly focused onwhat happen on some soil chemical properties and the

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Asian J. Plant Sci., 16 (3): 109-131, 2017

N

P

N

P

N

P

0 100 200 300 400 500 600

Midwest USA

North China

Western Kenya

InputOutput

kg haG1

amount, activity and diversity of soil microorganisms when thecrop production inputs are applied for crop productionsystems. The evidence from Ethiopia is rather almost none andtherefore this study includes literature from overseas, in anattempt to establish the main effects and to draw someconclusions applicable to all users in the world.

SOIL HEALTH

There is increasing recognition of soil as an importantnon-renewable asset that needs to be managed well andlooked after19. Soil health is defined as the capacity of a soil tofunction, within ecosystem and land use boundaries, tosustain biological productivity, maintain environmental qualityand promote plant and animal health20. It considers thechemical, physical, biological and ecological properties of soilsand the disturbance and ameliorative responses by landmanagers. Soil health also describes the capacity of soil tomeet performance standards relating to nutrient and waterstorage and supply, biological diversity and function,structural integrity and resistance to degradation6.Nonetheless, it should be emphasized that these functionsoperate by complex interaction with the abiotic physical andchemical environment of soil. Both natural and agriculturalsoils are the habitat for many different organisms whichcollectively contribute to a variety of soil-based goods andservices21. However, these soil-based biological processes maybecome disturbed or improved by different factors such asaddition of agricultural inputs, improper land cultivation,climatic conditions etc.22. More specifically, Under-use,over-use and adequate use of crop production inputsdetermine the soil health of an environment as discussedpreviously6. For instance Fig. 1 shows differences in nutrientinputs and outputs at three locations representing under-use,

over-use and adequate use of fertilizers. Western Kenya ischaracterized by low inputs of N and P in marked contrast tothe situation in China and the USA. The N outputs at theKenyan site are much larger than the inputs, leading tosubstantial nutrient depletion or “soil mining” and consequentlong-term degradation of soil health. On the other hand, highfertilizer nutrient inputs in China greatly exceed nutrientoutputs and point towards substantial risks of nutrient lossesto the environment. With almost similar inputs and outputs ofboth N and P, soil health in the Midwest USA is better than ineither the Kenyan or Chinese sites23.

In Ethiopia and worldwide productions and consumption ofcrop production inputs: Pesticides include chemicallysynthesized compounds, devices or organisms that areregularly utilized in agriculture to manage, destroy, attack orrepel pests, pathogens and parasites. Pesticides include bothorganic and inorganic moieties and may be classified intodifferent groups based on their chemical composition24. Over1990s, the global pesticide sale remained relatively constant,between 270 to 300 billion dollars, of which 47% wereherbicides, the remaining were insecticides, fungicides/bactericides and the others. Over the period 2007-2008herbicides ranked the first in three major categories ofpesticides (insecticides, fungicides/bactericides, herbicides).Fungicides/bactericides increased rapidly and ranked thesecond7,17 . Europe is now the largest pesticide consumer inthe world followed by Asia. Countries like China, United States,France, Brazil and Japan are the largest pesticide producers,consumers or traders in the world. Although, most of thepesticides worldwide are used to fruit and vegetable crops,developing countries like Ethiopia used to mainly cerealcrops25. In the developed countries pesticides, mainlyherbicides are mostly used7.

Fig. 1: Total agronomic inputs and outputs of N and P in agricultural soils at Western Kenya, North China and Midwest USA23

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Asian J. Plant Sci., 16 (3): 109-131, 2017

Although chemical pesticide usage in Ethiopia washistorically low, recent developments in increased foodproduction and expansion in floriculture industry haveresulted in higher consumption of chemical pesticides.Recently, Ethiopia has been considered as the largestaccumulator of obsolete pesticides in the whole of Africa25.According to the Ethiopian Federal Environmental ProtectionAuthority (EFEPA)26 pesticides are mainly imported foragricultural purposes while some amounts of pesticides areimported for health care and industrial purposes. Both publicand private enterprises are engaged in pesticide importationbusiness. In contrary, there is one factory that formulatespesticides within the country25,26. Large quantities of pesticidesare imported annually to Ethiopia. In this regard, currently,about 20 organizations are actively involved in importationand sale of pesticides and over 3000 tons of various types ofpesticides that are worth more than USD 20 million areimported annually26.

In the medium term, global fertilizer consumptionwould grow moderately at an annual rate of 1.7%, to reach199.4 Mt nutrients in 201927. Increases are projected for allthree major nutrients, with average annual growth rates of1.3% for N, 2.1% for P and 2.4% for K. Total sales in the fertilizerand industrial sectors in 2019 are forecast at 264 Mt nutrients,representing a 10% increase over 2014. In Ethiopia, over thelast 10 years, total fertilizer imports have increased by morethan 50%, from less than 370,000 Mt in 2002 to almost570,000 Mt in 2011, with a spike of 627,000 Mt in 2009.Fertilizer carryover stocks averaged 33% of imports between2002 and 2011, with a high of 61% in 2002 and a low of 12%in 2007. Fertilizer sales and consumption have increased bymore than 100% between 2002 and 2011, with an averagerate of 6% yearG1, more so for urea than for diammoniumphosphate28. The information on world consumption oforganic fertilizer is very fragmented and difficult to present acomprehensive review in this study. However, organicagriculture using organic fertilizer is now practiced in morethan 130 countries with a total area of 30.4 million ha in0.7 million number of organic farm11,12. This constitutes about0.65% of the total agriculture land of the world12.

IMPACT OF FERTILIZERS ON SOIL HEALTH

For optimum plant growth, nutrients must be available insufficient and balanced quantities. Soils contain naturalreserves of plant nutrients but these reserves are largely informs unavailable to plants and only a minor portion isreleased each year through biological activity or chemicalprocesses. This release is too slow to compensate for theremoval of nutrients by agricultural production and to meet

crop requirements29. Therefore, fertilizers are designed tosupplement the nutrients already present in the soil. The useof chemical fertilizer, organic fertilizer or biofertilizer has itsadvantages and disadvantages in the context of nutrientsupply, crop growth and environmental quality. Theadvantages need to be integrated in order to make optimumuse of each type of fertilizer and achieve balanced nutrientmanagement for crop growth8,30,31.

Impact of inorganic fertilizers on soil health: Most inorganicfertilizers in the world are applied to systems with regular andsignificant nutrient exports in harvested products, such aslands under arable cropping8,30. Various studies conducted atlaboratory, pot and filed level revealed that mineral fertilizershad different effects on soil health. The application ofchemical fertilizers causing accumulation of acid soils such ashydrochloric and sulfuric acids creates a damaging effect onsoil referred to as soil friability. The different acids in the soildissolve the soil crumbs which help to hold together the rockparticles. Soil crumbs result from the combination of humus ordecomposed natural material such as dead leaves, with clay.These mineral rich soil crumbs are essential to soil drainageand greatly improve air circulation in the soil. As the chemicalsin the chemical fertilizers destroy soil crumbs, the result is ahighly compacted soil with reduced drainage and aircirculation32,33.

Addition of Organic fertilizer increased Effective CationExchange Capacity (ECEC) by 16% while it reduced ininorganic fertilizer plots34. Bulk Density (BD) and soil pHdecreased while total porosity, Water Holding Capacity (WHC)improved with the application of increased level of Nfertilizers34,35. Gypsum amendment was superior in reducingthe chemically available heavy metals (Fe, Mn, Zn, Cu, Ni andCd) in the heavy clay salt-affected soil35. The experiment atlaboratory inoculation pointed out that the addition of200 mg N kgG1 soil as ammonium sulfate to 2 pasture soils ofvarying P status resulted in a decrease in microbial P, nochange in the turnover of added C and an increase in Nmineralization during 168 days of incubation36. Long termexperiment on chemical fertilizers usage showed that soilphysical characteristics such as bulk density were changed inlong-term and it was increased compared to control soil. Theheavy metals accumulations in soil were highly affected andthe concentration of some metals such as cadmium hasreached a limit beyond the standard for agricultural purposes.The results also showed that fortunately the concentration ofother metals is not beyond the standard36.

In contrary, an increase in soil respiration and microbial Pbut no effect on microbial N and a decrease in various enzymeactivities upon addition of 500 mg P kgG1 soil as calcium

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diphosphate were reported by Bunemann et al.8. The additionof N, P, K and S at 100, 20, 100 and 20 mg kgG1 soil,respectively, to a range of soils followed by incubation for20 days, resulted in minor changes (increase or decrease) ofsoil respiration and microbial C, N and P that remained within20% difference from the non-amended controls8. Ammoniumaddition did not change the composition of the microbialcommunity during 28 days of incubation but led tocommunity shifts after 16 weeks of incubation37. Usingmolecular techniques in a range of pot experiments, soil pHand N and P fertilization can affect the microbial communitycomposition but that substrate availability, e.g. in the form ofroot exudates in the rhizosphere, appears to be the mainfactor determining the community composition in therhizosphere38. It is thus, important to consider the potentialfeedback from improved plant nutrition when examiningfertilizer effects on soil health8. Moreover, the addition ofmineral N did not affect Arbuscular Mycorrhizal Fungi (AMF)while increasing additions of inorganic P decreased the rate ofroot length colonization39. A decrease in AMF root colonizationwas also observed in pastures after 15-17 years of mineral Pand N fertilization40 (Table 1).

Many field experiments have shown a lack of response ofthe microbial biomass and earthworms to inorganic fertilizers(Table 2, 3). Where a decrease in microbial C was observed, itwas usually accompanied by a decrease in soil pH afterapplication of N or S fertilizers41. Other methods such asmicrobial enumeration by plate counts, enzyme activities42

and nematode counts43, which are possibly more sensitivethan measurements of microbial biomass, show variablechanges due to mineral fertilization (Table 1). For instance,although the total number of nematodes was not affectedby N fertilization and a concomitant decrease in pH, somenematode species increased, whereas others weredecreased41.

There was absence of changes in microbial C inresponse to N fertilization and a related decrease in pH in the 2 long-term field experiments44. This study is interesting,because in the same study microbial C was found to becorrelated to levels of organic C as induced by different croprotations. Several long-term field experiments in whichinorganic and organic fertilizer inputs have been comparedare indicated in Table 3 and 4. Several studies showed thatthere was a good correlations between the microbial biomassand soil organic C. Although soil organic C levels are oftenincreased by inorganic fertilization compared with thenon-fertilized control, even greater increases in soil organic Care usually achieved in treatments receiving organicamendments8. This is also reflected in the fact that whereasinorganic fertilizers show variable effects on soil organisms

and soil pH, organic amendments have only been reported tohave insignificant or positive long-term effects (Table 2).

The amounts of microbial C and N under sugarcane after59 years of differential crop residue management and NPKfertilization and showed that the microbial biomass wasdirectly influenced by residue management and indirectly byNPK fertilization through increased residue inputs42. Anotherstudy in the same trial revealed the interaction of soilacidification with negative effects and organic matteraccumulation with positive effects on soil organisms andenzyme activities42. The long term field experimentexemplifies that agro-ecosystems can be relatively slow torespond to changes in management and thus illustrates thevalue of long-term field experiments8. The excellentcorrelation between microbial C and soil organic C found after100 years of constant management practices remaineddisturbed 2 years after a change in crop rotation and cropresidue management. The time required to reach a newequilibrium is a factor that may confound the results frommany short-term studies.

The comparison of various long term experiment on N, Pand K fertilizers, liming and manure treatments revealedthat ammonium fertilizers decreased pH and CEC, causing adegradation of hydraulic properties, whereas basicamendments increased pH and CEC45,46. Aggregate stabilitywas lowest in acid plots, intermediate in basic plots andhighest in plots treated with manure. A short term studysuggested that ammonium nitrate enhanced soil porosity by18%, compared with 46% increase in a manure treatment30.Since soil respiration almost doubled in the mineral fertilizertreatment compared with the unfertilized control, the authorsdiscussed a potential priming effect of N addition on thedecomposition of soil organic matter (Table 1). A decreasedamount or activity of soil organisms after mineral fertilizationcould be due to the toxicity of metal contaminants containedin mineral fertilizers8,36,41. In general, N and K fertilizers containvery low levels of contaminants, whereas P fertilizers oftencontain significant amounts of cadmium, mercury and lead8.Metal contaminants are, however, most prevalent in wasteproducts from urban and industrial areas8,47. Long termchronic toxicity due to gradually accumulating metals appearsto be far more common than immediate, acute toxicity.Quality control of fertilizer products is therefore required. Thisapplies in particular to any new products. For example, theapplication of rare earth elements such as lanthanum, whichis increasing in China, was shown to decrease soil respirationand dehydrogenase activity at high application rates8,48. Suchobservations warrant more detailed investigation into

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Asian J. Plant Sci., 16 (3): 109-131, 2017

114

Table 1: S

umm

ery of

effe

cts o

f ino

rgan

ic fe

rtilize

rs on so

il he

alth

Test plant

sTim

e fra

me

Fertilize

rs (k

g ha

G1)

Effect on so

il he

alth

(Am

ount

(%) a

nd activity

of c

ontrol)

Refere

nces

Pot e

xper

imen

ts w

ith w

hite

5 wee

ks20

0 P

# (Sod

ium

dihyd

roge

nNeg

ative effect: Clov

er ro

ot le

ngth

colon

ized

by AM

F (20-

30%)

Ryan

and

Ash

60

clov

er and

ryeg

rass

phos

phate)

No ch

ange

on ryeg

rass ro

ot le

ngth

colon

ized

(%)

Pot e

xper

imen

ts w

ith w

heat

6 m

onth

17-8

6 P (Trip

le su

per

Neg

ative effect: Ro

ot colon

ization (60-

90%); Po

sitive effect: F

ungi (4

80%), Gram!ve

bac

teria

(140

%);

Rubio et

al.3

9

phos

phate, pho

spha

te ro

ck)

no cha

nge on

micro

bial P, e

arth

wor

ms

Postur

e 2 wee

ks0-

120 P (Sup

er pho

spha

te,

Posit

ive effect on fu

ngi (48

0%), Gram!ve

bac

teria

(140

%); No ch

ange

on m

icro

bial P, e

arth

wor

ms;

Sarath

chan

dra et

al.4

1

phos

phate ro

ckpa

stur

e pr

oduc

tion increa

sePa

stur

e10

wee

ks40

N (A

mm

onium

nitr

ate)

Posit

ive effect: N

itrifica

tion, am

mon

ifica

tion; no ch

ange

on m

icro

bial, e

arth

wor

ms;

Micro

bial C and

NLo

vell an

d Hatch

64

Whe

at-can

ola

1-2 se

ason

s20

S (E

lem

ental s

ulfu

r or

Neg

ative: D

iver

sity (B

iology

); no

cha

nge on

micro

bial C;

Ladh

a et

al.6

5

amm

onium

sulfa

te)

Pastur

ePa

stur

e 61

P (S

uper

Pho

spha

te)

No ch

ange

on Micro

bial P and

S; inc

reas

es h

erba

ge

Adeo

ye et a

l.14

Pastur

e 4 ye

ars

400 N (U

rea)

Neg

ative effect: M

icro

bial C (8

0%), dive

rsity

(Biology

), Meloido

gyne

(10%

), plan

t-as

sociated

(68%

) and

Sarath

chan

dra et

al.4

1

fung

al-fe

eding (82%

) nem

atod

es; N

o ch

ange

on to

tal n

ematod

es; N

egative effect on pa

ratylenc

hus (

1677

%)

Cano

la-fa

llow

2 ye

ars

50-1

00 S (E

lem

ental s

ulfer)

Neg

ative: Fun

gal C

FUs (

38%), pr

otoz

oa (4

-25%

), m

icro

bial C (4

9-98

%), re

spira

tion (67-

86%); po

sitive effect:

Micro

bial S (1

36-1

68%), ac

id pho

spha

tase

(106

-130

%)

Gup

ta and

Ger

mida6

6

Pastur

e 5 ye

ars

44 S (E

lem

ental s

ulfer)

Neg

ative effect on m

icro

bial C (6

0%), re

spira

tion (54%

), hy

phal le

ngth

(24%

), fu

ngal CFU

s (23

%), pr

otoz

oaGup

ta and

Ger

mida6

6

(29-

71%); no

effe

ct on Ba

cter

ial a

nd actinom

ycet

es CFU

s; po

sitive effect on M

icro

bial S (1

78%), ac

idph

osph

atas

e (141

%); pH

increa

sed by

1.0 units, O

C de

crea

sed

Whe

at ro

tatio

ns

9-13

yea

rs0-

80 N

(Am

mon

ium

nitr

ate)

Neg

ative effect: M

icro

bial C (6

8-86

%), pH

dec

reas

ed by by

0.4-1

.0 units; n

o ch

ange

on C an

d N m

iner

alization

Martik

aine

n et

al.6

7

Pastur

e 7-

23 yea

rs12

-37 P, 12-

26 S

No ch

ange

on ea

rthw

orm

s; po

sitive effect on m

icro

bial P (1

68-3

00%), m

icro

bial N

Chan

68

(106

-163

%), to

tal n

ematod

es (1

23-2

23%)

Pastur

e 15

-17 ye

ars

27 P (S

uper

phos

phate,

Neg

ative effect on: C

love

r and

grass ro

ot le

ngth

colon

ized

by AM

F (67-

79%); pH

redu

ced by

0.1-0

.9 units;

Ryan

69

Diam

mon

ium

pho

spha

te)

17 N

(Ure

a)m

icro

bial C re

late

d to

OC; no ch

ange

on m

icro

bial C

Suga

rcan

e59

-60 ye

ars

140 N, 2

0 P, 140

KNeg

ative effect on: D

ehyd

roge

nase

, arylsu

lfatase

, alkaline ph

osph

atas

e; pos

itive

effe

ct: e

micro

bial

Graha

m and

Hay

nes4

2

C (119

-136

%), FDA

hydr

olys

is rate

, acid ph

osph

atas

e; no ch

ange

; OC increa

sed, pH dec

reas

ed by 0.7 un

its;

no cha

nge pr

otea

se, res

piratio

n# m

g kg

G1 so

il

Asian J. Plant Sci., 16 (3): 109-131, 2017

115

Table 2: Com

parativ

e effects o

f ino

rgan

ic and

org

anic fe

rtilize

rs on so

il or

ganism

s as c

onclud

ed fr

om field ex

perim

ents (F

YM, farm

yard

man

ure)

Test plant

sTim

e fra

me

Fertilize

rs (k

g ha

G1)

Effect on so

il he

alth

(am

ount

(%) a

nd activity

of c

ontrol)

Refere

nces

Maize

-pas

ture

rotatio

n5

18 N

(Am

mon

ium

nitr

ate)

Neg

ative effect on Gram

-ve ba

cter

ia (8

5%); no

cha

nge on

total P

LFAs

Gram

+ve

bac

teria

; pos

itive

effe

ct on

Peac

ock et

al.8

3

FYM (2

52 N

)Gram

+ve

bac

teria

(120

%), to

tal P

LFAs

(170

%), Gram

-ve ba

cter

ia (1

15%); pH

redu

ced by 0.6 un

its, OC increa

sed

Cove

r cro

p12

100 N (A

mm

onium

nitr

ate),

No ch

ange

on m

icro

bial C, m

icro

bial C cor

relate

d to

OC; pos

itive

effe

ct on m

icro

bial C (2

00-3

50%) a

nd m

icro

bial

Leita

et a

l.84

75 P (S

uper

phos

phate), 1

50 K

C (243

%)

(Sup

erph

osph

ate); C

ompo

st(500

-150

0 N); FY

M (5

00)

Arab

le cro

ps34

-36

80 N

(CaN

); 80

N (A

mm

onium

No ne

gativ

e effect, p

ositive

effe

ct on m

icro

bial C (1

42%); Neg

ative effect on Micro

bial C(13%

); ne

gativ

e effect

Witt

er et a

l.85

sulfa

tc); FY

M (4

t ha

G1 yea

r);on

micro

bial C(69%

), po

sitive effect on m

icro

bial C (2

09%); in gen

eral pH re

duce

d with

AS an

d se

wag

e slu

dge;

Sewag

e slu

dge

micro

bial C and

resp

iratio

n re

late

d to

OC

Whe

at-fa

llow ro

tatio

n55

90 N

Neg

ative effect on am

idas

e, ure

ase; no ch

ange

on ac

id and

alk.pho

spha

tase

, arylsu

lfatase

, gluco

sidas

e;Bu

nem

ann et

al.8

pH re

duce

d by

0.6 units

Whe

at69

67 N

, 15 P, 28 K

Neg

ative effect on Fa

st-g

rowing

Parh

am et a

l.86

Bacter

ia; n

o ch

ange

on: Bac

teria

l and

fung

al CFU

, alk. p

hosp

hata

se,

phos

phod

iester

ase, pyrop

hosp

hatase

; pos

itive

effe

ct on: M

icro

bial C, a

cid ph

osph

atas

e, sl

ow-g

rowing

bacter

ia; p

H re

duce

d by -0.5 un

itsPa

stur

e10

035

N (A

mm

onium

sulfa

te)

Neg

ative effect on m

icro

bial P, C

Colvan

et a

l.87

60 P

Posit

ive effect on m

icro

bial P

67 K

Posit

ive effect on ph

osph

atas

e35

N, 6

0 P, 67 K

Posit

ive effect on m

icro

bial P, p

hosp

hatase

FYM (2

0 t h

aG1 y

ear)

Posit

ive effect on m

icro

bial P, p

H in

crea

sed by 0.6 un

itsW

heat-sug

ar bee

t11

287

N, 4

0 P, 75 K

Posit

ive effect on m

icro

bial C; M

icro

bial C re

late

d to

OC

Hou

ot and

Cha

usso

d88

FYM (1

tons

haG

1 yea

r)Po

sitive effect on m

icro

bial C

cucu

mbe

r (Cu

cum

is Sa

tiva)

com

post of p

lant

Matur

e co

mpo

st of p

lant

resid

ues w

as highe

r in sa

turatio

n pe

rcen

t and

lower

in C/N

ratio

, pH, e

lectric

al

Mah

mou

d et

al.2

9

resid

ues

and an

imal

cond

uctiv

ity and

bulk de

nsity

than

the an

imal and

mixed

com

posts

and m

ixed

com

posts

Nitr

ogen

and

pho

spho

rus c

onte

nt of t

he so

il sig

nific

antly

increa

sed, as d

id th

e so

il or

ganic m

atte

r, with

the increa

se of o

rgan

ic nitr

ogen

app

lied

Com

bina

tion of

org

anic and

inor

ganic fertilize

rs cou

ld in

crea

se so

il fertility

It also

con

firm

ed th

at com

posted

org

anic w

aste

s can

be us

ed to

subs

titut

e fo

r aro

und 25

% of c

hem

ical

nitrog

en fe

rtilize

rs

Asian J. Plant Sci., 16 (3): 109-131, 2017

116

Table 3: Com

parativ

e effects o

f ino

rgan

ic and

org

anic fe

rtilize

rs on so

il he

alth

as c

onclud

ed fr

om field ex

perim

ents (F

YM, farm

yard

man

ure)

Test plant

sTim

e fra

me

Fertilize

r (kg

haG

1 )Effect on so

il he

alth

(am

ount

(%) a

nd activity

of c

ontrol)

Refere

nces

Tea (C

amellia

sine

nsis

L.)

2 yea

rCo

coa hu

sk, c

ow dun

gAb

out 3

.0-4

.6, 0

.08-

0.21

, 0.69-

1.79

, 0.36-

0.76

, 0.17-

0.24

and

31.5-

5.45

kg N, P

, K, C

a, M

g an

d C ha

G1, res

pectively co

uld be

Ipinm

orot

i et a

l.30

recy

cled

to th

e so

il th

roug

h pru

ned m

ater

ials

from

tea

seed

lings

tre

ated

with

enr

iche

d m

anur

es c

ompa

red to

1.17,

0.05

, 0.25, 0.69, 0.18 an

d 40

.84 kg

haG

1 for

sim

ilar e

lem

ents fo

r NPK

trea

ted plan

ts

Rice

-soy

bean

-rice

4 yea

rsPa

ddy straw and

inoc

ulan

ts +

30Th

e so

il fertility viz., s

oil o

rgan

ic carbo

n co

nten

t, so

il av

ailable nitrog

en, p

hosp

horo

us and

pot

assiu

m built up

sign

ifica

ntly

Son et

al.9

7

N-6

0 P2

05- 3

0 K2

0un

der ap

plication in

orga

nic fe

rtilize

r co

mbine

d w

ith c

ompo

sted

pad

dy s

traw

or ino

culant

s or b

oth co

mpo

sted

pad

dystraw and

inoc

ulan

ts as c

ompa

red to

the trea

tmen

ts th

ose ap

plied on

ly in

orga

nic fertilize

rsBr

injal

2 yea

rs60

% org

anic +

40% in

orga

nic

The or

ganic m

atte

r co

nten

t an

d ava

ilability of N

, P, K

and

S in

soil wer

e increa

sed by

org

anic m

atte

r app

lication. O

n th

e U

llah et

al.9

8

othe

r han

d so

il pH

was

increa

sed with

che

mical app

lication th

an org

anic.

Maran

th3 yea

rs0 kg

haG

1 man

ure, 2 to

ns haG

1 org

anic

The or

ganic m

atte

r inc

reas

ed by 23.3 and

0.6% in

the se

cond

and

third

yea

r res

pectively in th

e plot

trea

ted with

org

anic

Adek

ayod

eco

mpo

st and

200

kg ha

G1co

mpo

st, while the

re w

as n

o su

ch inc

reas

e tren

d in

the plot

trea

ted with

200

kg NPK

haG

1 . Th

e or

ganic m

atte

r con

tent

an

d Ogu

nkoy

a99

NPK

15-

15-1

5co

rrelated

pos

itive

ly w

ith th

e yield an

d vitam

in C con

tent

of a

maran

th.

Suga

rcan

e3 yea

rsfarm

yard m

anur

e (25 to

ns haG

1 ),

The plot

s which

rece

ived

FYM

at 2

5 to

ns haG

1 +RD

F re

cord

ed highe

st org

anic carbo

n (0.55%

) and

ava

ilable N (2

26 kg ha

G1)

Bune

man

n et

al.8

com

post (2

.5 to

ns haG

1 ) an

d NAD

EPm

axim

um ava

ilable P2

O5 an

d K2

O (3

8.89

and

254

kg haG

1 ) w

as o

bser

ved in

plots w

hich

rec

eive

d pre

ss m

ud c

ake at

com

post (5

.0 to

ns haG

1 )12

tons

haG

1 +RD

F as

pres

s m

ud c

ake is

a rich so

urce

of ph

osph

orus

(2.76

%). D

ecre

ase in

pH in m

anur

ed p

lots w

as

attribut

ed to

increa

se in

partia

l pre

ssur

e of

CO

2 and

org

anic acids

due

to org

anic m

atte

r dec

ompo

sition

Maize

15

yea

rsNo fertilize

r app

lication (con

trol),

The Ag

greg

ate stab

ility w

as si

gnifica

ntly highe

r on a

pplic

ation of farm

yard

man

ure (F

YM) alon

e. OC w

as s

ignific

antly

Gom

ez et a

l.100

application of

farm

yard

man

ure

high

er on co

mbine

d app

lication of FY

M, Mav

uno fe

rtilize

r an

d to

p dre

ssing. Miner

al fer

tilizer

s con

tribut

e m

ore to

the

application of

FYM

, Mav

uno

increa

se of O

C th

an org

anic fe

rtilize

rs

Fertilize

r and

top dr

essin

gMaize

4 yea

rs(C

allia

ndra calot

hyrsus

, Leu

caen

aCa

ttle m

anur

e pr

oved

to be th

e m

ost e

ffective an

d im

prov

ed so

il fertility by increa

sing pH

, cations

(Ca, K a

nd M

g) and

C.

Mug

we et

al.1

01

tricha

ndra, T

ithon

ia diver

sifolia,

Callian

dra, Leu

caen

a, Tith

onia and

her

bace

ous l

egum

es gen

erally re

duce

d so

il pH

, C and

N b

ut inc

reas

ed Ca, K and

Mg.

Muc

una pr

uriens

, Cro

talaria

Cattle m

anur

e is

ther

efor

e an

impo

rtan

t res

ource fo

r maint

aining

Soil O

rgan

ic M

atte

r (SO

M) in th

e area

and

in oth

er si

mila

r oc

hroleu

ca and

cattle

man

ure)

area

s with

arable-

lives

tock

system

s. Re

duction of

soil C an

d N by th

e high

qua

lity or

ganic m

ater

ials

sugg

ests th

at th

eir r

ole

= ch

emical fe

rtilize

rin m

aint

aining

SOM in

the long

-ter

m is

lim

ited in th

is area

. A so

und nu

trient

man

agem

ent s

yste

m sh

ould st

rive to

mak

e a

balanc

e be

twee

n m

axim

izing crop

pro

duction an

d su

staining

soil qu

ality

Asian J. Plant Sci., 16 (3): 109-131, 2017

117

Table 4: E

ffects o

f anim

al m

anur

es, b

ioso

lids a

nd com

posts o

n so

il he

alth

Com

pare

d trea

tmen

tsEffects

Refere

nces

Poultry m

anur

e, gyp

sum

+dolom

ite, o

ther

sMan

ured

trea

tmen

t had

highe

st m

icro

bial C

Sharpley

et a

l.102

Long

-ter

m ann

ual a

pplic

ation of

farm

yard

man

ure, con

trol

Man

ure ad

ditio

n en

hanc

ed m

icro

bial biom

ass a

nd xylan

ase an

d inve

rtas

e ac

tivity

Poll et

al.1

03

3 ye

ars p

oultr

y m

anur

e, FYM

, ses

bania an

d gliricidia re

sidue

s, co

ntro

lOrg

anic m

anur

es in

crea

sed m

icro

bial biom

ass,

activ

ity, d

iver

sity an

d C tu

rnov

erDines

h et

al.1

04

Man

ure, m

iner

al fe

rtilize

r, co

mbine

d m

anur

e an

d fertilize

rMan

ure±

N and

P fe

rtilize

r tre

atm

ents re

stor

ed O

C an

d m

icro

bial C to

the leve

l of t

he native so

dDines

h et

al.1

04

Lab. in

cuba

tion of

soil am

ende

d with

shee

p m

anur

e at various

soil m

atric

Man

ure increa

sed so

il re

spira

tion in all co

mbina

tions

of s

oils

and m

atric

pot

entia

ls. M

icro

bial biom

ass i

ncre

ased

mos

tTh

omse

n et

al.1

05

pote

ntials

and clay

con

tent

swith

the ad

ditio

n of

man

ure to

the sa

ndiest so

ilSu

rface

mulch

es of g

rass clip

ping

s, Lu

cern

e stem

s, co

mpo

sted

man

ure,

Only gr

ass c

lipping

s stim

ulated

deh

ydro

gena

se activity

in th

e so

il m

easu

red afte

r 1 yea

r. Eu

calypt

us yard was

te and

Youn

g et

al.9

6

euca

lypt

us, o

lean

der o

r pine ch

ip w

aste

, chipp

ed con

stru

ction was

tegr

ass c

lipping

s cau

sed sh

ifts i

n ba

cter

ial p

opulations

and

increa

sed ba

cter

ial d

iver

sity bu

t only at th

e so

il su

rface

Sing

le app

lication of

pou

ltry m

anur

e, N

PK fe

rtilize

r to so

il afte

r wild

fire

Poultry m

anur

e ap

plication increa

sed m

icro

bial biom

ass C

, partic

ularly at h

igh do

se. L

ittle or n

o ch

ange

s as a

con

sequ

ence

Villa

r et a

l.106

of ino

rgan

ic fe

rtiliza

tion

Bios

olids (

30-1

20 to

ns haG

1 )Increa

se in

earth

wor

m abu

ndan

ceBa

ker e

t al.1

07

Sing

le app

lication of

bioso

lids f

rom

5 tr

eatm

ent p

lant

s app

lied to

one

soil.

Sym

biot

ic effe

ctiven

ess o

f rhizo

bium

dep

ende

nt on so

il type

and

leve

l and

sour

ce of b

ioso

lids,

not o

n ba

sis of h

eavy

Mun

n et

al.1

08

Bios

olids f

rom

1 plant

app

lied to

6 so

ilsm

etal con

cent

ratio

nsLo

ng-ter

m FYM

, met

al-con

tam

inated

sewag

e slu

dge, N

PK m

iner

al fe

rtilize

rFY

M-tre

ated

soil th

an in

NPK

and

slud

ge-am

ende

d so

ils. R

elatively sm

all h

eavy

-met

al con

cent

ratio

ns dec

reas

ed m

icro

bial

Abay

e et

al.1

09

C an

d ba

cter

ial n

umbe

rs, inc

reas

ed m

etab

olic quo

tient

and

cha

nged

micro

bial com

mun

ity 40 ye

ars a

fter m

etal in

puts cea

sed

Seve

ral c

ombina

tions

of s

ludg

e an

d co

al ash

, con

trol, N

PK fe

rtilize

rMicro

bial C and

soil en

zym

e ac

tivities

increa

sed with

all am

endm

ents; h

ighe

st at e

qual pro

portions

of c

oal a

sh and

slud

ge.

Chau

dhur

i et a

l.110

Mob

ile fr

actio

ns of C

d an

d Ni c

orre

late

d with

micro

bial C

Shor

t-te

rm in

cuba

tion, se

wag

e slu

dge, com

posted

turf

and plan

t res

idue

sCo

mpa

red with

com

post, s

ewag

e slu

dge ca

used

gre

ater

increa

ses i

n so

il re

spira

tion, m

icro

bial C,and

met

abolic quo

tient

,Ya

ng et a

l.111

espe

cially w

ith in

crea

sing ap

plication rate

2 ye

ars o

f sew

age slu

dge ap

plied to

de-

surfa

ced so

ilsMicro

bial biom

ass n

ot affe

cted

by slu

dge, but

met

abolic activity

and

org

anic m

atte

r miner

alization en

hanc

ed. Inc

reas

ed so

il Al

vare

z et

al.1

12

resp

iratio

n fro

m sl

udge

-am

ende

d so

il re

pres

ente

d 21

% of C

app

lied th

at yea

r and

15%

of C

app

lied th

e ye

ar befor

eSing

le app

lication of

bioso

lids

6yea

rs afte

r app

lication, am

ende

d plot

s had

increa

sed m

icro

bial re

spira

tion, nitr

ogen

miner

alization, ro

ot colon

ization by

AM,

Barb

arick et

al.1

13

micro

bial biom

ass.

No ch

ange

in m

etab

olic quo

tient

Asian J. Plant Sci., 16 (3): 109-131, 2017

processes of accumulation, bioavailability and threshold levelsof elements contained in fertilizers that can be toxic to soilhealth.

Soil health is also influenced by increased rate ofdecomposition of low quality or high C:N ratio organic inputsand SOM when fertilizers are applied to the soil. Fertilizerapplication leads to enhancement of microbial decomposeractivity, which has been previously limited by low nutrientconcentrations in the organic materials, although in a fewstudies added inorganic N has had either a neutral or even aninhibitory effect on the decomposition of low-N plantmaterials49. Long-term use of fertilizers in crop production,however, leads to soil organic matter accumulation6 and soilhealth improvement through addition of increasing amountof litter and root biomass to the soil. It suggests that theapplication of N fertilizer can have complex interactive effectson C transformations in the soil.

Some of the commonly used chemical fertilizers such asammonium sulfate [(NH4)2SO4], ammonium nitrate (NH4NO3),urea (NH2CONH2), triple super phosphate [Ca (H2PO4)2] andpotassium chloride (KCl) affects soil health (Table 3-4).Ammonium sulfate (NH4)2SO4) is one of the synthetic Nfertilizer and contains 21N-0P-0K + 24% S. In the soil, it reactswith water to produce sulfuric acid (H2SO4). Sulfuric acid has apH of less than 1. It is extremely toxic and kills organisms.Hydrogen ions released from the acid replace alkalineelements on the cation exchange sites, depleting the soil ofnutrients. The free oxygen created in this reaction oxidizes theorganic matter of the soil causes a low level “combustion"(burning) of the organic matter. This is a purely chemicalreaction which depletes the organic matter. In calcareous soils(soil with excess calcium) the sulfuric acid reacts with calciumcarbonate (CaCO3) to form gypsum (CaSO4 = Calciumsulfate)50. Gypsum is a salt and attracts water to it and awayfrom soil organisms and plant roots. In anaerobic conditionsgypsum and water form hydrogen sulfide (H2S), which is atoxic gas. Gypsum is banned from landfills. Sulfuric acid is amajor component of acid rain50.

Ammonium nitrate (NH4NO3) contains 34N-0P-0K. In thesoil, it breaks down into ammonium (NH4

+) and nitrate (NO3G).The ammonium is consumed by plants and fungi or bydenitrifying bacteria which eventually convert it to nitrate51.The nitrates are consumed by soil organisms, leached orconverted to nitrogen gas and volatilized. The free oxygencreated through these processes oxidizes the organic matterof the soil and causes a low level "combustion" (burning) ofthe organic matter. This is a chemical reaction which depletesthe organic matter. Some biological soil scientists advocatethe use of small amounts of ammonium nitrate under specific

circumstances even though it is prohibited for use underorganic standards51,52. Urea (NH2CONH2) contains 46N-0P-0K.The urea is consumed by bacteria which convert it to(excrete) anhydrous ammonia (which is a gas) and carbondioxide (= 2(NH3)+CO2)52. Anhydrous ammonia is highly toxicand kills soil organisms. If urea is applied to the soil surface,the gases quickly dissipate. However, in the presence of highair humidity anhydrous ammonia gas vapours form. These areheavier than air and can accumulate in low lying areas. If ureais incorporated into the soil, the ammonia gas reacts withwater (H2O) to produce ammonium hydroxide (NH4OH), whichhas a pH of 11.653. It is highly caustic and causes severe burns.This creates a toxic zone in the immediate vicinity of theapplied urea that kills seeds, seedlings and soil dwellingorganisms. Within a few days further chemical reactions in thesoil release the ammonium ion NH4

+, which then follows thesame path as naturally occurring ammonium, with any excessnitrate created in this way leached into the environment, etc.

Triple super phosphate [Ca (H2PO4)2] contains 0N-46P-0K.This is produced by treating phosphate rock (apatite) witheither sulfuric acid or phosphoric acid, making it extremelyacidifying52. When applied to the soil it reacts with calcium toform tri-calcium phosphate, which is water insoluble, i.e.,requiring microbial action for breakdown. Even in a soil withhealthy microbial activity only about 15-20% of thisphosphorous is easily available to plants, considerably less insoil which does not have good microbial diversity53. Theproduction of each ton of phosphoric acid is accompanied bythe production of 4 ½ tons of calcium sulfate, also known asphosphogypsum. This is a highly radioactive product andalso contains heavy metals and other impurities. Dependingon the production process, radioactive substances andheavy metals can be extracted into the fertilizer. The highconcentration of radioactive polonium-210 in tobacco isthought to be associated with the use of acid-extractedphosphate fertilizers54.

Potassium chloride (KCl) contains 0N-0P-60K.This productcontains about 50% potassium and 50% chloride. In the soilthe chloride combines with nitrates to form chlorine gas. Thiskills microbes. Applying 1 pound of potassium chloride to thesoil is equivalent to applying 1 gallon of clorox bleach. Or inother words: 2 ppm chlorine are generally thought to besufficient to sterilize drinking water potassium chlorideapplication typically results in chloride levels as high as50-200 ppm53. Potassium chloride contains very highamounts of potassium, which can result in an unbalancedphosphate:potash ratio. This ratio ideally ranges from 2:1(most soils) to 4:1 (grasses). Excess potassium in the soil canlead to a calcium deficiency in plants, since plants absorb

118

Asian J. Plant Sci., 16 (3): 109-131, 2017

calcium, magnesium and potassium largely in the ratio inwhich they are present in the soil. In the soil excess potassiumcauses a loss of soil structure53. Reduced soil air levels result inreduced root respiration and the production of toxiccompounds in plants. Reduced soil air and insufficient calciumeach also result in the reduction of soil microbes and thecorresponding reduced breakdown of organic matter/nutrientavailability to plants. In drilling potassium is used to “close” thesoil, because it disintegrates the clay particles (“ages” the clay)and effectively seals the soil55. Effects of Organic fertilizers on soil health: Since mostorganic fertilizers are waste products; their application rate isoften determined by availability rather than demand7,8. Mostamendments are applied primarily to benefit plant growth.In contrast to inorganic fertilizers, however, effects on thesoil’s physical, chemical and biological properties are intendedas well in the following section. Besides, in the followingsections, we try to establish some links between theproperties of various organic inputs and their effects on soilhealth (Table 2, 3).

Compostable organics: Compostable and compostedmaterials vary widely in characteristics such as dry mattercontent, pH, salinity, carbon content, plant nutrientconcentrations, non-nutrient elements and microbial types,numbers and activity6. Onwudiwe et al.56 reported thatapplication of municipal solid waste did not cause significantimprovement in some soil physical properties such as soilaggregate stability, saturated hydraulic conductivity, bulkdensity and porosity. Although studies of amendments varywidely in nature of materials, application rates andexperimental conditions, amendment with raw andcomposted organics generally results in increased microbialproliferation in the soil (Table 3). The duration of observedincreases in soil organisms depends on the amount andproportions of readily decomposable carbon substrates addedand the availability of nutrients, particularly nitrogen57.However, soil chemical, physical and microbial characteristicsof amended soils often return to their baseline within a fewyears58. Sustained changes in microbial biomass, diversity andfunction are more likely where organic amendments areongoing as is the case in organic and biodynamic farms59.However, an increase in microbial populations may not beseen when system productivity is limited by nutrient input orwater supply60.

Manures and sewage sludge generally have highersalinity than municipal garden wastes and salts can build upin soil with repeated heavy applications61,62. Sewage sludge

(biosolids) often contains heavy metals such as copper, zinc orcadmium, especially where industries contribute to the wastestream. Heavy metals can affect microbial processes morethan they affect soil animals or plants growing on the samesoils. For example, nitrogen-fixing rhizobia were far moresensitive to metal toxicity than their host plant clover. Thisresulted in N deficiency of clover due to ineffective rhizobia insludge-amended soils. Sewage sludge and livestock manuremay also contain active residues of therapeutic agents used totreat or cure diseases in humans and animals63. Green wastesfrom farms and gardens are typically lower in nutrientconcentrations than manures or sewage sludge’s but maycontain residues of synthetic compounds such as herbicides,insecticides, fungicides and plant growth regulators.Composting degrades some but not all such compounds,depending on the nature of the pesticide and the specificcomposting conditions.

In general terms compost will modify Soil Organic Matter(SOM) levels depending on compost quality and when/whereapplied. This often leads to increases in organic carbon andtotal nitrogen in topsoil. Equilibrium is achieved after longperiods of time and this is affected by soil type, climate, by themeans of exploitation and the quality/quantity of thecompost. Soil pH is generally increased or stabilized this cansave lime inputs in some circumstances. The Cation ExchangeCapacity (CEC) of SOM is higher than that of clay minerals soraising SOM will lift overall soil CEC. In terms of the effects onphysical properties compost use can lead to larger and morestable aggregates. Mature compost is better than youngcompost in this respect. Over the longer term (>3 years) soildensity decreases-increased aeration has been seen but therehas only been a small number of studies. The majority ofstudies showed increased water-holding capacity andinfiltration though this was in the longer term studies. It wasnoted that many field studies did not provide a consistentpicture of the details of the composts used e.g. ingredients,management of the composting process and qualityparameters. If mineral fertilizers were added this was often notstated (Table 1).

Humic substances: Humus in soil has traditionally beenseparated into humin, humic acid and fulvic acid based onextraction with an alkaline solution and subsequentprecipitation after addition of an acid8. The fractions typicallyrank in their resistance to microbial decomposition in theorder humic acid> fulvic acid>humin70. Concentrated sourcesof organic material such as peat, composts and brown coal(oxidized coal, lignite, leonardite) also contain humicsubstances and are often marketed on the basis of their humic

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Asian J. Plant Sci., 16 (3): 109-131, 2017

and fulvic acid contents as determined by similar procedures.Contents of humic acids vary, however. Some of thechemically extracted humic and fulvic acid separates arethemselves sold as soil amendments. In discussion of organicamendments, a clear distinction must be made betweenproducts containing humic substances and those productsthat are humic (or fulvic) acids extracted from the primarysources listed above. Humic substances can stimulatemicrobial activity directly through provision of carbonsubstrate, supplementation of nutrients and enhancednutrient uptake across cell walls. Valdrighi et al.71 reported thatincreasing amounts of compost or brown coal-derived humicacid stimulated aerobic bacterial growth but had only slighteffects on actinomycetes and no effect on filamentous fungi.

Differences in microbial response were related to themolecular weight of the humic acids, with the lower weightfractions, typical of composts, causing greater microbialstimulation than the higher molecular weight fractionsextracted from brown coal71. Application of humic substancesmay induce changes in metabolism, allowing organisms toproliferate on substrates which they could not previously use.Both heterotrophic and autotrophic bacteria can bestimulated by humic acid addition, mostly through theenhanced surfactant-like absorption of mineral nutrients,although heterotrophs also benefit from the direct uptake oforganic compounds70,71. Nitrifiers (chemotrophs) cannot usehumic acids as an alternative carbon and energy source71.

The principal indirect effects of humic substances on soilorganisms are through increased plant productivity bymechanisms as listed below but excessive applications cannegatively affect plant growth71,72, possibly through reducedavailability of chelated nutrients73. Field studies vary widely inthe applied amounts of humic substances and in outcomes8,73

found no effect of commercial humate applied at 8.2 t haG1 onmicrobial activity or microbial functional groups (total fungi,actinomycetes, total Gram-negative bacteria, fluorescentpseudomonas and P. capsici) in a sandy soil used to grow bellpeppers. Similarly, after 5 years of annual applications of100 L haG1 liquid humic acid to a horticultural soil74, found noeffect on microbial biomass or enzyme activity. They ascribedthe lack of effect to the low rates recommended by themanufacturer because of high product costs. Municipal solidwaste compost and sewage sludge were more affordable andled to significant increases in microbial biomass in the samestudy73. Calculated from laboratory studies that 67.5 kg haG1

of humic substances were needed for effective application toa sandy soil but thought beneficial effects to plants may onlyoccur in semi-arid or arid areas when applied in combinationwith irrigation and mineral nutrients.

Combined use of chemical and organic fertilizers: There isincreased emphasis on the impact on environmental qualitydue to continuous use of chemical fertilizers75. The integratednutrient management system is an alternative and ischaracterized by reduced input of chemical fertilizers andcombined use of chemical fertilizers with organic materialssuch as animal manures, crop residues, green manure andcomposts. Management systems that rely on organic inputs asplant nutrient sources have different dynamics of nutrientavailability from those involving the use of chemical fertilizers.For sustainable crop production, integrated use of chemicaland organic fertilizer has proved to be highly beneficial.Several researchers have demonstrated the beneficial effect ofcombined use of chemical and organic fertilizers to mitigatethe deficiency of many secondary and micronutrients in fieldsthat continuously received only N, P and K fertilizers for a fewyears, without any micronutrient or organic fertilizer29,31,75. Afield experiment was conducted for 7 years continuously toevaluate the influence of combined applications and organicand chemical fertility buildup and nutrient uptake in a mint(Mentha arvensis) and mustard (Brassica juncea) croppingsequence76. Results indicated that integrated supply of plantnutrients through FYM (farmyard manure) and fertilizer NPK,along with Sesbania green manuring, played a significant rolein sustaining soil fertility and crop productivity. Based on theevaluation of soil quality indicators, the use of organicfertilizers together with chemical fertilizers, compared to theaddition of organic fertilizers alone, had a higher positiveeffect on microbial biomass and hence soil health77.Application of organic manure in combination with chemicalfertilizer has been reported to increase absorption of N, P andK in sugarcane leaf tissue in the plant and ratoon crop,compared to chemical fertilizer alone (Table 2-5)78.

The comparison of the change of chemical and biologicalproperties in soils receiving FYM, poultry manure andsugarcane filter cake alone or in combination with chemicalfertilizers for 7 years under a cropping sequence of pearl milletand wheat results showed that all treatments except chemicalfertilizer application improved the soil organic C, total N, P andK status. Increase in microbial biomass C and N was observedin soils receiving organic manures only or with the combinedapplication of organic manures and chemical fertilizerscompared to soils receiving chemical fertilizers79. This studyshowed that balanced fertilization using both organic andchemical fertilizers is important for maintenance of soilorganic matter content and long-term soil productivity in thetropics where soil organic matter content is low. The effects oforganic fertilization and combined use of chemical andorganic fertilizer on crop growth and soil fertility depend on

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Asian J. Plant Sci., 16 (3): 109-131, 2017

the application rates and the nature of fertilizers used.Application of 15 tons FYM haG1 significantly increased soilorganic matter and available water holding capacity butdecreased the soil bulk density, creating a good soil conditionfor enhanced growth of the rice crop80. Positive balances ofsoil N and P resulted from combined application of FYM andinorganic N and P sources. Application of 15 tons haG1 FYMand 120 kg N haG1 resulted in 214.8 kg haG1 N positive balancewhile application of 15 tons haG1 FYM and 100 kg P2O5 haG1

resulted in a positive balance of 69.3 kg P2O5 haG1 availableP. The compost manure and compost manure+NPK showeda greater potential for increasing plant macronutrients (N, P,K, Ca and Mg) contents81. The result showed that combinedapplication of Municipal solid waste with NPK performedbetter than sole application of either Municipal solid waste orNPK fertilizer82 (Table 2, 5).

Microbial inoculants: Inoculation with natural or geneticallyengineered microbial formulations can be broadly categorizedaccording to whether they are intended to (a) exist on theirown in the bulk soil, (b) populate the rhizosphere, (c) formsymbiotic associations with plants or (d) promote microbialactivity on leaf or straw surfaces. To achieve the desired effectin the field, the inoculant organism must not only survive butestablish itself and dominate in the soil or rhizosphere8.Survival depends firstly on the quality of the inoculant itself,i.e., purity, strain trueness, viable numbers, the degree ofinfectivity and level of contaminants89. Secondly, theestablishment and proliferation of inoculant in the soilenvironment are determined by many edaphic and climaticfactors, the presence of host organisms (for symbionts andendophytes) and, most importantly, by competitiveinteractions with other microorganisms and soil fauna90.Effects of inoculation on indigenous soil organisms cantherefore either result from direct addition effects andinteractions with indigenous soil organisms or from indirecteffects via increases in plant growth by one or several of themechanisms.

Positive effects of inoculants on the soil microbial biomassmay be short-lived and increases in biomass or activity caneven be due to the indigenous population feeding on thenewly added microorganism89,90. The most successful andwidely studied inoculants are the diazotroph bacteria(Rhizobium, Bradyrhizobium, Sinorhizobium and Frankia)used for symbiotic fixation of N2 from air. Provided soilconditions are favorable for rhizobia survival90,91 inoculationcan increase microbial C and N in the rhizosphere comparedwith uninoculated soils91. Population changes can be limitedto the season of inoculation if the newly added organism is

not as well adapted to the soil conditions as the indigenouspopulation90. Inoculant application research is increasinglyfocusing on co-inoculation with several strains or mixedcultures enabling combined niche exploitation, cross-feeding,complementary effects and enhancement of oneorganism’s colonization ability when co-inoculated with a rhizosphere-competent strain.

An example is the use of phosphorus-solubilizing bacteriato increase available phosphorus along with mycorrhizae thatenhance phosphorus uptake into the plant. Saini et al.92

achieved maximum yields of sorghum and chickpea at half therecommended rates of inorganic fertilizer when a combinationof mycorrhizae, N2-fixing bacteria and phosphorus-solubilizingbacteria was added. Increases in microbial biomass C, N and Pin soils of inoculated treatments were strongly correlated withN and P uptake of the plants. Specific ‘helper’ bacteria mayimprove the receptivity of the root to the fungus to enhancemycorrhizal colonization and symbiotic development withplant roots. Similarly, legume root nodulation can beenhanced by co-inoculation with Azospirillum, whichincreases root production and susceptibility for rhizobiuminfection and may also increase secretion of flavonoids fromroots that activate nodulation genes in Rhizobium. Asignificant reduction in indigenous actinobacterialendophytes upon inoculation of soil with a commercialmulti-organism product, compared with no change indiversity after inoculation with a single species93. Trial with‘Effective Microorganisms’ (EM), a proprietary combination ofphotosynthetic bacteria, lactic acid bacteria and yeasts usedas a soil and compost inoculant, showed enhanced soilmicrobial biomass, plant growth and produce quality94. Theinteractions of microbial inoculants with indigenous soilorganisms are likely to be complex and a better mechanisticunderstanding is necessary to predict short- and long-termeffects.

Combined use of bio fertilizers with chemical or organicfertilizers: The activity of soil organisms is very important forensuring sufficient nutrient supply to the plant. If themicroorganisms find suitable conditions for their growth, theycan be very efficient in dissolving nutrients and making themavailable to plants. The application of PSB, Bacillusmegatherium var. phosphaticum, increased the PSBpopulation in the rhizosphere and P availability in the soil. Italso enhanced sugarcane growth, yield and quality95. Whenused in conjunction with P fertilizers, PSB reduced therequired P dosage by 25%. In addition, 50% of costlysuperphosphate could be replaced by a cheap rockphosphate, when applied in combination with PSB. The effects

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Asian J. Plant Sci., 16 (3): 109-131, 2017

of a combined treatment of multifunctional biofertilizer(mixture of Bacillus sp. B. subtilis, B. erythropolis, B. pumilusand P. rubiacearum) plus 50% chemical fertilizer (½CF+biofertilizer) on a treatment of with chemical fertilizer (CF)and biofertilizer on the growth of lettuce were compared byYoung et al.96. Results showed there was a 25% increase oflettuce yield for the treatment of ½ CF+biofertilizer comparedto that of the CF treatment, indicating that at least 50% ofchemical fertilizer can be saved as multifunctional biofertilizer was used along with chemical fertilizer. The effects ofmultifunctional biofertilizer (mixture of Bacillus sp. B. subtilis,B. erythropolis, B. pumilus and P. rubiacearum) on rhizospheremicrobial activity and the growth of water celery in a fieldexperiment96. Results showed that the dry weight of watercelery in the treatment with 50% organic compound fertilizerwith multifunctional biofertilizer (MC+½ OCF) was increasedby 34% compared to the treatment with 100% OrganicCompound Fertilizer (OCF) added. In addition, the beneficialbacterial counts including mineral PSB, cellulolytic bacteriaand N2-fixing bacteria in the rhizosphere of water celery in theMC +½ (OCF) treatments were increased 102-104 CFU/gin(Table 4-5).

Integrated use of chemical, organic and bio fertilizers:Increased attention is now being paid to developing anIntegrated Plant Nutrition System (IPNS) that maintains orenhances soil productivity through balanced use of all sourcesof nutrients, including chemical fertilizers, organic fertilizersand bio fertilizers. The basic concept underlying the IPNS is theadjustment of soil fertility and plant nutrient supply to anoptimum level for sustaining desired crop productivitythrough optimization of the benefits from all possible sourcesof plant nutrients in an integrated manner75. The experimentconducted in a field to evaluate the effects of ChemicalFertilization (CF), organic fertilization (compost-n andcompost-p), combined use of chemical and organic fertilizer(compost-p + urea) and integrated use of chemical andorganic fertilizer along with biofertilizer [½ (compost-p+urea)+biofertilizer] on the growth of cabbage and maize (residualeffect) and soil fertility. The contents of mineral N (NH4

+

+NO3G) and Bray-1 P in all treatments, except CK, were higherthan those of the CF treatment, showing the benefits ofbiofertilizer and compost by supplying and enhancing therelease of N and P. Excess inputs and excess accumulation ofP in soil usually increase their potential to contribute solubleand particulate P to surface waters and result in P-driveneutrophication. The content of Bray-1 P in the test soil was69 mg kgG1, rated as “high” in terms of P availability. There aremany suggestions in the literature that significant rising of

Bray-1 P content is not good for a soil with a high level of Pavailability, from the economic and environmental standpoint.The Bray-1 P content of the soil was approximately twice ashigh in the Compost-N treatment compared to the CFtreatment, showing significant P accumulation in the soil. Thisindicated that reducing half the amount of compost and ureacombined with inoculants of mixed strains of beneficialmicroorganisms has considerable potential to lessen Paccumulation in the soil and saves the input of chemical andorganic fertilizers75.

PESTICIDES

The results from literature on the effects of selectedpesticides on soil health are shown in Table 4 (herbicides),Table 5 (insecticides and nematicides) and Table 6(fungicides). There is clearly a paucity of data (particularly onphysical and chemical property of the soil) in internationalliterature on the effects of a large number of pesticides on soilhealth. Most of this review has focused on soilmicroorganisms. Pesticides that reach the soil can alter the soilmicrobial diversity and microbial biomass. Any alteration inthe activities of soil microorganisms due to applied pesticideseventually leads to the disturbance in soil ecosystem and lossof soil fertility120. Numerous studies have been undertakenwhich highlight these adverse impacts of pesticides on soilmicroorganisms and soil respiration77,121. In addition to this,exogenous applications of pesticides could also influence thefunction of beneficial root-colonizing microbes such asbacteria and arbuscular mycorrhiza, fungi and algae in soil byinfluencing their growth, colonization and metabolicactivities122. The pesticides that reach the soil can interact withsoil microorganisms in several ways:

C It can adversely affect the growth, microbial diversity ormicrobial biomass of the soil microflora. For example,sulfonylurea herbicides (metsulfuron methyl,chlorsulfuron and thifensulfuron methyl) were reportedto reduce the growth of the fluorescent bacteriaPseudomonas strains that were isolated from anagricultural soil123. The Pseudomonas spp. is known toplay an important ecological role in the soil habitat andhence its reduction can adversely affect soil fertility

C Pesticide application may also inhibit or kill certain groupof microorganisms and outnumber other groups byreleasing them from the competition124. For example,increase in bacterial biomass by 76% was reported inresponse to endosulfan application and that reduced thefungal biomass by 47%125

122

Asian J. Plant Sci., 16 (3): 109-131, 2017

123

Table 5: Effe

ct of a

nim

al m

anur

es, b

ioso

lids a

nd com

posts o

n so

il or

ganism

sCo

mpa

red trea

tmen

tsEffects

Refere

nces

Com

post of b

ioso

lids,

woo

d was

te and

gre

en w

aste

Soil ba

sal res

piratio

n, m

icro

bial C and

ana

erob

ically m

iner

al sa

ble N w

ere sig

nific

antly

increa

sed in th

e am

ende

d plot

s.Sp

eir e

t al.1

14 and

Can

ali e

t al.1

15

No effects o

n rh

izob

ial n

umbe

rs or m

icro

bial biose

nsor

s (Rh

izot

ox C and

lux-m

arke

d Es

cher

ichia co

li)Co

mpo

sts o

f dist

iller

y was

te and

live

stoc

k m

anur

e, pou

ltry

Param

eter

s related

to pot

entia

lly m

iner

al sa

ble C sh

owed

sign

ifica

nt differ

ence

s am

ong th

e trea

tmen

ts. N

o diffe

renc

esW

ells

et al.1

16

man

ure, m

iner

al fe

rtilize

r con

trol

wer

e ob

served

in biodive

rsity

inde

xes

Com

posts o

f woo

dy m

ater

ial w

ith eith

er m

anur

e (p

oultr

yBo

th com

posted

trea

tmen

ts highe

r in m

icro

bial C th

an m

iner

al fe

rtilize

r tre

atm

ents, b

ut tr

ial w

as of s

yste

ms s

o th

ere

Zhan

g et

al.1

17

and ho

rse) or s

ewag

e slu

dge, se

veral m

iner

al fe

rtilize

r tre

atm

ents

wer

e also

oth

er differ

ing factor

s9-

year st

udy of

trad

ition

ally com

posted

FYM

, 2 ty

pes o

fFY

M in

crea

sed m

icro

bial biom

ass,

dehy

drog

enas

e ac

tivity

, dec

ompo

sition (cot

ton strip

s), b

ut not

sacc

harase

activity

,Miyitt

ah and

Inub

ushi

118

biod

ynam

ically com

posted

man

ure

micro

bial bas

al res

piratio

n, o

r m

etab

olic qu

otient

. Biody

nam

ic m

anur

e pr

eparation de

crea

sed so

il m

icro

bial bas

al re

spira

tion and

met

abolic quo

tient

com

pare

d to

non

-biody

nam

ic m

anur

e. A

fter 1

00 day

s, de

com

posit

ion was

faster

in plots w

hich

rece

ived

biody

nam

ic FYM

than

in plots w

hich

rece

ived

no or

non

-biody

nam

ic FYM

Com

posts o

f soy

milk

resid

ues,

cow m

anur

e, pou

ltry

Soil re

spira

tion in

crea

sed ra

pidly in

itially, bu

t pa

tter

ns d

iffer

ed am

ong th

e co

mpo

sts.

Com

posted

soym

ilk tr

eatm

ent

Fran

co et a

l.119

man

ure an

d se

wag

e slu

dge

gave

highe

r CO

2-evo

lutio

n an

d lower

met

abolic quo

tient

than

the ot

her c

ompo

sts

Gluco

se, m

aize

stalks

, or m

aize

stalk co

mpo

st add

edTh

e add

ition

of or

ganic su

bstrates

(gluc

ose, m

aize

stalks

and m

aize

stalk c

ompo

st) to

con

tam

inated

soils

had

no

Han

da et a

l.120

to so

ils con

tam

inated

with

cru

de oil

syne

rgist

ic effe

ct on th

e de

com

posit

ion of

cru

de oil bu

t pro

duce

d a m

arke

d increa

se in

micro

bial biom

ass,

alth

ough

the

increa

se w

as sm

aller t

han in unc

ontam

inated

soils

. Com

post dec

reas

ed th

e stre

ss con

ditio

ns cau

sed by

oil

cont

amination as

mea

sure

d by

a re

duction in m

etab

olic quo

tient

Table 6: Im

pact of h

erbicide

s on no

n-targ

et so

il or

ganism

sAc

tive ch

emicals

Effects

Refere

nces

Atrazine

Sign

ifica

nt activation of

soil ur

ease

activity

(up to

100

-fold in

crea

se) a

nd su

ppre

ssion of

inve

rtas

e en

zym

ePa

nda an

d Sa

hu13

4

Butach

lor

Very to

xic, su

ppre

ssing gr

owth

, sex

ual m

atur

ation an

d co

coon

pro

duction of

the ea

rthw

orm

Drawida willsi

follo

wing sin

gle do

se at r

ecom

men

ded rate

Busse et a

l.135

Glyph

osate

Glyph

osate Ba

cter

ia re

duce

d. Fun

gi and

actinom

ycet

es in

crea

sed. M

icro

bial activity

increa

se by 9-

19%. Inc

reas

ed glyph

osate de

grad

ation with

repe

ated

app

lication

Arau

jo et a

l.136

Glyph

osate

Shor

t ter

m cha

nges

to com

mun

ity st

ructur

e. In

crea

sed m

icro

bial activity

and

no long

-ter

m cha

nges

to com

mun

ity st

ructur

eDelga

do et a

l.137

Glyph

osate, parqu

et

Activ

ation of

ure

ase an

d inve

rtas

e so

il en

zym

es, b

ut glyph

osate su

ppre

ssed

pho

spha

tase

activity

(up to

98%

)Pa

nda an

d Sa

hu13

4

Glyph

osate an

d 2,4-

DB

No effect of s

ingle do

se to

soil on

gro

wth

or s

urviva

l of t

he earth

wor

ms A

porre

ctod

ea tr

apez

oide

s, A.

caliginos

a, A

. long

a or

A. ros

eaSing

h an

d Ry

an13

8

Oxy

fluor

fen, oxa

diaz

onBo

th her

bicide

s stim

ulated

micro

bial pop

ulations

and

increa

sed av

ailability of

pho

spho

rus i

n rh

izos

pher

e so

il of

rice

Filip

and

Tes

arov

a139

Pend

imet

halin

So

il ne

matod

es and

oth

er in

verteb

rate

s red

uced

, plant

-rhizo

bium

sym

bios

is re

duce

d at her

bicide

rate

s as l

ow as 0

.5-1

.0 kg ha

G1Kinn

ey et a

l.140

Pros

ulfu

ron

Sign

ifica

nt re

duction in pro

duction of

N2O

and

NO fo

llowing N-b

ased

fertilize

r app

lication: Signific

ant r

educ

tion in nitr

ifica

tion

Chen

141

Asian J. Plant Sci., 16 (3): 109-131, 2017

C Applied pesticide may also act as a source of energy tosome of the microbial group which may lead to increasein their growth and disturbances in the soil ecosystem.For example, bacterial isolates collected from wastewaterirrigated agricultural soil showed the capability to utilizechlorpyrifos as a carbon source for their growth126

C Pesticides can alter and/or reduce the functional structureand functional diversity of microorganisms but increasethe microbial biomass127. In contrast, application ofpesticides can also reduce the microbial biomass whileincreasing the functional diversity of microbialcommunity. For example, methamidophos and ureadecreased the microbial biomass and increased thefunctional diversity of soil as determined by microbialbiomass and community level physiological profiles128

Herbicides: The herbicides (Table 6) generally had no majoreffects on soil health, with the exception of butachlor, whichwas shown to be very toxic to earthworms at agricultural rates.The authors showed, however, that butachlor had little effecton acetylcholinesterase activity. Phenmedipham inducedavoidance behavior in earthworms and collembola. Theseeffects are expected to be relatively short lived asphenmedipham is broken down moderately rapidly (25-dayhalf-life) in soil. Other effects of herbicides on soil organismswere mainly isolated changes in enzyme activities. Glyphosate,for example, was shown to suppress the phosphatase activityby up to 98% in a laboratory study; however, urease activitywas stimulated by glyphosate as well as atrazine.

Insecticides: Insecticides (Table 7) were generally shown tohave a greater direct effect on soil health than herbicides8.Organophosphate insecticides (chlorpyrifos, quinalphos,dimethoate, diazinon and malathion ) had a range of effectsincluding changes in bacterial and fungal numbers in soil,varied effects on soil enzymes as well as reductions incollembolan density and earthworm reproduction. Carbamateinsecticides (carbaryl, carbofuran and methiocarb) had a rangeof effects on soil organisms, including a significant reductionof acetylcholinesterase activity in earthworms, mixed effectson soil enzymes and inhibition of nitrogenase in Azospirillumspecies.

Persistent compounds including arsenic and lindanecaused long-term effects, including reduced microbialactivity129, reduced microbial biomass and significantdecreases in soil enzyme activities. Azoxystrobin, have recentlybeen shown to effect on a biocontrol agent used for thecontrol of Fusarium wilt130, illustrating potentialincompatibilities of chemical and biological pesticides. The

insecticides methyl parathion and especiallypentachlorophenol have been shown to interfere withlegume-rhizobium chemical signaling. Reduction of thesesymbiotic chemical signaling results in reduced nitrogenfixation and thus reduced crop yields131. Root noduleformation in these plants saves the world economy $10 billionin synthetic nitrogen fertilizer every year132. When the naturalnutrient cycling in the ecosystem is interfered in any way bypesticides or other sources of pollution, it will lead to declinein soil fertility and soil productivity. Long term experiment oninsecticides usage showed that soil physical characteristicssuch as bulk density were changed in long-term and it wasincreased compared to control soil133. The heavy metalsaccumulations in soil were highly affected and theconcentration of some metals such as cadmium has reacheda limit beyond the standard for agricultural purposes. Theresults also showed that fortunately the concentration of othermetals is not beyond the standard36.

Soil fumigants: Soil fumigants are designed to eliminateharmful soil organisms and any competition for soil resourcesbetween soil organisms and the crop8. In spite of this, soilfumigants have not always been found to have significanteffects on soil health (Table 8). Soil fumigants had long-termeffects on various soil functions141. The long-term effects offumigants were shown to be reduced by the addition ofcomposted steer manure, with normal biological activitybeing observed 8-12 weeks following high application ratesof the fumigant142. In the absence of the organic amendment,little recuperation (resilience) of soil function was detectedeven after 12 weeks.

Pesticide formulation: The formulation is the chemical andphysical form in which the pesticide is sold for use. The activeingredient (a.i.) is the chemical in the formulation that has thespecific effect on the target organism. In addition to the activeingredient, the formulation of a pesticide may also influencesoil health. This is, however, an aspect that is rarelyinvestigated. Little is known about the environmental fate ofadjuvants after application on agricultural land. Adjuvantsconstitute a broad range of substances, of which solvents andsurfactants are the major types8. Non-ionic surfactants such asAlcohol Ethoxylates (AEOs) and alkylamine ethoxylates(ANEOs) are typical examples of pesticide adjuvants8. Thesurfactant in the Roundup formulation polyoxyethylene amine(POEA) was significantly more toxic to Microtox bacteriumthan glyphosate acid or the IPA salt of glyphosate. EvenRoundup was found to be less toxic143. The toxicity ofglyphosate acid was concluded to be a result of its inherent

124

Asian J. Plant Sci., 16 (3): 109-131, 2017

125

Table 7: Im

pact of ins

ectic

ides

and

nem

aticides

on so

il he

alth

Activ

e ch

emicals

Effects

Refere

nces

Diazino

n Sign

ifica

nt in

crea

se in

deh

ydro

gena

se activity

and

dec

reas

e in alkaline ph

osph

omon

oester

ase fo

r up to

30 da

ys fo

llowing trea

tmen

tLo

ureiro

et a

l.146

Dim

etho

ate

Shor

t-te

rm re

duction in m

icro

arth

ropo

d nu

mbe

rs (C

ollem

bola), bu

t rec

over

y in num

bers afte

r tim

e. Com

mun

ity st

ructur

e re

maine

d diffe

rent

iate

d.Lo

ureiro

et a

l.146

Slight

redu

ction in so

il m

icro

bial biom

ass (

mea

sure

d by

ATP

)Im

idac

lopr

id

Sign

ifica

nt in

crea

ses i

n de

hydr

ogen

ase an

d ph

osph

omon

oester

ase ac

tivities

whe

n us

ed as s

eed dr

essin

g, effe

ct la

sting p to

60 da

ysLo

ureiro

et a

l.146

Lind

ane, dim

etho

ate

Colle

mbo

la avo

id so

il with

lind

ane (10-

20 m

g kg

G1) a

nd dim

etho

ate (5-2

0 m

g kg

G1), while earth

wor

ms a

voided

dim

etho

ate at 2.5 m

g kg

G1Am

orim

et a

l.147

Arse

nic

Arse

nic co

-con

tam

ination was

show

n to

inhibit t

he bre

akdo

wn of

DDT an

d a co

ncom

itant

redu

ction in m

icro

bial activity

was

foun

dVa

n Zw

iete

n et

al.1

29

Beno

myl

Ench

ytraeid wor

ms a

voids b

enom

yl in

stan

dard

avo

idan

ce te

st pro

cedu

res

Sagg

ar et a

l.148

Carb

aryl

Activ

ation of

ure

ase an

d inve

rtas

e so

il en

zym

es, b

ut su

ppre

ssion of

pho

spha

tase

enz

yme

Pand

a an

d Sa

hu e

t al.14

9

Carb

ofur

an, m

alathion

Sign

ifica

nt re

duction in ace

tylcho

lines

terase

activity

in earth

wor

ms (

D. w

illsi)

for u

p to

45 da

ys (c

arbo

furan)

and

75 da

ys (m

alathion

)Men

on et a

l.150

Chlorp

yrifo

s, qu

inalph

os

Redu

ced ox

idative ca

pability of

the so

ils as m

easu

red by

redu

ced de

hydr

ogen

ase ac

tivity

and

inhibite

d iro

n re

duction

Dick

151

Malathion

Sh

ort-te

rm im

pacts o

f stand

ard ap

plication rate

s of m

alathion

on ea

rthw

orm

repr

oduc

tion lasting fo

r 105

day

sMen

on e

t al.1

50

Table 8: Im

pact of fun

gicide

s on so

il he

alth

Activ

e ch

emicals

Effects

Refere

nces

Beno

myl

Supp

ression of

resp

iratio

n, st

imulation of

deh

ydro

gena

se activity

, effe

cts w

ere less not

icea

ble with

org

anic m

atte

r add

ition

Mer

ringt

on et a

l.152

Sign

ifica

nt lo

ng-ter

m effe

cts o

n m

ycor

rhizal colon

ization (80%

redu

ction)

, red

uctio

n in fu

ngal to

bac

teria

l ratios a

nd nem

atod

e nu

mbe

rsBu

nem

ann et

al.8

Earthw

orm

s avo

id ben

omyl at 1

mg kg

G1 so

ilAm

orim

et a

l.147

Capt

an

Supp

ression of

resp

iratio

n an

d de

hydr

ogen

ase ac

tivity

; inc

reas

es in

am

mon

ium

NMer

ringt

on e

t al.1

52

Fung

al le

ngth

and

den

sity, and

micro

bial C and

N si

gnifica

ntly re

duce

dBu

nem

ann et

al.8

Copp

erEa

rthw

orm

pop

ulations

avo

id so

ils w

ith con

cent

ratio

ns as l

ow as 3

4 m

g kg

G1. L

ack of

bre

akdo

wn of

org

anic carbo

n su

gges

t pot

entia

l lon

g-te

rm im

plications

Van Zw

iete

n et

al.1

29

Increa

sed m

etab

olic quo

tient

indica

ting m

icro

bial st

ress at 2

80-3

40 m

g Cu

kgG

1 . Sign

ifica

ntly re

duce

d m

icro

bial biom

ass a

nd ra

tio of m

icro

bial biom

ass t

o OC

Gaw

et a

l.153

Redu

ced pe

rform

ance

of s

oil fun

ctions

resu

lting

in re

duction of

DDT de

grad

ation

Mon

kied

je et a

l.154

Chloro

thalon

il Su

ppre

ssion of

resp

iratio

n, st

imulation of

deh

ydro

gena

se activity

Mer

ringt

on et a

l.152

Man

coze

b, chlor

otha

lonil

Sign

ifica

nt re

duction in pro

duction of

N2O

and

NO fo

llowing N-b

ased

fertilize

r app

lication: Signific

ant r

educ

tion in nitr

ifica

tion

Kinn

ey et a

l.140

Chloro

thalon

il, azo

xystro

bin

Both

fung

icides

toxic to

the bioc

ontrol age

nt Fus

arium

oxy

spor

um st

rain CS-20

which

has

bee

n us

ed to

redu

ce in

cide

nce of

Fusa

rium

wilt

Frav

el et a

l.130

Met

alax

yl, m

efen

oxam

Re

duce

d en

zym

e ac

tivity

, in pa

rticular deh

ydro

gena

se activity

, for

up to

90 da

ys. Inc

reas

ed bac

teria

l num

bers w

ith in

crea

sing do

ses,

but t

oxic to

N fixe

rsMon

kied

je et a

l.154

at 1 m

g kg

G1 (m

efen

oxam

) and

2 m

g kg

G1 (m

etalax

yl)

Asian J. Plant Sci., 16 (3): 109-131, 2017

acidity. In another study, demonstrated that the presence ofethylamine in a glyphosate formulation had major effects onBradyrhizobium144,145, whereas the active ingredient(glyphosate) had little if any effect. In formulation, effectsincluded reduced nodulation in a soybean crop8.

CONCLUSION

Organic amendments such as manure, compost, biosolidsand humic substances provide a direct source of C for soilorganisms as well as an indirect C source via increased plantgrowth and plant residue returns. Herbicides showed lesssignificant effects on soil health, whereas negative effects ofinsecticides and fungicides were more common. The soundmanagement of crop production inputs must attempt toensure both an enhanced and safeguarded environment.

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