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Basic Concepts in Nutrient Management
for Organic FarmingJonathan Deenik
Assistant Specialist, Soil FertilityDepartment of Tropical Plant and Soil Sciences
Outline
• Feed the soil• Diagnosis of Nutrient
Deficiencies• Soil tests
Feed the Soil• Feed the bugs!
- Microorganisms- Bacteria- Fungi- Actinomycetes- Protozoa- Algae
- Nematodes- Macrofauna
- Earthworms
Organic Approaches
Cover Crops and Compost“Feed the Soil”
SupplementalHigh N
Fertilizers
Courtesy E. Brennan
Incorporating cover crops adds plant nutrients and conditions soil
Courtesy E. Brennan
Sunn hemp is a good source of N
Sudan grass adds a lot of OM
http://www.wiu.edu/AltCrops/Othercrops_files/sunn-hemp.gif J.L. Deenik
Why are Cover Crops Important?
Cover Crops
Soil Fertility
Soil Biology
Arthropod Pests
Weeds
Soil Organic Matter
Diseases
Rotations
Nutrient Leaching
Soil Erosion
Courtesy E. Brennan
Compost conditions the soil
http://compost.tamu.edu/demos/palopinto/compost.jpg
Compost• Require large inputs over time• Not necessarily a source of plant nutrients in
the short-term• Low N content (≈1.0%), only 15% available in
the first year• Improves physical, chemical, and biological
properties• Maintenance/enhancement of soil quality.
Courtesy E. Brennan
Manures as FertilizersTwo Important Questions?
1. What is the N content of the manure?
3. How long does it take for the N to go from organic form to inorganic form?
Norg NH4+ NO3
-
Plant Available
Manures as Fertilizers
Chicken manure addedat ≈16 tons per acre
Dairy Manure addedat ≈40 tons per acre
Chicken Manure
N M
iner
aliz
ed (m
g kg
-1)
0
50
100
150
200
250
Wahiawa
Dairy Manure
N M
iner
aliz
ed (m
g kg
-1)
0
50
100
150
200
250Wahiawa
Swine Manure
0 5 10 15 20 25 30 35
N M
iner
aliz
ed (m
g kg
-1)
0
50
100
150
200
250
Wahiawa
Waialua
Waialua
Weeks
Waialua
0 5 10 15 20 25 30 35
Other N Rich AmendmentsWaialua Soil Wahiawa Soil
Weeks
0 2 4 6 8 10 12 14 16 18 20 22 24 26
N M
iner
aliz
ed (m
g kg
-1)
0
50
100
150
200
250
300
350
400
Fish/Blood MealKukui NutSunn Hemp
Weeks
0 2 4 6 8 10 12 14 16 18 20 22 24 26
0 T/acre CM
2.5 T/acre CM
5 T/acre CM
10 T/acre CM 16-16-16
Adding Chicken Manure to a Fertile Soil
Field ExperimentsWahiawa Soil
lb N per Acre
0 100 200 300 400 500 600 700
Tota
l Fre
sh B
iom
ass
(lb/a
cre)
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
Chicken manureDairy manureSwine manure16-16-16 Control
How Much to Add?1. Information
- crop N requirement- N content of amendment- expected amount of N that will mineralize
- high N materials ≈80% (>6%)- chicken manure ≈40-60%- dairy manure ≈30-40%
2. Example calculationFBM DM200/(0.1*0.8)= 200/(0.01*.3)=2,500 lb per acre 66,700 lb per acre
Supplemental Fertilizers
Supplemental Fertilizers
• To raise pH- Reduce existing/potential toxicities- Increases P availability- pH range 5.5 - 7.0- Liming can be expensive because
soils are buffered (clay content and OM)
• To supply Ca- Highly weathered soils are almost
always deficient in Ca
Liming is Important
Sources of Soil Acidity
Correcting Soil Acidity
Al3+ + H2O Al(OH)2+ + H+
Liming Reactions:
CaCO3 + H2O Ca2+ + HCO3- + OH-
OH- + H+ H2O
HCO3- + H+ H2CO3
Al3+ + 3OH- Al(OH)3
Liming
Tons CaCO3 per Acre
Summary• Soil health and productivity are maintained by
regular inputs of organic matter• Cover crops are a key component of soil
management• High N inputs may be required in intensive
vegetable production systems• How much to add depends on crop requirement,
N content, and N availability from the material• In weathered tropical soils acidity can be a
problem, and it must be corrected with liming
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