soil and water conservation for dry zone of sri lanka
TRANSCRIPT
Soil and Water ConservationSoil and Water ConservationInduction Training for EU - SDDP staff November 2013
Dr. P.B. Dharmasena – National Consultant/ Agriculture and Water Management
Climate Change & Soil Climate Change & Soil Resource Productivity Resource Productivity
Climate change
Soil productivity
decline
Deforestation
Mis-management of land
Mis-practices of agriculture
Land development plan under the Land development plan under the projectproject
Ampara: 40 haVavuniya: 260 haMannar: 260 haAnuradhapura: 40 haMoneragala: 40 haTotal: 640 ha
3
Implementation Partner: Department of Agriculture
Human population growth, forest decline and green revolution
0
5
10
15
20
25
30
1870 1890 1910 1930 1950 1970 1990 2010 203001020
3040
5060
7080
90
Forest
PopulationSri Lankan trend
Green Green RevolutionRevolution
High yielding varietiesMechanized agricultureChemical fertilizer and agro-
chemicalsCommercialized agriculture
ImpactsImpactsHigh yielding varieties – High input
requirements, susceptible to pest and diseases, drought, salinity etc.
Mechanization - soil environment – physically disturbed◦Soil erosion, nutrient loss, water loss, weed
problemChemical fertilizer and agro-chemicals –
soil acidity, heavy metals, micro-nutrients deficiency, health hazards etc.
Accelerated erosionAccelerated erosion
Highly erosive rainfalls occur in low lying areas – Dharmasena (1992)
Elevation in m (amsl)
Erosivity (t.m/ha)
Location
Potential annual soil loss (mt./ha)Land slope (%)
2 4 6
AnuradhapuraGalgamuwaHorowpothanaKantaleMahailluppallamaMaradankadawalaPolonnaruwa
27263134252833
52516166485364
84 83 99108 78 87104
Potential erosion in selected locations of the central dry zone
Source: Dharmasena, 1992Erosion from dry zone agricultural lands can not be
over-looked
Tank Year Capacity (ha.m)
SedimentationVolume (ha.m)
% Rate(ha.m/year)
Paindikulama SiwalagalaMarikaragama
198419871990199019861990
30.228.025.819.936.235.3
9.711.914.18.69.6
10.5
24.329.835.330.221.022.9
0.730.73
0.23Source: Dharmasena, 1992
Major Problems in the Dry Major Problems in the Dry Zone Upland FarmingZone Upland Farming
Erosion of fertile top soil
Emergence of obnoxious weeds
Declining soil fertility
Difficulty of land preparation
Process of Soil ErosionProcess of Soil ErosionDisaggregation
of soilTransport of soil
particle by water
Deposition in depressions, streams, rivers and reservoirs
Types of Soil erosionTypes of Soil erosion
Splash erosionVertical erosion Inter-rill erosionRill erosionGully erosionStream bank
erosion
• Erosion of fertile top soil• Reduction of soil moisture holding capacity• Gradual decline of the suitable arable lands• Gully formation and land slides• Sedimentation of low lying areas and reservoirs
Consequences of soil erosion
Soil Erosion
Tank Sedimentation
Rain-fedFarming
Tank Capacity
Tank IrrigatedFarming
Vicious circle in tank-village farmingVicious circle in tank-village farming
Population Pressure
Land slope(%)
Spacing (m)
Runoff (m3/hr)
Bund height (cm)
DrainDepth (cm)
Top width (cm)
< 2
2 – 44 – 66 – 88 - 10
1510765
165100756050
3025252020
1510101010
7050504040
Recommendations for soil conservation bunds
Drain depth
Bund bottom width
Bund height
Drain top width
Dharmasena,1998
Contour drains Lock & Spill
Contour bunds Stone bunds
Contour cropping
Mulching
Cover crops Mixed cropping
Strip cropping Minimum tillage
Crop residues Alley cropping
Alley cropping
Wel
l Dra
ined
,
RBE,
< 3
0 cm
Wel
l Dra
ined
,
RBE
, 30-
60 c
mW
ell D
rain
ed, R
BE
> 60
cm
Mod
erat
ely
Drai
ned,
RBE,
> 6
0 cm
Impe
rfect
ly Dr
aine
d
RBE
Poor
ly Dr
aine
d L
HG
Land Use Model Cross SectionLand Use Model Cross SectionRecommended for RBE – LHG Recommended for RBE – LHG combinationcombination
Village Forest Fruit
Forest Rain-fed/ homestead
Irrigated upland
Irrigated lowland
50 m
60 m
50 m
35 m
LAND USE MODEL ALONG CATENA
Home Garden
Irrigated Upland
Farm tract
Village road
Fruit Forest
Village Forest
Irrigated Lowland
Irrigation canal
35 m
Storm water diversion drain
Diversi
on bund and drai
n
Common drain
Cultivated landCultivated land
Main irrigation canal
Natural drainage
Irrigable land
Homestead
Other field crops
Village forest
Main road
Village road
Farm tract
Communal lands
Tank
Lower CanalUpper Canal
Fruit forest gardens
Upstream reservation
Downstream reservation
How we conserve soil?• A = RKLSCP• A = RK (LS)max Ec., where, • A = Soil loss (mt/ha), R = Erosivity (mt.m/ha), K
= Erodibility• (LS)max = Maximum slope - length factor one
can achieve by manipulating land slope and length in a given piece of land and
• Ec = soil and crop management factor termed as Erosion Coefficient.
How we conserve soil?
1. Increase soil cover– Leave all the crop
residues in the field,– Conservation tillage that
leaves the residues on the soil surface,
– Apply organic materials as manures or mulch,
– Adopt inter-cropping and relay cropping,
– Leave the weed residues on the surface
How we conserve soil?
2. Increase soil organic matter content– Apply compost, – Add green
manure, – Add liquid
fertilizer,– Apply straw
mulch
How we conserve soil?3. Increase water infiltration
and moisture retention capacity– Maintain a protective
cover of residues over the soil,
– Reduce wind velocity by installing wind breaks,
– Create surface roughness between the crop rows,
– Keep fallow periods between cropping,
– Apply organic fertilizer, Adopt contour ridging,
– Reduce the land slope by terracing
How we conserve soil?4. Reduce runoff
– Collect the runoff in structures within which the water can infiltrate
– Construct structures that collect and lead the runoff away from the field
– Establish permeable barriers along the lines of contour to reduce runoff velocity
How we conserve soil?5. Improve rooting
conditions– Loosen the soil around
plants to reduce compaction and increase porosity
– Improve drainage by placing drainage channels where soils are poorly or imperfectly drained
– Make furrows or raised beds