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