The Management of Crop Production on Steep Slopes

MSc 556 Land Husbandry in Drought Prone Areas

Richard Cobb

Why Cultivate Steep Slopes?

Many reasons why so-called marginal land is cultivated

• Population Pressure

• Resource Pressure

Issues relating to cultivation on steep slopes

Erosion control

• Slope Stability

• High Rainfall Intensity

• Surface Runoff

Tillage

Water Retention (Rice)

Traditional methods of crop management on steep slopes

• Perhaps the oldest form of large-scale land management specifically for

steep slopes is TERRACING. The process involves the creation of steeps on

the hillsides to aid in water retention (Rice), reduction in soil erosion and

ease of tillage. However, Terracing can result in less stable hillsides (Chorley

et al, 1984), expensive (labour and capital) and have high maintenance.

• Also used are FALLOW, COVER CROPS and DRAINAGE DITCHES to

reduce the impact of rainfall on bare soils prone to erosion.

Traditional methods of crop management on steep slopes: Case study

Land Use, Soil Loss and Sustainable Agriculture in Rwanda

Issues: High Population

Steep Slopes

High Rainfall Intensity

Traditional methods used are Terracing and drainage ditches.

Due to high rainfall intensity, terraces are commonly destabilised resulting in

mass soil movement. Drainage ditches often aid the process of gully erosion

due to high runoff.

Traditional methods of crop management on steep slopes: Case study cont.

Hedgerows and grass strips have been introduced to improve slope stability but

due to the reduction in cultivatable land, farmers are beginning to cultivate

further more marginal areas.

Cropping systems that minimise erosion have not been successful as farmers

are unwilling to move away from traditional settlement patterns and farming

practices

Management Techniques

• Contour hedgerows are the process by which woody shrubs are planted along

hillside contours to aid in natural terrace creation through deposition of eroded

material. Contours are typically found using an ‘A’ frame. Plants chosen for

contour hedgerows can provide crops for human or animal consumption

•Ally Cropping is a continuation or adaptation of contour hedgerows. The

process involves crops being planted in Alley’s or rows inside the contour

hedgerows. Crops are chosen for their suitability to the specific inter-hedgerow

spaces, commonly with relationship to their ability to grow on lessening

amounts of residual water (top to bottom)

Management Techniques cont.

•Cover crops, including grass strips, have been shown to prevent soil erosion at

times when land is in fallow or when terraces have been destabilised. Grass strips

can act in a similar way to contour hedgerows by initiating the deposition of

eroded material and stabilising slopes. Cover crops provide soil stability when soil

would otherwise be left bare. Species can be chosen to provide green manure or

nitrogen fixing properties.

• Agroforestry is the general mix of trees and agriculture. With regards to the

management of agriculture on steep slopes, trees can provide many benefits. They

can be used in conjunction with, or as an alternative, to woody shrubs in contour

hedgerows to provide timber, fruit crops or fodder. They also may have soil

fertility benefits through nitrogen fixing or leaf drop. Trees can also be used to

stabilise slopes above cultivated areas to prevent mass soil movement.

Management Techniques Case study

Agroforestry in Guatemalan Agriculture

Case study is based on the Chiquimula district in the Guatemalan highlands

• Forest cover removed due to population pressure

• Traditional agricultural practises employed: Wet season cultivation of Corn

and Beans; Dry season uncovered fallow.

• The result was high soil erosion at the start of the wet season before crops

prevented soil loss. As no terracing or soil conservation techniques were in

operation, all soil eroded was lost and deposited in the valley areas.

Management Techniques Case study cont.

An agroforestry scheme was introduced through participatory extension. The

farmers new of a local tree species Madre de Cacao (Gliricidia sepium) which

was known to have many beneficial properties.

Gliricidia was traditionally used to improve soil fertility when grown in

conjunction with Cocoa (Cacao) crops. Gliricidia Has nitrogen fixing properties.

It was also known provide good timber for construction and woodwork as well as

high fuel-energy properties.

The trees were planted along contours at 15m spacing. Spacing was dependant on

a number of variables: The tree species, the degree of slope and the direction in

comparison to the sun. These variables determine the amount of available

sunlight for crops within contour tee lines.

Management Techniques Case study cont.

Crop residues were also lined along contours to aid with soil fertility but to cause the

least interruption to cultivation

In this study, no quantifiable data was recorded. However, through the continuation

of participatory meetings, it was established that there was an increase in crop yield

and an ‘observed’ decrease in annual soil fertility. Farmers felt that the benefits that

were gained from the tree products were sufficient to justify the loss of cropping

land and also that they were aware of the benefits that soil conservation would bring

to their yields.

Agroforestry in Guatemalan agriculture. (2000) Benson institute

Conclusions

• Although traditional soil conservation techniques are well established, they are not always effective.

• ‘Off the shelf’ erosion control techniques may not be effective or appropriate to locations and cultures. Even if deemed to be so, take up of ‘new’ technology may not occur due to traditional practices and cropping systems.

• Need for participatory implementation/facilitation of soil conservation schemes to ensure sustainability.

• Local Knowledge about appropriate species and practices is vital.

References

Clay, D. and Lewis, L.A. Land use, Soil loss and sustainable agriculture in Rwanda. 1996. New York: Plenum Press

CFSCDD Soil Conservation in Ethiopia. 1986. Ministry of Agriculture, Ethiopia

Elliot,C. Management of Vertisols under semi-arid conditions. 1987. IBSRAM Pimentel, D. World soil erosion and conservation. 1993. Cambridge University Press

Syers,J.K. and Rimmer, D.L. Soil science and sustainable land management in the tropics. 1994. CAB International

Agroforestry in Guatemalan agriculture. (2000) Benson institute