The Management of Crop Production on Steep Slopes

1. MSc 556 Land Husbandry in Drought Prone Areas The Management of Crop Production on Steep Slopes Richard Cobb

2. Why Cultivate Steep Slopes? • Many reasons why so-called marginal land is cultivated • Population Pressure • Resource Pressure

3. Issues relating to cultivation on steep slopes • Erosion control • Slope Stability • High Rainfall Intensity • Surface Runoff • Tillage • Water Retention (Rice)

4. 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.

5. 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.

6. 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

7. 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)

8. 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.

9. 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.

10. 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.

11. 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

12. 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.

13. 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. IBSRAMPimentel, 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