Crop and natural resource management studies

Objective
Study crop and natural resource management systems that will improve and sustain productivity in major cassava ecologies

Background information and methodology
Although cassava as a crop performs relatively well under harsh conditions, research has demonstrated profitable responses to improvements in crop and soil management. Cassava requires relatively little nitrogen to achieve high yields, so that it responds to no more than 100kg/ha of nitrogen after which diminishing marginal returns set in. Phosphorus is the most important nutrient for obtaining yield increase in cassava. It has also been shown that cassava extracts more potassium from the soil than any other element. Potassium deficiency leads to lower dry matter and starch content and consequently higher cyanogenic potential. The relationships between the nutrient uptake and what the plants return to the soils by way of debris under continuous cultivation is not clearly understood.

With increasing population pressure and continual degradation of the physical environment, increasing proportion of cassava cultivation is being done under very marginal conditions: unstable climates, unreliable rainfall, fragile and degraded poor soil. COSCA data show that chemical fertilizers are applied to about 8% of cassava fields and manure to about 7% of the fields. While fallow periods decline as population density increases, the use of organic manure, livestock grazing and other agricultural land use intensification cultural practices become more frequent in the cassava-producing zones. COSCA also shows that in cassava growing areas of sub-Saharan Africa, each farmer produces multiple crops in multiple fields. An average of 6 - 7 crops with a range of 1 to 15 crops were common. Only about 25% of the fields were planted to a single crop. Rice, yam and cassava were the crops grown most often as sole crops. It is clear that for cassava, mixed cropping is the usual practice. However, grown as a sole crop or as mixed crop, cassava is known to provide crop canopy, which protects soils from direct impact of rains and reduced soil erosion by water or winds. To sustain productivity under such a declining resource base calls for an evaluation of existing production practices and development of management systems for non-traditional cassava production areas.

As cassava increasingly becomes an industrial crop, measures, which take into consideration clean environments, are very essential. It is known for example that during gari processing, cyanide compounds may be inhaled in some large quantity (depending on the variety being processed) and also, the de-watered products may be toxic to other plants or animals.

Management practices, which will sustain and improve productivity, reduce disease and pest damage, contribute to other component interventions for their integrated control, and are environmentally friendly need to be developed. The performance of newly developed genotypes in the cropping systems needs to be assessed to achieve optimum interaction between genetic improvement and crop management research. National programs would be encouraged and assisted to adapt and use a farming systems orientation in their crop and natural resource management research. The many useful attributes of the farming systems approach assure that developed technologies are practical, realistic and will be productive in the African farmers' environment, thus enhancing transfer to and adoption by users.

Sub themes
¨ Crop management and variety evaluation in major cassava cropping systems
¨ Soil fertility and water management
¨ Integrated weed management systems

Expected Output
¨ Production constraints of the major cropping systems identified and opportunities for improvement proposed
¨ Indices and models to guide and accelerate cropping systems based germplasm improvement generated
¨ Competition models fitted for different cropping systems and agro-ecologies developed
¨ Patterns and models used to develop nutrient management strategies for increased cassava production
¨ Technologies for improved water use and conservation generated
¨ Fertility management recommendations for specific cassava cropping systems
¨ Weed management options identified and packaged

Indicators for monitoring impact
· Number of cropping systems characterized
· One selection model for each major cropping system and agro-ecology identified
· Two varieties suitable for each major cropping systems identified
· One fertilization package for each major cropping system available
· At least one variety adapted to low moisture conditions identified
· At least two water conservation technologies generated
· At least one package identified for weed management