Fn Gichuki

Dry spell analysis and maize yields for two semi-arid locations in East Africa

High variability in rainfall occurrence and amounts together with high evaporative demand create severe constraints for crop growth and yields in dry sub-humid and semi-arid farming areas in east Africa. Meteorological analyses on rainfall distribution are common, but generally focus on assessing drought occurrence on annual and seasonal basis. This paper presents two types of seasonal dry spell analysis, using easy accessible data on daily rainfall and evapotranspiration for two semi-arid locations in east Africa for 20-23 years. The meteorological dry spell analysis was obtained by Markov chain process, and the agricultural dry spell analysis used rainfall data in a simple water balance model also describing impact on maize (Zea mays L.) growth due to water availability on clay or sandy soil. The meteorological dry spell analysis showed a minimum probability of 20% of dry spells exceeding 10 days at both sites, increasing to 70% or more depending on onset of season, during approximate flowering and early grain filling stage. The agricultural dry spell analysis showed that maize was exposed to at least one dry spell of 10 days or longer in 74-80% of seasons at both sites. Maize on sandy soil experienced dry spells exceeding 10 days, three-four times more often than maize on clay soil during flowering and grain filling stages. In addition, the water balance analysis indicated substantial water losses by surface runoff and deep percolation as the crop utilised only 36-64% on average of seasonal rainfall. Such large proportion of non-productive water flow in the field water balance may provide scope for dry spell mitigation through improved water management strategies.

Contour Hedgerows and Grass Strips in Erosion and Runoff Control on Sloping Land in Semi-Arid Kenya

Most early alley cropping studies in semi-arid Kenya were on fairly flat land while there is an increase in cultivated sloping land. The effectiveness of aging contour hedgerows and grass strips for erosion control on an about 15% slope of an Alfisol was compared. The five treatments were Senna siamea hedgerows with tree prunings applied as mulch to crops (H + M), hedgerows with crops with prunings removed (H), mulch only applied to crops (M), crops with Panicum maximum grass strips (G), and a sole crop control of a rotation of maize (Zea mays) and cowpea (Vigna unguiculata). Cumulative results for four consecutive seasons showed that most successful treatment H + M reduced soil loss from just over 100 to only 2 Mg ha−1 (or t ha−1) and runoff from just below 100 to 20 mm as compared to the sole crop control C. Grass strips were less effective (15 Mg ha−1 and 46 mm, respectively). Cumulative maize yields (1993–1995) were reduced by 35% in H + M, 55% in H, and by more than 60% in G. Generally, the M plot produced similar yields to those of C. Cowpea yields were less affected than maize because mean rainfall was well above average during the cowpea seasons. The hedgerows, particularly in combination with mulch, and grass strips kept soil loss on steep slopes at tolerable and sustainable rates. Strong trade-offs between erosion control and crop productivity need not be a major deterrent to adoption by farmers, if the grass and trees provide other significant benefits to farmers.

Tillage methods and soil and water conservation in eastern Africa

Abstract This paper reviews some research studies on tillage methods influencing soil and moisture conservation in the eastern African countries of Kenya, Tanzania, Malawi and Ethiopia during the past four decades. Most of these studies were conducted in marginal rainfall (semi arid) areas and on shallow soils of various textures (sandy clay loam, sandy clay, clay and loam). The studies were meant to establish the effects of tillage and residue management practices on physico-chemical soil properties (i.e. structure, bulk density, soil moisture and organic matter contents), runoff and infiltration. This review emphasizes the importance of appropriate tillage and residue management methods (contour bunds and terraces, minimum tillage, tied ridging, mulching and conventional tillage) in providing soil conditions favourable for soil moisture conservation and subsequent crop performance and yield on smallholder farms.

Transient hydraulic modeling for improved canal system operation

Abstract A hydraulic model was developed to stimulate and help manage branching canal systems. Gate scheduling, one of the three operational modes available in the model, determines control structure and turnout settings with the objective of quickly stabilizing transient flow conditions, while maintaining flow levels at or near target values. Gate scheduling can be used to accurately match planned turnout deliveries and eliminate operational uncertainties. This can be accomplished through manual control structure operation, without infrastructure changes or automation equipment. Following field calibration, the model was applied to the scheduling of canal operations at an irrigation project in northeast Thailand. Field and model-generated data showed that significant operational improvements for canal networks can be achieved with the model. The model is implemented on IBM PC/AT or PS/2-type microcomputers with a five-minute simulation time step.

Sustainability concerns in African irrigation

Irrigation has and will continue to play an important role in enhancing food security and improving the standards of living for many inhabitants of rural Africa. However, irrigation is beset with increasing problems such as water scarcity, soil degradation, water pollution, organisational and management problems, high implementation costs, low productivity and rate of returns, operation and maintenance deficiencies and associated environmental health problems. Sustainability of irrigated agriculture predicates on alleviation of these problems in a cost-effective manner. This paper presents the status of irrigation in Africa, highlights the main sustainability concerns and suggests how some of the constraints can be alleviated.

Bright basins: do many bright spots make a basin shine?

In Bossio, Deborah; Geheb, Kim (Eds.). Conserving land, protecting water. Wallingford, UK: CABI; Colombo, Sri Lanka: International Water Management Institute (IWMI); Colombo, Sri Lanka: CGIAR Challenge Program on Water & FoodComprehensive Assessment of Water Management in Agriculture Series 6