Coping with drought : options for soil and water management in semi-arid Kenya

In semi-arid Kenya, episodes of agricultural droughts of varying severity and duration occur. The occurrence of these agricultural droughts is associated with seasonal rainfall variability and can be reflected by seasonal soil moisture deficits that significantly affect crop productivity. The aim of this study was to analyse agricultural drought, and to evaluate soil and water management options and strategies for sustainable crop production in drought-prone semi-arid Kenya. Research was conducted at an experimental site in Katumani and in Iiuni watershed, both in Machakos district. First the occurrence of dry and wet spells in Iiuni was modelled using a Markov model. The study revealed that the short rains (October-December) are more reliable for crop production than the long rains (March-May). A literature review on tillage methods for soil and water conservation in eastern Africa showed the importance of appropriate tillage practices and the benefits of residue management for improved soil moisture conditions. Especially conservation tillage techniques were found to be promising for the improvement of crop productivity under semi-arid climatic conditions. Moreover, farm yard manure application in combination with tillage appeared effective in reducing surface runoff from a crusting and compacting soil, especially during the early stages of the rainy season. At the watershed scale, the AGNPS model was applied to evaluate the effect of land use changes on watershed runoff volume. Changes in land use covering a period of nearly 20 years were significant, with an dramatic increase in the area for crop cultivation, but this did not have a significant effect on the hydrology. The reason is the widespread adoption of soil and water conservation measures (mainly bench terracing) that occurred during the same period. The last part of the thesis deals with suitable options for watershed conservation in semi-arid Kenya. Apart from technical solutions, the enabling conditions to farmers at various hierarchical policy levels are discussed. A few of these enabling conditions that are elaborated upon include agricultural policy, focus on smallholder agriculture and public-community partnership

Analysis of agricultural drought in Iiuni, Eastern Kenya: Application of a Markov model

In semi-arid Kenya, episodes of agricultural droughts of varying severity and duration occur. The occurrence of these agricultural droughts is associated with seasonal rainfall variability and can be reflected by seasonal soil moisture deficits that significantly affect crop performance and yield. The objective of this study was to stochastically simulate the behaviour of dry and wet spells and rainfall amounts in Iiuni watershed, Kenya. The stochastic behaviour of the longest dry and wet spells (runs) and largest rainfall amounts were simulated using a Markov (order 1) model. There were eight raingauge stations within the watershed. The entire analysis was carried out using probability parameters, i.e. mean, variance, simple and conditional probabilities of dry and rain days. An analysis of variance test (ANOVA) was used to establish significant differences in rainfall characteristics between the eight stations. An analysis of the number of rain days and rainfall amount per rain day was done on a monthly basis to establish the distribution and reliability of seasonal rainfall. The graphic comparison of simulated cumulative distribution functions (Cdfs) of the longest spells and largest rainfall amounts showed Markovian dependence or persistence. The longest dry spells could extend to 24 days in the long rainy season and 12 in the short rainy season. At 50% (median) probability level, the largest rainfall amounts were 91 mm for the long rainy season and 136 mm for the short rainy season. The short rains were more reliable for crop production than the long rains. The Markov model performed well and gave adequate simulations of the spells and rainfall amounts under semi-arid condition