Water productivity analysis for smallholder rainfed systems: A case study of Makanya catchment, Tanzania

Abstract

Decreasing food security as a result of ever-increasing population, less water availability and soil degradation is common in countries in sub-Saharan Africa. While most of the developed fresh water resources are heavily committed to irrigation, about 90% of sub-Saharan populations rely solely on rainfed agriculture for their livelihoods. The majority of the population is therefore not directly benefiting from developed water resources but are, in fact, subsistence rainfed farmers. Thus, in sub-Saharan Africa, techniques which help to improve water productivity (WP) can assist in alleviating the impacts of water scarcity especially for crop production purposes. A study was conducted in the semi-arid Makanya catchment in northern Tanzania where farmers depend on rainfed subsistence farming for their livelihoods. The objective of the study was to assess the effect of improved conservation agriculture techniques on WP of a maize crop. An assessment of the current WP in rainfed and partially supplementary irrigated agriculture was made. The crop water requirement for maize in the study area was found to be 508 mm/season by using the CROPWAT model compared to total received rainfall of up to 383.86 mm per study plot during the same period. An attempt was made to separate transpiration from evapotranspiration using a transpiration meter. Results indicate that, currently, WP for maize in the catchment is low (0.18–1.33 kg m −3). Introduction of improved techniques increased WP by between 90% and 110%. Infiltration rates also increased from 6 to 26 cm/h. The conclusion from the research is that, from a purely scientific view, there is room to significantly improve the water use techniques being applied for crop productivity through improving current smallholder farming practices A clear understanding and quantification of the water partitioning processes is required to maximise productive water use by the plant as transpiration and this is directly related to biomass production.