1TRENDS OF PRODUCTIVITY OF WATER IN RAIN-FED AGRICULTURE: HISTORICAL PERSPECTIVE By

In Sub-Sahara Africa, rain-fed agriculture is the dominant source of food production. It is likely going to remain so for the next foreseeable future. However, yields from rain-fed agriculture are often very low. But there is an enormous opportunity to raise crop yield of rain-fed agriculture especially by focusing on the aspect of increasing productivity of water. In order to formulate and adopt appropriate and adequate options for increasing productivity of water in rain-fed agriculture, there is a need to have an historical hindsight to the trend of productivity of water in rain-fed agriculture. In this paper, a historical analysis of the trend of productivity of water (PW) for five crops cultivated under rain-fed condition in Mbarali District, Mbeya Region, Tanzania, was carried out using secondary data. The crops include: maize, sorghum, beans, potato, and groundnut. The PW(rainfall) for maize, sorghum, potato, beans, and groundnut had peak values of 0.49kg/m3 in 1993/94, 0.47 kg/m3 in 1994/5, 3.06kg/m3 in 1993/94, 0.33kg/m3 in 1996/97, and 0.20kg/m3 in 1994/95 cropping seasons, respectively. Evapotranspiration deficit occasioned by either mid cropping-season dry spell or early cessation of rainfall and low rainfall utilization efficiency are the primary drivers of PW in rain-fed agriculture in the area. Other factors that are usually put forward by agricultural stakeholders in the region, which include poor soil nutrient and lack of proper crop management, are secondary and could be considered as spill over effects from these primary drivers of PW. Key Words: Productivity of water, crop yield, crop water requirement, evapotranspiration defici