Water productivity and the relative effects of salinity on crop yields for a surface irrigation scheme – a case of Insukamini Irrigation Scheme

Abstract

Increasing water productivity is generally explained as to either produce similar yield using less water or obtaining more crop yields using the same water resources. Water is becoming scarce due increase in population as well as competition with other non- agricultural demands. At Insukamini Surface Irrigation Scheme, farmers over apply water volumes with the idea that they can increase their yield. However the Scheme has been facing challenges of yield decline from 2009 to 2014. This study was therefore designed to quantify the current levels of water productivity and the relative effects of salinity to crop yield. Questionnaire survey and laboratory experiments were done to assess the crop water productivity, irrigation water and soil quality parameters and their impact on the yield of sugar beans and maize grain. The results indicated that the soil was saline with EC ranging from 0.52dS/m-0.58dS/m. A reduction in the yield over 7 years was noted and there was a low water productivity ranging between 0,37kg/m3 to 0.68kg/m3 for maize and 0.33kg/m3 to 0.62kg/m3 for sugar beans. The conclusion was that the salinity is as a result of salt accumulation from irrigation water, decline in yield is caused by salinity levels, crops being grown are not tolerable to the salinity levels, hence low water productivity. It was recommended that the farmers should grow more salt tolerant crops, correct the salinity, practice deficit irrigation and practice good irrigation management practices.