The effects of contour-based rainwater harvesting and integrated nutrient management on maize yields in semi-arid regions of Zimbabwe

In the smallholder farming areas located in semi-arid regions of Zimbabwe, low and unreliable rainfall distribution and poor soil fertility are the major factors limiting crop production. The negative effects of these biophysical factors have been worsened by climate change. However, the major challenges have been the lack of sustainable, low-cost water and nutrient management technologies for these semi-arid regions. The objectives of this study were to evaluate the effects of contour-based rainwater harvesting (RWH) namely tied contours (TC), infiltration pits (IP) which were compared with the standard contour (STDC), and intergrated nutrient management (INM) where cattle manure was used as basal fertiliser and Ammonium Nitrate (AN) as top dressing, on maize yields. Results showed that fields with RWH had higher yields compared to STDC. Average maize yields were 2210 and 1792 kg ha-1 for TC and IP which were 88% and 52% above STDC (1176 kg ha-1) respectively. Increasing nitrogen (N) levels resulted in a further increase in maize yields. Return on investment was negative during drier years and was significantly higher in RWH systems compared with STDC during wet seasons. Farmers need to reduce mineral fertiliser application during dry seasons since little rainwater is captured. We conclude that contour based RWH and INM can be used as sustainable low cost methods of crop production. Higher fertiliser application rates when rainfall is limiting, do not result in increased return on investiment.