Assessment of irrigation water productivity in Mkoba Scheme in Midlands Province and Silalatshani Scheme in Matebeleland South Province, Zimbabwe

Field measurements were done to quantify amount of irrigation water being applied. Data on yields harvested, amount of water being received from reservoir(s) and planting times was gathered from records of farmers and Departments of Irrigation and Agricultural Extension Services (AGRITEX). Average climatic conditions and crop water requirements were estimated using CLIMWAT 2.0 and CROPWAT 8.0. Data analysis was done using equations as well as Microsoft excel and Statistical Package for Social Sciences (SPSS) version 23 to produce tabulations, descriptions and graphs. Substantial water losses, in both Mkoba Irrigation Scheme and Silalatshani Irrigation Scheme due to the dilapidated irrigation infrastructure, were noted. Maize crop productivity was low, ranging below 50% of the national expected yield of 10-13 tonnes/ha. The collected data further indicated that physical water productivity for maize, beans and wheat was 1.1 kg/m3, 0.54 kg/m3 and 0.87 kg/m3 respectively in Mkoba Irrigation Scheme. Mkoba Irrigation Scheme had higher physical water productivity compared to Silalatshani Irrigation Scheme which had 0.35 kg/m3 for maize, 0.28 kg/m3 for beans and 0.45 kg/m3 for wheat. This suggests that shortages of water under gravity-fed smallholder irrigation increases water productivity as farmers would be conserving it more compared to a situation where the water would be in full supply. In Silalatshani Irrigation Scheme, the economic water productivity for maize was US$0.13/m3, US$0.42/m3 for beans and US$0.23/m3 for wheat. Water productivity was low in both irrigation schemes given the physical water productivity range of 0.3 – 2.0 kg/m3 for maize.本研究开展田间实测以量化灌溉用水量。研究人员从农户、灌溉与农业推广服务部（Departments of Irrigation and Agricultural Extension Services，AGRITEX）的档案资料中，收集了作物收获产量、水库供水量及播种日期相关数据。研究采用CLIMWAT 2.0与CROPWAT 8.0软件，估算区域平均气候条件与作物需水量。数据分析环节借助方程运算、Microsoft Excel以及社会科学统计软件包（Statistical Package for Social Sciences，SPSS）23.0版本完成，最终生成统计表格、描述性统计结果与可视化图表。研究发现，姆科巴灌区（Mkoba Irrigation Scheme）与锡拉察尼灌区（Silalatshani Irrigation Scheme）均因灌溉基础设施老化，出现严重水量损耗。玉米作物生产力低下，仅达到全国预期产量（10~13吨/公顷）的50%以下。所收集的数据进一步显示，姆科巴灌区的玉米、菜豆与小麦实物水生产力分别为1.1 kg/m³、0.54 kg/m³与0.87 kg/m³。姆科巴灌区的实物水生产力高于锡拉察尼灌区，后者的玉米、菜豆与小麦实物水生产力分别为0.35 kg/m³、0.28 kg/m³与0.45 kg/m³。这表明，在重力自流型小农灌溉系统中，供水短缺反而会提升水生产力——相较于供水充足的场景，农户会更为注重节水。锡拉察尼灌区的玉米、菜豆与小麦经济水生产力分别为0.13美元/m³、0.42美元/m³与0.23美元/m³。结合玉米实物水生产力0.3~2.0 kg/m³的基准区间来看，两个灌区的水生产力均处于较低水平。