Water-use efficiency of sorghum and groundnut under traditional and current irrigation in the Gezira scheme, Sudan

In the Gezira irrigation scheme in central Sudan, serious symptoms of water waste have been identified in the last two decades, especially in sorghum and groundnut fields. To quantify losses, water-use efficiencies and related parameters were obtained for these two food crops under the traditional attended daytime water application and the newly evolved unattended continuous watering method. In this on-farm research, the neutron scattering method was used to determine the actual soil water deficits of the two crops. A simple Penman equation was used for approximating reference crop evapotranspiration and evaporation losses from standing water and wet soil surface. An updated approach using the Penman-Monteith equation was additionally applied. The study revealed wastage of irrigation water in both irrigation methods but at different rates and also differently for each crop. In the attended field, the average seasonal over-irrigation, which is the difference between average application depth Q and average soil moisture deficit SWD, was observed to range between 0.4 and 1.5 of SWD (0.3 and 0.6 of Q) and the corresponding values in the unattended field were 0.6 and 3.2 of SWD (0.4 and 0.8 of Q). Higher values are shown by the groundnut subplots, which crop also suffers from excess water, and by the drier year as well as in the unattended fields. A first approximation is given, still including readily available water at harvest, of minimum water requirements in attended watering for maximum yields. In the drier year, when more irrigation water was applied, an amount equal to 30-50% of these minimum water requirements was lost in evaporation from standing water/wet surface, which is the main unproductive water. More frequent land levelling aiming at minimum standing water in better attended irrigation and farm management (e.g. weeding) are priority measures proposed. The quantitative on-farm water waste determinations represent the innovative content of this paper. Knowing precisely how large the problem is and being able to quantify its components will contribute much to the arguments of those who wish to take the proposed measures.