Tropical wheat response to irrigation and nitrogen in a Sahelian environment. II. Biomass accumulation, nitrogen uptake and water extraction

The understanding of growth and yield determining processes and of a wheat crop by optimizing controllable production inputs in a Sahelian environment can lead to improved crop productivity. In a 2 year study, wheat response to incremental irrigation and nitrogen (N) supply on crop growth and its association with biomass yield was examined. Increasing irrigation resulted in progressively higher leaf area index, increased crop growth rate, and increased above-ground biomass. Increasing N supply up to 120 kg N ha−1 resulted in more leaf area, chlorophyll, crop growth rate and above-ground biomass. Interaction between irrigation and N was significant for biomass yield. The highest response of crop growth parameters to N application was seen in the fully irrigated regime, the degree of response declined with the magnitude of deficit irrigation. Full benefit of water was observed in maximizing biomass yield when N was supplied at the rate of 120 kg N ha−1 in both years, harvest index was maximized when both inputs were optimal. There was a strong association between productive tillers, crop growth rate during the reproductive phase, leaf area and chlorophyll production with above ground biomass. Rooting depth as estimated by water extraction patterns differed in three irrigation regimes and were modified by N supply. The evapotranspiration (ET) biomass yield relationship was linear with a regression slope of 20.6 kg biomass per mm of ET over both years. This study showed that reduction in biomass yield in wheat limits the feasibility of reducing irrigation in the Sahel if the goal is to maximize above ground biomass and harvest index per unit area. Optimization of water and N inputs during the cropping season is critical for wheat to enhance crop growth processes and subsequent biomass yield and harvest index. With a limited water supply, water managers can either provide water to a few growers to meet full crop demand or adopt deficit irrigation to supply water to a larger number of farmers, providing more equitable distribution of scarce resources.