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 as sociation with biomass yield was examined. Increasing irrigation resulted i n progressively higher leaf area index, increased crop growth rate, and inc reased above-ground biomass. Increasing N supply up to 120 kg N ha(-1) resu lted in more leaf area, chlorophyll, crop growth rate and above-ground biom ass. 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 mag nitude or deficit irrigation. Full benefit of water was observed in maximiz ing biomass yield when N was supplied at the rate of 120 kg N ha(-1) in bot h years, harvest index was maximized when both inputs were optimal. There w as a strong association between productive tillers, crop growth rate during the reproductive phase, leaf area and chlorophyll production with above gr ound biomass. Rooting depth as estimated by water extraction patterns diffe red in three irrigation regimes and were modified by N supply. The evapotra nspiration (ET) biomass yield relationship was linear with a regression slo pe of 20.6 kg biomass per min of ET over both years. This study showed that reduction in biomass yield in wheat limits the feasibility of reducing irr igation in the Sahel if the goal is to maximize above ground biomass and ha rvest index per unit area. Optimization of water and N inputs during the cr opping season is critical for wheat to enhance crop growth processes and su bsequent biomass yield and harvest index. With a limited water supply, wate r managers can either provide water to a few growers to meet full crop dema nd or adopt deficit irrigation to supply water to a larger number of farmer s, providing more equitable distribution of scarce resources. (C) 2001 Else vier Science B.V. All rights reserved.