Water–nitrogen relationships for wheat growth and productivity in late sown conditions

Field experiments were conducted on a sandy loam soil (Typic Ustochrept) to study the water–nitrogen yield relationships of late sown wheat under adequate and limited water supply conditions. The treatments comprised of four levels of irrigation (I0, no post-sown irrigation; I1, one irrigation at CRI stage; I2, two irrigations, each at crown root initiation (CRI) and flowering stages; I3, four irrigations each given at CRI, jointing, flowering and dough stages) in main plots and a combination of three N levels (0, 50 and 100 kg N/ha) and two levels of zinc as ZnSO4·7H2O (0 and 5 kg Zn/ha) in sub-plots of a split plot design and were replicated three times. Progressive increase in irrigations from 0 to 4 and nitrogen levels from 0 to 100 kg/ha, increased the average leaf area index (LAI), crop growth rate (CGR), relative growth rate (RGR) and net assimilation rate (NAR), yield attributes, wheat biomass and grain yield significantly (p ≤ 0.05) over the control (I0 and N0), in both the seasons, respectively. Analyses by multiple regression techniques reveled that LAI estimates with N uptake were much higher at 84% predictability than the estimate based on water use that could account for 75% of the variations only. Lower levels of water consumption by crop were seen to result in less leaf area therefore, resulting in lower biomass and grain yields at lower levels of irrigation. The highest rate of biomass gains of 53.1 kg/ha-mm was obtained during the 60–90 day period, a period that fell within the maximum growth phase of wheat, followed by 28.3 and 6.7 kg/ha-mm during 90–120 and 0–60 days after sowing (DAS) periods. The response of the above ground biomass to nitrogen uptake was higher (76.6 kg/ha-kg N uptake) during 60–90 DAS period than during the 0–60 DAS period (22.1 kg/ha-kg N uptake). Additive production functions therefore, took care of the stage sensitivity along with the complete water and nitrogen stresses as induced through different applications of water and nitrogen. The maximum growth rates in wheat were commensurate with highest levels of water use as well as nitrogen use observed during the 60–90 DAS period of growth. For this reasons, scheduling of water and nitrogen application ought to consider providing relatively less quantities of water during the 0–60 DAS period as compared to the 90–120 and 60–90 DAS periods respectively, in order to provide just sufficient amounts of water so as to enhance the uptake of available nitrogen required for optimum growth and development of wheat.