Maize nitrogen uptake, grain nitrogen concentration and root-zone residual nitrate nitrogen response under center pivot, subsurface drip and surface (furrow) irrigation

While the impact(s) of irrigation and nitrogen (N) levels on crop yields have been investigated separately, research lacks about how different irrigation methods coupled with different N application timing strategies under full and limited irrigation levels effect yield, soil nitrate nitrogen (NO3-N) residual and stover N uptake. Knowledge of these dynamics can help to establish effective water and N management guidelines for the same crop under different irrigation methods and irrigation levels. This research investigated maize (Zea mays L.) residual soil NO3-N concentration and stover and grain N uptake response to water under different irrigation methods [center pivot (CP), subsurface drip irrigation (SDI) and surface (furrow) irrigation (FI)] simultaneously. Three irrigation levels were imposed: (i) full irrigation treatment (FIT), (ii) limited irrigation (80% FIT and 60% FIT) and (iii) rainfed treatment (RFT). N treatments were: (i) traditional (TN) treatment in which seasonal N requirement was applied in spring as a pre-plant, (ii) non-traditional-1 (NT-1) in which 30% of the seasonal required N was applied as spring pre-plant, 40% and 30% as side-dress at V8 (8-leaf collar) and VT/VR (tasseling/silking) stages, respectively, and (iii) non-traditional-2 (NT-2) in which 25% of the seasonal required N was applied as spring pre-plant, 25%, 30% and 20% as side-dress at V8, VT/VR and R3 (i.e., kernel, milk) stages, respectively. The highest NO3-N residual was observed in the topsoil and residual NO3-N was more pronounced in the RFT followed by limited irrigation levels. The highest average stover N concentration, regardless of N treatments, was in the order of FI (1.99%)>SDI (1.94%)>CP (1.73%). Overall, irrigation levels significantly influenced (p < 0.05) seasonal stover N uptake in both growing seasons, regardless of N treatments and irrigation methods. In most cases, the highest seasonal stover N uptake was observed in the FIT and/or 80% FIT and the lowest values were observed with RFT. Grain N concentrations were higher in NT-1 and NT-2 than TN in SDI, whereas the CP seasonal grain N concentration had opposite trends with both NT-1 and NT-2 having higher seasonal grain N concentration than TN. The highest grain N uptake was observed in the SDI-NT-1, followed by CP-NT-2 and FI-TN under limited irrigation treatments. The coupled irrigation and N treatments of 80% FIT-NT-2-CP, 60% FIT-NT-1-SDI and 80% FIT-NT-2-SDI had ≥ 5 mg kg−1 residual NO3-N in the 0.60 m soil layer in drier year in 2016. The trend was opposite in wetter year in 2017 and there was an increasing NO3-N content trend (≥5 mg kg−1) in the 0.60–1.20 m soil layer. The highest NO3-N concentrations were observed in the RFT, NT-1, and NT-2 across irrigation methods, indicating that the irrigation management and in-season N application treatments significantly (p < 0.05) influenced the NO3-N magnitudes. Soil residual NO3-N had quadratic relationship with the seasonal total soil water supply; and soil residual NO3-N increased with decreasing total water supply. The quantitative analyses presented here can aid to improve N and water productivity and reduce unnecessary applied N in for maize under the conditions similar to those presented in this research.