Spatial and temporal maize soil water extraction (Depletion) dynamics: Part II. Impact of water and nitrogen management strategies on soil water extraction

A soil water extraction (depletion) model was used to assess the impacts of water and nitrogen (N) management on maize soil water extraction patterns every 0.30 m to 1.50 m soil depth under a linear-move sprinkler irrigation system in the 2011 and 2012 growing seasons at the South Central Agricultural Laboratory (SCAL) near Clay Center, Nebraska. Three irrigation regimes [fully irrigated treatment (FIT), limited irrigation (75% FIT), and rainfed] with five N levels (0, 84, 140, 196, and 252 kg ha^-1) of each treatment were investigated. The two growing seasons had substantially different climatic conditions in terms of solar radiation, air temperature, relative humidity, wind speed, and vapor pressure deficit. In terms of precipitation, 2011 was 24% below normal and 2012 was 50% below normal. Spatial and temporal soil water extraction amounts and patterns were influenced by irrigation regime, N fertilizer rate, variability in soil properties, and climatic conditions. However, individual soil layer water extraction was affected more by differences in soil properties and irrigation regimes as compared with N fertilizer rates. Profile (0-1.50 m) soil water extraction in 2012 was significantly affected by irrigation (p_0.05 < 0.0001), but the N rate effect was not significant (p_0.05 = 0.0654). No interaction was observed between irrigation and N rate on seasonal profile extraction amount, but an interaction between soil depth and irrigation amount was observed (p_0.05 <0.0001). Maximum soil water extraction occurred in the top (0-0.30 m) soil depth for all treatments, and extraction amount decreased with depth. Soil water extraction under irrigated conditions followed the conical water uptake pattern; however, high evaporative demands in 2012 resulted in deep rooting under rainfed conditions. The percent of total extraction in the 1.20-1.50 m depth for rainfed conditions in 2012 was 8%, 6% ±1.3%, 8% ±1.0%, 7% ±2.6%, and 9% ±5.9% for 0, 84, 140, 196, and 252 kg N ha ^-1, respectively, as compared with a maximum percent extraction of 5% ±1.2% under irrigated conditions. Rainfed soil water extraction was more susceptible to inter-Annual variability; however, all treatments were greatly influenced by soil layering. Strong relationships (R² > 0.98) were observed between cumulative growing degree days (GDD) and cumulative soil water extraction amounts for both 2011 and 2012. The developed extraction vs. GDD relationships were also related to days after planting (DAP) and maize growth and development stages to aid agricultural producers and their advisors when assessing irrigation timing and amount.