Comparative analyses of variable and fixed rate irrigation and nitrogen management for maize in different soil types: Part I. Impact on soil-water dynamics and crop evapotranspiration

Understanding the soil-water dynamics and maize evapotranspiration (ETc) under variable rate irrigation (VRI) and variable rate fertigation (VRF) management with respect to soil spatial variability constitutes the basis for developing effective variable rate water and nitrogen management strategies. This long-term research was designed to quantify and compare the soil-water dynamics, including available water (AW), and ETc during vegetative and reproductive growth periods of VRI, fixed rate irrigation (FRI) and no-irrigation (NI) under fixed rate fertigation (FRF), VRF and pre-plant (PP) nitrogen management in three different soil types [Crete silt loam (S1); Hastings silty clay loam (S2) and Hastings silt loam (S3)] with different topography in the same field under the same environmental and management conditions. The research was conducted in the Irmak Research Laboratory in south central Nebraska, U.S.A., in 2015, 2016 and 2017 maize (Zea mays L.) growing seasons under a variable-rate linear move sprinkler irrigation system. No effect of irrigation and nitrogen fertilizer on AW was observed in the vegetative period. Overall, greater AW was observed in S3 as compared with S1 and S2 due to lower elevation. Maize ETc during the vegetative period was significantly (P < 0.05) impacted by soil type in all three years and by nitrogen treatment in two of the three years. The vegetative ETc in S1 was 27 and 19 mm greater than S2 and S3, respectively, for the pooled 2015, 2016 and 2017 data. During the reproductive period, both ETc and AW were impacted by nitrogen and irrigation treatments, but differently in different soil types and years. Average reproductive ETc for FRI and VRI in 2015, 2016 and 2017 was 175 and 178 mm; 294 and 241 mm; 258 and 206 mm, respectively. Averaged across three years, ETc under FRI was significantly (P < 0.05) greater than in VRI; however, in 2015, no significant difference (P > 0.05) in ETc between FRI and VRI was observed in any soil type. Similarly, in 2017, no significant difference in reproductive ETc was observed between VRI and FRI in S1. During reproductive period, averaged across years, soil types and irrigation treatments, the PP nitrogen treatment had greater ETc and lower AW than VRF and FRF. The results indicate that vegetative period ETc was primarily affected by soil type, weather conditions (evaporative demand and soil wetting) and nitrogen fertilizer application timing. The findings of this research showed that soil-water dynamics is a strong function of not only management practices (irrigation and nitrogen treatments), but also soil type, topography and soil physical properties, which all need to be taken into account for effective management of VRI and FRI under VRF, FRF or PP nitrogen management in different soil types. This research quantified the impact of these management practices on soil-water dynamics and ETc which can be used as a guidance.