|dc.description.abstract||The unpredictable rainfall distribution patterns and high spatial variability in soil texture are promoting changes in irrigation and fertilization management. Irrigation systems are helping farmers to achieve consistent yields, regardless of the rainfall conditions, while irrigation scheduling methods are contributing to increase irrigation efficiency. Several studies have looked at the relationship between irrigation application, available water in the soil and N fertilizer uptake as a way to optimize yield and minimize environmental impacts. In Alabama, few studies of this type have been conducted.
Studies were conducted during two growing seasons (2014 and 2015) at two locations in Alabama. The objective of the study conducted at Tennessee Valley Research and Extension Center (TVREC) was to evaluate the interactions between two irrigation scheduling methods (Pan evaporation and Sensor-based) and four N rate applications (0-control, 202, 269 and 336 kg ha-1) on grain yield, aboveground biomass, plant N concentration, N uptake and Nitrogen Use Efficiency (NUE) on corn. The objective of the study conducted at E.V. Smith Research and Extension Center (EVSREC) was to evaluate the advantages and disadvantages of two irrigation scheduling methods (Checkbook and Sensor-based) on corn growing in Central Alabama.
In the TVREC study, irrigation scheduling methods consisted of the Pan evaporation method and Sensor-based method. The Pan evaporation method is based on managing the estimated crop’s evapotranspiration (ET) using Pan Evaporation values and the crop’s consumptive water use. The Sensor-based irrigation scheduling method is based on soil matric
potential values recorded by soil moisture tension sensors installed in a field. A soil water depletion of 35% of plant available water was set as irrigation threshold for the Sensor-based irrigation treatment, and then each irrigation event was initiated when the soil matric potential reached the soil water depletion threshold. The study located at EVSREC used the same Sensor-based method following a soil water depletion of 35% plant available water as the irrigation threshold. However, it was compared with Checkbook method, which is based on the soil water balance estimated using water lost by evapotranspiration (ET) and its replacement through rainfall or irrigation.
Results obtained in the first study at TVREC showed that 29% more water was applied on average using the Pan evaporation irrigation scheduling method compared to the Sensor-based. However, the amount applied from the two irrigation scheduling methods did not present statistical differences in terms of grain yield, aboveground biomass, or NUE. Also, technical problems with the irrigation pump during silking and grain filling periods may affect the grain yield response to N fertilizer and water application in both years. The growing season of 2014 received 138 mm of irrigation water on the plots under the Pan evaporation irrigation scheduling method and the Sensor-based irrigation scheduling method received 122 mm on the plots fertilized with 202 kg N ha-1 and 99 mm on the plots fertilized with 269 and 336 kg N ha-1. The greatest grain yield was 14203 kg ha-1 achieved on the plot fertilized with 269 kg ha-1. In 2015, the Pan evaporation plots received 215 mm of irrigation and the Sensor-based plots received 152 mm at 202 and 336 kg N ha-1 plots and 127 mm at 269 kg N ha-1 plots and the greatest yield was 13809 kg N ha-1 achieved on the plot fertilized with 336 kg N ha-1
The results of the second study at EVSREC showed that the Checkbook irrigation scheduling treatment resulted on more water application than Sensor-based treatment during both growing seasons. However, there were not statistically significant grain yield differences with respect to both irrigation scheduling treatments. In contrast, the two irrigation scheduling methods resulted in comparable values for total profit per hectare. In 2014, Checkbook and Sensor-based treatment plots located on zone A showed yield of 10181 kg ha-1 and 9696 kg ha-1, respectively. Also, the irrigation application was 193 mm in the Checkbook plots and 60 mm in the Sensor-based plots. In zone B, the Sensor-based and Checkbook treatment plots achieved yield of 9673 kg ha-1 and 9584 kg ha-1, respectively. Moreover, the irrigation amount applied in the Sensor-based treatment (91mm) was lower than Checkbook treatment (193 mm). In the growing season of 2015, zone A showed yield of 13597 kg ha-1 and 12674 kg ha -1 on the Sensor and Checkbook plots, respectively. In zone B, yields were 13417 kg ha -1 and 11659 kg ha-1 on the Checkbook and Sensor-based plots, respectively. The irrigation amount was the same in both zones, 121 mm applied in the Checkbook plots and 70 mm applied in the Sensor-based plots.
Further studies are necessary to improve the knowledge of sensor technology as a tool for irrigation scheduling method. For example, research addressing the SMP corresponding the FC for the various soils in Alabama would help to determine more accurate values of PAW. In addition, the evaluation of different irrigation threshold values is important, because different threshold values would likely produce different results in terms of crop production.