Pore Water Nitrate and Phosphate in Coastal Plains Soils with Corn Production: Impact of Irrigation Scheduling.

Site-specific irrigation management system has the potential to reduce leaching of nitrogen and phosphorus from the crop root zone, but this has not yet been fully demonstrated in the field. There is a need to find scheduling method to precision-apply water for maximum agronomic and environmental utility. Proper irrigation and nutrient management can reduce nutrient leaching while maintaining crop yield, which is critical in enhancing the sustainability of agricultural crops on soils with low water and nutrient holding capacities. A three-year (2012-2014) field study was conducted to evaluate and compare the effects of three irrigation scheduling methods (ISM): Irrigator Pro (IPRO); Normalized Difference Vegetative Index (NDVI) and Soil Water Potentials (SWP) and two levels of N applications (NM): 157 and 224 kilogram N per hectare (kg N/ha) on pore water nitrate (NO₃) and phosphate (PO₄) in four soil types (ST) with corn production in Coastal Plains, USA. Soil pore water NO₃ varied significantly with ISM and NM, but not with ST. The IPRO method had the lowest soil water pore NO₃ (11.1 milligram per liter, mg/L) followed by SWP (16.5 mg/L) and NDVI (17.9 mg/L). The low N application rate resulted in lower NO₃ concentration (13.4 mg/L) than the high N rate (17.0 mg/ L). Concentrations of soil water pore NO₃ and PO₄ varied significantly (p≤0.01) with soil depths. Soil water pore PO₄ was not affected by ISM, NM and ST. The use of IPRO reduced the concentration of pore water nitrate by about 39% and 33% when compared with NDVI and SWP, respectively. Irrigator PRO may have some advantages in terms of minimizing the concentration of pore water NO₃ and PO₄ being leached during irrigation when compared with NDVI and SWP. Since the IPRO method resulted in lower soil water pore NO₃ and PO₄ concentrations, results indicate scheduling method may be a way to reduce nutrient losses to leaching on these soils.