Impacts of irrigation scheduling on pore water nitrate and phosphate in coastal plain region of the United States

Agriculture is one of the largest sources of nutrient contamination, mainly inorganic nitrogen (N) fertilization of intensive crops, such as maize (Zea mays L). Proper irrigation 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 the effects of three irrigation scheduling methods (ISM): Irrigator Pro (IPRO); Normalized Difference Vegetative Index (NDVI); and Soil Water Potentials (SWP) and two rates of N applications (NM) on pore water nitrate and phosphate in four soil types (ST) with maize production in Coastal Plain Region, USA. Soil pore water nitrate varied significantly with ISM and NM, but not with ST. The IPRO method had the lowest soil water pore nitrate followed by SWP and NDVI. The low N application rate resulted in lower nitrate concentration (13.4 mg L−1) than the high N rate (17.0 mg L−1). Soil water pore phosphate 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. Using IPRO method resulted in lower soil water pore nitrate and phosphate concentrations, results indicate scheduling method may be a way to reduce nutrient losses. Results of our study suggest that irrigation management decision may affect nitrogen and phosphorus availability for achieving optimum yield of maize while potentially minimizing nutrient losses via leaching.