Potential use of precision conservation techniques to reduce nitrate leaching in irrigated crops

ABSTRACT:

There is a continuing need to develop advanced nitrogen (N) management practices that increase N use efficiencies and reduce nitrate-nitrogen (NO₃-N) leaching. Our goal was to evaluate the use of geographic information systems (GIS), global positioning systems (GPS), modeling and remote sensing for reducing residual soil NO₃-N and NO₃-N leaching in a center-pivot irrigated corn (Zea mays L.) field. Specific objectives were: 1) to determine if productivity zones delineated using precision agriculture technologies could also correctly identify unique areas within corn fields that differed in residual soil NO₃-N and NO₃-N leaching potential; and 2) evaluate the potential to use remote sensing of crop productivity to reduce NO₃-N leaching losses. This study was conducted in northeastern Colorado during the 2000 and 2001 growing seasons in a 70 ha (173 ac) center-pivot irrigated commercial cornfield. For the first objective, initial and final soil samples after harvesting were collected at known locations in high, medium and low productivity areas across this field. For the second objective initial and final soil samples after harvesting were collected in a low productivity area where “in season” N management was conducted based on remote sensing data. Crop yields and total N were determined on plant samples located at the soil sampling coordinates. The N reflectance index was used to determine the “in season” N application. Remote-sensing-based N fertilization treatment occurred whenever the mean N reflectance index was lower than 0.95 and/or more than 50 percent of the area had an N reflectance index less than 0.95. For both studies, the nitrate leaching economic analysis package and GIS were used to evaluate NO₃-N leaching losses. We found that GIS, GPS, and modeling technologies can be used to identify and simulate the spatial residual soil NO₃-N patterns. Productivity zones delineated using precision agriculture technologies identified areas within corn production fields that differed in residual soil NO₃-N and NO₃-N leaching potential. This spatial variability was negatively correlated with the soil texture (P<0.001), having lower residual soil NO₃-N on the lower productivity sandier areas, which also had a higher NO₃-N leaching potential. The N Reflectance Index method can maximize the synchronization of “in season” N applications with corn N uptake needs to increase N use efficiencies and reduce NO₃-N leaching losses by 47 percent when compared to traditional practices (P<0.0001).