Monitoring nitrate-nitrogen and phosphorus in porous nursery containers and adjacent soil

Abstract

Nitrate-nitrite nitrogen and soluble phosphorus concentrations in the substrate of aboveground soft-sided porous nursery containers amended with controlled-release fertilizer and in adjacent native soil were monitored for 5 months in 2003, and for 7 months in 2004 using suction lysimeters. In both 2003 and 2004, phosphorus concentrations were higher in container substrate than in native soil throughout the monitoring period. In 2003, nitrate-nitrite nitrogen concentrations were higher in container substrate than in adjacent native soil for the fi rst 6 weeks of monitoring. For three of the four monitoring dates during the fi rst 6 weeks, nitrate-nitrite nitrogen concentrations in the container substrate were above 15 ppm, the lower limit for production. Nitrate-nitrite nitrogen concentrations in the native soil on these same dates were below 10 ppm, the maximum allowable concentration in drinking water. Thereafter, nitrate-nitrite nitrogen concentrations in the container substrate decreased and were similar to concentrations in native soil, ranging from 2.8 to 3.2 ppm for the last 4 weeks. In 2004, the lysimeters used for monitoring soil water were installed 42 inches deeper below the soil surface than 2003 (6 inches). Nitrate-nitrite nitrogen concentrations in the container substrate solution were consistently below 15 ppm, the lower limit for production, possibly due to excessive rain. Nitrate-nitrite nitrogen concentrations in the native soil exceeded 10 ppm, the maximum allowable concentration in drinking water, at four sampling events.