Agricultural practices influence dissolved nutrients leaching through intact soil cores

Nitrogen and P leaching from agricultural land to ground water poses a threat to water quality, but it may be possible to control dissolved nutrient leaching by choosing appropriate management practices. The objective of this study was to evaluate the effects of agricultural practices on dissolved N and dissolved P leaching from topsoil to subsurface soil after crop harvest. Intact soil cores and small disturbed soil columns were collected from a factorial (tillage X crop X fertilizer source) field experiment, 3 yr after the treatments were established. Soils were leached with synthetic rainwater in the laboratory and nutrient loads (kg ha(-1)) were calculated. Dissolved N and dissolved P loads were not affected by tillage and were similar following corn (Zea mays L.) (in a continuous corn rotation) and soybean [Glycine Mar (L.) Merr.] (in a soybean/corn rotation) production. Soils receiving inorganic fertilizer had a 70% greater nitrate (NO3-N) load and 48% less dissolved reactive P than soils receiving organic fertilizer, suggesting that fertilizing soils with a combination of inorganic and organic fertilizers might be a good way to reduce both NO3-N and dissolved reactive P transport to water systems. The NO3-N load increased as the soil NO3-N concentration increased (R-2 = 0.36) while the dissolved reactive P load was positively related to the soil Mehlich-3 P concentration (R-2 = 0.50) and soil P saturation ratio (M3-PSR) (R-2 = 0.55). These results suggest that the leaching of dissolved N and dissolved P compounds is influenced more by the type of fertilizer applied than tillage or cropping practices.