Seasonal Changes in Flow and Nitrate-N Loss from Subsurface Drains

Abstract

Subsurface drainage from thirty-six, 0.4-ha plots was monitored for three years (1990 to 1992) from chisel plow, moldboard plow, ridge till, and no-till systems with continuous corn and corn-soybean rotations. Data were analyzed in four seasonal stages to determine variations in drain flows and nitrate-N contents in drain effluent. The hypothesis of this study was that differences among tillage systems would change during the monitoring season as rainfall patterns varied and as plots were fertilized and cultivated. Forty-five to 85% of the annual nitrate-N loss through subsurface drainage occurred in the spring and fall when crops were not actively growing. These losses, however, were not significantly different among tillage systems. Relative changes in drain flows and nitrate-N concentrations before and after summer cultivation were similar among the four tillage systems even though no-till and ridge till systems were undisturbed before this time. Nitrate-N losses or concentrations did not increase during the stage following fertilizer application. No-till plots had significantly higher subsurface drain flow than moldboard plow plots only under continuous corn, possibly an effect of reduced yields from long-term no-till continuous corn. Nitrate-N concentrations in drain effluent from moldboard and chisel plow systems, however, were significantly greater than concentrations from no-till and ridge till systems for all crop rotations. Lower nitrate-N concentrations from no-till and ridge till systems may have resulted from greater bypass flow, denitrification, and immobilization under nonplowed systems.