|Bjorneberg, David - Dave|
Submitted to: Transactions of the ASAE
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/6/1996
Publication Date: N/A
Citation: Interpretive Summary: Nitrate-nitrogen concentrations of subsurface drain effluent frequently exceed the maximum contaminant level of 10 mg/L set by the Environmental Protection Agency. High concentrations are especially concerning if the drains discharge into a water body that is used as a drinking water source. Nitrate in subsurface drainage is also an economic loss to producers because the nitrogen is no longer available for crop use. This study was conducted to determine if four tillage systems affected subsurface drainage differently during the growing season. Results from this study indicate that chisel and moldboard plow plots had higher nitrate concentrations than no-till and ridge till plots. These conservation tillage systems did not, however, significantly decrease the mass of nitrate in subsurface drainage. Differences among tillage systems did not change during the year. A large percentage (45 to 85%) of the annual nitrate loss occurred in the spring and fall when crops were not growing. The mass of nitrate loss can be reduced by decreasing the drainage volume. Cover crops planted in the fall may reduce these early and late season losses by using available water and nitrogen in the soil.
Technical Abstract: Subsurface drainage was monitored for three years (1990-1992) from 36, 0.4-ha plots with no-till, ridge till, chisel plow, and moldboard plow tillage systems and continuous corn and corn-soybean crop 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 eighty percent 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 seasonal 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 may have resulted from greater bypass flow, denitrification and immobilization under non-plowed these systems.