Crop and tillage management effects on water flow and nitrate-nitrogen loss through subsurface drains

Data were collected from subsurface drains on 36, 0.4-ha plots at Iowa State University's Northeast Research Farm near Nashua, IA to determine crop and tillage management effects on water flow and nitrate-N loss through subsurface drains. From 1990 to 1992, four tillage systems (chisel plow, moldboard plow, ridge till and no-till) were used with two crop rotations (continuous corn (Zea mays L.) and corn-soybean (Glycine max L. (Herr.)) rotation) and a single-spring fertilizer application. From 1993 to 1995, tillage systems were reduced to chisel plow and no-till, while fertilizer management changed to include single-spring fertilizer, spring-summer split fertilizer and fall manure application.; The amount of nitrate-N lost in subsurface drainage was influenced more by subsurface drainage volume than nitrate-N concentration in drain effluent. Tillage had minimal effects on drainage volume, although no-till plots showed greater preferential flow than chisel plow plots. Significant differences in drain flow only occurred under continuous corn between 1990 and 1992, when the no-till system had higher drain flow than moldboard plow.; Tillage affected nitrate-N concentrations in drain effluent during 1990 to 1992. Moldboard plow plots had higher concentrations than no-till plots possibly because of differences in bypass flow, denitrification and mineralization. Nitrate-N concentrations were not influenced by tillage after management systems were changed. However, plots where continuous corn had been grown for 15 yr had higher drain flows and nitrate-N losses in 1993 than where corn was planted into plots that had been rotated with soybean.; Nitrate-N concentrations and losses were always higher with continuous corn than with corn-soybean rotation. Corn yields with split fertilizer applications were as high or higher than yields from single application treatments, but nitrate-N losses were essentially the same. Swine manure was difficult to apply at desired rates, resulting in wide variations in yield, nitrate-N concentrations and nitrate-N losses among years. This suggests that manure should be used to supply only a portion of crop nitrogen needs with additional fertilizer added based on late-spring soil nitrate tests.