Comparison of Timing and Volume of Subsurface Drainage under Perennial Forage and Row Crops in a Tile-Drained Field in Iowa

Subsurface drainage systems in Iowa increase the productivity of annual row crops, such as corn and soybeans, but also contribute to alterations in the hydrological balance of the region and leaching of nutrient pollutants, such as NO3-N. This study’s objective was to determine whether perennial forage orchardgrass can reduce the volume and change the timing of subsurface drainage in tiled fields in Iowa, thereby contributing to reductions in NO3-N leaching and moderating changes in the hydrology. Research was conducted at Iowa State University’s Agricultural Drainage Water Research Site, located in northwest Iowa. Six 0.05 ha plots (three control and three treatment plots), each including subsurface drainage with continuous flow monitoring, were planted to row crops (RC) consisting of either a corn-soybean rotation or continuous corn from 1990-2004 (the pretreatment period). During the treatment period (2006-2011), control plots remained in RC while treatment plots were planted to perennial forage (PF), a mixture of orchardgrass, red clover, and ladino clover, succeeding to a monoculture of orchardgrass. During the pretreatment period, control and treatment plots showed no difference in subsurface drainage. During the treatment period, over the entire drainage season (March to November), PF did not decrease subsurface drainage; however, during the month of May, PF decreased subsurface drainage by 32% (p \u3c 0.05). Early spring, including May, is a critical period for drainage in Iowa, as wet field conditions and a lack of vegetative cover contribute to a majority of the drainage and leaching of NO3-N from row crop fields during this period. Further research including different perennial species is needed, and investigations in different geographical regions are needed, as differences in precipitation and weather will affect the timing and volume of subsurface drainage