|Fausey, Norman - Norm|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/1999
Publication Date: N/A
Citation: N/A Interpretive Summary: Subsurface drainage is necessary for profitable agriculture in humid regions including the Midwest Cornbelt. The subsurface drains accelerate the removal of excess water from the highly productive soils allowing timely planting and providing a well aerated root zone for the crops. Soluble nutrients, especially nitrogen, within the soil move with the drainage water and are discharged into surface streams. This is undesirable from an environmental and an economic perspective. Water table management can be achieved by regulating the discharge at the outlet of the subsurface drainage system. Such management has a beneficial effect by reducing the amount of nitrogen discharged with the drainage water. This report illustrates that by managing the water table through controlled drainage and subirrigation, crop yields of corn and soybeans can be increased with consequent increased uptake of nitrogen by the crops. Further, the amount of nitrogen remaining the soil at the end of the growing season is reduced, thereby reducing the potential for loss of nitrogen with the drainage water during the non growing season.
Technical Abstract: Increasing concern over nitrate contamination of surface waters has prompted the development of agricultural water table management systems that may reduce nitrate loss in subsurface drainage outflow. Such systems utilize subirrigation by adding water into the root zone through the existing subsurface drainage lines during the growing season and controlling drainage by elevating the drainage outlet and controlling outflows during the non-growing season. We compared different soil nitrogen pools, crop yields, and N uptake in a corn-soybean rotation in plots that were managed with either subirrigation (water table at 40 cm) and controlled drainage (SI/CD) or with subsurface drainage alone (SD). We found nitrate concentrations to be significantly reduced at the 30-75 cm depth in SI/CD managed plots compared to plots managed as SD. Microbial biomass N (MBN) at the soil surface (0-15 cm) was significantly increased in plots planted the previous year in soybeans. Yields and total crop uptake of N were significantly greater in SI/CD plots compared to SD plots most likely due to the ability of SI/CD management to relieve soil water stress during the growing season. A partial N budget in corn plots during the 1996-1997 growing and non-growing seasons indicated that SI/CD compared to SD primarily reduces the potential loading of nitrate to surface waters through its ability to increase the crop uptake of applied N, rather than through increased denitrification. Our results indicate that SI/CD can be utilized to reduce the potential leaching of nitrates into surface waters through its influence of plant uptake of applied N and reduction of nitrate concentrations deeper within the soil profile.