U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Date of this Version



Published in Clean Water - Clean Environment - 21st century: Team Agriculture - Working to Protect Water Resources. Conference Proceedings, Volume 2: Nutrients. March 5–8, 1995. Kansas City, Missouri. American Society of Agricultural Engineers, 1995, pp. 235-238.


An irrigated study comparing monoculture corn and corn-soybean systems is being conducted on a uniform site in the Platte Valley of Nebraska. Four corn hybrids differing in yield potential, maturity, and stay-green characteristics are used in both the monoculture and rotation systems with five N-fertilizer rates. Stalk nitrate-nitrogen concentrations determined in mature corn plants at harvest have been used in many areas of the country as an indicator of the amount of N available to those plants. In this study, stalk nitrate-nitrogen concentrations (taken after the 1992 and 1993 growing seasons) reflected differences in N status between and within the two cropping systems. Higher stalk nitrate-nitrogen concentrations were obtained with increasing N-fertilizer rates in both cropping systems, but they tended to be greater in the corn-soybean rotation, which indicated the presence of greater amounts of residual N in this system as compared to continuous corn. These data support the results obtained for grain yield in both years in that the corn in rotation required less N fertilizer to achieve optimum (maximum) yield, therefore leaving greater amounts in the soil, which were indicated by the greater stalk nitrate-nitrogen concentrations. A companion study conducted at the West Central Research and Extension Center at North Platte, Nebraska, is using 14 percolation lysimeters to measure nitrate leaching in irrigated monoculture corn and corn-soybean systems. Leachate continuously collected at the base of the lysimeters in 1991, 1992, and 1993 indicated 28% less water and 19% less nitrate leached from the corn-soybean rotation than from continuous corn. These differences were primarily due to more aggressive soil water extraction by soybean late in the growing season and lower N fertilizer requirements. Increased soil water extraction late in the growing season tended to reduce the off-season leaching following soybean, whereas water leached during the off-season following corn was similar for corn following soybean and continuous corn.