Environmental and production effects from variable rate nitrogen fertilizer to winter wheat in England

At 2 fully replicated experiments on winter wheat in England, uniform and variable rate application of N fertilizer were compared. The variable rate N treatments were 172 to 282 kgha(-1) at site A (shallow soil over chalk) and 78 to 143 kgha(-1) at site B (silty alluvial soil). Variable rate N had no effect on grain yield at either site, but there were indications of an environmental benefit at site A. The N balance and soil mineral N (SMN) levels after harvest were related to the depth of soil over chalk. Summer drought reduced yields at this site which may have resulted in an overestimation of the N rates used, thereby reducing treatment differences that may have occurred in a more normal season. N balance and amounts of residual SMN were not measured at site B.