Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 30, 1998
Publication Date: N/A
Interpretive Summary: The amount of nitrogen applied to corn is based on the average productivity of the soils in the field in an average year. In years when plants are stunted by drought, much of the nitrogen remains in the soil after corn harvest (called residual nitrogen) because the plants cannot use all of the applied nitrogen. Winter wheat can be grown as a cover crop to trap this residual nitrogen. The ability of wheat to trap residual nitrogen depends on soil conditions, and soil conditions vary throughout most fields. We found that cover crops are reliable at trapping nitrogen in areas with the highest corn yields because at those sites, wheat growth and nitrogen scavenging were uniformly high. On the other hand, using wheat to scavenge N may have had limited potential in areas of fields that had the lowest corn yield because there was too wide a range in the ability of the wheat to grow. These sites were mainly near depression areas. This information is important to farmers seeking ways to reduce production costs and to protect surface and ground waters from nonpoint N contamination.
Technical Abstract: Cereal winter cover crops can trap the residual fertilizer N left in the soil from preceding cash crops, but their ability to do so partially depends on the soil conditions that determine growth. Our objective was to determine site-specific effects of soil variation on biomass and N accumulation by a wheat (Triticum aestivum L.) cover crop that was grown after a droughted corn (Zea maize L.) crop. In 1993, corn was grown with an applied fertilizer N rate of 129 kg/ha on an 8-ha field near Florence, SC. Nitrogen removed by grain at 10 locations ranged from 14 to 41 kg N/ha. Wheat was planted in November without additional fertilizer N. Inorganic soil N to a depth of 90 cm was measured on 22 March 1994 and ranged from 49 to 95 kg/ha. Biomass accumulation by mid-May ranged from 2032 to 7914 kg/ha, and N accumulation ranged from 19 to 52 kg/ha. Most of the variability in wheat growth was caused by differences in sites within and among soils associated with depression areas. Around these depression areas, site-specific management of N inputs appears more effective than cover crops at reducing N losses to the environment. In other areas, cover crops should be predictable and reliable in trapping N and increasing soil organic matter.