Corn Growth with Foliar Nitrogen, Soil-Applied Nitrogen, and Legume Intercrops

Corn (Zea mays L.) production under current N fertilizer recommendations can result in soil degradation and N pollution of groundwater. Sources of N such as intercropped legumes or foliar spray might reduce fertilizer N requirements while improving soil quality through legume growth. The objective of this study was to compare corn growth using combinations of foliar and soil urea applications, as well as legume intercrops in combination with soil fertilizer N. Field experiments were conducted for 3 yr on two Typic Humaquepts, a Ste. Rosalie clay and an Ormstown silty clay. Foliar applications of 20 kg N ha⁻¹ applied in late July or late August, or both, were compared at 0 and 140 kg N ha⁻¹ of soil-applied urea. The effects of a legume intercrop on corn yield were determined by planting legumes at the same time as corn, at three rates of added N (0, 70, and 140 kg N ha⁻¹). Treatments were placed on the same plots each year, providing an assessment of cumulative effects. Plant dry-matter yields and soil mineral N were determined. Plots were fall-plowed each year and planted after conventional soil preparation. Foliar N increased yields only in one site-year. Intercropping lowered corn yields by about 2 tonnes ha⁻¹ in five site-years, except for one wet year on the Ormstown site when intercrops did not affect corn yields. Added N increased corn yields independently of intercropping, indicating little cumulative effect of legumes on soil N supply. Legume intercropping and foliar-applied urea were not effective alternatives to the use of soil-applied urea N as far as grain corn yield is concerned. Contribution from the Dep. of Renewable Resources and the Dep. of Food Sci. and Agric. Chem., Macdonald College of McGill Univ. Supported by the Natural Science and Engineering Res. Council, Canada. Strategic Grant G1252.