Leaching and Uptake of Nitrogen Applied to Annual Grass and Clover‐Grass Mixtures in Lysimeters1

Abstract

AbstractThe annual grassland soils of California are nearly always N deficient. If early winter feed is desired and total production is to be increased, N must be added, either by a legume or through N fertilization. Comparison of these two N sources in terms of forage and protein production and groundwater pollution is important for efficient management of land, water, and N resources.This study was initiated to measure the effect of N fertilization on forage yields, N‐uptake by the plants, and N leached from the soil where grass grew alone or from clover‐grass mixtures.Grass (soft chess, Bromus mollis L.) growing alone, grass plus subclover (Trifolium subterraneum L.), and grass plus rose clover (T. hirtum All.) were grown in lysimeters on Josephine soil with and without N applied in the autumn of each of 4 years.Nitrogen fertilization increased winter forage yields and N‐uptake in all species mixtures. However, in the spring harvest, clover‐grass mixtures yielded as much forage and N‐uptake without N as with N applied. Apparent recovery of the applied N in the forage was 25% for the grass, −2% for the subclover‐grass, and 0% for the rose clovergrass. The amount of apparent fertilizer N found in drainage water was 37% from grass, 58% from subclover‐grass, and 50% under rose clover‐grass. Without N fertilization the N leached was about the same from clovergrass as from grass alone. Of total N leached, 94% was in the fall, 6% in winter, and less than 1% in spring, whereas the total drainage water was divided 43% in the fall, 54% in whiter, and 3% in spring. With N fertilization, NO3‐N in the water in the fall was 45 ppm from clover‐grass and 38 ppm from grass. Without applied N, the NO3‐N values were 25 ppm in the fall and were 1/10 as great in winter and about 1/100 in spring. There was no rain in the summer.