Nitrogen flows in grazed pastures. II. Study of flows and their effects on leaching.

摘要

The prediction of nitrate leaching risks implies the comprehension of nitrogen flows in grazed pastures. An experiment with lysimeters buried in 2 plots (one with pure ryegrass [Lolium] with 250 kg N/ha per year, the other with a grass/clover mixture and no nitrogen) grazed by pregnant heifers was set up to study the effects of sward type and season on the characteristics and variability of animal returns, and on the fate of urine nitrogen after emission. The risks of nitrate leaching in relation to the amounts of nitrogen involved in the grazing cycles are specified. Using 15N techniques it was possible to investigate the fate of nitrogen in plants, soil and water, according to its origin (fertilizer and/or urine). The buffering capacity of the two sward types is discussed.