Nitrogen Budgets and Soil Nitrogen Leaching of Beef Production System Based on Forage Production.

在1999年和2000年对放牧和刈割两种利用方式下的草地氮收支进行了研究。将含有高羊茅、鸭茅和白色三叶草的牧场（0.9公顷）分为两个（1999年）或三个（2000年）区域：一个最初放牧区域和切割后放牧的干草或青贮饲料区域。一群4-5头牛（小母牛或日本黑牛或荷斯坦牛）在一个、两个和所有地区放牧。放牧时间较长的地区牧草氮生产量高于放牧时间较短的地区牧草氮和干草氮的总和。流入土壤的氮作为肥料（仅在1999年应用）或动物排泄物的量似乎与牧草产量的差异之间的地区。各地区的全草氮盈余值在各年中非常相似。但1999年氮素盈余高于2000年。结果表明，造成这种差异的原因是1999年只施用了化肥，2000年青贮产量高于1999年干草产量。仅在2000年调查了土壤中某些形态的氮素含量。不同地区土壤速效氮含量差异不大。长期放牧区土壤矿化氮含量高于短期放牧区。因此，更长时间的放牧可能会导致土壤中氮素淋溶的增加。

Nitrogen budgets on a pasture being utilized for both grazing and cutting were investigated in 1999 and 2000. A pasture (0.9 ha) containing tallfescue, orchardgrass and white clover was divided into two (1999) or three (2000) areas : an initially grazed area and areas grazed after cutting for hay or silage. A herd of 4-5 cattle (heifers or steers of Japanese Black or Holstein) grazed at one, two and all of the areas. The amount of herbage N production from the areas where cattle grazed for longer period was higher than the sum of N of grazed herbage and harvested hay from the areas where cattle grazed for shorter period. The amount of N inflow to soil as fertilizer (applied in 1999 only) or animal excreta seemed to relate to the difference in herbage production between the areas. The value of N surplus for the whole pasture was very similar among the areas in each year. But the N surplus in 1999 was higher than that in 2000. It is suggested that the difference was caused by the facts that fertilizer was applied only in 1999 and that silage production in 2000 was higher than that of hay production in 1999. Soil nitrogen contents of some forms were investigated only in 2000. There was little difference in available nitrogen contents in soil among areas. The mineralized soil nitrogen contents in the longer-grazed areas were higher than those in the shorter grazed area. So, longer-grazing may have lead to some increase in nitrogen leaching from soil.