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

1999年和2000年对同时用于放牧和割草的牧场的氮素收支进行了调查。一个拥有高羊茅、果园草和白三叶草的牧场(0.9公顷)被分成两个(1999年)或三个(2000年)区域：最初放牧区和割草成草或青贮料后放牧区。一群4-5头牛(小母牛或日本黑白花或荷斯坦牛)在一个、两个和所有地区吃草。放牧时间较长的牧草N产量高于放牧时间较短的牧草和干草产量之和。作为肥料(仅在1999年施用)或动物排泄物流入土壤的氮量似乎与地区间牧草产量的差异有关。各地区间各年内全牧场氮素盈余值非常接近。但1999年的N顺差高于2000年。这种差异是由于1999年才开始施肥，2000年青贮料产量高于1999年干草产量所致。直到2000年才对某些形态的土壤氮素含量进行了调查。不同地区土壤速效氮含量差异不大。较长放牧区土壤矿化氮含量高于较短放牧区。因此，较长时间的放牧可能会导致土壤中氮素淋失的增加。

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.