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

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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.