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根据太湖南部长兴县农业统计资料,对该地区1949~2002年农业用地上N、P的剩余量作出评估。评估结果认为,1949~2002年期间,单位农业用地面积的N、P剩余量具有显著地增加趋势。20世纪50及60年代期间,N的剩余量增加缓慢,自70年代中期以后增加迅速。1996年达到历史最大值。1996年后,N剩余量呈现减少趋势。60年代初期以前,P处于亏损状态。1975~1980年期间,P剩余量呈现缓慢增长趋势,其后出现回落,自80年代中期以后出现迅速增加趋势。1992~1998年期间,P剩余量维持在35~45 kg/(hm2.a)之间的高水平变化,自1999年以后出现显著回落。
According to the agricultural statistics of Changxing County in the south of Taihu Lake, the remaining N and P of agricultural land in the area from 1949 to 2002 were evaluated. According to the assessment results, the N and P residuals of agricultural land per unit area increased significantly from 1949 to 2002. During the 1950s and 1960s, the surplus of N increased slowly, increasing rapidly since the mid-1970s. In 1996 reached the historical maximum. After 1996, the remaining amount of N showed a decreasing trend. Before the early 1960s, P was at a loss. From 1975 to 1980, the surplus of P showed a slow growth trend, and then dropped back, showing a rapid increase trend since the mid-1980s. From 1992 to 1998, P remained at a high level of 35-45 kg / (hm2.a), with a significant drop since 1999.