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。
The nutrient surpluses in regional agricultural land may partly discharge to natural waters, which will cause the eutrophication of rivers and lakes. Based on the long-term agricultural data of Changxing County in the south of Taihu Lake, the estimation of nutrient surpluses from 1949 to 2002 has been made. The results show that the annual specific nitrogen and phosphorus surpluses in the agricultural land have obvious increasing trends. The linear increasing rates of the surpluses are 3.66 kg N/(ha穉) and 0.65 kg P/(ha穉) for nitrogen and phosphorus respectively (R2=0.56, 0.46). In the 1950s and 1960s last century, the N-surplus increased slowly, but after the middle of 1970s it increased fast .By the year of 1996, it reached the maximum value of 319.9 kg/(ha穉). Since that time, it decreased. Before the earlier 1960s the P was in deficit. During 1975-1980 the P-surplus increased slowly and then it decreased. Since the middle of 1980s the P-surplus rose very fast and increased twenty times from 2.4 kg/(ha穉) in 1985 to 48.2 kg/(ha穉) in 1991. During 1992-1998, the P-surplus kept in high values between 35-45 kg/(ha穉). Since 1999 it decreased rapidly.
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