黄土区地膜覆盖对麦田土壤微生物体碳的影响

研究了1999年(丰水年)和2000年(干旱年)旱地条件下不同时间覆膜(不覆膜、覆膜30d、覆膜60d和全程覆膜)对春小麦(Triticum aestivum)农田土壤微生物体碳的影响．结果表明，1999年土壤微生物体碳平均为335．3mg·kg^-1干土，2000年平均为259．3mg·kg^-1干土，前者高出后者29．37％．2年中最高微生物体碳均出现在全程覆膜处理．1999年。土壤微生物体碳在覆膜60d时即接近最高值。该处理籽粒产量也最高．2000年。由于春小麦生育后期降水丰富。在整个生育期中，微生物体碳增长表现为“增长-平稳甚至出现下降-再增长”的梯形方式，到生育后期，各处理之间才出现显著差异。全程覆膜处理的微生物体碳后期大幅度增加。与1999年接近．2年中各处理的C／N处于7．732～9．042之间。远低于11．3的临界值，C／P处于300．8～719．6之间，均高于300的临界值，不利于土壤微生物体碳的增加．微生物和作物对土壤有效态氮和磷的吸收处于竞争状态，表明该农田生态系统有机质严重不足。已经构成了限制作物生产力发挥的雷耍因素．长期地膜覆蔫和大量伸用化肥将加剧这一问题的严重性。

Effect of plastic film mulching on soil microbial biomass in spring wheat field in semi-arid loess area

This paper studied the effect of different periods of plastic film mulching (M0-no mulching, M30-mulching for 30 days, M60)-mulching for 60 days, and M-mulching for whole growth period) on soil microbial biomass carbon (SMBC) of spring wheat field in semi-arid loess plateau. The mean SMBC in 1999 and 2000 was 335. 3 and 259.3 mg.kg-1 dry soil, respectively. It was 29. 3% higher in 1999 than in 2000. The highest SMBC was recorded at the harvest stage in M treatment for the two years. In 1999, a wet year with more rainfall, the SMBC of M60 and M treatments was significantly higher than those of MO and M30 in the mid-period of growth, reached its top at the end of the growth period. The highest grain yield was also achieved in M60.It was a dry year in 2000, but rainfall was rich in the latter growth period of spring wheat. SMBC increased at the beginning period of growth, and did not increase during the mid-growth period. It increased again during the latter period of growth, and showed a significant difference among the treatments. At the harvest stage of 2000, SMBC in M0 was the highest among all the treatments. It was similar between M and M60, and lower than that of M30. In the two years, the ratio of C/N ranged between 7.732~ 9.042, being lower than the threshold of 11.3, and the ratio of C/P was 300. 8-719.6, being higher than the threshold of 300. The two parameters showed that the increase of SMBC was inhibited because of the competition of soil available nutrients between soil microbes and crops. These indicated that soil organic matter content was so shortage that it became the key factor to restrict crop productivity. Under this condition, increasing crop productivity through the input of chemical fertilizers would conceal the problem of soil degradation, and result in a further decrease of soil quality. A long term plastic film mulching would make the problem more serious.