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CAS Workshop on Ecosystem Succession Theory and Practice of Ecological Restoration 半干旱黄土高原不同期间地膜覆盖春小麦农田的土壤微生物数量与肥力 李凤民
宋秋华 （兰州大学干旱农业生态国家重点实验室，兰州730000） 摘要：了解土壤微生物的数量和活力对我们认识土壤肥力动态是很有帮助的。本文选择典型半干旱黄土高原研究了不同时期地膜覆盖对春小麦农田土壤微生物数量和肥力的影响。实验设4个处理：CK-不覆盖，M30-从播种始覆盖30天，M60-从播种始覆盖60天，Mw-全生育期覆盖。在湿润的999年，土壤微生物数量主要受地表温度制约，而在干旱的2000年所有测定的微生物数量均下降，氨化细菌下降1.5%, 基本保持稳定，解磷细菌下降幅度最大，达86.6%，硝化细菌、亚硝化细菌、反硝化细菌、纤维素分解菌和放线菌分别下降36.6%, 47.2%, 72.2%, 49.7%, 26.1%。土壤有机碳含量同氨化菌、硝化菌、亚硝化菌、反硝化菌和纤维素分解菌均呈显著或极显著负相关。所有处理两个生长季C/N比较低，为7.732~9.042，可促进有机质分解和有机营养矿化。C/P比较高，范围是300.8~719.6。1999年土壤有效磷和解磷细菌数量呈显著负相关，而2000年无机磷转化强度同氨化菌、硝化菌、反硝化菌、纤维素分解菌、解磷细菌和放线菌呈显著正相关，表明无机磷的转化过程涉及到了很多类型的微生物。上述分析表明试验土壤中存在着一个正的反馈机制：覆膜/施化肥→C/N比下降→有机质分解加快→进一步降低C/N比。这个过程还同时导致有效磷的亏缺。因此，较长时期的覆膜/施用氮化肥将会增加土壤质量下降的风险，很低的有机碳含量是问题的关键。 关键词：黄土高原；半干旱区；土壤微生物数量；地膜覆盖；C/N, C/P比；春小麦；土壤肥力 Soil microbial numbers and fertility of plastic
film mulched cropland of spring wheat in semiarid area Li Fengmin
Song Qiuhua (State Key Lab of Arid Agroecology, Lanzhou University, Lanzhou 730000, China) Abstract: Knowledge of microbial numbers and activity in soil is essential for understanding the dynamics of soil fertility. We conducted an experiment to explore the soil microbial numbers and soil fertility effect of plastic film mulching for various durations at a spring wheat field located in the typical semi-arid Loss Plateau of China in two growing seasons. Four treatments were employed: CK- non-mulching, M30- mulching for 30 days after sowing (DAS), M60- mulching for 60 DAS and Mw- mulching for whole growing period. Soil microbial numbers in 1999, a wet year, were affected mainly by topsoil temperature. Severe drought in 2000 resulted in the decrease in almost all the soil microbial numbers, except number of ammonibacteria (AB) that decreased only by 1.5%. The most sensitive microbe to the severe drought was phosphorus bacteria (PB) which decreased by 86.6%. Other soil microbial numbers decreased by 36.6%, 47.2%, 72.2%, 49.7%, 26.1% for nitrite bacteria (NiB), nitrate bacteria (NaB), denitrobacteria (DB), cellulose decomposing bacteria (CDB) and actinomycetes (AM), respectively. Significantly negative correlation existed between soil organic C and the numbers of AB, NiB, NaB, DB, CDB. C/N ratio in all the treatments and years ranges between 7.732~9.042, which is favorable to decomposition of soil organic matter and mineralization of organic N. The significantly negative correlation was recorded between numbers of many groups microbes and soil N nutrients in the two years. C/P ratio in all the treatments in the two years dropped to the range of 300.8~719.6. The significantly negative correlation occurred between soil available phosphorus content and the numbers of PB in 1999. The significantly positive correlation between phosphorus transformation intensity and numbers of AB, NiB, DB, CDB, PB and AM in 2000 shows that many groups of soil microbes contribute to the phosphorus transformation process. The above analyses imply that a positive feedback cycle exists as the following: film mulching / chemical N fertilizer application→decreasing C/N ratio→promoting decomposition of soil organic matter→further decrease of C/N ratio. This process promotes the available P shortage. Thus, a risk for decreasing soil quality by film mulch for longer and chemical N fertilizer application exists in such cropland production, the low organic C in the soil is a key to the risk. Key words: loess Plateau; semiarid area; soil microbial number; plastic film mulch; C/N ratio, C/P ratio; spring wheat; soil fertility
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