中文摘要：

在水稻不同生育期分层采集稻田土壤剖面样品,研究不同耕作方式（常耕CT、免耕NT、稻草还田常耕CTS、稻草还田免耕NTS）、不同土层稻田土壤的氮素（N）形态及氮素转化菌特征.结果表明：在N素转化菌方面,水稻整个生育期0～5cm土层氨化细菌的数量以NTS处理最多;0～5cm和5～12cm土层亚硝化细菌数量CT处理高于NT处理,12～20cm土层则相反;NTS较CTS处理降低了0～20cm土层的亚硝化细菌和反硝化细菌数量;在水稻拔节期和成熟期,NT处理较CT处理提高了0～5cm土层的嫌气性固氮菌数量.在N素形态方面,水稻整个生育期NT处理碱解N和全N较集中分布在0～5cm土层,明显高于CT处理,而5～12cm和12～20cm土层比CT处理低;12～20cm土层的铵态氮和硝态氮含量NT与CT处理差异不显著,而NTS处理0～20cm土层的铵态氮和硝态氮含量均有所提高.相关分析和多元回归分析表明,铵态氮与氨化细菌、亚硝化细菌、反硝化细菌正相关程度最高,而碱解氮与嫌气性固氮菌正相关程度最高,均达极显著水平.综合各土层氮素转化菌数量与不同形态N含量,NTS更有利于稻田氮素供应与养分积累.

英文摘要：

Paddy soil samples were collected in layers （0-5, 5-12, and 12-20 cm） during rice growth period to investigate the characteristics of the N forms and N-transforming bacteria in the soil profile under different tillage patterns （no-tillage with straw returning, NTS; conventional tillage with straw returning, CTS; no-tillage, NT; and conventional tillage, CT）. In the whole rice growth period, ammonifying bacteria in 0-5 cm soil layer had the highest number under NTS, and nitrosobacteria in 0-5 cm and 5-12 cm soil layers were more abundant but in 12-20 cm soil layer were lesser under CT than under NT. Nitrosobacteria and denitrobacteria in 0-20 cm soil layer were lesser under NTS than under CTS. At elongating and ripening stages, anaerobic N-fixing bacteria in 0-5 cm soil layer were more abundant under NT than under CT. In the whole rice growth period, the alkali-hydrolyzable N and total N contents in 0-5 cm soil layer were significantly higher but in 5 -12 cm and 12-20 cm soil layers were lower under NT than under CT, and the NH4^＋ -N and NO3-N contents in 0-20 cm soil layer were higher under NTS but in 12-20 cm soil layer had no significant differences between NT and CT. Correlation analysis and multiple polynomial regression analysis further revealed that there were significant relationships between soil NH4 ＋ -N and soil ammonifying bacteria, nitrosobacteria and denitrobacteria, and between soil alkali-hydrolyzable N and soil anaerobic N-fixing bacteria. Among the test tillage patterns, NTS could be the more desirable one for the N supply and fertility maintenance of paddy soil.