不同耕作方式下稻田土壤的氮素形态及氮素转化菌特征

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0～5 cm土层氨化细菌的数量以NTS处理最多;0～5 cm和5～12 cm土层亚硝化细菌数量CT处理高于NT处理，12～20 cm土层则相反;NTS较CTS处理降低了0～20 cm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0～5 cm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0～5 cm土层，明显高于CT处理，而5～12 cm和12～20 cm土层比CT处理低;12～20 cm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0～20 cm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.

Characteristics of N forms and N-transforming bacteria in paddy soil under different tillage patterns.

Paddy soil samples were collected in layers (0〖KG-*2〗-〖KG-*7〗5, 5〖KG-*2〗- 〖KG-*7〗12, and 12〖KG-*2〗-〖KG-*7〗20 cm) during rice growth period to invest igate the characteristics of the N forms and N-transforming bacteria in the soi l profile under different tillage patterns (no-tillage with straw returning, NT S; conventional tillage with straw returning, CTS; no-tillage, NT; and conventi onal tillage, CT). In the whole rice growth period, ammonifying bacteria in 0〖K G-*2〗-〖KG-*7〗5 cm soil layer had the highest number under NTS, and nitrosobac teria in 0〖KG-*2〗-〖KG-*7〗5 cm and 5〖KG-*2〗-〖KG-*7〗12 cm soil layers were more abundant but in 12〖KG-*2〗-〖KG-*7〗20 cm soil layer were lesser under CT than under NT. Nitrosobacteria and denitrobacteria in 0〖KG-*2〗-〖KG-*7〗20 cm soil layer were lesser under NTS than under CTS. At elongating and ripening sta ges, anaerobic N-fixing bacteria in 0〖KG-*2〗-〖KG-*7〗5 cm soil layer were mo re abundant under NT than under CT. In the whole rice growth period, the alkali -hydrolyzable N and total N contents in 0〖KG-*2〗-〖KG-*7〗5 cm soil layer wer e significantly higher but in 5〖KG-*2〗-〖KG-*7〗12 cm and 12〖KG-*2〗-〖KG-*7 〗20 cm soil layers were lower under NT than under CT, and the NH4+-N and N O3--N contents in 0〖KG-*2〗-〖KG-*7〗20 cm soil layer were higher under NT S but in 12〖KG-*2〗-〖KG-*7〗20 cm soil layer had no significant differences be tween NT and CT. Correlation analysis and multiple polynomial regression analysi s further revealed that there were significant relationships between soil NH4 +-N and soil ammonifying bacteria, nitrosobacteria and denitrobacteria, and b etween 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.