Abstract:

Soil organic nitrogen (N) content was the most important indictors of changes of soil fertility. Soil N mineralization and the number of soil microorganisms were obvious changed under different fertilizer conditions. In order to explore the effects of different long-term fertilizer regimes on rhizosphere soil N mineralization and the number of soil microorganism under the double-cropping rice system in the southern of China, a long-term (37-year) location field experiment was conducted under the double-cropping rice system with four fertilizer regimes including chemical fertilizer alone (MF), rice straw and chemical fertilizer (RF), 30% organic manure and 70% chemical fertilizer (OM), and without any fertilizer input as a control (CK). Therefore, the effects of different long-term fertilizer regimes on rhizosphere soil microbial biomass nitrogen (SMBN) content, N mineralization rate, nitrification rate (NR), ammonification rate, the number of soil microorganisms, and the relationship between rhizosphere soil N transformation and soil physicochemical characteristics, number of soil microorganisms in the double-cropping rice field in the southern of China were investigated in this paper. This result indicated that rhizosphere soil organic carbon (SOC), total N, available N, NO₃^--N, NH₄⁺-N and inorganic N contents with OM treatments were significantly higher than that of RF, MF and CK treatments. This result showed that rhizosphere SMBN content with OM treatment was significantly higher than that of RF, MF and CK treatments. Compared to CK treatment, rhizosphere SMBN content with OM treatments increased by 24.1%. Meanwhile, this result showed that rhizosphere soil aerobic N mineralization rate, anaerobic N mineralization rate and ammonification rate in paddy field with OM treatment were significantly higher than that of MF and CK treatments. Rhizosphere soil NR with MF treatment was significantly higher than that of RF, OM and CK treatments. The number of rhizosphere soil nitrifying bacteria, denitrification bacteria and ammonifiers bacteria in paddy field with OM treatment were significantly higher than that of RF, MF and CK treatments. The number of rhizosphere soil azotobacteria in paddy field with RF treatment was significantly higher than that of MF, OM and CK treatments. Compared to MF treatment, yields of early rice and late rice with RF and OM treatments increased by 10.6%, 13.4% and 10.4%, 7.1%, respectively. Rhizosphere soil aerobic N mineralization rate, anaerobic N mineralization rate, and NR had significant positive correlations with soil pH, number of soil nitrifying bacteria, and denitrification bacteria, but had negative correlations with SOC, total N, available N, NH₄⁺-N, and inorganic N contents, respectively. As a result, it is beneficial to increase rhizosphere soil N mineralization and number of soil microorganisms, and enhance soil fertility in the double-cropping rice field by applying 30% organic manure and 70% chemical fertilizer.

Key words: long-term fertilizer, double-cropping rice field, rhizosphere, soil N mineralization, soil microorganism

摘要：

土壤有机氮含量是评价土壤质量变化的重要肥力指标，土壤氮矿化及其微生物数量易受不同施肥措施的影响。为明确南方双季稻区长期不同施肥模式对根际土壤氮矿化及其微生物数量的影响，以长期（37年）定位施肥试验田为平台，系统分析了不同施肥模式[单独施用化肥 (MF)、秸秆还田+化肥 (RF)、30%有机肥+70%化肥 (OM) 和无肥对照 (CK)]下双季稻田根际土壤微生物量氮含量、氮素矿化、硝化和氨化速率、氮循环微生物数量的变化特征，及土壤氮转化与理化特性、微生物相关性。结果表明，OM处理根际土壤有机碳、总氮、碱解氮、硝态氮、氨态氮和无机氮含量均显著（P<0.05）高于RF、MF和CK处理。OM处理根际土壤微生物量氮含量最高，比CK处理增加24.1%。OM处理根际土壤有氧氮矿化率、厌氧氮矿化率和氨化速率均为最高，均显著高于MF和CK处理（P<0.05）；MF处理根际土壤硝化速率为最高，显著高于RF、OM和CK处理（P<0.05）。OM处理根际土壤硝化细菌、反硝化细菌和氨化细菌数量均显著高于RF、OM和CK处理（P<0.05）；RF处理根际土壤固氮菌数量显著高于MF、OM和CK处理（P<0.05）。RF和OM处理早稻、晚稻产量分别比MF处理增加10.6%、13.4%和10.4%、7.1%。根际土壤有氧氮矿化率、厌氧氮矿化率、硝化速率与土壤pH、硝化细菌、反硝化细菌数量均呈显著正相关（P<0.05），与土壤有机碳、总氮、碱解氮、氨态氮、无机氮含量均呈显著负相关（P<0.05）。因此，采取30%有机肥措施有利于增加双季稻田根际土壤氮矿化及其微生物数量，培肥稻田土壤。

关键词: 长期施肥, 双季稻田, 根际, 土壤氮矿化, 土壤微生物