紫云英与稻秸还田对稻田土壤硝化潜势的影响

  【目的】  种植利用绿肥和稻秸还田是水稻土培肥的重要措施。硝化作用是氮循环中的关键过程，我们研究了绿肥与稻秸还田对土壤硝化作用的影响，以明确紫云英–稻秸联合还田下的稻田硝化作用机制。  【方法】  水稻盆栽试验共设8个处理，分别为:对照(CK)、单独紫云英(MV)、单独稻秸(RS)、紫云英+稻秸(MV+RS)、单施氮肥(N)、紫云英+氮肥(MV+N)、稻秸+氮肥(RS+N)、紫云英+稻秸+氮肥(MV+RS+N)。研究了在不施氮和施氮条件下，紫云英、稻秸不同利用方式对土壤性状及硝化作用的影响，并通过特异性细菌抑制剂(卡那霉素和大观霉素)研究了氨氧化细菌(AOB)和氨氧化古菌(AOA)对硝化作用的相对贡献。  【结果】  MV+RS+N处理提高了土壤全氮和有机质含量，降低了碱性水稻土的pH。在早稻分蘖期，MV+RS+N处理显著提高了土壤中铵态氮和硝态氮含量。早稻移栽前，MV+RS 处理显著增加了土壤硝化潜势(NP)， 而MV处理相较CK降低了NP。早稻分蘖期，氮肥添加显著提高了NP。早稻拔节期和晚稻收获期，RS和MV+RS处理均降低了NP。早稻移栽前，MV+RS处理同时降低了土壤恢复硝化强度(RNP)，以及AOA和AOB在恢复硝化强度中的贡献(RNP_AOA和RNP_AOB)，并降低了RNP_AOB在RNP中的占比。早稻分蘖期，CK和N处理，MV+N处理提高了RNP_AOB，而在早稻拔节期，MV+RS+N处理相比MV+RS处理提高了土壤RNP及RNP_AOB。早稻收获期，MV、RS及MV+RS处理均降低了稻田土壤RNP。在不同生育期中，早稻分蘖期的NP与硝态氮含量显著正相关，其他时期相关不显著。土壤NP与土壤 pH 和硝态氮含量呈显著正相关，与土壤微生物量碳 (SMBC) 和土壤微生物量氮 (SMBN) 含量呈显著负相关。RNP_AOA与土壤pH和铵态氮含量呈显著正相关。  【结论】  紫云英–稻秸联合还田降低了碱性水稻土pH，并在水稻生育早期显著提高而在生育后期显著降低了土壤硝化潜势。硝化潜势与土壤pH和硝态氮含量呈显著正相关。早稻分蘖期和早稻拔节期以RNP_AOB占主导，紫云英–稻秸联合利用较CK降低了RNP_AOB；早稻和晚稻收获期则以RNP_AOA占主导，紫云英–稻秸联合还田相较于单独还田提高了RNP_AOA。

Effects of returning Chinese milk vetch and rice straw to the field on the nitrification potential of paddy soil

  【Objectives】  Returning green manure and rice straw to the field are important methods of improving paddy soilfertility. Nitrification is a key process in the N cycle, but its regulation by the co-utilization of green manure and rice straw is unclear.   【Methods】  A total of eight treatments were set up in a pot experiment, including: No soil amendment as control (CK), the addition of milk Vetch (MV), rice straw (RS), milk vetch + rice straw (MV+RS), chemical N fertilizer (N), milk vetch + chemical N fertilizer (MV+N), rice straw + chemical N fertilizer (RS+N), and milk vetch + rice straw + chemical N fertilizer (MV+RS+N). The pot experiment was conducted to study the effects of co-incorporation of Chinese milk vetch (Astragalus sinicus L.) and rice straw (RS) on soil properties and nitrification under N or no N fertilization. The effects of specific bacterial inhibitors (kanamycin and spectinomycin) were used to distinguish the relative contribution of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) to nitrification.   【Results】  MV+RS+N increased the total nitrogen (TN) and soil organic matter (SOM) but decreased the pH of the alkaline paddy soil. At the tillering stage of early rice, MV+RS+N increased ammonium nitrogen and nitrate-nitrogen in the soil (P < 0.05). Before transplanting the early rice, MV+RS increased the soil nitrification potential (NP), while MV reduced NP compared to the control (P < 0.05). Moreover, N increased NP (P < 0.05) . At the jointing stage of early rice and the harvest stage of late rice, RS and MV+RS reduced NP. Before transplanting early rice, MV+RS reduced the recovered nitrification potential (RNP), the contribution of AOA to RNP (RNP_AOA), the contribution of AOB to RNP (RNP_AOB), and reduced the proportion of AOB in RNP. At the tillering stage of early rice, compared with the CK and N, MV+N increased RNP_AOB. At the jointing stage of early rice, MV+RS+N increased RNP and RNP_AOB compared with MV+RS. At the harvest stage of early rice, MV, RS, and MV+RS all reduced the RNP of paddy soil. There was a positive correlation (P < 0.05) between NP and NO₃?-N content at the tillering stage, NP and soil pH and NO₃?-N, and a negative correlation (P < 0.05) between soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN). There was a positive correlation (P<0.05) between RNP_AOA and soil pH and ammonium nitrogen.  【Conclusions】  The co-incorporation of Chinese milk vetch and rice straw reduced soil pH, increased soil nitrification potential in the early stage of rice growth, and reduced soil nitrification potential later. Nitrification potential positively correlates with soil pH and nitrate N. RNP_AOB was dominant in the early rice’s tillering and jointing stage. The co-utilization of milk vetch and rice straw reduced RNP_AOB compared with CK. RNP_AOA was dominant in the harvest stage of early and late rice. The co-utilization of milk vetch and rice straw increased RNP_AOA compared with the single return of the former or latter to the field.