缓/控释复合肥料对土壤氮素库的调控作用

采用小麦盆栽生物试验、实验室化学分析和仪器分析方法研究了缓/控释复合肥料(SRF)对土壤氮素养分库中不同组分(微生物量氮、固定态铵、NH4+-N、NO3--N、铵离子周转库)动态变化的影响及其与小麦吸收氮素养分的关系。结果表明,在小麦分蘖初期,SRF处理土壤微生物量氮、NH4+-N含量较普通复合肥料(CCF)低,此后整个小麦生育期的土壤微生物量氮、NH4+-N含量的总体变化趋势以SRF处理高于CCF处理,其中SRF处理的小麦土壤NH4+-N含量较CCF处理高108.1%—271.7%;在小麦生长前期,SRF处理土壤固定态铵含量较CCF低;在小麦生长中期,SRF处理土壤固定态铵含量较CCF处理高;与CCF处理比较,SRF处理小麦土壤硝态氮含量经历先升高后降低、在生育后期又升高的趋势。在小麦生育前期,CCF处理土壤"铵离子周转库"由371.3 mg/kg降至259.1 mg/kg;SRF处理土壤"铵离子周转库"由306.5 mg/kg升至324.5 mg/kg。在小麦需氮量较高的拔节期,CCF处理土壤"铵离子周转库"与前一次之差值仅为34.18 mg/kg,而SRF处理则达到77.21 mg/kg,表明小麦生育前期SRF土壤"铵离子周转库"能够固定更多的铵离子,降低铵离子的损失;在小麦需氮量较高的时期,"铵离子周转库"则释放更多的铵离子以供给小麦吸收利用。小麦生长初期CCF处理释放养分速率较快,小麦植株吸氮量高于SRF处理;生长中、后期SRF处理释放养分量较CCF处理高,此阶段小麦吸氮量以SRFCCF。不同处理对小麦吸氮量的影响与对小麦生物量变化是基本一致的,即初期以CCFSRF,中后期以SRFCCF,收获期SRF处理较CCF处理分别提高小麦生物量15.32%、吸氮量13.51%。相关分析表明,小麦生物试验中SRF处理土壤微生物量氮、固定态铵以及"铵离子周转库"的动态变化与小麦吸氮量之间达到显著或极显著负相关关系(r=-0.8728*—-0.9006**),SRF调控土壤氮素库的能力较CCF更强,能更好的协调土壤氮素养分供应与小麦氮素需求间的动态平衡和提高肥料氮素利用效率。

Effects of slow/controlled release compound fertilizers on the forms of soil nitrogen

A pot experiment combined with lab work was conducted to study effects of slow/controlled-release compound fertilizers (SRF) on dynamic changes of soil N components (microbial biomass nitrogen(MN), fixed-ammonium(FN), ammonium nitrogen(AN), nitrate nitrogen (NN) and ammonium ion flux (AIF)) in relation to N uptake by wheat. Results indicated that the SRF treatment reduced amount of soil MN and AN at the early wheat growing stage compared to the common compound fertilizer (CCF) treatment but this was reversed thereafter. The amount of soil AN in the SRF treatment was 108.1% to 271.7% higher than that in the CCF treatment since the mid-stage. The SRF treatment reduced amount of soil FN at the early wheat growing stage, increased FN at the mid-growing stage, and drove NN from high to low and then back to high in the whole growing season compared to the CCF treatment. Soil AN not being timely absorbed by wheat tends to transform into soil MN or soil FN as long as supply of soil AN was adequate, while soil MN or FN tends to be mineralized to AN as soil available N is diminished by wheat. Thus, soil MN and FN can be regarded as N pools which can balance to some extent the N mineralization and immobilization that controls amount of AN in soil or soil AIF. At the early stage the soil AIF reduced from 371.3 mg/kg to 259.1 mg/kg in the CCF treatment but increased from 306.5 mg/kg to 324.5 mg/kg in the SRF treatment. At the elongation stage when wheat requires maximum N supply, the difference in soil AIF between the first two times was measured as only 34.18mg/kg in the CCF treatment but up to 77.21mg/kg in the SRF treatment. The change of soil AIF showed that the SRF treatment could maintain higher soil AN to meet wheat demand at the early growing stage, which could favor reducing N losses through emissions and leaching if any. During the early growing stage, N availability to wheat in the CCF treatment might be much higher than in the SRF treatment, resulting in much higher N uptake by wheat in the former than in the latter. With time, the SRF treatment released more N than the CCF treatment and this was evidenced by higher N uptake by wheat in the SRF treatment. The pattern of N uptake by wheat was in coincidence with accumulation of wheat biomass, namely CCF>SRF at the early stage and SRF>CCF at the mid-later stage. At maturity, the biomass and N uptake of wheat in the CCF treatment were 15.32% and 13.51% higher than in the SRF treatment, respectively. The fluctuated amounts of soil MN, FN and AIF in the SRF treatment were significantly and negatively correlated with amounts of N uptake by wheat (r=-0.8728*--0.9006**), showing much stronger ability of the SRF in regulating soil N transformation to maintain good balances between soil N supply and crop demand and favoring improvement of N use efficiency. Therefore, compared to the common compound fertilizer, the SRF is more favorable to wheat.