外源化肥氮素在土壤有机氮库中的转化及关系

Transformation of external chemical nitrogen in soil organic nitrogen fractions and their relationship

【目的】本研究旨在探明外源化肥氮在土壤不同有机氮库中的动态转化及关系,为实现化肥氮素养分高效利用的有效调控提供理论依据。【方法】利用15N示踪技术(15N标记尿素,丰度10.3%),以江西红壤性水稻土为研究对象,通过土壤培养试验,研究农民习惯施肥水平下,水稻不同生育期外源化肥氮在土壤有机氮库(氨基酸态氮、氨基糖态氮、酸解铵态氮、酸解未知氮和非酸解有机氮)中的转化及关系。采用通径分析方法,评估来自外源化肥氮的有机氮各组分之间的转化关系。【结果】1)土壤中氨基酸态氮和氨基糖态氮中来自外源的化肥氮(氨基酸态氮-15N和氨基糖态氮-15N)含量从分蘖期到拔节期显著升高(P<0.05),从拔节期到灌浆期显著降低(P<0.05),全生育期两个组分中来自外源化肥氮的含量最高值分别为26.5和8.4 mg/kg,均出现在分蘖期和拔节期之间;酸解性铵态氮中来自外源的化肥氮(酸解性铵态氮-15N)含量从分蘖期到成熟期逐渐降低,全生育期的动态转化符合指数递减方程;酸解未知态氮中来自外源的化肥氮(酸解未知态氮-15N)含量随着生育期的延长逐渐达到动态平衡,最大值接近12.8 mg/kg;非酸解性有机氮中来自外源的化肥氮(非酸解性有机氮-15N)含量在全生育期的变化符合对称方程,最低值7.9 mg/kg出现在拔节期和灌浆期之间。2)在水稻营养生长阶段的分蘖期和拔节期,外源化肥氮分别以酸解性铵态氮和氨基酸态氮为主要方式结合到土壤有机氮库中,其含量分别占施入化肥氮的21.5%和14.8%;在水稻营养生长和生殖生长并进阶段(灌浆期)和生殖生长阶段(成熟期),外源化肥氮主要结合到非酸解性有机氮库中,分别占施入化肥氮的8.7%和12.7%。3)土壤各有机氮库中来自外源的化肥氮之间存在相互转化的关系,酸解性铵态氮库起到了"暂时库"的作用,生育前期在土壤中固持氮,当可利用性氮受限时,又可以作为有效氮库释放氮供作物吸收;在整个生长期中氨基酸态氮库对外源化肥氮的转化积累起到了"过渡库"的作用,固持在氨基酸中的化肥氮可以转化成酸解性铵态氮和氨基糖态氮。4)灌浆期和成熟期植物吸收的来自外源的化肥氮与氨基酸态氮-15N和酸解铵态氮-15N的关系更密切。【结论】外源化肥氮在土壤中转化的过程中酸解性铵态氮起到了"暂时库"的作用,氨基酸态氮起到了"过渡库"的作用,非酸解性有机氮可作为氮素的"稳定库"存在,外源氮在这几个主要的氮库中动态转换以保持土壤-作物体系中氮素的循环。

Objectives]In this study,the transformation and re1ationshiP of externa1 chemica1 N in soi1 organic nitrogen( SON)fractions were determined during one growing season of rice in order to Provide a theoretica1 basis&nbsp;for reasonab1e ferti1izer aPP1ication and the effective adjustment to N ferti1izer.[Methods]A Pot exPeriment was carried out on a subtroPica1 Paddy soi1 in Jiangxi Province,and a tota1 N 180. 0 kg/ha(15 N 1abe1ed urea,atom 10. 3%)was aPP1ied to a rice croP during one growing season under the conventiona1 farmer Practices. Distribution and dynamics of the chemica1 N ferti1izer in different SON fractions( i. e. ,amino acid N,amino sugar N, hydro1ysab1e ammonium N,hydro1yzab1e unknown N and acid inso1ub1e N)were measured. Path ana1ysis was used to eva1uate the transformation Process between SON derived from the ferti1izer in soi1-P1ant system.[Results]1 ) The accumu1ation of ferti1izer-derived N in different SON fractions was season-sPecific. The recovery contents of the ferti1izer-derived N in soi1 amino acid N and amino sugar N at the jointing stage are significant1y higher than those at the ti11ering stage( P<0. 05 ). The enrichments of 15 N are significant1y dec1ined from the jointing stage to fi11ing stage( P<0. 05 ). The dynamics of enrichment of 15 N in soi1 amino acid N and amino sugar N during the growing season can be fitted as a Gauss equation,the maximum contents are 26. 5 and 8. 4 mg/kg,resPective1y,which are found between the ti11ering stage and jointing stage. The enrichment of 15 N in hydro1ysab1e ammonium N is dec1ined gradua11y from the ti11ering stage to harvest stage,and the dynamics of the enrichment of 15 N in soi1 hydro1ysab1e ammonium N cou1d be exPressed as an exPonentia1 dec1ine equation. The enrichment of 15 N in hydro1yzab1e unknown N is gradua11y in a dynamica1 equi1ibrium from the ti11ering stage to harvest stage,and the dynamics of the enrichment of 15 N in soi1 hydro1ysab1e unknown N can be fitted as an exPonentia1 equation. The enrichment of 15 N in acid inso1ub1e N can be fitted as a symmetry equation,and the minimum of the enrichment of 15 N is 7. 9 mg/kg, which is found between the jointing stage and fi11ing stage. 2 )At the ti11ering stage and jointing stage of rice, Preferentia1 enrichment of 15 N is found in soi1 hydro1ysab1e ammonium N and amino acid N,accounting for 21. 5%and 14. 8% of the tota1 N of the chemica1 N ferti1izer,resPective1y. The accumu1ation of residua1 ferti1izer-derived N in acid inso1ub1e N is higher at the fi11ing and harvest stages,accounting for 8. 7% and 12. 7% of the tota1 N of the chemica1 N ferti1izer,resPective1y. 3 )The Path ana1ysis indicates that the hydro1ysab1e ammonium N is a temPorary Poo1 for raPid chemica1 N ferti1izer retention and is aPt to re1ease N for croP uPtake simu1taneous1y. In contrast,the amino acid N cou1d serve as a transitiona1 Poo1 of avai1ab1e N in soi1 system through transferring into hydro1ysab1e ammonium N and amino sugar N. 4)The ferti1izer-derived N in hydro1ysab1e ammonium N and amino acid N are c1ose1y re1ated to ferti1izer-derived N in croP uPtake.[Conclusions]In a P1ant-soi1 system,the ferti1izer N cyc1ing during a growing season is c1ose1y re1ated to temPora1 Patterns of ferti1izer N transformation into different SON fractions. The ferti1izer-derived N can be derived into three Poo1s with different avai1abi1ities. The hydro1ysab1e ammonium N fraction can serve as a temPorary Poo1 containing readi1y avai1ab1e N to be re1eased fast,whi1e the amino acid N can be considered as a transitiona1 Poo1 for the transformation of the hydro1ysab1e ammonium N and amino sugar N,and the acid inso1ub1e N is tight1y associated with ferti1izer N stabi1ization. ImPortant1y,there is an interim shift among the three substantia1 N Poo1s to maintain soi1 N cyc1ing and suPP1y in a soi1-P1ant system.