长期施肥对水稻土不同功能有机质库碳氮分布的影响

土壤有机质(SOM)对于维持农业生产力、提高土壤质量和增加土壤固碳均具有非常重要的意义。以红壤水稻土35年的长期定位试验为依托,借助近期发展的物理―化学联合分组方法,探讨了长期施肥对水稻土不同功能SOM库含量、SOM库碳氮含量变化和分配比例的影响。结果表明,长期施肥尤其是有机无机配施处理显著增加了未保护游离SOM库(c POM和f POM)和纯物理保护SOM库(i POM)在土壤中的含量以及它们的土壤有机碳(SOC)和全氮(TN)含量。未保护游离SOM库的SOC和TN含量占总有机碳和全氮比例在有机无机配施处理下最高,分别达35.9%和33%。与CK相比,有机无机配施使生物化学保护库非水解游离粉粒组(NH-d Slit)和非水解游离黏粒组(NH-d Clay)含量分别降低了15%和9.5%(p0.05)。物理―化学保护SOM库、物理―生物化学保护SOM库以及化学保护SOM库含量受长期施肥影响不显著。综上,研究表明土壤不同功能SOM库对长期施肥的响应不同。有机无机配施是提升红壤水稻土SOM数量和质量的最佳培肥措施。

Effects of Long-term Fertilization on Distribution of Carbon and Nitrogen in Different Functional Soil Organic Matter Fractions in Paddy Soil

Objective] Soil organic matter (SOM) plays an important role in maintaining soil productivity,improving soil quality and sequestrating C.Changes in SOM due to management practices are usually difficult to quantify on the background that the soil already has a large relatively stable SOM pool.Therefore,it is recommended to use SOM fractions as early indicators of effects of management practices on soil quality.Meanwhile,understanding changes in different fractions of functional SOM as affected by long term management practice may help develop reasonable management strategies to optimize productivity and sustainability of the agroecosystem.Method] Based on a 35-year long-term fertilization experiment,effects of fertilization on SOM relative to functional fraction were explored with the recently developed physical-chemical fractionation method.In the present study,six functional SOM fractions were isolated,including non-protected free labile SOM,physically protected SOM,physico-biochemically protected SOM,physico-chemically protected SOM,chemically protected SOM and biochemically protected SOM,and changes in these six fractions of SOM,concerning size of the fraction and to tal nitrogen (TN) and Soil organic Carbon (SOC) contents and ratio in the fraction,under the long-term fertilization were analyzed.The long-term fertilization experiment was designed to have four treatments,that is,treatment CK (no fertilization),treatment N (chemical N fertilizer only),treatment NPK (N,P,K fertilizers),and treatment NPKM (chemical N,P,K fertilizers plus organic manure).Result] Results show that longterm application,especially treatment NPKM,significantly increased the percentages of non-protected SOM (cPOM and fPOM) and physically protected SOM (iPOM) and the contents of SOC and TN therein.The SOC and TN content in the non-protected fraction of free SOM was the highest in Treatment NPKM,reaching up to 35.9％ and 33％,respectively,indicating that this fraction of SOM is probably the major storage pool for SOC and TN,and easily affected by human management practices.Compared with Treatment CK,Treatment NPKM significantly decreased the content of non-hydrolyzable free silt (NH-dSilt) and non-hydrolyzable free NH-dClay by 15％ and 9.5％,respectively,in the bio-chemically protected fraction.However,it did not have much effect on the sizes of physico-chemically protected SOM fraction,physico-biochemically protected SOM fraction and chemically protected SOM fraction.All these indicate that these three fractions of SOM are relatively stable,or that they peak or approach to saturation in maintenance capacity.Conclusion] To sum up,this study demonstrates that different functions of SOM respond to long-term fertilization differently.Combined application of organic and inorganic fertilizers is the optimum fertilization measure to enhance the quantity and quality of SOM in the red paddy soil,and the effect is especially obvious on non-protected and physically protected SOM fractions.