地下水位和长期施肥对红壤性水稻土有机碳矿化特征的影响

Effects of Groundwater Tables and Long-term Fertilization on Mineralization of Organic Carbon in Red Paddy Soil

以1982年开始的长期定位试验红壤性水稻土为对象,采用室内模拟培养试验方法,对耕层土壤有机碳矿化特征进行分析,以探究两个地下水位(20 cm、80 cm)下,长期不同施肥处理(高量有机肥+化肥(2/3OM)、常量有机肥+化肥(1/3OM)、单施化肥(NPK))红壤性水稻土有机碳矿化特征和差异。结果表明,较高的地下水位促进土壤有机碳累积,提高了高量有机肥和常量有机肥处理的土壤有机碳矿化速率,且增加了其有机碳累积矿化量(Ct)及潜在可矿化有机碳量(C0),但土壤有机碳累积矿化率在施用化肥的条件下表现为减少。长期不同施肥的红壤性水稻土土壤有机碳矿化特征在不同地下水位条件下变化明显,2个地下水位的土壤有机碳含量、土壤有机碳矿化速率及有机碳累积矿化量高低排序均表现为:2/3OM>1/3OM>NPK;20 cm地下水位长期施用2/3OM和1/3OM土壤有机碳累积矿化率分别较NPK高出53.32%(P<0.05)、15.44%,80 cm地下水位则分别低出5.56%、17.95%(P<0.05);20 cm地下水位2/3OM和1/3OM处理的土壤潜在可矿化有机碳量(C0)显著高于NPK处理,而80 cm地下水位C0表现为1/3OM处理显著低于NPK处理;地下水位对相同施肥处理土壤有机碳周转常数(k)影响不明显,而在同为80 cm的地下水位条件下,长期施用有机肥可显著提高k。因此,长期不同施肥对红壤性水稻土有机碳累积矿化率、潜在可矿化有机碳量及周转常数的影响在不同地下水位条件下发生变化。

【Objective】As an essential biochemical process in soil,mineralization of soil organic carbon(SOC)is closely related to release of soil nutrients,maintenance of soil quality,and formation of greenhouse gases.Mineralization of soil organic carbon varied in characteristic with soil properties and environment,while fertilization and groundwater table are two key environmental factors affecting soil properties.The objective of this study is to explore dynamics and characteristics of SOC mineralization in red paddy soil under long-term fertilization relative to pattern of the fertilization and groundwater table,in an attempt to provide certain guidance for rationalizing nutrient management programs.【Method】A long-term field experiment,initiated in 1982,was designed to have 3 fertilization treatments(2/3OM,1/3OM and NPK)and 2 groundwater tables(at 20 cm and 80 cm in depth).In Treatment 2/3OM organic manure was applied at a rate to make up 2/3 of the total N supply;in Treatment 1/3OM organic manure at a rate to make up 1/3;and in Treatment NPK,Urea to make up the total N supply.In all the 3 treatments,P and K was applied the same in rate.Each treatment had 3 replicates.Soil samples were collected from the topsoil layer,0-10 cm in depth,before ploughing in 2017.Cumulative emission and mineralization rate of carbon dioxide were determined with the incubation method.First-order kinetic model was used to calculate potential mineralization and turnover rates.【Result】Groundwater table had a significant impact on characteristics of organic carbon mineralization;SOC content in Treatment 2/3OM,1/3OM and NPK was 20.66%,23.30%and 17.97%,respectively,higher when the groundwater table was at 20 cm in depth than when it was at 80 cm in depth;Mineralization rate,cumulative mineralization and potential cumulative mineralization(C0)of SOC in Treatment 2/3OM and 1/3OM was also higher in the former case than in the latter case,whereas in Treatment NPK reverse tendencies were observed;Obviously mineralization of SOC in red soil varied significantly with fertilization pattern and depth of groundwater table.In terms of content,mineralization rate and cumulative mineralization of SOC,the three treatments exhibited an order of 2/3OM>1/3OM>NPK.When the groundwater table was at 20 cm in depth,Treatment 2/3OM and 1/3OM was 53.32%and 15.44%higher than Treatment NPK,respectively,in SOC cumulative mineralization rate,but when the groundwater table was at 80 cm in depth,Treatment 2/3OM and 1/3OM was 5.56%and 17.95%,respectively,lower.Meanwhile,in the case of the former,Treatment 2/3OM and 1/3OM significantly higher than Treatment NPK in potential mineralizable soil organic carbon(C0),but in the case of the latter,Treatment 1/3OM was significantly lower than Treatment NPK,and in the case of the former,the treatments did not vary much in SOC turnover constant(k),whereas in the case of the latter,Treatments 2/3OM and 1/3OM were significantly higher.【Conclusion】In conclusion,high groundwater table is conducive to accumulation of soil organic carbon,increase of cumulative mineralization,cumulative mineralization rates and potential cumulative mineralization of SOC in red soil under long-term application of organic manure,but lowers SOC cumulative mineralization rate in the soil under long-term application of chemical fertilizer.The effects of long-term fertilization on cumulative mineralization rate and potential cumulative mineralization of SOC in red paddy soil vary with depth of groundwater table.