典型区域秸秆和有机肥混土填埋后的腐解特征

Decomposition Characteristics of Straw and Organic Fertilizer Mixed Soil After Landfill in Typical Area

【目的】秸秆和有机肥是我国农田主要有机物料来源,翻压旋耕是其主要的还田方式,明确其在我国典型农田土壤中的腐解过程特征和驱动因素,可为更好利用秸秆资源与合理施用有机肥提供科学依据。【方法】在我国典型黑土、潮土和红壤上开展大田有机物料混土填埋试验。设置4种处理:小麦秸秆混土(WS+soil)、玉米秸秆混土(MS+soil)、猪粪混土(PM+soil)和牛粪混土(CM+soil),按土重﹕物料碳=100﹕4.5,称取物料土壤混合物200 g装于尼龙袋填埋于土壤中,填埋后1年内采样6次,之后2—2.5年采样一次,满3年采样一次,共8次采样。分析各混土有机物料的腐解差异,采用双指数方程明确易分解有机碳库和难分解有机碳库比例和腐解速率,阐明各土壤中有机物料的快速腐解速率、慢速腐解速率及积温转折点,并用随机森林模型来量化物料组成和环境因素分别对腐解速率的相对贡献。【结果】秸秆混土的腐殖化系数为22%—43%,有机肥混土的为45%—58%。有机肥混土腐解较秸秆慢,区域间差异不大,从北往南有机物料腐解加快,且秸秆腐解较有机肥快。秸秆的易分解有机碳库比例(70%—87%)高于有机肥的易分解有机碳库比例(57%—83%),且秸秆易分解碳库的腐解速率k1为(1.0%·a^(-1)—4.9%·a^(-1)),高于有机肥的k1(0.7%·a^(-1)—1.1%·a^(-1))。秸秆在3种土壤上的积温转折点差别不大,积温转折点约为3700℃,在此积温之前为快速腐解,之后为慢速腐解阶段。而有机肥的快速腐解和慢速腐解积温转折点差异从北往南逐渐增大,且有机肥的积温转折点为秸秆的2—5倍。土壤积温和土壤有机碳含量均是混土秸秆和有机肥腐解的主要驱动因素,对其腐解率贡献了约17%和13%。另外,对混土秸秆腐解的最主要驱动因素为土壤碳氮比,而对混土有机肥来说是时间因素。【结论】秸秆较有机肥腐解快,秸秆的易分解有机碳库比例高和腐解速率快是造成其腐解快的主要原因之一。对于秸秆来说碳氮比是影响其腐解的主要因素,对于有机肥来说则是时间,因此秸秆还田应多考虑土壤和物料自身碳氮比,对于有机肥则应充分考虑其长期效应。

【Objective】Straw and manure are the main sources of organic materials in China,and rotary tillage is the main way of returning farmland.In this study,the characteristics and driving factors of their decomposition process in typical farmland soils in China were investigated to provide a scientific basis for better utilization of straw resources and rational application of manure.【Method】The landfill experiment of field organic material mixed with soil was carried out on a typical black soil,fluvo-aquic soil,and red soil in China.Four treatments were set up:wheat straw plus soil(WS+Soil),maize straw plus soil(MS+Soil),pig manure plus soil(PM+Soil),and cow manure plus soil(CM+Soil).All the organic materials(8 g carbon)were mixed with 200 g of soil in a nylon mesh bag buried in soil,six samples were taken within one year after landfilling,once from 2 to 2.5 years after landfilling,and once in 3 years,then a total of eight samples were taken.The decomposition differences of organic materials in different mixtures were analyzed.The double exponential equation was used to clarify the proportion and decomposition rate of easy-to-decompose carbon pool and refractory organic carbon pool,and to clarify the fast decomposition rate,slow decomposition rate and accumulated temperature turning point of organic materials in each soil.The random forest model was used to quantify the relative contribution of material composition and environmental factors to the decomposition rate.【Result】The humification coefficient of straw pluil was ranged from 22%to 43%,and that of manure plus soil was ranged from 45%to 58%.The decomposition rate of manure plus soil was slower than straw plus soil,and there was little difference between regions.Besides,the decomposition of organic materials was accelerated from north to south,and the decomposition of straw was faster than that of organic fertilizers.The proportion of decomposable organic carbon poor of straw(70%-87%)was higher than that of organic fertilizer(57%-83%),and the decomposition rate of straw decomposable carbon pool k1(1.0%·a^(-1)-4.9%·a^(-1))was higher than that of organic fertilizer k1(0.7%·a^(-1)-1.1%·a^(-1)).There was little difference in the turning point of accumulated temperature of straw in the three types of soil.Before 3700℃,it was the stage of rapid decomposition,and then it was the stage of slow decomposition.On the other hand,the difference in accumulated temperature at the turning point of rapid decomposition and slow decomposition of organic fertilizer gradually increased from north to south,and the accumulated temperature at the turning point of organic fertilizer was 2-5 times higher that of straw.Soil accumulated temperature and soil organic carbon content were the main driving factors of mixed soil straw and organic fertilizer,contributing about 17%and 13%of the decomposition rate,respectively.In addition,the main driving factor for mixed soil straw was the ratio of soil carbon to nitrogen,but the main driving factor for mixed soil organic fertilizer was the time.【Conclusion】Straw returning to the field decomposed faster than organic fertilizer,and the high proportion of easily decomposable organic carbon pool with fast decomposition rate of straw was one of the main reasons for the difference.For straw,the ratio of carbon to nitrogen was the main factor affecting its decomposition,and for organic fertilizer,it was time.Therefore,the ratio of carbon to nitrogen of soil and material should be considered to regulate the decomposition of straw,and the long-term effect of organic fertilizer should be fully considered.