长期氮肥施用对玉米根茬矿化分解的影响

摘要

通过室内培养和田间分解试验,研究了施氮量为N0、120和240 kg/hm2处理的玉米根茬(R0、R120、R240)在15和45 cm两个肥力条件不同的土层中有机碳矿化分解特性及其对土壤活性有机碳组分的影响.结果表明,在室内矿化培养条件下,根茬CO2累积释放量和潜在碳矿化量均为R120＞R240 ＞R0;R120和R240根茬碳矿化率在表层土壤(15 cm)和底层土壤(45 cm)中分别较R0提高21.1％、12.7％和45.3％、33.7％.在田间埋藏分解条件下,分解386 d后R0、R120和R240根茬碳残留率在表层土壤中分别为36.3％、25.2％和28.7％,在底层土壤中分别为38.4％、30.6％和31.1％;根茬碳残留率与其C/N、木质素含量以及木质素/N正相关,而与根茬全氮含量呈负相关关系,表明根茬分解率随着其本身全氮含量的增加而提高;添加玉米根茬显著增加土壤微生物量碳含量143％ ～297％,增加土壤可溶性有机碳含量19.9％ ～ 118.2％.综上可见,长期施用氮肥影响作物根系的养分组成,显著提高其全氮含量,在评价土壤碳、氮养分循环时,应注重长期氮肥施用对作物残茬养分累积及其在土壤中分解、转化的影响.%The experiment was conducted to study the decomposition characteristics of maize roots organic carbon (C) derived from N 0,120 and 240 kg/hm2 treatments (marked as R0,R120 and R240,respectively) in the 15 cm and 45 cm soil depths with various fertility,and to evaluate the effect of roots C decay on soil labile organic C,through indoor incubation and field decomposition conditions.The results showed that,cumulative CO2 release and potential C mineralization amount ranked in the order that R120 ＞ R240 ＞ R0 under indoor incubation condition.And in contrast to R0,the C mineralization rates of R120 and R~0 increased by 21.1％ and 12.7％ in the topsoil (15 cm),and increased by 45.3％ and 33.7％ in the subsoil (45 cm),respectively.Mter 386 d field decomposition,the C residual ratios of R0,R120,and R240 were respectively 36.3％,25.2％ and 28.7％ in the topsoil,and were 38.4％,30.6％ and 31.1％ in the subsoil.It showed positive correlations between root C residual ratios and their C/N ratios,lignin contents,and lignin/N ratios,while performed a negative correlation between root C residual ratios and their total N contents.This result indicated that root decomposition ratio improved with its N content increasing.Soil microbial biomass C and soluble organic C contents improved significantly by 143％ ～ 297％ and 19.9％ ～ 118.2％,respectively in the maize roots addition treatments.It was concluded that considering the influence of N fertilizer application on the nutrient compositions of crop roots,especially increasing root N content,the effects of long-term N addition on the nutrient accumulation of crop residues and their decay and cycling in farmland ecosystem should be paid more attention in soil C and N turnover evaluation.