长期秸秆深翻还田及养分管理对潮土有机碳矿化影响

Effects of long-term deep tillage,straw returning and nutrient management on organic carbon mineralization of fluvo-aquic soil

为了明确耕作方式与养分管理对华北潮土土壤有机碳矿化的影响。基于连续15 a(2007—2022年)耕作与养分管理模式长期定位试验开展研究,长期定位试验分为农民习惯耕作管理模式(秸秆不还田+浅旋耕RP-S,rotate plow without straw return)和高产耕作管理模式(秸秆还田+深翻耕DP+S,deep plow with straw return)2个主处理,以及对照施肥(CK)、农民习惯施肥(CON)和优化施肥(OPT)3个副处理,共计6个处理。于2022年10月,采集表层(0~20 cm)土壤样品,分析土壤有机碳及活性碳组分含量与土壤碳库管理指数,并采用室内培养法,测定土壤有机碳矿化速率,利用一级动力学方程拟合土壤有机碳潜在可矿化量和碳半周期,应用结构方程模型揭示长期不同耕作模式与养分管理措施下,土壤有机碳的周转规律。多年试验数据得出,在RP-S条件下,C/N(SOC and TN ratio)总体呈逐渐下降趋势,在DP+S条件下,C/N总体呈先降后增趋势。秸秆还田+深翻耕处理显著提高了土壤活性有机碳组分含量(P<0.05),且碳库管理指数(CPMI,carbon pool management index)提升显著(P<0.05)。与农民习惯施肥相比,优化施肥可以显著提高土壤有机碳含量12.35%。在DP+S条件下,优化施肥显著提高了土壤易氧化有机碳(ROC,readily oxiedozable carbon)与CPMI。各处理土壤有机碳矿化速率均在1 d达到最大,而后1~10 d迅速下降,10 d后缓慢下降直至稳定,有机碳矿化速率随时间呈对数函数型变化,不同处理土壤有机碳矿化速率均符合一级动力学模型。秸秆还田+深翻耕显著提高了累积矿化率(潜在可矿化量与土壤有机碳的比值)23.59%,而优化施肥可以显著降低累积矿化率22.12%。土壤有机碳矿化累积量(C_(t))与土壤有机碳(SOC,soil organic carbon)、土壤活性碳组分和土壤碳库管理指数均呈极显著正相关关系(P<0.01),与土壤潜在可矿化有机碳量(C_(0))呈显著正相关关系(P<0.05),结构方程模型表明,耕作管理、微生物碳(MBC,microbial biomass carbon)和ROC是影响土壤有机碳周转能力和固碳能力的直接因素,耕作与施肥管理可通过对土壤有机碳及活性碳组分的影响,间接影响土壤有机碳周转能力,进而影响土壤固碳能力。长期秸秆深翻耕还田结合优化施肥有利于提高土壤固碳能力,促进农田资源的增碳及可持续利用。

Soil organic carbon(SOC)mineralization is closely related to the terrestrial ecosystem carbon cycle and global climate change.Reasonable tillage and nutrient management can be adopted to improve the carbon accumulation and sequestration potential in soil.It is urgent to explore the relationship between tillage-nutrient management and SOC stability in the process of soil biochemistry,within the context of carbon sequestration and emission reduction.Therefore,this study aims to clarify the effects of tillage and nutrient management on SOC mineralization in fluvo-aquic soil of North China.A 15-year long-term positioning experiment was carried out on the tillage and nutrient management(2007-2022).Two main treatments were set:rotate plow without straw return(RP-S),and deep plow with straw return(DP+S).Three secondary treatments were set:controlled fertilization(CK),Conventional fertilization(CON),and Optimized fertilization(OPT),with a total of six treatments.Soil samples were collected at 0-20 cm depth in October 2022.Some parameters were measured,including the contents of SOC and activated carbon components,as well as the carbon pool management index.SOC mineralization rate was determined by the incubation method.A first-order kinetic model was used to calculate the potential mineralization and turnover rates.The structural equation model was fitted to reveal the turnover and sequestration of SOC under different tillage and nutrient management.The experimental results show that the C/N(SOC and TN ratio)generally shared a decreasing trend under the condition of RP-S,while the C/N generally shared an increasing first and then decreased trend under the condition of DP+S.Compared with the RP-S,DP+S treatments increased the contents of activated carbon components in soil,and the carbon pool management index(CPMI)increased significantly.Compared with CON,OPT significantly increased the content of SOC,with incremental rates of 12.35%.OPT significantly increased the readily oxidizable carbon(ROC)and CPMI with the condition of DP+S.SOC mineralization rates were the highest in the 1 d and then decreased rapidly.After 10 d incubation,SOC mineralization rates decreased slowdown until it stabilized.The SOC mineralization rate was in agreement with the logarithmic function.Nutrient management enhanced the mineralization rates of SOC in the fluvo-aquic soils in the following order:OPT,CON,CK.SOC mineralization rates in all treatments were consistent with the first-order kinetic model.DP+S significantly increased the cumulative mineralization rate(value of C_(0)/SOC)by 23.59%(C_(0) is potential mineralizable organic carbon content in soil),while the OPT significantly reduced the value of C_(0)/SOC by 22.12%.The accumulative mineralization of SOC(C_(t) is accumulation of soil organic carbon mineralization during cultivation time t)was significantly and positively correlated with the SOC,activated carbon components,and soil carbon pool management index(P<0.01),both of which were significantly and positively correlated with Potential mineralizable of SOC(C_(0))in the fluvo-aquic soils(P<0.05).Tillage management,microbial biomass carbon(MBC),and ROC were the direct factors of SOC mineralization and sequestration potential in soil.Tillage and fertilization management dominated the SOC mineralization by the contents of SOC and activated carbon components,then impacting soil carbon sequestration potential.According to the SOC accumulation content,the direct positive impact of long-term deep plow with straw return treatment on soil carbon sequestration potential can be fully counteracted by the indirect negative effect of the increase in SOC and activated carbon components on soil carbon sequestration potential.In conclusion,Long-term DP+S with OPT significantly improved the stability of soil structure and the SOC sequestration potential.Optimal fertilization reduced the cumulative SOC mineralization rate of soil and then enhanced the SOC accumulation and sustainable utilization of farmland resources.The finding can also provide ideal farmland management to optimize the combination of tillage and fertilization in fluvo-aquic soil of North China.