Abstract

Soil carbon (C) pools and biological indicator plays an important role in maintaining soil quality. Land use change from naturally undisturbed to intense cultivation had significant impact on C storage due to change in soil biological properties. The present study was conducted to understand the impact of land use change from the uncultivated to intensively cultivated soils under rice–wheat and cotton–wheat cropping system on labile and stable C pools, soil microbial and enzymatic activity, and a change in nutrient availability. The Olsen’s P concentration was significantly (p < 0.05) higher in soils under rice–wheat, while ammonium acetate (NH₄OAc)-K was higher in the uncultivated soils, compared with others. Soils under cotton–wheat cropping system had significantly lower total organic carbon (TOC) in contrast to rice–wheat soils. The uncultivated soils had the highest TOC concentration, which was ∼20.2% higher than rice–wheat and ∼46.4% than the cotton–wheat soils. The water extractable organic carbon (WEOC) was the smallest organic C fraction (∼0.31%–0.40% of TOC), and was significantly lower in cotton–wheat soils. The basal soil respiration (BSR) and mineralization quotient (qM) were significantly higher for rice–wheat, compared with the cotton–wheat soils. These microbial indices were improved due to increased alkaline phosphates (Alk-P) and dehydrogenase (DHA) enzymatic activity in soil. Soil microbial biomass C (MBC) was significantly higher (by ∼31.7%–57.3%) in the uncultivated than the cultivated soils which has increased the C mineralization in soil. The stable C pool comprised ∼68.8% of TOC in the uncultivated soils, almost similar to rice–wheat soils (∼68.5%), but higher than cotton–wheat soils (∼61.9%). The stable C pool leads to C rehabilitation indicated by higher C management index for rice–wheat soils. The principal component analysis (PCA) distinct the uncultivated soils from the cultivated soils under two cropping systems based on BSR and labile C (Fract. 2) in PC₁ (explaining ∼82.7% of total variability), and the microbial (qmic) and mineralization (qM) quotient in PC₂ (∼17.3% variability). These indicators were most influential for studying C dynamics of the natural ecosystem and restoring the cropland ecosystem by suitable soil management practices.

摘要

土壤碳（C）库和生物指示剂在保持土壤质量方面起着重要作用。由于土壤生物学特性的变化，土地利用从自然不受干扰的耕作方式向集约耕作方式的转变对碳存储有重要影响。进行本研究的目的是了解水稻-小麦和棉花-小麦种植系统下未耕种土壤向集约耕作土壤的变化对不稳定和稳定的碳库，土壤微生物和酶活性以及养分利用率的变化的影响。 在水稻和小麦下，土壤中的Olsen P浓度显着较高（p <0.05），而乙酸铵（NH ₄与其他相比，未耕种土壤中的OAc）-K较高。与水稻-小麦土壤相比，棉花-小麦种植系统下的土壤总有机碳（TOC）明显较低。未经耕种的土壤的TOC浓度最高，比稻麦高约20.2％，比棉麦高约46.4％。可水提取的有机碳（WEOC）是最小的有机碳分数（约占TOC的0.31％至0.40％），在棉麦土壤中明显较低。与棉麦相比，稻麦的基础土壤呼吸（BSR）和矿化商（qM）要高得多。由于增加了土壤中的碱性磷酸盐（Alk-P）和脱氢酶（DHA）的酶活性，这些微生物指标得到了改善。土壤微生物生物量碳（MBC）显着升高（约31.7％–57）。3％）在未耕种土壤中比在耕作土壤中增加了土壤中C的矿化度。在未耕种的土壤中，稳定的碳库约占总有机碳的68.8％，几乎与稻麦土壤（约68.5％）相似，但高于棉麦土壤（约61.9％）。稳定的碳库可以通过较高的稻麦土壤碳管理指数来指示碳的恢复。主成分分析（PCA）将两种基于BSR和不稳定C的种植系统中的未耕种土壤与耕作土壤区分开来（Fract。2）稳定的碳库可以通过较高的稻麦土壤碳管理指数来指示碳的恢复。主成分分析（PCA）将两种基于BSR和不稳定C的种植系统中的未耕种土壤与耕作土壤区分开来（Fract。2）稳定的碳库可以通过较高的稻麦土壤碳管理指数来指示碳的恢复。主成分分析（PCA）将两种基于BSR和不稳定C的种植系统中的未耕种土壤与耕作土壤区分开来（Fract。2）₁（约占总变异性的82.7％），以及PC _2中的微生物（qmic）和矿化（qM）商（约17.3％的变异性）。这些指标对于研究自然生态系统的碳动态以及通过适当的土壤管理方法恢复农田生态系统最具影响力。