The adoption of conservation agriculture (e.g., no‐till system) has been recognized as pivotal to maintaining soil functions, but the potential of this system to enhance organic carbon (OC) quantity and quality and how this OC is stabilized in soils are not well established. In this study, we evaluated the effects of land‐use types (native vegetation (NV) vs. no‐till system (NT)) on OC stocks and on the chemical composition of organic matter (OM), and sought to understand the mechanisms that govern OC protection in the studied highly weathered soils. To achieve these objectives, we used an OC fractionation scheme in a combination of solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopic analyses in soils from six farms in southern Brazil. Our results showed smaller OC stocks (whole soil) under NT than under NV in four of the six sites. In addition, the OC stock differences between land‐use types were larger in coarser textured soils and in those where conventional tillage was used before the adoption of NT. Among fractions, particulate organic carbon (POC) represented only 8% of the whole OC stock but was the fraction most affected by land‐use type. In contrast, the humus organic carbon (HOC) fraction contributed 78% of the whole OC stock and was little altered by land‐use type. Resistant organic carbon (ROC) represented 14% of the whole OC stock and it was altered by land‐use type, demonstrating that this fraction is not as inert as previously thought. Overall, OM chemical composition was quite similar between land uses, with O‐alkyl‐C being the predominant C type. This labile component was further highly correlated with OC stock and silt + clay contents, indicating that the accumulation of OC in these highly weathered soils is mainly a response to the association between labile C compounds and minerals.

中文翻译：

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响应巴西南部不同土地利用的有机碳库和有机物化学成分

人们已经认识到采用保护性农业（例如免耕系统）对于维持土壤功能至关重要，但是该系统提高有机碳（OC）的数量和质量以及如何在土壤中稳定该有机碳的潜力并不理想。已确立的。在这项研究中，我们评估了土地利用类型（原生植被（NV）与免耕系统（NT））对超氧化物歧化库和有机物化学成分（OM）的影响，并试图了解其作用机理。在研究的高风化土壤中控制OC保护的元素。为了实现这些目标，我们将OC分级方案与固态^{13结合使用}巴西南部六个农场土壤中的C核磁共振波谱分析。我们的研究结果表明，在六个地点中的四个地点，NT下的OC储量（整个土壤）比NV下的要少。此外，在较粗糙的质地土壤和采用NT之前使用常规耕作的土壤中，土地利用类型之间的OC存量差异更大。在各部分中，颗粒有机碳（POC）仅占整个OC存量的8％，但受土地利用类型的影响最大。相比之下，腐殖质有机碳（HOC）占整个OC存量的78％，并且几乎不受土地利用类型的影响。抵抗性有机碳（ROC）占全部OC存量的14％，并且已因土地利用类型而改变，表明该部分的惰性不如先前所想。全面的，土地用途之间的OM化学成分非常相似，其中O-烷基-C是主要的C类型。这种不稳定的成分还与OC含量和粉土+粘土含量高度相关，这表明这些高度风化的土壤中OC的积累主要是对不稳定的C化合物与矿物质之间联系的一种反应。