Soil tillage increases the susceptibility of agricultural soils to erosion and organic carbon losses, but tillage effects could be mitigated through other management practices such as crop rotation. Here, we evaluated the 30-year impacts of tillage intensity and cropping system on surface soil bulk density, nutrient availability, dry aggregate size distribution, and water-stable aggregation. This study was established in 1980 in eastern Nebraska USA, and included six tillage treatments of varying intensity (no-till, ridge till, disk till, subsoil rip, chisel plow, moldboard plow) and four crop rotation treatments (continuous soybean [Glycine max (L.) Merr.]; soybean-corn [Zea mays L.]; corn-soybean, continuous corn) in a randomized block design with six replicates. Surface soils were sampled in 2011 and soil aggregate properties assessed, including occluded particulate organic matter (oPOM) in micro/macroaggregates (0.053–0.5 mm) and mega-aggregates (>2.0 mm). Because of significant treatment differences in bulk density, soil properties were converted to an equivalent soil mass (ESM) basis to more accurately assess management effects. After 30 years, only the main effects of tillage and crop rotation were significant for most measured soil properties. Surface soil organic carbon (SOC) stocks (ESM for ∼0−30 cm soil depth) decreased with tillage intensity, and stocks were higher when corn was included in the cropping system. Dry aggregate size distributions shifted towards smaller size classes as tillage intensity increased and whenever corn was included in the cropping system. As a result, aggregate mean weight diameter (mm) followed a similar trend. Soil stocks of water-stable mega-aggregates also decreased with increasing tillage intensity. In near-surface soils (0–7.5 cm), highly-erodible aggregate oPOM was highest in no-till soils and was more sensitive to tillage disturbance (56–69% loss) than mega-aggregate oPOM (5–35% loss). Even in no-till soils, highly-erodible aggregate oPOM concentrations decreased under continuous corn compared to rotated systems likely due to greater frequency of fertility management-related soil disturbances (i.e. fertilizer injection annually vs every two years). These results suggest that cropping systems that maximize plant carbon inputs can partially mitigate soil erosion risks due to long-term tillage, but that other crop management-related soil disturbances (i.e. method of fertilizer application) could limit the mitigating effect of cropping system.

土壤耕作增加了农业土壤对侵蚀和有机碳损失的敏感性，但耕作效果可以通过其他管理措施（例如轮作）减轻。在这里，我们评估了耕作强度和耕作制度对地表土壤容重，养分有效性，干性骨料粒径分布和水稳性骨料的30年影响。这项研究于1980年在美国内布拉斯加州东部建立，包括六种不同强度的耕作处理（免耕，垄作，盘耕，底土撕裂，凿犁，mold板犁）和四种作物轮作处理（连续大豆[ Glycine max（L.）Merr。]；大豆玉米[ Zea maysL.]; 玉米-大豆，连续玉米），随机分组，重复六次。2011年对地表土壤进行了采样，并评估了土壤的团聚体性质，包括微/宏观团聚体（0.053-0.5毫米）和巨型团聚体（> 2.0毫米）中的颗粒有机物（oPOM）。由于堆密度在处理方面存在显着差异，因此将土壤特性转换为等效土壤质量（ESM），以更准确地评估管理效果。30年后，对于大多数测得的土壤特性而言，只有耕作和农作物轮作的主要影响才很明显。随着耕作强度的增加，表层土壤有机碳（SOC）储量（ESM在土壤深度约0-30 cm处）减少，而将玉米纳入耕作系统后，土壤有机碳储量则更高。随着耕作强度的增加以及每当玉米被包括在耕作系统中时，干骨料的粒度分布就会向较小的粒度等级转移。结果，总平均重量直径（mm）也遵循类似的趋势。随着耕作强度的增加，水稳定的大型骨料的土壤储量也减少了。在近地表土壤（0–7.5厘米）中，高度免耕土壤的oPOM在免耕土壤中最高，并且对耕作扰动（损失56-69％）的敏感性高于巨型聚集oPOM（损失5-35％） 。即使在免耕土壤中，与轮作系统相比，在连续玉米下，高侵蚀性总oPOM浓度也降低了，这可能是由于与肥力管理相关的土壤干扰发生的频率更高（即，每年喷施肥料，而每两年喷施一次）。