ABSTRACT

Conservation agriculture practices have been widely implemented to improve soils and their sustainability. Here, we investigated the impacts of long-term conservation tillage (CS) on soil aggregates and their associated carbon (C) in a typical sandy Ultisols. The short-term effect of cover cropping was also investigated. Soils (0–5 and 5–15 cm) were collected from fields under 40-years CS and conventional tillage (CV), in which cover crop and fallow treatments were embedded as a split-plot design for four years. Soils were tested for bulk density, pH, mean weight diameter, dry aggregate distribution, and C contents. The CS only resulted in higher total C (TC) concentrations (13.56 ± 1.14 g kg⁻¹) than CV (10.06 ± 0.53 g kg⁻¹) at 0–5 cm. Similar depth impacts were observed in various aggregate size fractions (2000–250 µm, macroaggregates; 250–53 µm, microaggregates; 0–53 µm, clay-silt fraction). Soils were dominated by macroaggregates (>50%) at both depths with associated C concentrations following the order of clay-silt fraction > microaggregates > macroaggregates. Nonetheless, after accounting for soil bulk density long-term CS did not result in higher TC stocks than CV at both depths. Cover crops demonstrated no effect on C stocks at both depths. Poor soil structure and low clay contents of the tested soils may partially explain these neutral impacts, while relatively lower residue returns of cover crops to cash crops may also confound the positive management outcomes. Novel management practices to increase soil organic C in the bulk soils by increasing organic inputs and the soils’ capacity to preserve the inputs are needed.

摘要

保护性农业实践已得到广泛实施，以改善土壤及其可持续性。在这里，我们调查了长期保护性耕作（CS）对典型沙质Ultisols中土壤团聚体及其相关碳（C）的影响。还研究了覆盖作物的短期效应。从40年CS和常规耕作（CV）下的田地中收集土壤（0–5和5–15 cm），其中将遮盖作物和休耕处理作为分块设计嵌入其中，为期四年。测试土壤的堆积密度，pH，平均重量直径，干骨料分布和C含量。CS仅导致总C（TC）浓度（13.56±1.14 g kg ^-1）比CV（10.06±0.53 g kg ^-1）高）在0–5厘米处。在各种不同的骨料级分中（2000-250 µm，大骨料； 250-53 µm，微骨料； 0-53 µm，粘土-粉砂级分）也观察到了类似的深度影响。在两个深度上，土壤均以大型骨料为主（> 50％），且相关的碳浓度遵循粘土-粉粒级分>微骨料>大型骨料的顺序。但是，在考虑了土壤容重之后，在两个深度上，长期CS不会导致TC储量高于CV。覆盖作物在两个深度都没有对碳库产生影响。土壤结构差和被测土壤的粘土含量低可能部分解释了这些中性影响，而覆被作物相对于经济作物的残留回报相对较低，也可能使积极的管理成果感到困惑。