Aims

Cover crop species selection for soybean (Glycine max) production under no-tillage (NT) management may affect soil organic C sequestration by altering the quantity and quality of C inputs, thereby affecting cropping system sustainability. If so, the underlying mechanisms for such regulation are still unclear.

Methods

We assessed changes in soil C and N fractions at 0-0.1 m depth and soil C stock at 0-0.6 m depth during the last three years of dry-season cover cropping in a soybean production system managed with NT for 9 years on a Rhodic Hapludox in Sao Paulo, Brazil. Dry-season management treatments were repeated yearly in a split-plot scheme. Main plots during the fall-winter were (1) ruzigrass (Urochloa ruziziensis), (2) grain sorghum (Sorghum bicolor), and (3) the intercropping of ruzigrass and sorghum. Subplots during spring prior to planting soybean were (a) pearl millet (Pennisetum glaucum), (b) sunn hemp (Crotalaria juncea), and (c) forage sorghum (Sorghum bicolor).

Results

Soil C and N fractions were affected according to crop residue characteristics of the rotations. Higher soil C stocks in 2012 and 2015 (7 % an average) were observed at 0.2–0.4 m depth by ruzigrass compared to sorghum. High crop residue input with ruzigrass in the fall-winter sequestered 0.61 Mg C ha^− 1 yr^− 1 at 0-0.1 m soil depth compared with lower C sequestration using grain sorghum (0.29 Mg C ha^− 1 yr^− 1).

Conclusions

The quantity and quality of crop residues impact its retention on soil surface controlling the dynamics of soil C and N fractions and can be considered relevant for soil C sequestration. These aspects could contribute to the mitigation of atmospheric CO₂ in crop production systems.

中文翻译：

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热带免耕大豆轮作旱季管理对土壤有机碳的影响

目的

免耕（NT）管理下大豆（Glycine max）生产的被覆作物物种选择可能会通过改变碳输入量和质量而影响土壤有机碳固存，从而影响耕作系统的可持续性。如果是这样，这种监管的基本机制仍不清楚。

方法

在Rhodic上使用NT进行9年管理的大豆生产系统中，我们评估了过去三年的旱季覆盖作物种植期间，深度0-0.1 m处土壤C和N分数的变化以及深度0-0.6 m处土壤C储量的变化。巴西圣保罗的Hapludox。一年一度的分季计划重复进行旱季管理治疗。秋冬期间的主要地块是（1）ruzigrass（Urochloa ruziziensis），（2）谷物高粱（Sorghum bicolor）和（3）间作的ruzigrass和高粱间作。大豆播种前春季的子图为（a）珍珠粟（Pennisetum glaucum），（b）he麻（Crotalaria juncea）和（c）饲草高粱（Sorghum bicolor）。

结果

土壤C和N的比例根据轮作的农作物残留特征而受到影响。与高粱相比，2012年和2015年，紫菜草在0.2-0.4 m深度处土壤碳储量较高（平均7％）。在秋冬季，在土壤深度为0-0.1 m时，高品位的紫杉草隔离了0.61 Mg C ha ^-1 yr ^-1，相比之下，使用谷物高粱的较低C隔离（0.29 Mg Cha ^-1 yr ^-1）。

结论

作物残渣的数量和质量会影响其在土壤表面的保留，从而控制土壤C和N组分的动态，并被认为与土壤C固存有关。这些方面可以有助于减轻作物生产系统中的大气中的CO ₂。