黄土高原旱地不同种植系统对土壤水稳性团聚体及碳氮分布的影响

以黄土高原连续进行了27年的长期定位试验为对象,研究了粮-草长周期轮作、粮-豆短周期轮作、玉米连作和小麦连作系统土壤团聚体及其碳氮分布特征,并分析了土壤碳氮分布与土壤团聚体及其碳氮含量之间的关系。结果表明:黄土高原旱作农田土壤中0.053 mm团聚体含量最高,占土壤质量的35%,长周期轮作系统0~20 cm和20~40 cm土层土壤0.25~2 mm团聚体含量高于玉米连作、小麦连作和短周期轮作系统,而0.053 mm团聚体含量低于这3种轮作系统,且长周期轮作系统土壤团聚体的平均重量直径和几何平均直径也较高。种植系统对团聚体有机碳和全氮分布的影响主要体现在0~20 cm土层土壤,长周期轮作系统土壤中2 mm和0.25~2 mm团聚体有机碳含量显著高于其他种植系统,0.25 mm团聚体有机碳含量与其他种植系统差异不显著。长周期轮作系统团聚体全氮含量均显著高于其他种植系统,碳氮比则呈现出相反的趋势。土壤总有机碳、氮含量与团聚体有机碳、氮含量呈极显著正相关关系。土壤有机碳和全氮含量的变化主要取决于0.25~2 mm和0.053~0.25 mm团聚体有机碳和全氮的变化,而且有豆科植物苜蓿长期参与的长周期轮作系统可以有效改善土壤结构,提高土壤和团聚体的有机碳和全氮含量。

Effects of cropping systems on distribution of water-stable aggregates and organic carbon and nitrogen in soils in semiarid farmland of the Loess Plateau

In this paper, we examined the distribution of water stable aggregates and organic carbon(OC) and nitrogen(N) in soils under different cropping systems, using a 27-year field experiment in the Loess Plateau. The relationships between OC and N contents in bulk soil and aggregates were also analyzed. Results showed that <0.053 mm aggregates, accounting for 35%, dominated the soil mass in 0~20 and 20~40 cm soil layers in the semiarid farmland of the Loess Plateau. The percentage of 0.25~2 mm aggregates was higher, but that of <0.053 mm aggregates was lower in the grass-grain rotation system than the other cropping systems. In the grass-grain rotation system, mean weight diameter and geometrical mean diameter of soil aggregates were also greater. The significant effects of cropping system on OC and N associated with aggregates mainly occurred in 0~20 cm layer. The OC content in >2 mm and 0.25~2 mm aggregates was significantly higher in grass-grain rotation system than in the other systems, while OC content in 0.053~0.25 mm and <0.053 mm aggregates did not differ among different cropping systems. The grass-grain system showed higher N content and lower C/N ratio in each aggregate compared with other systems. The OC and N content in bulk soils was positively correlated with OC and N content associated with aggregates. These results suggest that the responses of OC and N in the bulk soil to cropping systems mainly depend on OC and N associated with 0.25~2 mm and 0.053~0.25 mm aggregates. Additionally, grass-grain rotation system has greater potential to improve soil structure and increase the content of OC and N associated with aggregates.