苜蓿作物轮作模式对土壤团聚体稳定性及有机碳的影响

本研究以苜蓿?作物轮作试验为研究对象,探讨了苜蓿?苜蓿(L-L)、苜蓿?休闲(L-F)、苜蓿?小麦(L-W)、苜蓿?玉米(L-C)、苜蓿?马铃薯(L-P)和苜蓿?谷子(L-M)6种轮作模式对陇中黄土高原雨养农田苜蓿土壤团聚体稳定性以及土壤总有机碳含量的影响。结果表明:不同轮作模式下土壤机械稳定性团聚体以≥0.25 mm团聚体为优势团聚体,均占72.17%以上,而土壤水稳性团聚体以0.25 mm团聚体为优势团聚体,均占95.18%以上。随着土层深度的增加,各处理≥0.25 mm的团聚体数量及平均重量直径(MWD)均随之增加,而水稳性大团聚体数量及MWD值无明显规律性。与L-L处理相比,L-C和L-P处理0~30 cm耕层土壤≥0.25 mm的团聚体含量分别增加5.94%和1.12%,L-C处理的MWD表现为最高,而其他轮作处理则不同程度降低了≥0.25 mm团聚体含量及MWD;随着土层深度的增加,6种不同轮作模式的土壤有机碳含量均呈现逐渐降低的趋势,在0~30 cm的耕层土壤,较之L-L处理,L-W、L-C、L-P和L-M处理均从不同程度上降低了土壤有机碳含量,其中L-P处理有机碳含量最低,降低了18.68%。相关性分析表明,土壤总有机碳分别与2~5 mm、1~2 mm、0.5~1 mm和0.25~0.5 mm粒径的水稳性团聚体比例以及MWD表现出极显著正相关,而与0.25 mm粒径的水稳性团聚体呈极显著负相关。综上所述,苜蓿?玉米轮作模式能明显增加土壤团聚体机械稳定性,而不同苜蓿?作物轮作模式对土壤团聚体的水稳性影响较小,土壤有机碳含量在很大程度上影响着土壤水稳性团粒结构的形成与稳定性,二者密切相关。

Effects of lucerne-crop rotation patterns on soil aggregate stabilityand soil organic carbon

A local experiment of lucerne-crop rotation system was conducted on dry farmlands of the Loess Plateau in Central Gansu Province to determine the distribution characteristics of soil aggregate stability and soil organic carbon. The experiment included six rotation patterns — lucerne-lucerne (LL), lucerne-fallow (LF), lucerne-wheat (LW), lucerne-corn (LC), lucerne-potato (LP) and lucerne-millet (LM). Soil aggregate characteristics and organic carbon content were investigated after crop harvest. The results showed that ≥0.25 mm aggregate was the dominant component of the mechanically stable aggregates of soil, which accounted for >72.17% of the mechanically stable aggregates. However, the <0.25 mm aggregates was the dominant component of the water stable aggregates, which exceeding 95.18% of the water stable aggregates. The content of the≥0.25 mm aggregates of soil and its mean weight diameter (MWD) increased with increasing soil depth, while larger water stable aggregates content and MWD were irregularly changed. Compared with LL treatment, the ≥0.25 mm aggregates contents of LC and LP treatments increased by 5.94% and 1.12%, respectively, at soil depth of 0-30 cm. The MWD in LC treatment was the highest among all treatments. Soil organic carbon (SOC) content decreased with increasing soil depth in all rotation patterns. Compared with LL rotation pattern, SOC contents in LF, LC, LP and LM treatments all declined to different extents at 0-30 cm soil depth, especially, it significantly decreased by 18.68% in LP treatment. The correlation analysis indicated that SOC content had significantly positive relation with water stable soil aggregates of 2-5 mm, 1-2 mm, 0.5-1 mm, 0.25-0.5 mm and MWD, while it had significantly negative relation with<0.25 mm soil aggregate content. In conclusion, LC rotation pattern significantly increased the mechanical stability of soil aggregates. However, the effect of different rotation patterns on water stable soil aggregates was negligible. Furthermore, SOC content significantly influenced the formation and stability of water stable aggregate.