稻田复种轮作休耕对土壤团聚体分布及稳定性的影响

稻田土壤团聚体的比例结构及稳定性状况,对水稻健康可持续发展具有重要影响。2 0 1 2—2 0 1 7年进行冬季不同复种轮作休耕长期定位试验,设置冬闲双季稻、冬种紫云英、油菜、大蒜和轮作双季稻5个处理,利用湿筛法对稻田土壤粒径1~2mm、0.5~1mm、0.25~0.5mm和0.25mm土壤团聚体的百分含量、平均质量直径(MWD)、平均几何直径(GMD)和分型维数(D)进行测定计算。结果表明,在0~50cm土层中,早、晚稻收获后土壤以0.5mm粒级的微小团聚体为主,各处理累积含量分别为78.1%~84.8%和85.6%~91.1%,而0.5 mm较大的团聚累积含量分别为13.1%~21.9%和8.9%~14.4%;同时显著增加了早、晚稻土壤性大团聚体(0.25mm)的百分含量,并相应地减少了微团聚体百分含量,早稻较晚稻表现更为突出;早、晚稻田土壤水稳定性团聚体D指标值的影响不显著,而MWD、GMD达到显著性差异(P0.05)。由此可见,稻田复种轮作及秸秆双重还田,有利于早晚稻田减少微小团聚体而形成大团聚体,早稻季相比晚稻更为显著,能显著增加早、晚稻田土壤团聚体的稳定性(P0.05),提高早、晚稻产量,这对南方稻田可持续发展具有重要意义。

Effects of Rotation and Fallow in Paddy Field on Distribution and Stability of Soil Aggregates

Objective] Proportion and stability of soil aggregates are important factors affecting healthy and sustainable development of paddy soil. Method] A long-term stationary experiment on effects of crop rotation systems, including multi cropping, crop rotation and winter fallow, on paddy field was carried out in the years from 2012 to 2017. The experiment was designed to have five treatments: Double-cropping rice plus winter fallow land, double-cropping rice plus milk vetch in winter, double-cropping rice plus canola in winter, double-cropping rice plus garlic in winter and double-cropping rice plus ?. Soil samples were collected from the 0~50 cm soil layers of the plots of the five treatments for analysis, using the wet screening method, of proportions of the aggregates, 1 ~ 2 mm, 0.5 ~ 1 mm, 0.25 ~ 0.5 mm and 0.25 mm in particle size, separately and then, mean weight diameter (MWD), mean geometric diameter (GMD) and fractal dimension (D) of the fractions of soil aggregates was calculated, separately. Result] Results show that regardless of treatment, the soil aggregates in the 0~50 cm soil layer were dominated with the fractions of 0.25 ~ 0.25 mm and < 0.25 mm in the time periods after the early or the late rice was harvested, and the two fractions reached 78.1% ~ 84.8% and 85.6% ~ 91.1%, separately, in cumulative content, while the fraction of aggregates of 1 ~ 2 mm and 0.5~1 mm, was only 13.1% ~ 21.9% and 8.9% ~ 14.4%, respectively. Obviously the cultivation of early and late rice increased the fractions (>0.25), but reduced those (< 0.25mm), and the effect of early rice was more prominent than that of late rice. The two crops also affected MWD and GMD significantly, but not D. Conclusion] It is, therefore, quite obvious that the systems of multiple cropping rotations and two crops of rice plus straw returning are favorable to formation of large-sized aggregates rather than fine aggregates and the effect of increasing water-stable aggregates is more significant with early rice than with late rice, which in turn improves yield of the two crops. All the findings in this experiment are of great significance to the sustainable development of rice production in South China.