稻麦轮作区秸秆还田对水稻土结构的影响

为探明稻麦轮作区秸秆还田对水稻土结构的影响,依托常熟农业生态试验站25 a的长期定位试验,研究秸秆还田对水稻土容重、团聚体分布及稳定性、团聚体有机碳分布和孔隙大小分布的影响。试验设不施肥(CK)、单施化肥(NPK)、化肥和半量秸秆还田(NPKS1)、化肥和全量秸秆还田(NPKS2)等处理。采集各小区耕层水稻土,通过湿筛的方法测定团聚体分布及稳定性,通过X射线CT扫描和图像处理得到孔隙结构信息。结果显示,与CK相比,单施化肥(NPK)能显著提高土壤有机碳含量、降低土壤容重,对团聚体分布及稳定性、大孔隙度(大于0.032 mm)、孔隙大小分布没有显著影响。与NPK处理相比,秸秆还田(NPKS1、NPKS2)分别使土壤容重降低14.0%和19.4%,有机碳含量提高10.0%和23.1%,但是对团聚体分布及稳定性影响不显著;化肥和半量秸秆还田(NPKS1)对大孔隙度和孔隙大小分布没有显著影响,化肥和全量秸秆还田(NPKS2)的大孔隙度(大于0.032 mm)提高了110.6%,各当量孔径范围的孔隙度也明显提高(大于1.5 mm除外)。结果表明,经过25 a的秸秆还田,稻麦轮作区全量秸秆还田能够降低土壤容重,增加土壤有机碳含量和各级团聚体中有机碳含量,增大土壤总孔隙度和大孔隙度,改善水稻土的物理结构;而半量秸秆还田没有显著改善水稻土的孔隙结构。

Effects of Straw Incorporation on Paddy Soil Structure in Rice-Wheat Rotation System

The effects of straw incorporation on the structure of a paddy soil in a rice-wheat rotation system were studied. Undisturbed and bulk soil samples were collected from the top layer (0~10cm) of a paddy soil in a 25-year long-term field experiment in Changshu Agro-ecological Experimental Station. There were four treatments: no fertilization (CK);balanced chemical fertilization (NPK);incorporation of harvested rice/wheat straw at a moderate rate of 2.25t dry-weight per hectare per season plus balanced chemical fertilizers (NPKS1);incorporation of harvested rice/wheat straw at a high rate of 4.50t dry-weight per hectare per season plus balanced chemical fertilizers (NPKS2). Soil aggregate size distribution and stability were determined by wet sieving method. Soil pore size distribution was measured by using X-ray computed tomography and image processing. Compared with the CK treatment, the NPK treatment increased soil organic carbon (SOC) content and decreased soil bulk density significantly, while no significant difference was found for the aggregate size distribution, macroporosity (greater than 0.032mm) and pore size distribution. Compared with the NPK treatment, straw incorporation treatments, NPKS1 and NPKS2, increased SOC by 10.0% and 23.1%, respectively, and reduced soil bulk density by 14.0% and 19.4%, respectively. Soil aggregate size distribution and water stability was not affected by straw incorporation. The macroporosity (greater than 0.032mm) and pore size distribution of NPKS1 were not significantly different from the NPK treatment. However, the macroporosity (greater than 0.032mm) of NPKS2 was 110.6% greater than that of the NPK treatment. In the rice-wheat rotation system, incorporation of total harvested rice/wheat straw plus balanced chemical fertilizers could improve soil physical structure by decreasing soil bulk density, increasing organic carbon content of bulk soil and each size fraction, increasing total porosity and macroporosity. While incorporation of total harvested rice/wheat straw plus balanced chemical fertilizers did not improve soil physical properties significantly.