Plastic mulch is widely used for vegetable cropping in the mid-Yunnan plateau, southwestern China. However, the effects of plastic mulch on soil physical properties are poorly understood. A field experiment was conducted to evaluate the effects of different plastic mulch patterns (narrow and wide plastic mulch) and rotations (broccoli-zucchini-winter wheat and broccoli-zucchini-fallow) on soil physical properties and soil organic carbon content in a vegetable production system at a research station in the region. The experiment comprised four treatments and laid out in the field using randomized complete block design replicated nine times. The soil (0-20cm) under wide plastic mulch retained more water than the soil narrow plastic mulch under the vegetable growing season over 3 consecutive severe drought years. Significant decline (11%) of surface soil (0-5cm) organic carbon was observed in 2012 compared with in 2010, but soil organic carbon and physical properties did not differ significantly between the two different plastic mulch patterns. The higher macro-porosity, aggregate stability, Ksat and lower bulk density in the plastic mulched ridges imply that the conversion from narrow-plastic-mulch to wide-plastic-mulch increases mulched area thereby conserving larger area soil structure in the croplands. Although increased catch crop stubble retention in the furrows apparently improved surface soil macro-porosity and saturated hydraulic conductivity, the autumn rotary cultivation in broccoli-zucchini-winter wheat rotation system has significantly decreased (5%) surface soil organic carbon. The results suggested that continued use of vegetable-cereal crop rotation system, even with stubble retention, may result in loss soil organic carbon. Further research that covers wetter years should be taken to assess effects of vegetable-cereal crop rotation pattern on soil physical properties in this region.
