Assessing the effects of land use change from rice to vegetable on soil structural quality using X-ray CT

Abstract

The conversion of cereal to vegetable represents a significant shift in land use in China, and it causes significant changes in soil properties. Most studies have only focused on chemical or biological properties; few have investigated soil structure. Soil structure, especially macropore space, is very important for plant growth because of its relation to important soil functions and processes, such as gas diffusion and water permeability. The objective of this study was to assess the effect of land use conversion from rice to vegetable on soil macropores (>50 μm) measured by computed tomography (CT) and to examine the relationships between CT-measured pore characteristics and soil chemical properties. By using space instead of time, we sampled three land uses – rice/wheat rotation (RWR), open-field vegetable (OFV) and plastic-greenhouse vegetable (PGV) – in a tilled and plow pan layer in a suburban area of Nanjing, China, and analyzed the basic physicochemical properties and CT-measured macropore characteristics. The results showed that the tilled layer soil had a significant response to the land use change. The macroporosity decreased from 11.5% under RWR to 8.0% under OFV and 5.8% under PGV, and the decreased portion consisted mainly of elongated large macropores (>1000 μm). In addition, the macropore morphology of vegetable fields also showed degradation, with a higher degree of anisotropy (DA) and lower fractal dimension (FD) and connectivity compared to those under RWR, but PGV experienced a higher degree of degradation than did OFV. This study also showed that soil structure degradation was significantly correlated with decreasing soil organic matter (SOM). Increasing the amount of organic fertilizer applied might improve the SOM content and therefore improve the soil structure. Based on the linear regression equation, adding 1 g of SOM per kilogram of soil can improve the macroporosity by 0.54 m3 m−3.