Effects of simulated puddling intensity and pre-drying on shrinkage capacity of a paddy soil under long-term fertilization

Abstract

Soil structure in paddy fields is affected by different practices such as long-term fertilization and temporal puddling and drying. However, their interactive effects remain unclear. The objectives of this study were to determine the effects of long-term fertilization on soil structural stability at different puddling intensities and to determine the effects of puddling intensity and pre-drying on shrinkage behavior upon drying. Soil samples were taken from long-term experiments established in 1981 and puddling intensity was simulated by mixing soil in water at different speeds using an electronic mixer. Compared with no fertilization and chemical fertilization treatments, the organic amendment treatments had higher soil organic carbon concentration, and larger aggregate stability under the low and moderate puddling intensities. The shrinkage capacity (COLE) of the puddled soils ranging from 0.124 to 0.229 was larger in the organic amendment treatments than in other treatments without pre-drying. The difference in COLE among the treatments diminished with increasing puddling intensity and after the pre-drying. The shrinkage curves and their fitted parameters demonstrated that the larger shrinkage capacity in the organic amendment treatments resulted from the increases in the macro- and meso-pores due to the presence of more large size aggregates after puddling. The macro-pores were lost after the intensive puddling and the meso-pores collapsed after the pre-drying at the proportional shrinkage stage, resulting in no differences in the shrinkage curve among the field treatments. These results suggest that continuous organic amendment may be needed to maintain a porous structure of paddy soil through the increase in resistance to puddling and its influence on the shrinkage capacity upon drying.