Changes of Soil Water–Stable Aggregates after Rice–Crawfish Rotation in Low-lying Paddy Fields: A Case Study in Jianghan Plain of China

Abstract

ABSTRACT Crawfish aquaculture in low-lying paddy fields is implemented after middle-season rice is harvested, namely, Rice–crawfish rotation (RCR), and has been practiced for almost 30 years in Jianghan plain of China. However, little information is available on the effects RCR has on soil aggregates and water stability. Some soil properties were obtained by field sampling and analysis including mean weight diameter of soil aggregate (MWD), geometric mean diameter (GMD), fractal dimension (FD), and agglomerate with particle size more than 0.25 mm (R0.25) after RCR was implemented in low-lying paddy fields. Soil samples were taken from paddy fields that are used separately for RCR and mid-season rice monoculture (CK), and the depth of sampling on a soil profile is 0–20, 20–40, and 40–60 cm from the top to below. RCR’s duration in different paddy fields is 1, 7, 13, 18, and 23 years, marked as RC1, RC7, RC13, RC18, and RC23, respectively. The results showed that in the 0–60 cm soil layer, the water-stable aggregates of soil in the paddy field for RCR were mainly composed of large aggregates (particle size more than 5 mm) and micro-aggregates (particle size less than 0.25 mm), and with the increase of RCR’s duration, aggregate content is increased for large aggregates and declined for micro-aggregates; at the same time, the RCR for long term increases the mean weight diameter, geometric mean diameter and R0.25 of each soil layer, reduces the Fractal dimension, where there is a significant positive correlation (P < 0.05) between mean weight diameter (geometric mean diameter) and R0.25, a significant negative correlation (P < 0.05) between mean weight diameter (geometric mean diameter) and fractal dimension; the content of aggregate (<0.25 mm) is significantly negatively correlated with mean weight diameter (P < 0.05), geometric mean diameter, R0.25, respectively, and positive correlative with fractal dimension. Therefore, it was determined that RCR for long-term production is conducive to form soil water-stable large aggregates, correspondingly, to reduce micro-aggregates and improve the stability of water-stable aggregates.