Rotation crop root performance and its effect on soil hydraulic properties in a clayey Utisol

Abstract

Poor soil hydraulic properties (SPH) limit the productivity of clayey Utisol (red soil) under a humid subtropical climate in southern China. The roots performance of rotation crops was compared, and the effects on SPH were investigated in the field. Five treatments (two cultivars of oilseed rape, one-year-old lucerne, and one- and five-year-old vetiver) were employed as pre-crops before summer maize, and their root performances were examined in spring. The soil-water characteristic curve (SWCC) and soil porosity were measured with soil cores, saturated hydraulic conductivity (Ks), and near-saturated hydraulic conductivity with a tension infiltrometer in situ. The two rape cultivars had the thinnest root diameter at an average of 0.45−0.50 mm and the shallowest distribution at a depth of 40 cm, while two vetivers had the thickest mean root diameter at 0.79 mm and the deepest distribution >80 cm. Taproot crops of rape and lucerne did not show stronger rooting ability than fibrous root crops of vetivers. All crops increased soil total and aeration porosity, but no bio-pores larger than 2 mm were formed. Rapes were beneficial for increasing soil aeration porosity (diameter >30 μm), while vetivers increased active capillary porosity (30−0.2 μm). The SHP, namely, SWCC and Ks, was improved by all crops, with the best effects in the five-year old vetiver due to its higher root length density (RLD) and the balanced distribution between diameter classes. Ks was significantly correlated with RLD (p < 0.001) but insignificantly correlated with root diameter (p = 0.9929). The SHP was improved mainly by RLD and influenced by root diameter distribution, suggesting that fine roots played a key role in forming aeration and active capillary pores.