Background The southern subtropical region is an important agricultural production area in China. In this region, soil erosion and land degradation become seriously due to agricultural production, climatic conditions and other reasons. Soil quality can be influenced by exogenous electrolyte entering the soil during agricultural production and life. Aggregates are the basic units of soil structure and play an important role in maintaining soil fertility and soil structure. In this study, we investigated the effect of exogenous electrolytes on the stability of lateritic red soil aggregate developed from granite and sand shale in the southern subtropical region.

Methods Sand shale lateritic red soil was collected from Wuming, Nanning, Guangxi and granite lateritic red soil from Longxu, Wuzhou, Guangxi. The selected study areas in both places are hilly terrain. The soil was collected from both sites in its original state and then air dried in the laboratory. The dry sieving method sieved out >3.00-5.00 mm aggregates. The aggregates of >3.00-5.00 mm of lateritic red soil developed from sand shale and granite parent material in the south subtropics were treated by three methods of Le Bissonnais method with 0, 0.05, 0.10, 0.20, 0.50 and 1.00 mol/L NaCl, KCl, MgCl₂ and CaCl₂ solutions as media.

Results 1) The mean weight diameter (MWD) under fast-wetting treatments (FW), slow-wetting treatments (SW), and pre-wetting shock treatments (WS) showed a decreasing trend with the increase of electrolyte concentration. MWD values decreased faster before 0.10 mol/L and slowed down thereafter. 2) The particle size content of the aggregates changed with the increase of electrolyte solution concentration. When electrolyte solution concentration increased, the content of the >3.00-5.00 mm decreased. In three wetting treatments, the particle size content of granite lateritic red soil aggregates largely decreased with the decreasing of particle size, whereas the size order of the sand shale lateritic red soil aggregates was not consistent among treatments. 3) In static conditions, aggregate stability (AS) changed dramatically within the first 2 min of submersion in the solution, and the AS in pure water was greater than that in the electrolyte solution. 4) The stability of the 2 aggregates under different treatments was different. The stability of granite lateritic red soil aggregates was higher under dissipation and non-uniform expansion, and the opposite under mechanical crushing. The relative mechanical crushing index of both aggregates was smaller than relative shaking index, indicating that both aggregates were more sensitive to dissipative effects.

Conclusions This study shows that electrolyte addition can reduce the stability of aggregates and change the aggregates particle size content. The stability of the aggregates can be changed significantly within a short time when submerged in solution. These results provide reference for soil improvement, soil conservation and sustainable utilization of cultivated land in the southern subtropical region.