Soil particle size distribution and aggregates stability as affected by cultivated orange daylily communities

Background/Question/Methods

Particle size distribution (PSD) and aggregates stability in soils are fundamental soil properties and are widely used to estimate other soil properties, such as hydraulic conductivity, nutrient availability and macrofauna activity. Plant communities are expected to have considerable influence on PSD and aggregates stabilization in soils through aboveground and belowground biomass supply. However, few studies were conducted to evaluate the influence of the horticultural systems on PSD and aggregation in soils and thus soil erosion. Horticultural farming is the most common practice in southwestern China and such horticultural systems are used for growing a mass product of vegetables and fruits and preventing soil erosion. In this study, the characteristics of PSD and aggregation in soils were investigated under various years’ cultivated Orange daylily (Hermerocallis fulva L.) communities in Jin Fengxi watershed in Sichuan Province, China. The objective of this study was to test the impact of horticultural systems on PSD and aggregates stability in soils. Soil samples were taken from 1-, 2-, 3- and 4-year cultivated Orange daylily lands (as L₁, L₂, L₃ and L₄) and a bare land (without plant cover) as a control (as L_c). The PSD, aggregates size distribution (ASD), mechanical composition, microaggregates and water stable aggregates in soils were measured. Fractal model was employed to describe the fractal dimension (D_m) of PSD.

Results/Conclusions

The result showed that sand content in the 0–20 cm soil depth was highest in L_c and decreased in an order L_c > L₁ > L₂ > L₃ > L₄. The D_m decreased from 2.79 to 2.63, following the order L₄ > L₃ > L₂ > L₁ > L_c, The D_m value was negatively related to the ratio of soil particle (>0.05mm) and positively to the ratio of soil particle (<0.05mm). The longer the land was cultivated using Orange daylily, the less contents of sand in the soils and the lower the values of D_m. Particularly, the significantly positive correlations were found  between Dm values and particle (<0.01mm) content in soils. The fractal dimension of microaggregates (D_s) decreased from 2.61 to 2.49 and in an order L_c > L₁ > L₂ > L₃ > L₄. The mechanical and water stable aggregates were improved in the cultivated Orange daylily lands compared to the control. Our results demonstrated that Orange daylily community significantly improved soil structure in the study area and the influence of the horticultural systems on soil structure was enhanced with the cultivated time. The fractal dimensions of soil properties are useful parameters which are able to monitor the changes in soil structure under the horticultural systems.