Synergistic effects of biochar and carboxymethyl cellulose sodium (CMC) applications on improving water retention and aggregate stability in desert soils.

Making improvements to the water-holding characteristics and water-erosion resistance of desert soils, particularly in inland extremely arid areas, is vital for achieving both sustainable water resource utilisation and food security. The aim of this study is to evaluate the effects of the co-application of biochar and carboxymethyl cellulose sodium (CMC) on the physical properties of sandy desert soil, including infiltration rate, saturated water conductivity, field water-holding capacity and aggregate stability. Sandy desert soil samples were collected from jujube plantations on the southern edge of the Taklimakan Desert in the Hotan Prefecture, Xinjiang, China. Five CMC application ratios (C0:0, C1:0.01 g/kg, C2:0.02 g/kg, C3:0.04 g/kg and C4:0.08 g/kg) and five biochar application ratios (B0:0, B1:1.0 g/kg, B2:2.0 g/kg, B3:4.0 g/kg and B4:8.0 g/kg) were designed and a total of 11 experimental treatments were performed, which were labelled as CK (control group), B2C0, B2C1, B2C2, B2C3, B2C4, B4C4, B0C2, B1C2, B3C2 and B4C2. Compared with CK, the combined application of biochar and CMC reduced the soil bulk density (BD) by 1.29-9.41% and the saturated hydraulic conductivity (Ks) by 29.64-94.98%, and increased the soil saturated water content (SSWC) by 8.81-30.74% and the water holding capacity (WHC) by 13.91-36.87%. Similarly, the water-stable aggregates that were co-applied with biochar and CMC increased by 29.10-256.86%. This resulted in significant improvement in the stability of sandy desert soil against water erosion. The principal component analysis (PCA) results found B4C4 to have the best comprehensive improvement effect. Therefore, 0.08 g/kg of CMC and 8.0 g/kg of biochar were used as recommended for improving the hydraulic properties of desert soils. Generally, CMC and biochar have a mutually complementary effect on improving sandy desert soil, providing new ideas and approaches for the improvement of soil and the sustainable development of agriculture in desert areas.

Combined effects of the earthworm casts application and fallow time on runoff and sediment loss by raindrop splashing in the Loess Plateau, China.

The importing of sources of exogenous organic carbon is an effective method for the prevention of soil degradation in sloping soils. Earthworm casts (ECs) have been recognised as a contributor to long-term carbon protection, but relatively few studies have examined the temporal impact ECs have on the achievement of this goal and its efficacy in the mitigation of soil erosion challenges in the Loess Plateau region in China. This study conducted field simulated rainfall experiments as a means of investigating the effects of five ECs (0, 200, 400, 600 and 800 g/m2, labelled CG, E1, E2, E3 and E4) on runoff, sediment and soil aggregate composition after 60, 90 and 150 days of fallow. As E4 was fallow for 150 days, the total runoff, runoff coefficient and total sediment amount decreased by 34.0%, 37.6% and 82.80% in comparison to CG. The runoff and sediment analytical models were able to accurately simulate the runoff and sediment yield processes through ECs application (R2≥0.704, RMSE≤1.108, NSE≥0.513). After being fallow for 150 days, soil sorptivity (S) increased from 0.151 cm/min0.5 to 0.310 cm/min0.5 as ECs application quantity increased. In contrast, the calibration constants of splash erosion (Cr) decreased from 0.150 to 0.090 and runoff erosion (Cf) decreased from 0.120 to 0.081. ECs were found to considerably enhance the number of aggregates that were more prominent than 0.25 mm in size. When E4 was fallow for 150 days, the fraction of >0.25 mm aggregate (WSA0.25) increased by 120.69% in comparison to CG. The mean weight diameter (MWD) grew by 105.96%, the geometric mean diameter (GMD) increased by 98.81% and the soil erodibility value K improved by 43.78%. When the amount of ECs was 800 g/m2, the stability of soil aggregates was effectively improved against water erosion while runoff and sediment transport were controlled. This can help improve the current soil and water loss situation in the Loess Plateau while also improving cultivated land soil quality. At the same time, a longer fallow period time promotes soil aggregate formation. This study is focused on the exceptional performance of ECs in limiting soil erosion on the Loess Plateau in China, which may provide novel solutions for soil and water conservation and the prevention of non-point source pollution.

Effects of Bacillus subtilis on carbon components and microbial functional metabolism during cow manure-straw composting.

This study is the first to investigate the changes in the composting process and carbon conversion in a cow manure-straw compost matrix with Bacillus subtilis added at four different levels (0, 0.5%, 1%, and 2% w/w compost), and to explain the mechanism responsible for carbon conversion through microbial functional metabolism. Inoculation with Bacillus subtilis at 2% had the best effect on fermentation among all treatments, but it inhibited the synthesis of total organic carbon and humus. Bacillus subtilis at 0.5% reduced mineralization in the cooling and maturity stages of composting, and enhanced the humification of carbon. The total organic carbon and humic sequence contents were significantly higher with Bacillus subtilis at 0.5% (12.5% and 20.2%, respectively) than Bacillus subtilis at 2% (P < 0.05). Redundancy analysis demonstrated that the pH and microbial functional metabolism were closely related to carbon sequestration during composting.

Mathematical model of sediment and solute transport along slope land in different rainfall pattern conditions.

Rainfall erosion is a major cause of inducing soil degradation, and rainfall patterns have a significant influence on the process of sediment yield and nutrient loss. The mathematical models developed in this study were used to simulate the sediment and nutrient loss in surface runoff. Four rainfall patterns, each with a different rainfall intensity variation, were applied during the simulated rainfall experiments. These patterns were designated as: uniform-type, increasing-type, increasing- decreasing -type and decreasing-type. The results revealed that changes in the rainfall intensity can have an appreciable impact on the process of runoff generation, but only a slight effect on the total amount of runoff generated. Variations in the rainfall intensity in a rainfall event not only had a significant effect on the process of sediment yield and nutrient loss, but also the total amount of sediment and nutrient produced, and early high rainfall intensity may lead to the most severe erosion and nutrient loss. In this study, the calculated data concur with the measured values. The model can be used to predict the process of surface runoff, sediment transport and nutrient loss associated with different rainfall patterns.