Changes in soil biochemical properties following application of bentonite as a soil amendment

Bentonite is a natural soil amendment that can reduce soil water loss and increase crop yield, but there are few studies about how bentonite influences soil biochemical properties. A field experiment was conducted with a millet [Setaria italic (L.) Beauv.] crop to evaluate the effect of bentonite amendments on soil biochemical properties including soil organic C, total N and total P, and soil microbial biomass C, N and P (MBC, MBN and MBP respectively) in the 0–20 cm soil layer in a semi-arid region in northern China from 2011 to 2015. Treatments included six rates of bentonite amendments (0, 6, 12, 18, 24 and 30 Mg ha−1) applied only in 2011, and a control with no bentonite amendment. Application of bentonite significantly increased soil microbial biomass parameters (MBC, MBN and MBP), soil organic C, and total N and total P over the five-year experimental period. MBC, MBN and MBP increases ranged from 5 to 50%, 3–42% and 3–34%, respectively; soil organic C, and total N and total P increases ranged from 1 to 15%, 1–19% and 0–17%, respectively. Bentonite also significantly increased MBC/MBN, MBC/MBP and MBN/MBP ratios, but it had no effect on soil C/N, C/P and N/P ratios. The application rate of 18 Mg ha−1 had the greatest effect in the first year, whereas 30 Mg ha−1 bentonite had the greatest effect in the fifth year. Increases in soil microbial activity and nutrient cycling and availability were attributed to higher soil water content accompanying the bentonite amendment resulting in improved plant growth and organic matter inputs to the soil providing increased substrates for microbes. Our results show that bentonite as a soil amendment can enhance sustainable agriculture production in semi-arid areas.