Effects of cyanobacteria- and moss-biocrusts on soil aggregate stability and splash erosion in croplands of the China Mollisols area.

Abstract

To investigate the effects of biocrusts development on aggregate stability and splash erosion of Mollisols and to understand its function in soil and water conservation, we collected biocrusts (cyano crust and moss crust) samples in croplands during the growing season and measured the differences in aggregate stability between biocrusts and uncrusted soil. The effects of biocrusts on reduction of raindrop kinetic energy were determined and splash erosion amounts were obtained with single raindrop and simulated rainfall experiments. The correlations among soil aggregate stability, splash erosion characteristics, and fundamental properties of biocrusts were analyzed. The results showed that compared to uncrusted soil, the cyano crust and the moss crust decreased the proportion of soil water-stable aggregates <0.25 mm by 10.5% and 21.8%, respectively, while their soil water-stable aggregates 5-10 mm were 4.0 and 8.8 times as that of uncrusted soil. In contrast to uncrusted soil, the macroaggregate content (R0.25), mean weight diameter (MWD), and geometric mean diameter (GMD) of biocrusts were 31.5%, 76.2%, and 33.5% higher, respectively. In addition, biocrusts reduced raindrop kinetic energy by an average of 0.48 J compared to uncrusted soil. The breakthrough raindrop kinetic energy of cyano crust and moss crust were 2.9 and 26.2 times as that of uncrusted soil, while the reduction of raindrop kinetic energy by cyano crust with high biomass was 1.3 and 6.6 times as that of medium and low biomass, respectively. Under the single raindrop and simulated rainfall conditions, biocrusts reduced splash erosion amounts by 47.5% and 79.4%, respectively. The proportion of aggregates >0.25 mm in the splash soil particles of biocrusts (37.9%) was 40.3% lower than that of uncrusted soil, while the proportion of aggregates >0.25 mm decreased as biocrust biomass increased. Moreover, the aggregate stability, splash erosion amount, and fundamental properties of biocrusts were significantly correlated. The MWD of aggregates was significantly and negatively correlated with the splash erosion amount under single raindrop and simulated rainfall conditions, indicating that the improved aggregate stability of surface soil caused by biocrusts accounted for reducing splash erosion. The biomass, thickness, water content, and organic matter content of biocrusts had significant effects on aggregate stability and splash characteristics. In conclusion, biocrusts significantly promoted soil aggregate stability and reduced splash erosion, which had great significance to soil erosion prevention and the conservation and sustainable utilization of Mollisols.