RESUMO
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.
Assuntos
Briófitas , Cianobactérias , Ecossistema , Microbiologia do Solo , Solo , China , Água , Produtos AgrícolasRESUMO
We selected typical croplands in the black soil region of Northeast China to analyze the characteristics of biocrusts during the growing season, including species composition, thickness, coverage, and biomass (chlorophyll content). We collected bareground soil and biocrusts samples with chlorophyll content of 5-15, 15-25, 25-35, and 35-50 mg·g-1, and measured the soil disintegration rate and soil maximum disintegration ratio of each sample using a force gauge in the laboratory. The results showed that: 1) biocrusts dominated by algae and moss were frequently developed in the croplands, with Stigeoclonium and Bryum capillare as the most common species, respectively. The thickness and biomass of algal crusts were significantly lower than moss crusts, with a successional trend from algal crusts to moss crusts. 2) The coverage, thickness, and biomass of biocrusts in croplands were negatively correlated with the frequency and intensity of tillage disturbance. For instance, the values of those characterisitics were only 27.8%, 1.52 mm, and 6.49 mg·g-1 on average, respectively, in traditional tillage croplands, and increased to 83.5%, 2.74 mm, and 34.16 mg·g-1, respectively, in the croplands with conservational tillage. 3) Biocrusts considerably reduced the disintegration of surface soil, particularly in the layer of biocrusts. Compared to the bareground soil, the soil disintegration rate of biocrusts, with four levels of biomass (with chlorophyll content of 5-15, 15-25, 25-35, and 35-50 mg·g-1), was reduced by 43.1%, 50.1%, 55.5%, and 59.8%, respectively, while the soil maximum disintegration ratios were reduced by 11.4%, 17.7%, 33.2%, and 36.6%, respectively. 4) Soil disintegration rate and maximum disintegration ratio were significantly and negatively correlated with the biomass and thickness of biocrusts, indicating that the impacts of biocrusts on soil disintegration were primarily caused by the improvements in physical properties of surface soil. In conclusion, biocrusts were frequently deve-loped in croplands in the black soil region of Northeast China, owing to less disturbance following the conversion from traditional tillage to conservational tillage. They had the potential to protect surface soil against disintegration and improve soil anti-scourability, which was critical for soil conservation in croplands in this region.
