Ted M. Zobeck

Soil degradation is one of the most serious ecological problems in the world. In arid and semi-arid northern China, soil degradation predominantly arises from wind erosion. Trends in soil degradation caused by wind erosion in northern China frequently change with human activities and climatic change. To decrease soil loss by wind erosion and enhance local ecosystems, the Chinese government has been encouraging residents to reduce wind-induced soil degradation through a series of national policies and several ecological projects, such as the Natural Forest Protection Program, the National Action Program to Combat Desertification, the “Three Norths” Shelter Forest System, the Beijing-Tianjin Sand Source Control Engineering Project, and the Grain for Green Project. All these were implemented a number of decades ago, and have thus created many land management practices and control techniques across different landscapes. These measures include conservation tillage, windbreak networks, checkerboard barriers, the Non-Watering and Tube-Protecting Planting Technique, afforestation, grassland enclosures, etc. As a result, the aeolian degradation of land has been controlled in many regions of arid and semiarid northern China. However, the challenge of mitigating and further reversing soil degradation caused by wind erosion still remains.

This study evaluated microbial communities of soil (0–10 cm) as affected by dryland cropping systems under different tillage practices after 5 years. The soil type was an Olton sandy loam with an average of 16.4% clay, 67.6% sand and 0.65 g kg⁻¹ of organic matter (OM). The cropping systems evaluated were grain sorghum (Sorghum bicolor L.)—cotton (Gossypium hirsutum) (Sr_g-Ct), cotton-winter rye (Secale cereale)-grain sorghum (Ct-Rye-Sr_g), and a rotation of forage (f) sorghum (Sorghum bicolor L. and Sorghum sudanense) with winter rye (Sr_f-Rye), which were under no-tillage (nt) and conventional tillage (ct) practices. Soil microbial communities under cotton based cropping systems (Sr_g-Ct and Ct-Rye-Sr_g) showed lower fungal:bacterial ratios compared to the soil under Sr_f-Rye. Soil under Sr_f-Rye showed higher population densities of Bacteroidetes and Proteobacteria while lower Actinobacteria compared to Sr_g-Ct and Ct-Rye-Sr_g. Chloroflexi, Gemmatimonadetes and Verrucomicrobiae were higher in tilled soil compared to the no-tilled plots. Regardless the limited irrigation available to sustain agricultural production within these dryland cropping systems, this study demonstrated that differences in microbial communities are more affected by crop rotation than tillage management history. Although soil fungal diversity was not analyzed in this study, pyrosequencing suggests that tillage practices can affect bacterial phyla distribution in this sandy soil.