|Zobeck, Teddy - Ted|
Submitted to: Trade Journal Publication
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/1/2010
Publication Date: 6/7/2010
Citation: Acosta Martinez, V., Dowd, S.E., Bell, C., Lascano, R.J., Booker, J.D., Zobeck, T.M., Upchurch, D.R. 2010. Microbial community composition as affected by dryland cropping systems and tillage in a semiarid sandy soil. Diversity. 2(6):910-931. Interpretive Summary: This study is the first one evaluating the effects of dryland crop rotations and different tillage practices on soil microbial communities in the Texas High Plains. Although it is known that conservative tillage practices have many benefits on soil conservation, we have not found yet signs of changes in soil microbes under the conservation tillage plots of this study compared to the conventionally tilled plots after 5 years. Our study indicates that soil changes with conservative tillage may take longer in these soils and/or climate. Even though water limitations in semiarid regions for dryland production occasionally can cause crop failure and disrupt the cropping sequence history, we found differences in soil microbial communities among three crop rotations studied. Soil microbes were increased with the use of cover crops in rotations with cotton, sorghum or haygrazer; which may indicate positive changes to the functioning of sandy soils in this region.
Technical Abstract: 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 is an Olton sandy loam (Fine, mixed, superactive, thermic Aridic Paleustolls) with an average of 16.4% clay, 67.6% sand and 0.65 g kg-1 of OM. The cropping systems evaluated were sorghum (Sorghum bicolor)-cotton (Gossypium hirsutum) (Sr-Ct), cotton-winter rye (Secale cereale)-sorghum (Ct-Rye-Sr), and haygrazer (another variety of Sorghum bicolor L.)-winter rye (Hay-Rye), which were under no-tillage (nt) and conventional tillage (ct) practices. Our previous studies found that tillage treatments did not affect soil MBC, MBN and enzyme activities (EAs) important for nutrient cycling (i.e., ß-glucosidase, a-galactosidase, ß-glucosaminidase, alkaline phosphatase, phosphodiesterase, and arylsulfatase). However, rotations with a winter cover crop history (Ct-Rye-Sr and Hay-Rye) enhanced soil MBN (1.7 times higher) and EAs (up to 2 times) compared to Sr-Ct after 3 years only. In our current study (after 5 years), Sr-Ct and Ct-Rye-Sr showed similar soil MBC, MBN, EAs, total C and organic C, which were lower than in soil under Hay-Rye. Soil microbial communities were bacterial dominated under cotton based cropping systems (Sr-Ct and Ct-Rye-Sr) compared to Hay-Rye. Bacterial diversity indexes were higher under tillage treatments compared to no-tilled treatments regardless of the cropping system, and showed this trend as affected by the cropping systems: Sr-Ct> Ct-Rye-Sr =Hay-Rye. Soil under Hay-Rye showed higher Bacteroidetes and Proteobacteria while lower Actinobacteria compared to Sr-Ct and Ct-Rye-Sr. The higher bacterial diversity indexes in tilled soil may reflect the higher Chloroflexi (i.e., Sr-Ct and Ct-Rye-Sr), Gemmatimonadetes and Verrucomicrobiae compared to the no-tilled plots. This study demonstrated that differences in dryland cropping systems and tillage management history can affect microbial communities and the soil functioning of sandy soils in semiarid regions, regardless the limited irrigation available to sustain every year growing season.