|Zobeck, Teddy - Ted|
Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2011
Publication Date: 8/1/2011
Citation: Acosta Martinez, V., Lascano, R.J., Calderon, F.J., Booker, J.D., Zobeck, T.M., Upchurch, D.R. 2011. Dryland cropping systems influence microbial biomass and enzyme activities in a sandy soil in a semiarid region. Biology and Fertility of Soils. 47(6):655-667. Interpretive Summary: In dryland agriculture in semiarid regions, crop establishment is not always possible because precipitation may not be sufficient. Modification of soil properties can improve the soil quality and functioning including soil water capture and storage capacity for crop production in dryland conditions. ARS scientists established a study near Lubbock, Texas in 2003 to compare the soil properties under different dryland cropping systems and tillage management. After only 3 years, this study detected increases in soil microbial community size and enzyme activities important for nutrient cycling under rotations with a winter cover crop such as cotton-rye-sorghum and haygrazer-rye compared to continuous cotton or sorghum-cotton at 0-10 cm soil depth. After 5 years, higher soil total C was found under Hay-Rye compared to the other systems. In addition, microbial properties were already impacted in all alternative systems (haygrazer-rye, cotton-rye-sorghum and cotton-sorghum) studied compared to continuous cotton. Several microbial properties indicative of increased soil water availability were also higher under the alternative rotations to continuous cotton. However, continuation of this study is vitally important for the long-term evaluation and confirmation of these trends, and their implications in water management, soil quality and crop productivity in dryland.
Technical Abstract: In dryland ecosystems, crop establishment is not always guaranteed because precipitation may not be sufficient at planting. Sandy soils under dryland agriculture in the Texas High Plains region of USA have extremely low organic matter (OM) content (< 1%) and thus, hold low water and nutrients to sustain crop productivity. Thus, it is important to identify cropping systems history that impact beneficially soil quality. This study evaluated microbial communities and functionality as affected by dryland cropping systems under conventional and no-tillage practices in an Olton sandy loam soil (Fine, mixed, superactive, thermic Aridic Paleustolls) with an average of 16.4% clay, 67.6% sand and 0.65 g kg-1 of OM. Cropping systems varied from low to maximum cropping intensity (CI) including grain sorghum (Sorghum bicolor)-cotton (Sr-Ct), cotton-winter rye (Secale cereale)-sorghum (Ct-Rye-Sr), and haygrazer (a forage variety of Sorghum bicolor L.)-winter rye (Hay-Rye). During the first 5 years, tillage treatments did not affect soil (0-10 cm) microbial biomass C and N (MBC, MBN) and enzyme activities (EAs) involved in C, P and S nutrient cycling. After 3 yrs, rotations with a winter cover crop (Ct-Rye-Sr and Hay-Rye) enhanced soil MBN (1.7 times higher) and EAs (up to 2 times) compared to Sr-Ct. After 5 yrs at the end of this study, Sr-Ct and Ct-Rye-Sr showed similar soil MBC, MBN, and EAs, and Hay-Rye showed higher soil total C compared to Ct-Rye-Sr and Sr-Ct. Comparison of Sr-Ct plots with continuous cotton (Ct-Ct), in nearby research plots that we were managing, revealed that it took 5 yrs to detect higher soil total C, MBC, and EAs under Sr-Ct. PCA plots using several fatty acid methyl esters (FAMEs) revealed differences in soil microbial community structure due to the current crop being planted rather than by the cropping history, but there were differences in soil microbial community structure due to tillage practices. This study demonstrated improvements in soil microbial biomass and enzyme activities, and thus, nutrient cycling with the use of winter cover crops in dryland cropping systems despite the growing season and desired crop sequence was not always possible due to lack of precipitation in certain years.