Microbial communities in soil profile are more responsive to legacy effects of wheat-cover crop rotations than tillage systems

Authors: ANIL, SOMENAHALLY - Texas A&M Agrilife; Dupont, Jesse; BRADY, JEFFREY - Texas A&M Agrilife; MCLAWRENCE, JAVID - Texas A&M Agrilife; Northup, Brian; Gowda, Prasanna

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2018
Publication Date: 5/16/2018
Citation: Anil, S.C., DuPont, J.I., Brady, J.A., McLawrence, J., Northup, B.K., Gowda, P. 2018. Microbial communities in soil profile are more responsive to legacy effects of wheat-cover crop rotations than tillage systems. Soil Biology and Biochemistry. 123:126-135. https://doi.org/10.1016/j.soilbio.2018.04.025.
DOI: https://doi.org/10.1016/j.soilbio.2018.04.025

Interpretive Summary: Winter wheat is a major cereal crop in the world due to its high protein content and high caloric value. Dual-purpose wheat (winter grazing and grain harvest in early summer) with summer fallow is the most common agronomic system in the Southern Great Plains. Large quantities of nitrogen fertilizers are applied to achieve higher biomass for grazing and later grain yields, however much of this fertilizer can be lost to waterways or the atmosphere, representing a monetary loss for producers and negative impacts on the environment. Additionally, conventional tillage practices can negatively impact soil structure and its capability to produce optimal yields. This study examined how the use of alternative fertilizer and tillage practices could affect the potential for loss of nitrogen as well as soil quality. Cowpea, a legume, was used for a source of “green nitrogen” as a summer cover crop and to reduce the needs for inorganic nitrogen fertilizer. No-till was used as a comparison to conventional tillage operations. While cowpea and no-till did not significantly affect soil carbon and nitrogen levels in the short term, there was a notable increase in beneficial fungi during the wheat growing season in plots that had been rotated with cowpea. This increase in beneficial fungi could be beneficial for building the soil’s health and offering stability to the production of winter wheat in the Southern Great Plains.

Technical Abstract: Declining trends in soil health under continuous monoculture systems of winter wheat are a concern for sustainable production in the Southern Great Plains of the US. This study was conducted to evaluate the long-term implementation of conservation tillage in combination with nitrogen treatments and summer cover crop (cowpeas) rotations with winter wheat, for their legacy effects on soil health attributes of microbial communities and soil organic carbon (SOC). Microbial biomass and composition were estimated in relation to soil parameters in the soil profile during the annual rotation cycle of wheat and cover crops. Results demonstrated that positive legacy effects of cover crop rotations were evident, as arbuscular mycorrhizal fungi (AMF) biomass during the wheat-growing season was significantly higher in cover crop treatments (by around 30-70%) compared to summer fallow treatment. Some taxons such as Acidobacteria, Actinobacteria, Proteobacteria (>70% of prokaryotic relative abundance) and Ascomycota (> 50% of fungal relative abundance) were the predominant groups detected in all experimental treatments. Microbial composition did not significantly change at phylum level, although some reorganization at OTU level was evident throughout the soil profile, mostly because of nitrogen treatments. Several Glomeromycota OTUs were significantly altered by soil depth and by nitrogen fertilization, which suggest that subsurface mycorhizosphere interactions were distinct from surface soil. The main effects of tillage treatment did not significantly alter the microbial abundance and their diversity. None of the experimental treatments sufficiently altered SOC levels at whole profile level, indicating that differences in microbial biomass-C did not contribute to noticeable changes in SOC.