Microbial processes and community structure as influenced by cover crop residue type and location during repeated dry-wet cycles

Authors: THAPA, RESHAM - University Of Maryland; TULLY, KATHERINE - University Of Maryland; HAMOVIT, NORA - University Of Maryland; YARWOOD, STEPHANIE - University Of Maryland; Schomberg, Harry; CABRERA, MIGUEL - University Of Georgia; REBERG-HORTON, S. CHRIS - North Carolina State University; Mirsky, Steven

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2021
Publication Date: 12/9/2021
Citation: Thapa, R., Tully, K., Hamovit, N., Yarwood, S., Schomberg, H.H., Cabrera, M., Reberg-Horton, S., Mirsky, S.B. 2021. Microbial processes and community structure as influenced by cover crop residue type and location during repeated dry-wet cycles. Applied Soil Ecology. https://doi.org/10.1016/j.apsoil.2021.104349.
DOI: https://doi.org/10.1016/j.apsoil.2021.104349

Interpretive Summary: In agricultural fields, cover crop residues are either incorporated into or left on the soil surface. While surface residues are subjected to extreme drying between dew, rainfall or irrigation events in the field, incorporated residues, on the other hand, experience a more stable moist environment. Such differences in water dynamics between incorporated and surface residues will have huge consequences in carbon (C) and nitrogen (N) cycling in cover crop-based cropping systems. In this study, we investigated the effect of residue management (residue type and location) on microbial processes and community structure during repeated dry-wet cycles. We found that incorporated residues recycled greater amount of C and N back into soil than surface residues. The magnitude of the effect of residue location on decomposition and subsequent N mineralization is greatly affected by differences in residue water dynamics which in turn is influenced by dry-wet cycles. We also found that incorporated residues were more colonized by soil prokaryotes and saprophytic fungi. Cover crop type had greater effect on soil prokaryotic and fungal communities than residue location. As we experience more frequent heat, drought, and rain events than anytime in the past, our work will help farmers shape residue management decisions as it relates to residue persistence and N availability under future climate change scenarios. This work will also be used by researchers to inform future research and cover crop decomposition.

Technical Abstract: Soil microorganisms play a critical role in cover crop (CC) residue decomposition and nutrient cycling in agroecosystems. However, the impact of CC residue management and dry-wet cycles on soil and residue microbiota and their potential ecosystem functions is largely unknown. To fill these knowledge gaps, an incubation experiment was conducted with two CC residues, crimson clover (Trifolium incarnatum L.) and cereal rye (Secale cereale L.), and two residue locations (incorporated vs surface-applied). Each CCs by location treatment was subjected to four dry-wet cycles (20-d each) for a total of 80-d. Crimson clover residues had higher water storage capacities than cereal rye, and the rate at which water was lost from surface-applied CC residues increased after each successive wetting event. Rapid drying of surface-applied CC residues quickly suppressed CO2 fluxes, which increased immediately upon rewetting. Incorporated CC residues maintained water content for longer duration than surface-applied residues and showed greater colonization by soil prokaryotes and saprophytic fungi. Thus, significantly more C and N were mobilized from incorporated residues by 80-d than from surface-applied residues (p<0.05). Due to differences in residue chemistry, CC residue types have a stronger impact on soil N levels than residue location. Thus, residue chemistry strongly influenced soil prokaryotic and fungal diversity, community structure, and functionality. While crimson clover-amended soils (N-rich environments) were dominated by copiotrophs, oligotrophs dominated cereal rye-amended soils (N-poor soil environments). On the other hand, residue location may have a greater effect than residue type in determining residue microbiota, particularly prokaryotes. Based on these findings, we can conclude that the effect of residue location on C and N mineralization during repeated dry-wet cycles is primarily explained by differences in water dynamics between incorporated and surface-applied CC residues.