Soil carbon mineralization, enzyme activities and crop residue decomposition under varying soil moisture regimes

Authors: Chatterjee, Amitava; Taylor, Jason; Strauss, Alana; Locke, Martin

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2023
Publication Date: 11/10/2023
Citation: Chatterjee, A., Taylor, J.M., Strauss, A., Locke, M.A. 2023. Soil carbon mineralization, enzyme activities, and crop residue decomposition under varying soil moisture regimes. Article e20601. Soil Science Society of America Journal. https://doi.org/10.1002/saj2.20601.
DOI: https://doi.org/10.1002/saj2.20601

Interpretive Summary: Flooding reduces the rate of organic matter decomposition, as low soil oxygen levels result in declining microbial activity. However, the degree of reduction in decomposition rate depends on organic matter characteristics, indicated in part by the ratio of carbon and nitrogen concentrations. Decomposition rates of corn, cotton, sorghum, soybean and sweet potato stalks were measured after they were added to two dominant soil types in the Mississippi Delta. The soils were compared at both 50% and 100% of total potential soil water-holding content while soil carbon dioxide release was measured during 74-day laboratory incubations. Soil carbon dioxide release was reduced by 46% for soils at 100% potential moisture content compared to 50% soil water content. Sweet potato stalk lost 57% of its weight, whereas cotton and corn lost 36% of their biomass after 74 days of incubation. These results identify soil flooding as a management option for land managers to limit the loss of soil carbon as carbon dioxide, although the reduction in loss will depend on the crop type. These results will be of interest to soil carbon researchers and to agronomists and land managers when designing crop rotations that consider the relative decomposition rates.

Technical Abstract: Flooding influences residue decomposition and soil carbon (C) and nitrogen (N) mineralization through creating anoxic conditions; but the magnitude of decomposition depends on residue quality or CN ratio. Surface soils (0-15 cm) were collected from agricultural fields under two dominant soil series, Alligator and Forestdale in the Lower Mississippi River basin (LMRB). Both soils were incubated with five crop residues, corn (Zea mays), soybean (Glycine max), cotton (Gossypium hirsutum), sorghum (Sorghum bicolor), and sweet potato (Ipomea batatus), at 50% and 100% water filled-porespace (WFPS). Soil carbon dioxide (CO2) efflux was measured during 74 days of incubation. Soil, moisture level, and residue type had a significant effect on soil inorganic nitrogen (N) and enzyme activity. Forestdale soil had higher total C and N than Alligator, but Alligator had higher inorganic N, CO2 efflux, aryl sulfatase (AS); phosphatase (AP), and ß-N-acetyl glucose aminidase (NAG) than Forestdale. Release of labile C from residue dictates the microbial metabolism or loss of CO2. Cumulative soil CO2 efflux was reduced by 46% at 100% WFPS (754 mg C g-1) compared to 50% WFPS (1399 mg C g-1 soil). Soils with corn residue had higher AS activity (333 µmoles kg-1 hr-1) than soybean (286 µmoles kg-1 hr-1) but similar to cotton, sorghum, and sweet potato. On the contrary soybean treated soil had higher AP activity (2306 µmoles kg-1 hr-1) than soils treated with other residues. Residue quality influence the residue decomposition kinetics. At the end of incubation, sweet potato residue had the lowest remaining biomass (42.8%), significantly lower than cotton (64.1%), corn (63.7%), and sorghum (63.2%), but similar to soybean (48.6%). Residue quality had a strong influence on decomposition and mineralization of C and N along the moisture gradient.