Cereal rye cover crop inputs disproportionately stimulate soil carbon- and phosphorus- but not nitrogen-hydrolytic enzyme activities in long-term maize–soybean rotations

Authors: LYU, JING - University Of Illinois Urbana-Champaign; O'Brien, Peter; Ruis, Sabrina; Olk, Daniel; DINNES, DANA - Retired ARS Employee; Papanicolaou, Athanasios; RODRIQUEZ-TORRES, IVANELLIS - University Of Illinois Urbana-Champaign; MARGENOT, ANDREW - University Of Illinois Urbana-Champaign

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Obtaining and sustaining high corn and soybean grain yields depends on appropriate management of soil nutrients. These crops need nutrients like carbon (C), nitrogen (N), and phosphorus (P), which are supplied by fertilizer application, existing soil nutrient pools, and degradation of crop residue. The amount of nutrients released by the crop residue that is available to plants remains poorly understood, partly because the amount of crop residue left in the field depends on management choices. For example, corn that is harvested for animal feed (i.e., silage) leaves almost no crop residue, while incorporating cover crops such as cereal rye during times of year that corn and soybean are not growing leaves more residue. Soil enzymes, substances that cause crop residue to degrade and release nutrients, are often used to better understand nutrient balances. This study investigates how C, N, and P enzyme activities change when different amounts of crop residue are left in the field by comparing systems that harvest either corn grain or corn silage with and without cover crops. The results showed that enzymes associated with C and P cycling are linked with the amount of crop residue, which means that more residue leads to faster nutrient release. However, the enzymes associated with N cycling were not closely linked to crop residue inputs, which indicates that N cycling is more influenced by fertilizer applications and soil organic matter than the amount of residue. Soil C is an important indicator of soil health, so understanding these processes is critical to maintaining or regenerating long-term soil health. Fertilizer N and P applications are often a major expense for farmers in the region, so understanding how these enzymes influence soil N and P levels can help farmers identify the best application rate to reduce fertilizer inputs. Thus, these findings are especially valuable to growers, researchers, and crop advisors to understand how cover crops and residue management decisions can influence long-term soil health and contribute to more economical fertilizer applications.

Technical Abstract: Long-term crop rotations can alter residue inputs and nutrient balances, yet how these changes translate to changes in soil enzyme activities that mediate carbon (C), nitrogen (N), and phosphorus (P) cycling remains insufficiently resolved. We measured soil hydrolytic enzyme activities under grain- and silage-maize (Zea mays L.) with and without cereal rye (Secale cereale L.) cover crop in a 21-year maize–soybean (Glycine max L.) rotation field experiment in Iowa, within the U.S. Corn Belt. Under a maize silage rotation, cover cropping increased C- and P-hydrolytic activities compared to no cover cropping: ß-glucosidase (+61%), cellobiohydrolase (+140%), phosphodiesterase (+82%), and phosphomonoesterase (+40%), even after normalizing to soil organic C. Co-occurring increases suggest a nonlinear and substrate-induced activity response to cover crop residue inputs. In contrast, N-hydrolytic enzyme activities (protease, glycine-, leucine-, alanine-, and methionine-aminopeptidases) showed no or inconsistent responses to crop rotation or cover cropping, despite estimated negative N balances under maize silage rotations. This suggests that microbial N acquisition is buffered by long-term fertilization and mineralization of soil organic matter, and/or that enzyme activity assays may not fully capture N cycling shifts. These results indicate that biochemical pathways of C and P cycling mediated by enzyme activities are coupled through substrate inputs from crop and cover crop residue, whereas N cycling is partially decoupled under maize–soybean systems that dominate central North America. Our findings further underscore that soil enzyme activities may reflect biogeochemical equilibrium states rather than simple indicators of nutrient limitation in intensively managed agroecosystems.