Cover crops impact to carbon-nitrogen cycling and wheat yields

Authors: Mubvumba, Partson; DELAUNE, PAUL - Texas A&M Agricultural Experiment Station; HONS, FRANK - Texas A&M University

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/2023
Publication Date: 9/30/2023
Citation: Mubvumba, P., Delaune, P.B., Hons, F.M. 2023. Cover crops impact to carbon-nitrogen cycling and wheat yields. Soil & Tillage Research. 13:2023. https://doi.org/10.1016/j.soisec.2023.100107.
DOI: https://doi.org/10.1016/j.soisec.2023.100107

Interpretive Summary: Cover crops plays a very important role in enhancing soil ecosystem services and functions for sustainable production. However, they have a direct impact in carbon-nitrogen cycling. Integrated monoculture crop-livestock production systems are harmful to soil ecosystems. Texas A&M University and USDA Crop Production Systems Research Unit in Stoneville conducted a study to evaluate the impact of a cover crop (CC) mixture introduced in the summer fallow period of a dryland continuous wheat system to determine effect of carbon and nitrogen cycling to subsequent wheat yields. Treatments were conventional tillage (CT) and combinations of no-tillage (NT), CC, grazing (G), and intercropping (I) wheat with radishes and turnips. Cover crops high C:N residues tied up nitrogen making it unavailable for main crop reducing yields by up to more than a third. However, CC added double NT organic nitrogen to the soil and protected carbon and nitrogen (N) in soil microaggregates compared to CT. It is important to monitor soil N when using cover crops to avoid N deficiency. Early termination can help mitigate the problem.

Technical Abstract: Cover crops (CC) play an important role in enhancing soil ecosystem services and functions for sustainable production. However, they have a direct impact in carbon-nitrogen cycling. Dual purpose (graze/grain) monoculture wheat production systems are prevalent in semi-arid regions where precipitation is erratic, and cattle production is a major practice often accompanied by low-resource input farming to reduce risk. Monoculture practice aggravated by grazing is harmful to sustainable soil ecosystem services and function. The impact of a CC mixture introduced in the summer fallow period of a dryland continuous wheat system was evaluated to determine influence on carbon and nitrogen cycling and subsequent wheat yields. Treatments were conventional tillage (CT) and combinations of no-tillage (NT), CC, grazing (G), and intercropping (I) wheat with radishes and turnips. Cover crops dominated by grasses added high C:N residues that immobilized inorganic nitrogen and added organic nitrogen by at least twice NT non CC treatments to the soil system. Tillage resulted in rapid mineralization of nitrogen reducing organic N by 3.6% compared to NT fallow treatments. Cover crops sequestered N and C by 47-60% and 47-52% respectively in microaggregates compared to CT fallow. On average, CC reduced wheat yields by 25% and 40% compared to NT and CT fallow respectively in the final year of study. Grazing and intercropping showed no significant effects. Semi-arid environments require careful planning cognizant of species selection, rainfall forecasting, termination timing for CC utilization to be fully beneficial with synchronous N mineralization to mitigate potential catastrophic immobilization of nitrogen.