Will cover crops enhance profitable soil carbon sequestration?
Much attention has been and is continuing to be accorded to the benefits derived from inserting cover crops [CC] into commonly used cropping systems. Cover crops have long been promoted to enhance soil health, reduce soil erosion during the time between summer crops, scavenge nutrients not used by a summer commodity crop, and improve control of problematic weeds that plague summer crops. Cover crops are now being promoted to enhance the sequestering of carbon [C] in the soil. This additional source of biomass will provide a C source for soil microbes that also enhance soil C when they die [see article here]. However, inserting CC’s into any cropping system must either enhance profitability, or at the very least, must not reduce net returns from a cropping enterprise.
In an article titled “Cumulative impact of cover crops on soil carbon sequestration and profitability in a temperate humid climate” that appears in the journal Scientific Reports [2020 30:13381], authors Chahal et al. provide results from a study that was conducted to 1) evaluate the cumulative effects of CC’s on soil C sequestration, primary crop productivity, and profit margins, and 2) determine if current and projected C prices may provide an effective strategy for incentivising the quantity of soil C that is sequestered by CC’s. Major points from that study follow.
• The long-term use of CC’s as a vehicle for soil C storage, and the economics of their use, have generally been overlooked.
• The experiments reported in the above publication were established in 2007 [Site A] and 2008 [Site B] in the humid temperate climate at Ridgetown, Ontario, Canada [42°26 N lat.]. Experiments at each site were continued for 9 years. Soil texture at both sites was a sandy loam, and the initial soil organic matter [SOM] was 3.8%. Initial soil organic carbon [SOC] was not determined.
• Four CC treatments [oat, oilseed radish (OSR), cereal rye (CR), and a mixture of OSR and CR] and a no-CC control were used to evaluate the potential for their C sequestration and generation of positive economic returns.
• Crop rotation was identical at both sites, and consisted of grain and vegetable crops followed by CC’s that were planted in either July, Aug., or Sept., depending on the main or primary crop harvest date. CC’s were terminated the following spring each year by either glyphosate (CR) or winter termination.
• Over the 9 years of the study, OSR had the greatest cumulative [main crop and CC] C, and the no-CC treatment had the least. At both sites, soil C inputs were attributed to CC.
• CC treatments had greater SOC content at both sites.
• In this study, there was no discernable relationship between crop yield and SOC content. However, there was less crop yield variability across years in the CC treatments.
• In this 9-year study, the added costs for the CC treatments were not compensated for by the revenues generated by the insignificantly greater yields of the main crop. Thus, CC use reduced profit.
• When the additional value of soil C storage was considered (based on a carbon price of about $22/ton), profits were greater in the OSR and OSR + CR treatments than in the no-CC treatment. Thus, financial compensation would likely be required for cover cropping to be profitable no matter what CC species is used.
• The results from this study indicate that 1) CC’s will increase soil C storage, 2) all CC treatments had greater SOC than the no-CC treatment, 3) all CC treatments had main crop yields that were as good as or better than those from the no-CC treatment, 4) profits from summer crops are likely to decrease when CC’s that produce no additional income are used, and 5) since CC use resulted in lower profits, implementation of a compensation policy for producers to sequester C in soil will likely be needed to offset the lost profits.
It is recognized and noted that the location of this study was much farther north than the northernmost locations in the midsouthern U.S. Thus, the findings reported in the above article are likely not transferrable when CC’s are used in the Midsouth. However, the finding that financial compensation in the form of payment for soil C sequestration will be required to offset the added cost from CC use will likely be the case at any location. The amount of the required compensation will depend on how much C sequestration will occur with the myriad CC species that can be used, and this will be strongly influenced by climate conditions in the area where the CC’s are used. Click here for an article on this website that discusses how payment for carbon credits can be used to encourage the adoption of conservation practices such as CC’s in the U.S. farming sector.
Composed by Larry G. Heatherly, Mar. 2023, larryh91746@gmail.com