Carbon is a major essential element required for life on earth to be maintained. The quantity of carbon on earth is effectively constant. The carbon cycle is a major biogeochemical cycle in which carbon is exchanged among the atmosphere, autotrophic plants, heterotrophic organisms, and the soil. Carbon as carbon dioxide in the atmosphere is a vital greenhouse gas that has for 10,000 years reradiated some of the earth’s escaping longwave infrared energy back to earth in order to maintain a stable optimal global temperature. Perplexingly, since the start of the industrial revolution in 1750, carbon emissions into the atmosphere has increased from the extraction and burning of geologic fossil fuels causing the mean global temperature to progressively increase above the planets optimal level.
The Paris Agreement of 2015 was intended for the worlds countries to commit to reductions of greenhouse gas emissions and to transition to low-emission economies. Unfortunately, these projected changes have not occurred as scheduled. By the fall of 2023, less than 10% of the necessary Paris Agreement changes had been accomplished. Offending industries have ineffectively spent greater effort searching for proxy compensations rather than researching workable solutions.
As early as 2017, the plausibility of using livestock agriculture as a potential climate mitigation strategy by improving soil carbon sequestration in grazed grasslands has been seriously considered by the United Nations. A substantial increase in the quantity of organic carbon from atmospheric carbon dioxide captured and fixed during plant photosynthesis and stored in grassland soils would be as effective at reducing the rate of global warming as reducing carbon dioxide emissions from fossil fuel burning (FAO 2017).
The United Nations report on Global assessment of soil carbon in grasslands was completed in February 2023. Grasslands occupy 8.65 billion acres of the worlds land area with 4.9 billion acres of grassland used for grazing livestock (FAOSTAT 2016). The average global improved grazed grassland to a soil depth of 12 inches has stored a mean of 22.30 tons C/ac. The basic minimum essential quantity of organic carbon input into grassland soils to mitigate carbon dioxide emissions would be at 0.08 to 0.18 tons C/ac/yr. However, the greenhouse gas mitigation potential of the worlds grazinglands is quantitatively estimated to be 0.5 metric tonnes C/ha/yr or the conversion value of 0.22 tons C/ac/yr (FAO 2023).
The improved natural grasslands of North America occupy the combined area of the north and south mixed grass prairie are the more productive native grasslands minus the high sand and high clay sites has a mean quantity of stored SOC to a 12 inch depth at 26.76 tons C/ac and has a mean annual input of 1.1 tons C/ac/yr and has a mean minimum quantity of annual input needed to maintain the current storage level at 0.62 tons C/ac/yr (FAO 2023).
Grassland research at the Dickinson REC has evaluated the effects of three management treatments on the Northern Plains mixed grass prairie for 40 years. The mean quantity of stored SOC to a 12 inch depth on the nongrazed treatment was 33.25 tons C/ac with an annual input of 1.00 tons C/ac/yr. The mean quantity of stored SOC to a 12 inch depth on the seasonlong grazing treatment was 47.90 tons C/ac with an annual input of 0.84 tons C/ac/yr. The mean quantity of stored SOC to a 12 inch depth on the twice-over rotation grazing treatment was 64.34 tons C/ac with an annual input of 2.21 tons C/ac/yr (Manske 2023).
The mean quantity of stored SOC on the improved native mixed grass grasslands of North America determined by the United Nations study was 26.76 tons C/ac. The mean quantity of stored SOC on the native mixed grass grasslands of the Northern Plains determined by the DREC studies was 24.3% greater on the nongrazed treatment, 79% greater on the seasonlong grazing treatment, and 140.7% greater on the twice-over rotation grazing treatment. The annual SOC input rates on the nongrazed and seasonlong treatments were less than that on the combined north and south mixed grass grassland of the United Nations study. The annual SOC input rate on the twice-over treatment was 100.9% greater than that on the United Nations study.
The increases in the quantities of atmospheric carbon dioxide has been greater during the recent decade compared to the increases during the previous twenty years and has improved the effectiveness of plant photosynthetic processes that in turn removes increased quantities of carbon dioxide from the atmosphere and increases plant biomass growth if there is an increased quantity of available inorganic nitrogen to be used in assimilation of organic matter. The threshold quantity of inorganic nitrogen is 100 lbs N/ac (Wight and Black 1972, 1979) and greater quantities are more beneficial. The large biomass of rhizosphere microbes on the twice-over rotation treatment transform a mean 133 lbs inorganic N/ac/yr that increases plant growth biomass an average of 140% and thus also producing greater dead plant material and microbe carcasses entering the grassland soil increasing the rate of SOC storage to a mean of 2.21 tons C/ac/yr. The seasonlong and nongrazed treatments have lower soil microbe biomass and transform less than 100 lbs of available inorganic nitrogen/ac/yr at a mean of 82 lbs N/ac/yr and 56 lbs N/ac/yr, respectively.
Increasing soil organic carbon in grassland soils improves soil health, enhances soil aggregation, increases water holding capacity, improves water availability, increases nutrient availability, improves nutrient cycling, and improves ecosystem resiliency to drought conditions. The increase in grass biomass production, reduces land area per cow/calf pair, increase animal weight gain per acre, and increases the capture of greater wealth per acre.
Increasing grassland soil organic carbon by changing the grazing management practices will increase the intrinsic value of grassland ecosystems by improving the functionality of the soil biogeochemical processes and the grass plant physiological mechanisms that will increase the quantity of wealth captured from the land and it will help reduce the rate of global warming.
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