Role of livestock-derived amendments in soil organic carbon stocks in forage crops

The use of organic amendments for forage production has been promoted in recent years due to the adoption of sustainable agricultural practices and the increasing cost of mineral fertilizers. Organic manures can contribute with an extra carbon to the soil to the potential addition of carbon stocks. This study aimed to measure the capacity of different organic amendments commonly available in livestock farms for forage fertilization to influence the rate of soil organic carbon (SOC) under future climate change conditions. For this purpose, on-farm processed exogenous organic matter (EOM) was analyzed for fiber and organic carbon mineralization to obtain the percentage of decomposable EOM and resistant EOM (DEOM and REOM, respectively). The RothC model was run in grasslands and forage maize under different scenarios considering specific DEOM and REOM values. The results showed that the degradability of amendments could influence SOC dynamics. The SOC of grasslands after 38 years of simulation differed by >30 % between compost and the liquid fraction of cattle slurry. Forage crops were simulated under the RCP8.5 scenario and fertilized with amendments at the recommended amounts of nitrogen for these crops. As a result, SOC stocks had a better response to organic fertilization in grassland, except under the application of the liquid fraction, with a decrease in SOC of 16 %. In cropland, only the solid fraction from mechanical separation of slurry and compost applications increased the SOC stock from 13 % to 26 % in the 2020-2090 period. Our study provides insights into how the degradability of EOM can affect simulations of the SOC stock rate over time.