Increased shading in integrated agricultural systems in Southern Amazon reduces potential to store carbon and nitrogen in the soil

Integrated crop-livestock-forestry (ICLF) systems have been used for food production in tropical environments, offering significant benefits to their components. However, shading can alter the exchange of energy and matter within the systems, directly affecting plant development and animal behavior and, ultimately, interfering with soil C and N dynamics. The aim of this study was to evaluate soil C and N pools in nine-year old integrated systems under the conditions of southern Amazon. The experimental systems comprised crop-livestock under full sunlight (ICL), moderately shaded ICLF (ICLF_MS) and strongly shaded ICLF (ICLF_SS), implemented in Sinop, Mato Grosso state, Brazil. Incidence of photosynthetically active radiation in ICLF_MS and ICLF_SS was suppressed by 18 % and 50 %, respectively, compared with ICL. The ICL presented the highest stocks of soil organic carbon (SOC; 84.9 Mg ha⁻¹), total nitrogen (TN; 5.3 Mg ha⁻¹), dissolved organic C (160 mg kg⁻¹), and C and N stocks in the mineral-associated organic matter fraction, as well as the lowest C lability index. In contrast, ICLF_SS exhibited the lowest values for these parameters (SOC; 71.6 Mg ha⁻¹; TN 4.1 Mg ha⁻¹), indicating that shading alters soil C and N dynamics, resulting in reductions more than 15 % of SOC and 22 % of TN compared with ICL. Furthermore, ICLF_SS exhibited the highest levels of labile forms of C in the particulate organic fraction and the highest lability index. Hence, shading decreased the addition and stabilization processes of C and N in soil organic matter, resulting approximately 1.5 Mg ha⁻¹ year⁻¹ less C and 0.14 Mg ha⁻¹ year⁻¹ less N accrual. The results presented herein will support decision-making processes related to soil management strategies and the implementation of systems aimed at low-emission livestock-based protein production.