Green manuring with Calotropis procera influences soil organic fractions under arugula cultivation in the semi-arid region

The cultivation of arugula is a growing horticultural activity in Brazil, and its different production systems directly influence soil resilience and quality. In this context, the objective of this study was to evaluate the organic fractions of medium-textured Oxisol under arugula cultivation, as affected by the incorporation of varying quantities of biomass from Calotropis procera (Ait.) R. Br. (Apocynaceae), in a cultivation experiment conducted in the semi-arid environment of Rio Grande do Norte, Brazil. The treatments consisted of five biomass levels: 20, 40, 60, 80, and 100 t ha⁻¹ on a dry weight basis, and two additional treatments, one without fertilization and another with mineral fertilization, in a randomized complete block design. The evaluated characteristics included soil organic matter, total organic carbon, labile carbon (labile fraction), and humic substances (recalcitrant fractions) at a depth of 0-20 cm. The experimental results indicate how different quantities of C. procera biomass influence soil organic fractions. Statistical analysis revealed significant effects of the treatments on the variables total organic carbon (TOC), labile carbon (LC), soil organic matter (SOM), and total humic substances (THS), with values of (p < 0.05), demonstrating that biomass incorporation impacts soil organic properties. For TOC, the treatments of 80 and 100 t ha⁻¹ presented the highest averages, indicating that larger quantities of biomass promote the accumulation of organic carbon in the soil, essential for soil health and fertility. For LC, the 40 and 60 t ha⁻¹ treatments led, suggesting better dynamics of readily available carbon at intermediate biomass levels. Regarding SOM, the 80 and 100 t ha⁻¹ treatments also showed superior results, with averages higher than mineral fertilization and the unfertilized control. Finally, for THS, the 60, 80, and 100 t ha⁻¹ treatments were more effective in promoting recalcitrant fractions, crucial for the stability of organic matter. This approach contributes directly to preserving soil fertility and mitigating carbon emissions, which are essential in a global context of climate change. Furthermore, by valuing local resources such as the biomass of a regionally adapted plant, the study emphasizes agricultural practices that support environmental conservation and efficient food production, ensuring greater soil resilience to sustain long-term agricultural productivity.