Assessing management strategies for carbon storage in Mediterranean soils: double-cropping, no-tillage, and nitrogen fertilization reduction

In Mediterranean conditions, the historical use of traditional agricultural practices has led to a significant loss of soil organic carbon (SOC) and the associated benefits it provides. Consequently, it becomes imperative to explore effective strategies that promote the preservation and enhancement of SOC. Some promising practices to increase SOC are the use of double-cropping, conservation tillage, and reduced N fertilization. The aim of this study was to evaluate the combined effects of introducing a legume prior to maize, together with different tillage systems and mineral N fertilization rates on SOC and related fractions (particulate organic matter carbon, POM-C; mineral associated organic matter carbon, Min-C; and permanganate-oxidizable organic carbon, POxC). Additionally, the study aimed to investigate enzymatic activities associated with the carbon cycle. The study compared mono cropping maize (MC) versus legume-maize double-cropping (DC) with two tillage systems (conventional tillage, CT; no-tillage, NT), and three mineral N fertilization rates (zero, medium and high). The legumes employed were pea for grain (2019), vetch for green manure (2020), and vetch for forage (2021). The DC increased the SOC level by 10.6 % compared to the use of MC, with POM-C as the main fraction involved in this change. Thus, the employment of DC allowed for the maintenance of SOC levels, while the use of MC resulted in their reduction compared to the levels observed at the beginning of the experiment. NT exhibited higher values of SOC and its fractions POM-C and Min-C. These differences were observed only in the 0–10 cm depth layers. The use of NT enabled the maintenance of SOC compared to the initial studied period, while CT reduced SOC. The treatments with N fertilization achieved higher values of SOC and all the studied fractions compared to the unfertilized treatment. However, at the end of the experiment, it was found that the application of N fertilization, especially at high rates, led to a decrease in SOC. Additionally, it was observed that the employment of DC and NT increased the enzymatic activities of dehydrogenase and β-glucosidase. The results of this study indicate that the utilization of legume-maize DC, as well as the implementation of NT and reduced N fertilization, are useful strategies to maintain SOC levels and improving the biological quality of the soil under Mediterranean irrigated conditions.