Carbon pools and microbial indicators in vineyard soils under organic and conventional fertilization in the São Francisco Valley, in a semi-arid tropical climate

Abstract

Soil management systems that do not prioritize conservation contribute to carbon (C) depletion in tropical environments. In the semi-arid region of Brazil, fruit farming has been a key driver for economic development, yet high agricultural yields depend on the use of costly inputs. We conducted a groundbreaking study in São Francisco Valley, northeastern Brazil, to investigate the effects of organic (OF) and synthetic fertilizers (CF) on carbon stock and stability, organic matter fractions, microorganismal carbon biomass (C-mic) and quality indexes, and C-CO₂ emissions up to the 1 m of depth in grapevine soils. Additionally, we compared the fertilized soils with their nearby native vegetation under the Caatinga biome. Compared to native vegetation, the OF and CF grapevine soils store 33 Mg ha^-1 in one year and 26 Mg ha^-1 in two years of establishment, respectively. The total labile C stock was found to be 10.2 Mg ha^-1 and 6.0 Mg ha^-1 at a depth of 1 m. We observed the development of C-mic at 40-100 cm (approximately 280 mg kg^-1) in the OF soil, which resulted in efficient C mineralization without disrupting microbial metabolism, which produced roughly 8.0 mg kg^-1 day^-1 of C-CO₂. The isotopic signature shows that C3 plants partially influence carbon and nutrient cycling in deeper OF soil layers. The soil in OF exhibited a high concentration of carbonate equivalent (32 g kg^-1) and calcium (6 g kg^-1), which resulted in the protection of labile C from decomposition. The Cambisols of viticultural farm under organic fertilization exhibited a balance of humic and fulvic acids fractions of organic matter, consequently, a potential stability of C. Our findings show that organic fertilization based on cassava juice, fish amino acids, and straw combined with manure under intensive irrigation contributes to an increase in C storage and microbial indicators in the soil. Therefore, this type of fertilization could be employed as a sustainable management system in grape farming in the Brazilian Northeast to improve soil conditions and crop yield under harsh environmental conditions.

Keywords: Caatinga biome; Fulvic acid; Grapevine; Labile; Organic C stock.