Does irrigated mango cultivation alter organic carbon stocks under fragile soils in semiarid climate?

Abstract

The Sub-middle São Francisco Valley is a center of intense activity of irrigated fruit farming, which may lead to alterations in soil attributes and processes compared with areas under native vegetation, in this case Caatinga. One of the attributes sensitive to such alterations is soil organic matter (SOM), considering the climatic semi-arid conditions, fragile soils (sandy soils) and the adopted management such as the organic residues deposition from pruning, goat manure fertilization, high availability of water, and nutrients. Thus, in order to evaluate the influence of irrigated mango cultivation on the C stocks of the SOM fractions in a Neossolo Quartzarênico in Petrolina – PE, Brazil, in two consecutive years (2014 and 2015), soil samples were collected in the 0–0.1 and 0.1–0.2 m layers in areas under irrigated mango (planting row and interrow) and Caatinga (taken as reference). The following variables were determined: contents of total organic carbon (TOC); carbon associated with humic substances – HS (fulvic acid fraction – FAF, humic acid fraction – HAF and humin fraction – HF); carbon associated with light fraction (LtF) and heavy fraction (HvF); and labile C (LC). Samples were collected to determine soil density, and the stocks of TOC and C associated with SOM fractions were calculated. Irrigated mango cultivation (soils collected in the row) led to higher stocks of TOC, C of HF and HS, compared with the Caatinga in both years evaluated. Irrigated mango cultivation (soils collected in the row) also resulted in increase in the stock of C in LtF in the 0–0.1 m layer in 2014. In the second year of evaluation, irrigated mango cultivation (soils collected in the row) caused increments of 26.09 and 35.29% in the TOC of the 0–0.1 and 0.1–0.2 m layers, respectively. There were no differences in the C of HS in the soil along the row of irrigated mango trees in the 0-0.1 and 0.1–0.2 m layers between 2014 and 2015. On the other hand, for soils of the interrow of irrigated mango, the C stocks of HS, HF and HvF were lower in 2015 than in 2014. In the semiarid climate and fragile soils, the increase in C stocks of SOM fractions is more limited to the row of irrigated mango, compared with the Caatinga.