Biomassa comercial, estoque de carbono e nitrogênio em plantio de Ilex paraguariensis com plantas de cobertura do solo no sul do Brasil

Abstract

Yerba mate (Ilex paraguariensis) is an endemic tree species in South America and is the primary non-timber forest product in the economy of the southern region of Brazil. Despite the importance of cultivation, there is still a scarcity of technical information for the nutritional management of yerba mate due to the frequent and intermittent harvesting periods, requiring a balanced soil-plant system to meet the plant's demand. The use of cover crops represents a highly advantageous management strategy for yerba mate cultivation, considered a sustainable alternative. These plants perform multiple functions in the soil, as their residues contribute to improving soil physical quality, nutrient cycling, and organic matter formation through decomposition. Additionally, cover crops contribute to carbon sequestration, playing an important role in mitigating greenhouse gas emissions. The objective of this study was to quantify biomass and estimate carbon and nitrogen stocks in the soil-plant system of seven-year-old Ilex paraguariensis under two soil cover conditions: forage peanut and spontaneous vegetation, with no fertilization or soil mobilization. The Ilex paraguariensis plantation was established in 2014 with a spacing of 2.0 x 2.5 m in the experimental area of the Soil Department at the Federal University of Santa Maria, on an Argissolo Vermelho-Amarelo Distrófico abrúptico (Utisol). The study was divided into two articles. The first article evaluated I. paraguariensis biomass (commercial and residual) and carbon and nitrogen stocks in compartments - leaf (LF), fine branch (FB), thick branch (TB), stem (ST), coarse roots (CR), fine roots (FR) of the cover crops (forage peanut and spontaneous vegetation), in above-ground and root (up to 0.10 m) parts, and the soil in layers up to a depth of 1 m. These evaluations were conducted in two harvests, referred to as "off-season" (Dec. 2021) and "main season" (Jul. 2022). The second article focused on the soil, the relationship of particulate and mineral-associated organic carbon (OC) and nitrogen (N) fractions with the physical-hydraulic behavior of an Argissolo Vermelho-Amarelo Distrófico abrúptico (Utisol), with I. paraguariensis cultivation under two soil cover conditions. The results showed that cover crops influenced the commercial biomass quantity of yerba mate, with forage peanut being a viable alternative efficient in biological nitrogen fixation, as observed by the nitrogen percentages in plant compartments. In this condition, the average value exceeded 4 kg of fresh commercial biomass yerba mate individual. In the soil, there was no significant difference in carbon and nitrogen stocks, except in the 0-10 cm e 0-30 cm layer during the main season. In the study of the relationship between particulate and mineral-associated C and N fractions with soil water retention curve (SWRC) parameters, direct correlations were not observed. Furthermore, in the soil condition with spontaneous vegetation as cover for I. paraguariensis (Ip-V), physical conditions, soil density, and porosity were superior compared to I. paraguariensis with forage peanut (Ip-F). It is noteworthy that in this study, soil was evaluated only once in December 2021 (off-season), highlighting the importance of more frequent long-term assessments. Overall, forage peanut is an excellent cover crop for Ilex paraguariensis cultivation, contributing to above and below-ground biomass.