Carbon stock assessment and comparison in soybean plantations in Southwest Brazilian Amazon

Abstract

A significant proportion of deforestation in the Amazon rainforest is for the expansion of agriculture and livestock. Several studies have been dedicated to determining the carbon stock in natural forests, however agricultural areas are still poorly researched. This work aimed to quantify the above and belowground carbon stock (CS) in soybean plantations in the State of Rondonia, Southwest region of the Brazilian Amazon, as well as to compare the results with the estimate of other possible land uses in the same region. Thus, a total of 50 sampling units 1 m² were quantified at random in order to measure aboveground and belowground biomass. The total biomass found was 7.55 Mg ha-1, with 6.73 Mg ha-1 (89.14%) corresponding to aboveground biomass and 0.83 Mg ha-1 (10.86%) corresponding to belowground biomass. The average total carbon stock was 3.49 Mg ha-1, ranging from 2.14 Mg ha-1 to 6.36 Mg ha-1. In comparing the study data with the Brazilian Inventory of Anthropic Emissions and Removals of Greenhouse Gases, it was observed that the change in the use of the mature Amazon Rainforest land for soybean cultivation resulted in the loss of 176.61 Mg ha-1 of C. Therefore, soybean cultivation can be an alternative in the absence of natural vegetation with no possibility of natural recovery, because in addition to grain production, it contributes to the carbon stock and nitrogen fixation in the soil. However, replacing natural vegetation is not an adequate practice for biomass and carbon stocks.