Plantas de cobertura no manejo de invasoras, no estoque de carbono do solo e na produtividade do guaranazeiro (Paullinia cupana var. sorbilis (Mart.) Ducke)

Abstract

The cultivation of guaranazeiro has economic, social and cultural importance in Amazonas, because it is cultivated on a large scale by family farmers. The seeds after benefited are used in the industry of concentrates, pharmacological and cosmetic. The potential as an agricultural crop and its management as to the control of weeds, provides actions to preserve the agro-ecosystem aiming at a sustainable agriculture. In this sense, the research aimed to evaluate the influence of cover crops on weed management, soil carbon stock and productivity of an agricultural system with guaranazeiro. The experimental design adopted was a randomized block design, with six treatments and four repetitions. The treatments were: T1-Brachiaria ruziziensis, T2-Canavalia ensiformis, T3-Mucuna deeringiana, T4-Arachis pintoi, T5-Weed species with mowing and T6-Weed species in free growth (Witness) evaluated in the years 2018, 2019 and 2020. The characteristics evaluated were: residue decomposition rate, nutrient stocks of the cover plants, percent soil cover, soil carbon stock, nutritional analysis, and guaranazar productivity. The data obtained were submitted to variance analysis and the F test was applied at 5% probability. For continuous variables, regression analysis was applied with the selection of equations that followed the trend of the original data and the highest coefficient of determination. The cover crops presented a high rate of residue decomposition. The legumes (Arachis pintoi, Canavalia ensiformes and Mucuna deeringiana) showed high initial nutrient contents and longer half-life for residue decomposition. The release of P, Ca and Mg was slower from the decomposition of the residues. K showed rapid initial release from decomposition of the cover plant residues. In 2019 and 2020 Brachiaria ruziziensis showed superior results compared to the other treatments, in the production of fresh and dry biomass, suppressing 100% of the weed plants in the two years evaluated. There was no significant difference between the cover species for organic matter, soil carbon and soil carbon stock data in the two years evaluated. In 2019, the cover plants did not affect the nutrient contents of guarana leaves and did not influence the productivity of dry seeds. Therefore, studies related to decomposition of cover plants taking into consideration longer periods, testing the dimensions of decomposition bags and amounts of plant material placed in the bags are recommended. Studies in Amazonian conditions to evaluate the carbon stocks in the soil as a function of the use of cover crops are still needed, observing mainly the research time and depth of soil collection for evaluation of these parameters.