Avaliação de fatores microbiológicos do solo e dos efeitos da adubação com magnésio em clones de seringueira em Manaus, Amazonas

Abstract

Native to the Amazon region, the rubber tree [Hevea brasiliensis (Willd. ex Adr. de Juss.) Muell. - Arg.] Is the main source of natural rubber. Its characteristics confer superiority in quality against the synthetic product, combining plasticity, impermeability, electrical insulation, resistance to friction and versatility of applications. Aiming to make possible the expansion of cultivated areas in Brazil, which was already the largest producer of natural rubber, studies with genetic improvement to obtain clones more resistant and productive have been carried out. However, it is of fundamental importance that the principles of plant mineral nutrition be considered throughout this process. Magnesium, for example, is an essential element for the growth and development of plants, also acting in defense mechanisms in situations of abiotic stress. In this sense, the present study aimed to evaluate the dry rubber production of three rubber tree clones and to study the effect of the application of magnesium on soil productivity and biological attributes. The experimental planting of rubber tree is located in the experimental station of the Brazilian Agricultural Research Corporation – Embrapa CPAA, Manaus – AM. It consists of clones originating from interspecific crosses with approximately 20 years of age. The evaluations in the area were carried out during the period from November 2017 to July 2018 and fertilization consisted in the application of increasing doses of Mg (20,25; 40,50 and 81 g plant–1 ) in the clones, with the dose of 40,50 g treatment control. The panels were stimulated over a period of 2 months, and then the application of Ethrel was started quarterly for the beginning of quantification of dry rubber. The production record per clone was performed through the mass of latex coagulated in the bowls, which after natural drying had their dry mass measured. Latex physiological parameters were analyzed: concentrations of sulfur (R– Sh), inorganic phosphorus (P), sucrose (Sac), lutoids rupture index (IRL), magnesium (Mg). The experimental data were analyzed in randomized blocks, with 3 blocks, and submitted to analysis of variance. For the determination of the microbial biomass (BMC), basal respiration (RB) and metabolic quotient (qCO2), the soil was collected in depth of 0 – 20 cm with the aid of Dutch soil and processed in the field in a 4 mm and packed in plastic bags. The experimental data were analyzed in randomized blocks, with 4 blocks, and submitted to analysis of variance. Significant correlations were observed between variables related to dry rubber production (inorganic phosphorus and thiols) and latex flow (sucrose and magnesium concentrations) at the 81 g plant–1 dose for the CPAA clone C01. Regarding the microbiological analyzes, it was observed, through the values of qCO2, that the CPAA C01 clone presents a higher balance and lower CO2 loss to the atmosphere compared to the CPPA C06 and CPAA C45 clones. In the evaluated experimental conditions, the application of magnesium sulphate as an isolated factor did not affect the dry rubber productivity of the studied rubber tree clones, however, it is a necessary practice for the replacement of the nutrients removed from the soil when the rubber tree is harvested.