Estoque de carbono e atributos edáficos em áreas de plantios de seringueira (Hevea Brasiliensis M. Arg.), mata e pastagem no Estado do Rio de Janeiro

Abstract

The state of Rio de Janeiro has 8,000 km2 of its area with climatic conditions adequate for rubber tree cultivation. This thesis presents, in three chapters, results about soil attributes, associated with rubber tree clones. In Chapter I, it was evaluated the soil fertility, nutritional status, growth and nutrient cycling in plantations of different clones of rubber tree (FX 3864, FDR 5788, PMB 1, MDX 624 e CDC 312) at seven years of age. The study was developed in the experimental research area of Empresa de Pesquisa Agropecuária do Estado do Rio de Janeiro (PESAGRO), in Silva Jardim municipality, Rio de Janeiro State. The soil nutrient levels were very low. All clones showed levels of macronutrients (N, P and K) below the critical levels. The MDX 624 and CDC 312 clones were better nourished than other clones. The MDX clone showed greater growth in diameter at chest level (DCL). The clones MDX 624, FDR 5788 and CDC 312 presented higher growth in total height (Ht). The litter nutrient contents of the clones followed the order: N > Ca > K > Mg > P. In the Chapter II, the objectives were to quantify carbon stocks in soil and biomass, and to evaluate the dynamics of organic matter in the same rubber tree clone plantations described in Chapter I. The planting of clones showed no difference in the stock of soil carbon at the depth of 0-40 cm, and the average soil carbon stock was 84.6 Mg ha-1. The carbon stock of biomass differed between the clones, the MDX 624 showed the largest stock of carbon in biomass (77.41 Mg ha-1). The average total carbon stock of cultivated areas (soil + biomass) was of 135.5 Mg ha-1. The difference in the amount and composition of litter resulted in changes to content of light organic matter in water and carbon content of humic substances. In Chapter III, the objective was to evaluate soil fertility, nutrient cycling, carbon storage, the dynamics of organic matter and attributes related to soil quality in areas with different usages, that were: one area with two clones of rubber tree (IAN 873 and FX 3864) with 28 years of age; one area of secondary forest; and a pasture with 16 years of implantation, all located in the municipality of Silva Jardim - RJ. The land usage resulted in differences in the following attributes, soil fertility, carbon storage and humic substances of organic matter. The cultivation of rubber tree maintained the carbon levels as originated from the forest and increased the carbon stored in soil to a depth of 0-0.5m. The clones behaved differently regarding to soil carbon storage: clone FX 3864 stocked 90.2 t ha-1 and clone IAN 873 had 101.5 t ha-1 at a depth of 0-0.4 m, being greater than the forest area (93.9 Mg ha-1) and pasture (71.1 Mg ha-1). The pasture presented the highest carbon content of microbial biomass (MBC), microbial biomass nitrogen (MBN) and basal respiration (BSR), but the area showed carbon losses (increased qCO2). The cultivation of rubber tree caused a decrease in the enzyme activity and microbiological attributes (MBC, BSR and qCO2) compared to the area of secondary forest; with the exception for FDA and arylsulfatase enzymes that showed greater activity in the area with rubber tree clones plantations.