Conversão de floresta de pinus em sistema plantio direto: indicadores físicos, químicos e microbianos em latossolo fase cerrado

Abstract

Despite the acknowledgement of the importance of microorganisms to sustain the ecosystem services in soil, there’s little comprehension of the fundamental processes which orient, maintain and affect the microbial diversity in soil and the role of the diversity per se in soil processes, especially due to the alterations in the systems for soil usage and management. The objective of the present study was to verify the interference of the substitution of the pinus forest by the direct planting system throughout the years of the implementation, regarding physical, chemical and microbiologic soil quality indicators, and also the interference in the structure, composition and abundance of microorganisms in yellow very argillaceous acric Latosol, in cerrado stage, in the depths of 0,00 – 0,05 and 0,05 – 0,10 m. To do so, an analysis was performed regarding physical properties (texture, soil density, macro and micropores, and total porosity) chemical properties (pH, P, K, Ca, Mg, Al, (H+Al), COT and N) and microbiologic properties (basal respiration, microbial biomass, metabolic and microbial quotients and activity of the enzymes urease, acid phosphatase, arylsulfatase and β-glycosidase) and also analysis of PCR-DGGE for studies of structure and composition of bacteria, fungi and diazotrophic bacteria. Soil quality is a function integrated by physical, chemical and biological properties. In the conversion of natural areas to pinus forests, these properties were negatively impacted with the reduction of the multinutritional level and soil structure alterations, reflected in lower microbial biomass up to 10cm in deepness. The physical and chemical indicators studied were not sensible to evaluate the impact caused by the conversion of pinus forest in direct planting system of up to the age of 8 years. However, it was confirmed the benefic effect by the adoption of more conservationist systems with improvement of these indicators through the time. The time to implement the direct planting system equal to 12 years was the closest one to cerrado in carbon content and the soil physical characteristics and in microbial biomass and activities as well. The results found in this paper reflect the lower soil quality in soils of areas converted in cultivation systems, but it highlights the importance of adopting a more conservationist system in the long term, such as the direct planting system. The chemical factors analyzed in this study, especially pH, A1 and COT, influenced directly the structure, composition and abundance of bacteria and fungi communities in the depths of 0,05 and 0,10 m.