Atributos e estoque de carbono do solo em sistemas de manejo do solo no município de Paragominas-PA-Brasil.

Abstract

The Amazonian soüs have a high degree of weathering which causes low fertxlity. Whereas soil is the basis for sustainable agriculture, it becomes necessary to adopt management practices that conserve and, or, restore their fertility. This work aimed to evaluate the chemical and biological attributes, the contents and fractions of carbon and nitrogen in the soil, in an Oxisol Yellow dystrophic, cultivated under tillage and conventional tillage. An experiment was conducted under field conditions in the experimental area of Embrapa Amazônia Oriental in the municipality of Paragominas-PA. The experimental design was made in randomized blocks, factorial 2x5 with three replications. The experiment consisted oftwo collection periods before (November-2010) and after (May-2011) the cultivation of com and five land use systems, conventional tillage (PC), three direct planting (PD), in rotation scheme and secondary forest (FS). Data analysis was performed using the sxgmaplot program version 11.0. The normal distribution and homogeneity of variances for each variable were tested using the Kolmogorov-Smimofftest, itis also was used multivariate analysis in the evaluation of soil fertility. The PC contributed to the reduction of microbial biomass carbon, with lower metabolic quotient. The sample collection periods influenced signifícantly on soil biological attributes evaluated. In the Latossolo that was studied, cropping systems affected the proportions of the fractions of total organic carbon ffom organic matter. The secondary forest showed up in general, quite different with respect to their chemical fertility compared to the areas used for agriculture, being closer to the no-tillage systems in the conventional tillage system. Despite the short time ofimplementing the PD showed better soil fertility when compared to PC.

In the city of Paragominas the Oxisols predominate. These are highly weathered and low fertility when subjected to improper handling and use quickly diminish the productive capacity. Among the soü properties, microhial biomass, basal respiration, metabolic quotient and nücrobial quotient have been presented as sensitive indicators of soil quality. The aim of this study was to evaluate the biológica, attributes, contents of total carbon and nitrogen in the soil for different tillage systems. The experiment was conducted under fíeld conditions in the experimental area of Embrapa Amazônia Oriental in the city of Paragominas-PA. The experimental design was randomized blocks, factorial 2x5, with three replications. The experiment consisted on two collection periods before (November-2010) and after (May-2011) maize cultivation and five land use systems, conventional tillage (PC), three no-tillage (PD), in layout rotalion. We evaluated the total organic carbon (COT), carbon from the soil microbial biomass (C-BMS), basal respiration, metabolic quotient (qCO^) and microbial quotient (qMIC%). We also evaluated the leveis of C and N in the soil. The PC promoted reduction of microbial biomass at ali depths sampled in sampling before planting com. It was observed larger values of qC02 on PC compared to secondary forest. Higher values of NT were found in the collection after the com harvest. The total organic carbon was sensitive, independem ofsoil tillage system.

Fractionation of organic carbon has been used as an indicator of changes in the soil caused by changes in land use and management system. The objective was to determine the fractions of organic carbon and total nitrogen in the soil (free light ffaction, occluded light fraction and the heavy fraction) in soils under tillage (PD), with different systems of crop rotation after maize cultivation. The study was conducted in the city of Paragominas-PA, using an experimental design of randomized blocks, factorial 4x4 with three replications. The factors were four systems of land use (three tillage systems and secondary forest as a reference). Soil samples were collected at 0-5, 5-10, 10-20 and 0-20 cm depth. The soil organic carbon was ffactionated granulometrically. At ali depths smaller carbon stocks were found in the treatments under PD íhan in secondary forest. Nitrogen heavy organic fraction was greater than 85% at ali depths. These results confirm the importance of physical fractions of soil organic carbon, as an indicator of changes in tool use and soil cultivation systems.

The management system affects the chemical properties of the soil, which may have significant effects on plant growth. The study aimed to evaluate the effect of soil tillage systems on the chemical attributes of Oxisol. The study was conducted in Oxisol. Using an experimental design of randomized hlocks with three replications. Two sampling periods were used, five systems of land use (three systems oftillage, conventional tillage and secondary forest as a reference). Soil samples were collected in the 0-5, 5-10, 10-20 and 0-20 cm. Principal components that were huilt from the correlation hetween the fifteen soil variahles studied multivariaíe analysis was used (pH, MO, P, Al, H+Al, K, Ca, Mg, SB, CTCef, CTCpot, V, m, ARE e ARG) being extracted in descending order of importance, considering terms of their contribution to the total variation of the data. The main component explained most of the variation data (49.20%). The principal components analysis provided interpretable components, enabling management strategies, from the establishment of priorities for interventions to be adopted.