Variação de atributos do solo sob sistemas agroflorestais

Abstract

The agricultural and livestock farming activities when disordered and intensive can cause degradation of the physical, chemical and biological soil properties. In this sense, conservationist systems of exploitation of natural resources have been important for providing the maintenance or increasing of soil quality, the example of agroforestry systems, characterized primarily by a combination of agricultural and forest species with agricultural crops and/or livestock activities. Thus, this study aimed to assess changes in chemical, physical and biological soil attributes in different periods and forest systems. For this, soil samples were collected in layers from 0 to 0.10; 0.10 to 0.20 and 0.20 to 0.40 m in an experiment located at the Research Center of Cocoa Farming – CEPLAC, in Alta Floresta – MT, in eutrophic Red-Yellow Utisol, clay loam texture. For this study, it was considered an experimental randomized block design in a subdivided plot arrangement 5x2, with four replications, with five forestry systems (native forest; Theobroma grandiflorum + Swietenia macrophylla; Theobroma grandiflorum + Tectona grandis; Theobroma grandiflorum + Cedrela fissilis; Theobroma grandiflorum + Schizolobium amazonicum) and two periods (rainy and dry season). In the soil samples were determined: pH, components of soil sorption complex, phosphorus (P), organic carbon (TOC) and organic matter (OMS), nutrient stocks, density, macro and microporosity, total porosity, aggregate stability, microbial biomass carbon, basal respiration, metabolic quotient and microbial quotient. In relation to the chemical attributes, the forest systems had little influence on soil acidity in which it was not harmful to crops. There was seasonality in TOC and OMS in the native forest and intercropping systems of Theobroma grandiflorum with Swietenia macrophylla and Cedrela fissilis, with the highest values found in the dry season. The highest levels and base and phosphorus stocks were found in the rainy season due to the effect of the decomposition of OMS in this period. The intercropping systems had lower soil base levels than the native forest, despite this, there was no change in the saturation of soil bases. The intercropping system between Theobroma grandiflorum + Schizolobium amazonicum had higher level and P stock in the soil in relation to other systems. Regarding the physical attributes, it was found that no intercropping system maintained the similar properties to the native forest, as well as, there was no difference between these. Nevertheless, the physical attributes of intercropping systems were not limiting to the development of the species. The native forest and the intercropping between Theobroma grandiflorum + Swietenia macrophylla stood out as the microbiological soil attributes, they were the most efficient in incorporating carbon to microbial biomass with lower metabolic quotient rates. In contrast, the system with Theobroma grandiflorum + Schizolobium amazonicum was the less efficient, with greater metabolic quotient. For all systems, there was reduction of biological activity in the dry season. In general, during the rainy season, highest values of nutrients were obtained. The SAF in the initial conditions of evaluation, seven years, showed satisfactory results, providing evidence that a temporal evaluation for the same period would fit more obvious results.