Fertilidade do solo em sistemas agroflorestais com palma de óleo na Amazônia.

Abstract

The oil palm (Elaeis guineensis Jacq.) is an oil palm widely cultivated in tropical regions and of great economic importance, commonly used in the food, cosmetics and biofuel industries. The cultivation of this palm tree in the Amazon has been carried out mostly in the conventional way (monoculture). However, the intensive use of this practice can lead to biological, physical, and chemical soil degradation. Agroforestry systems (AFS) with oil palm associated with conservationist management practices have been proposed as a more sustainable alternative to monoculture. The objective of the study was to evaluate if the oil palm agroforestry systems and management practices affect soil fertility. The study was conducted in the municipality of Tomé-Açu, Pará, in three experimental sites (Sites 1, 2 and 3) of the Oil palm-FSAP project. In each site there were two types of agroforestry systems with oil palm: 1) less biodiverse SAF (oil palm + legumes); and 2) more biodiverse SAF (oil palm + fruit and timber species). In Site 2, a fragment of secondary forest was selected as reference area (FLO) for comparison of soil fertility with the SAFs. Four random plots were established in each system. In the SAFs, soil samples in layers 0-5, 5-10, 10-20, 20-30, 30-50, 50-70 and 70-100 cm were collected in specific locations within each plot (management zones): crowning (ACP), carriage (CAR), stacking (PIL) and diversified strip (DIV). In the forest, we demarcated a random point per plot for soil sampling in the same layers as the crops. We evaluated the effects of the systems (SAFs and FLO) in the arable layer (0-20 cm) and in layers along the soil profile (0-5, 5-10, 10-20 and 20-30 cm) on chemical attributes: active acidity (pH), calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), aluminum (Al), organic matter (MO), potential acidity (H+Al), potential cation exchange capacity (CTCpH 7), effective cation exchange capacity (CTCe) aluminum saturation (m%) and base saturation (V%). The variability of fertility parameters of the different management zones in the SAFs up to the 100 cm soil layer was also evaluated. In general, the acidity in the cultivated soils was statistically lower compared to that in the forest, both for the arable layer and the stratified layers. In the 0-20 layer, the pH was approximately 20% higher in the crop soils than in the forest. The nutrient contents (Ca, Mg, K, and P) in the soil from the crops were statistically significantly higher than in the forest. The increases were 290, 280, 80 and 800%, respectively. The V (%) was on average 212% higher in the crops than in the forest. The management zones ACP, DIV and PIL presented in general fertility levels similar to each other when compared to CAR, mainly in the superficial layers. Liming, fertilization with mineral and organic sources and maintenance of organic matter.