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ABSTRACT:The use of fire to prepare agricultural areas is a technique still used by small farmers in eastern Amazon. This type of management changes the dynamics of soil nutrients, especially phosphorus, which constitutes the most limiting nutrient for crop production in tropical soils. This study was carried out to evaluate changes in phosphorus forms in an Argissolo Amarelo Distrófico (Ultisol) submitted to burning and trituration of secondary forest in eastern Amazon. The evaluated systems were: slashand-burn of vegetation; slash-and-mulch of vegetation; and secondary vegetation. The labile, moderately labile, moderately recalcitrant, available and total phosphorus fractions were assessed at the soil depths of 0.00-0.05, 0.05-0.10 and 0.10-0.20 m. The results showed a predominance of soluble P in acid (moderately labile P) over other forms in all management systems. The management systems influence the content and distribution of the forms of P, where the slash-and-mulch system presented the prevalence of the labile fraction, and the slash-and-burn system contained less labile forms. The slashand-mulch system favored the accumulation of labile P and total organic P.

The different tillage systems interfere with soil chemical attributes mainly due to the site of preparation techniques. The aim of this study was to determine, in two time evaluation periods, the changes in soil chemical attributes affected by three tillage systems in Yellow Oxissol. The experimental design consists of a randomized block design, with split-plot (Soil Tillage systems X Depths samples) with 3 repetitions in two evaluation periods (2009 and 2012). The treatments consisted of three tillage systems, being Conventional Tillage (CT); No-Tillage (NT) and Reforestation with Paricá (RP). The two depths sampled were 0-0.1 m and 0.2-0.3 m. The attributes were evaluated as pH, organic matter, macronutrients levels, exchangeable acidity and micronutrient level. The soil tillage systems significantly affected the soil chemical attributes. In the NT system, the chemical attributes Ca, Mg, MO, P, K, Mn and Zn are concentrated on the most superficial layer of the soil, whereas in the CT there is a distribution of these variables along the topsoil.

SEM RESUMO