ABSTRACT This study evaluated soil chemical and isotopic changes in soils of a chronosequence rainforest-sugarcane-pasture in the Atlantic Forest biome, Brazil. Soil samples were collected (0-20 cm) in areas of native Brazilian Atlantic rainforest, sugarcane plantation and pastures of Brachiaria decumbens. The soil analyses performed were: pH (water 1:2.5), P (Mehlich-I), (Al+3, H+Al, K+, Ca+2, Mg+2 and Na+), soil organic matter (SOM), N, organic carbon and δ13C and δ15N stable isotopes. The conversion of rainforest to sugarcane and pastures resulted in a reduction of the soil natural acidity. Forest areas had greater Al+3 and H+Al concentrations than cultivated areas. The conversion from forest to agricultural soil reduced Al+3 (44%) and H+Al (11%), approximately. Soils from pasture had a greater percentage of base saturation (37.3%) than forest soils (25.4%). Cation exchange capacity was strongly influenced by concentrations of K+, Ca+2 and Mg+2, but not by Na+. Carbon stable isotope (δ13C) was more depleted in forest areas (-28.14‰), followed by sugarcane (-21.33‰), and pastures (-19.54‰). The greatest δ15N values were found in sugarcane areas. The short chronosequence studied, had a strong influence of the conversion of the forest on the decrease of the natural acidity and modifications of the isotopic profile. The enrichment of soil δ13C was attributed to the changes from predominant C3 vegetation to C4 grasses.

ABSTRACT The objective was to evaluate the effect of three stocking rates (2, 3.9, and 5.8 animal units ha−1) and three fertilization levels (0, 150, and 300 kg N ha−1 yr−1) on herbage mass and nutritive value of elephantgrass (Pennisetum purpureum Schum.) cv. IRI-381. The experiment was conducted from May to August of 2009 and 2010 in Itambé, PE, Brazil, during the rainy season. Treatments were allocated in a split-plot arrangement in a completely randomized block design. The variables measured included leaf mass (pre- and post-grazing), botanical composition, soil cover, leaf area index, light interception, leaf angle, and concentrations of dry matter, organic matter, N, and in vitro digestible dry matter. When fertilized with 300 kg N ha−1 yr−1, leaf mass reached 18,560 kg ha−1. Leaf area index decreased with increasing stocking rate. The relationship between sward height and light interception was R2 = 0.0126. Increased stocking rate resulted in greater contribution of signalgrass [Brachiaria decumbens (Stapf.) R.D. Webster] in the botanical composition, with a contribution up to 29% in 2010. Elephantgrass nutritive value is directly affected by the fertilization levels and stocking rate, with highest nutrient concentrations observed with 2 AU ha−1 and 300 kg N ha−1 yr−1.