Abandoned pastures in eastern Amazonia. II. Nutrient stocks in the soil and vegetation

Soil nutrient concentration generally was independent of age or prior intensity of use in 13 pastures in the E Amazon near Paragominas, Para, Brazil. Pasture use has a significant effect on soil nutrient concentration when the sites are first abandoned, but this does not persist. Nutrient uptake by successional vegetation may substantially reduce soil nutrient stocks. Nutrient depletion of pastures abandoned 8 yr previously relative to total nutrient stocks in mature forest depended on pasture disturbance. Sites previously subjected to low use were only depleted of N, moderate-use sites were depleted of N and K, and heavy-use sites were depleted of N, K, Mg and possibly Ca and P. There was less nutrient depletion than the relatively small biomass of the successional sites would indicate, due to a higher proportion of nutrient-rich leaves and fine branches, enriched soil nutrient stocks relative to mature forest and, on the lightly disturbed sites, a large pool of nutrients in unburned woody residue. Decomposition of unburned woody residue may provide 50% of the nutrients taken up by vegetation during 8 yr of recovery following light pasture use, but only 15% following moderate use, and none following the most intense use. Recovery after disturbance is complex, and follows different patterns depending on the intensity of pasture use. (See also 90L/00420). -from Authors