Abstract
Pasture is the main form of land use in Amazonia. Over time the pasture grass loses vigor and yields decrease, indicating a certain degree of degeneration. The main causes of degradation are lack of pasture maintenance and subsequent weed infestation, the choice of regionally unsuitable forage species and excessive grazing. The main purpose of this study was to evaluate the impact of different recovery managements on soil chemical properties and grass yield of a degraded pasture in Rondônia. For this purpose, an experiment was installed in October 2001, consisting of five treatments: C = control; HA = harrowing + NPK + micronutrients; HE = Herbicide + NK + micronutrients; R = No-tillage rice + NPK + micronutrients; and S = No-tillage soybean + PK + micronutrients. The following N, P and K sources were used: ammonium sulfate for N, calcined phosphate for P and potassium chloride for K. The experiment was arranged in a randomized block design with four replications. The shoot dry matter yield of the grass was analyzed as of the 35th month of experimentation, in a dry and a rainy period. Phosphorus fertilization resulted in significant increases in Ca2+ and Mg2+ and increasing trend of P in the topsoil in the initial months of the experiment in treatments HA and S and increases in Ca2+ and P (trend) in the treatment R. The cumulative production of Brachiaria brizantha, from Sep/2004 to Mar/2005, was 30,025, 28,267 and 27,735 kg ha-1 shoot dry matter in the treatments HA, R and S, respectively. These values differed significantly from treatments C and HE, with 17,040 and 17,057 kg ha-1, respectively. It was concluded that phosphorus fertilization associated to pasture reform was effective to raise the dry matter yield of Brachiaria brizantha. Rice or soybean under no-tillage is recommended as a practice of pasture recovery, due to the residual effect of fertilization.
Highlights
IntroductionDeforestation in the Amazon is usually based on the slash-and-burn practice, followed by some years of crop planting and subsequent pasture installation for livestock farming (Fujisaka et al, 1996; Fujisaka & White, 1998; Martínez & Zinck, 2004; Cerri et al, 2007)
The felling of forests in the Amazon region for agricultural or livestock production is still boosting the regional and national deforestation rates, fuelling criticism, mainly internationally, of the loss of rainforest biodiversity, and the contribution to climate change and global warming, among other aspects.Deforestation in the Amazon is usually based on the slash-and-burn practice, followed by some years of crop planting and subsequent pasture installation for livestock farming (Fujisaka et al, 1996; Fujisaka & White, 1998; Martínez & Zinck, 2004; Cerri et al, 2007)
Rice or soybean under no-tillage is recommended as a practice of pasture recovery, due to the residual effect of fertilization
Summary
Deforestation in the Amazon is usually based on the slash-and-burn practice, followed by some years of crop planting and subsequent pasture installation for livestock farming (Fujisaka et al, 1996; Fujisaka & White, 1998; Martínez & Zinck, 2004; Cerri et al, 2007). Burning, considered to be cheap, provides a satisfactory grass yield during the first years of pasture use due to the increased concentration of basic cations from the ashes of the forest Soil fertility tends to decrease with time (Correa & Reichardt, 1995 and Moraes et al, 1996), resulting in loss of grass vigor (Dias & Griffith, 1998) and, after about 5–8 years of grazing activity, weed infestation increases significantly, while forage yield and quality decrease (Buschbacher et al, 1988; Fearnside, 1996). It is estimated that in the Amazon region more than 50 million hectares of forest have been converted into pasture and approximately half of this area is in some stage of degradation
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