Abstract
The objective of this work was to study the effect of grazing systems: rotational, continuous and the absence of cattle, in pastures of Brachiaria brizantha on microbial activity (respiratory, potential nitrification, solubilizing, and enzymatic) and on the chemical attributes (contents of organic carbon, total nitrogen, organic phosphorus, and moisture) of Eutrustox soil over one year. Eight Canchim breed animals were used. The samples were collected in the four seasons from 2005 to 2006. The average of organic C, organic P, and moisture contents, as well as potential nitrification and solubilizing activity and urease and acid phosphatase activities were significantly higher in the spring and/or summer than in autumn and/or winter. The total nitrogen amounts did not vary among seasons. While the respiratory activity was larger during winter and summer, cellulase activity was smaller during spring than in the other seasons. Except for organic P, higher values of the variables studied were observed in the rotational grazing. The results indicate that the hot and rainy season and the rotational grazing system cause increases in the soil microbiological and chemical attributes.
Highlights
Pastures can be considered as permanent crops because they are not submitted to management practices such as those observed for agricultural crops
The aim of the present study was to evaluate the effect of different grazing systems on the microbial activity responsible for the transformation of compounds related to the cycles of C, N and P, as well as on the chemical attributes of the pasture soil during a period of one year
The rotational grazing system has been adopted as the management system since 1997 with the establishment of grass Brachiaria brizantha cv. marandu
Summary
Pastures can be considered as permanent crops because they are not submitted to management practices such as those observed for agricultural crops. The carbon (C) input is higher than in cultivated areas (Schipper & Sparling, 2000). The most important supply of nutrients to the pasture comes from the decomposition of plant residues and animal excreta. An animal excreta is equivalent to 1,200 g of dung and 200 ml of urine (Allen et al, 1996). Mainly via faeces, increase the C input and soil biochemical activities (Haynes & Williams, 1999); have a low C:N ratio, manure is 20:1 and the urine of cattle is 3.9:1, allowing rapid mineralization (Whitehead, 2000); and accumulate in the soil, increasing organic matter stocks (Carran & Theobald, 2000). The effect of these systems on nutrient cycling has rarely been studied. Several microbial and biochemical analyses can be used to assess grazing impact on soil quality (Ingram et al, 2008)
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