Adição de esterco e pedoturbação em pastagens do noroeste do Rio Grande do Sul

Abstract

Cattle farming is one of the main agricultural activities in the country, playing a fundamental role in the primary economy, based on pasture food. The inappropriate use of these areas has been one of the main causes of the decline in the natural fertility of these soils, with more than half of Brazilian pastures, both native and cultivated, suffering some type of degradation. Thus, we sought to assess whether the decomposition of bovine manure improves the biological, physical and chemical properties of the soil in two pasture areas in the northwest region of Rio Grande do Sul, in the year 2019. The research used a hypothetical-deductive approach method, method of statistical procedure, with experimental research in the field, of quantitative character and technique of intensive direct observation, observation in the field and laboratory. Two experiments were implemented, one in annual pasture with grazing and the other in perennial pasture without grazing. The experiments were conducted in a randomized block design, with 3 treatments and 7 repetitions, totaling 21 experimental units of 2 m². The treatments used were: (SES) original condition of the area without the addition of manure; (ES) application of a 5 cm layer of fresh bovine manure; (ET) application of a 5 cm layer of fresh bovine manure and placing a protective screen against the entry of soil macrofauna. For biological analysis of the edaphic macrofauna, the TSBF method (Tropical Soil and Biology Fertility) was used, the chemical indicators analyzed were pH, P, K, MO, Ca, Mg, H + Al, CTCef, CTCp and base saturation and the physical indicators evaluated were density, total porosity, macroporosity, microporosity, degree of compaction and stability of aggregates in water. The grazing annual grazing area had an average biodegradation of 78% of the manure, showing improvement in the biological quality of the soil with an increase in individuals from the group of Coleoptera, Armadilidiidae, Oligochaeta and Mollusca, chemical improvement through the increase of nutrient contents such as P and K, and in the soil structure by decreasing the density and degree of compaction, and increasing the porosity of the soil in layers between 10 and 20 cm in the ES and ET, however, the layers of 5 to 20 cm showed high rates of degree of soil compaction in all treatments, verifying that animal trampling raises the degree of soil compaction to critical levels, decreasing their macroporosity. The biodegradation of 100% of the manure in the experiment in an area of perennial pasture without grazing, showed in ES and ET a greater number of individuals from the group of Coleoptera, Armadilidiidae and Oligochaeta, increased levels of nutrients P, K, Ca and Mg, and pH levels and base saturation and reduction of H + Al and effective CTC levels, in addition to an increase in macropores in the 0 to 5 cm layer. It is concluded that bovine manure improves chemical, physical and biological properties of soils of perennial and annual pastures, mainly with an increase in beneficial macrofauna, nutrient levels in the soil, and reduction of the degree of compaction and an increase in the amount of macropores.