Abstract
The objective of this study was to evaluate soil structure alterations that occurred in a typical Red distroferric Latossol under different grazing systems. In 2004, soil samples from three depths (0-2 cm, 2-7 cm, and 30-35 cm) were collected in a farm owned by the College of Veterinary of the Federal University of Goias, Goiânia, Goias State, Brazil, as it follows: I) soil under pasture with Panicum maximum cv. Tanzania, in a rotational grazing system, clump position (“C”); II) soil under pasture with Panicum maximum cv. Tanzania, in a rotational grazing system, among clumps position (“AC”); III) soil under pasture with Cynodon dactilum cv. Tifton 85, in a continuous grazing system; and IV) soil under Savannah, as reference. The implantation of pastures with Tifton 85 and Tanzania grasses changed physical properties of the soil, through the reduction of macropores (MAC) and increase in soil density (SD). Soils under pastures with Tifton 85 and Tanzania grasses (“C” position) presented larger mean geometric diameter (MGD), if compared to the soils under Savannah and pasture with Tanzania grass (“AC” position). Alterations in soil structure were more significant in the topsoil layer (0-2 cm and 2-7 cm depth). Stocking rates practiced in the pastures with Tifton 85 and Tanzania grasses were excessive and also the main reason for deteriorating physical soil properties. KEY-WORDS: Cynodon dactilum ; Panicum maximum ; continuous grazing system; rotational grazing system; stocking rate.
Highlights
Grasslands cover approximately 19.4 out of 34.1 million hectares of farming soil in the Goiás State (Cózer et al 2001)
In 2004, soil samples from three depths (0-2 cm, 2-7 cm, and 30-35 cm) were collected in a farm owned by the College of Veterinary of the Federal University of Goiás, Goiânia, Goiás State, Brazil, as it follows: I) soil under pasture with Panicum maximum cv
Not measured in the present study, the reasonable explanation for the low MAC value in those soils is the lower quantity of roots, resulting in less accumulation of organic carbon, which plays a major role in the formation and stabilization of macroaggregates, since it is known as an efficient cementing agent (Campos et al 1995)
Summary
Grasslands cover approximately 19.4 out of 34.1 million hectares of farming soil in the Goiás State (Cózer et al 2001). Pastures degradation has reached around 8 million hectares in the Goiás State (Goiás 2003), basically due to inadequate management. The adoption of inadequate grassland management implies in losses of physical quality of the soil, for medium and long terms, hindering the growth of roots, air circulation, and water infiltration (Carvalho Júnior et al 1998, Bertol et al 2000, Fregonezi et al 2001, Müller et al 2001). The pressure from grazing animals can reach up to 350-400 kPa (Betteridge et al 1999) and cause changes in density and porosity of the soil, especially in the first 3-6 cm depth (Gradwell 1960, Chancellor et al 1962, Gradwell 1966, Bertol et al 1998). One of the strategies that have been used to recover degraded pastures is the rotational grazing system, where fertilizations are a common practice and even irrigation, during the dry season, has been recommended (when this facility is available), Lima et al (2004) have reported that compaction and soil density, in a rotational grazing system pasture under irrigation, increases, if compared to the same pasture without irrigation
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