Soil shear strength under non-irrigated and irrigated short duration grazing systems

Abstract

Pasture productivity can drop due to soil compaction caused by animal trampling. Physical and mechanical alterations are therefore extremely important indicators for pasture management. The objective of this research was to: draw and evaluate the Mohr failure line of a Red Yellow Latossol under different pasture cycles and natural forest; calculate apparent cohesion; observe possible physical alterations in this soil; and propose a correction factor for stocking rates based on shear strength properties. This study was conducted between March/2006 and March/2007 on the Experimental Farm of Fundação de Ensino Superior de Passos, in Passos, state of Minas Gerais. The total study area covered 6 ha, of which 2 ha were irrigated pasture, 2 ha non-irrigated pasture and 2 ha natural forest. Brachiaria brizantha cv. MG-5 Vitória was used as forage plant. The pasture area was divided into paddocks. The Mohr failure line of samples of a Red Yellow Latossol under irrigated pasture equilibrated at a tension of water content of 6 kPa indicated higher shear strength than under non-irrigated pasture. The shear strength under irrigated pasture and natural forest was higher than under non-irrigated pasture. At a tension of water content of 33 kPa no difference was found in shear strength between management and use. Possible changes in soil structure were caused by apparent cohesion. The values of the correction factor were close to 1, which may indicate a possible soil compaction in prolonged periods of management.

Prediction of soil shear strength in agricultural and natural environments of the Brazilian Cerrado

“…Silva et al (2004) and Carvalho et al (2010) verified that soil use and management can influence cohesion intercept, internal friction angle, and, therefore, shear stress. Larney & Kladivko (1989) reported that shear stress increased in the surface of soils cultivated with moldboard plow.…”

“…The authors reported that higher levels of organic matter, associated with the soil aggregation model, the level of root entanglement in the soil, and with the presence of physical and chemical bonds between particles in native environments, resulted in higher soil aggregation and, therefore, in higher mechanical resistance. However, Carvalho et al (2010) found that irrigated pasture and natural bush have similar shear strength, higher than that of nonirrigated pasture. Moreover, the authors stated that the shear strength of soil samples with lower water content (-33 kPa) does not differ between managements.…”

“…Among these, stand out the evaluation of precompression stress (Silva et al, 2009;Pais et al, 2011;Iori et al, 2012b) and of the shear resistance of soil Carvalho et al, Pesq. agropec.…”

Physical properties of a Red-Yellow Latosol and productivity of a signalgrass pasture fertilized with increasing nitrogen doses

“…The soil of this study was not compacted, as the values found ranged from 0.48 to 0.52 m 3 m -3 in the layer 0-3 cm and from 0.46 to 0.51 m 3 m -3 in the layer 10-13 cm, indicating absence of soil compaction (Table 6). Carvalho et al (2010), working with a Red Latosol pasture cultivated with Brachiaria brizantha cv MG-5 Vitória under animal trampling, obtained a TPV value of 0.48 m 3 m -3 , indicating absence of compaction.…”

“…Soil compaction, characterized by the reduction of the porous space under external soil pressure, can be a major problem in heavily mechanized and/or trampled areas and is one of the key factors associated with soil degradation (Kondo & Dias Junior, 1999;Mosaddeghi et al, 2007;Carvalho et al, 2010;Pires et al, 2012). Soil compaction can result in a reduction in the productivity and longevity of pastures (Imhoff et al, 2000) and accelerate erosion processes (Oliveira et al, 2004).…”