83 research outputs found
Reduction of the frequency of herbaceous roots as an effect of soil compaction induced by heavy grazing in rangelands of SW Spain
Rangelands in SW Spain constitute the most extensive ranching system on the Iberian Peninsula. During the last few decades, a significant increase in livestock numbers, along with a progressive substitution of cattle for sheep, have led to land degradation processes such as the reduction of grass cover and increased soil compaction in heavily grazed areas. Nevertheless, a better understanding of how soil compaction affects grass production is still needed. In this study, some of the effects of soil compaction due to heavy grazing are analysed, mainly the reduction of the frequency of herbaceous roots and its relationships with bulk density and soil penetration resistance. The study was carried out in 22 fenced areas grazed under different intensities (animal stocking rates: 0.19-15.76 AU ha−1). Undisturbed soil core and bulk samples were collected at 3 depth intervals in order to determine select soil properties (texture, organic matter content, and bulk density). Additionally, soil penetration resistance was quantified at 890 random points at different depths and soil moisture contents. Frequency of herbaceous roots was estimated for each soil horizon in 47 soil profiles and categorized into 4 classes: none, few, common and many. Results showed negative relationships between bulk density (> 10 cm depth) and the content of soil organic matter from 0 to 5 cm (r =−0.061, p < 0.05) and 5-10 m depth (r = −0.824, p < 0.005). Furthermore, a tendency for decreasing mean values of soil penetration resistance as the frequency of herbaceous roots increased was also observed. The values observed confirm that soil compaction provoked by an excessive number of animals reduced the quantity of herbaceous roots. The value of 2 MPa traditionally accepted as restrictive for root growth is discussed. Findings presented here could be of interest for policy makers and farm owners to guide decisions about optimum animal stocking rates
The effect of pulsation on liquid-liquid mass-transfer resistances /
"AEC Research and Development Report""Chemistry - General.""July, 1958."Bibliography: p. 81-82.Operated by The University of ChicagoMode of access: Internet
Costs, Revenue, and Profit/Loss Patterns for HIV-Seropositive Patients in a Municipal New York City Hospital
Optimization study of biosorption of toxic metals from mining wastewater using Azadirachta indica bark adsorbents
Regulation of the Phosphotyrosine Content of Human Sperm Proteins by Intracellular Ca2+: Role of Ca2+-Adenosine Triphosphatases1
Superactivated Charcoal Versus Cholestyramine for Cholesterol Lowering: A Randomized Cross-Over Trial
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