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COSTA, N. de L.

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18/07/12 .:: Boletim Pecuário ::.1/2www.boletimpecuario.com.br/artigos/showartigo.php?arquivo=artigo1828.txt&tudo=sim   Artigos Técnicos  PHOSPHORUS CYCLING IN PASTURESThe recycling of phosphorus (P) is related to its stability (low solubility) and its lowmobility in soils. OP is relatively immobile in soil and has no gaseous forms. Removal of Pby cutting and / or grazing is the main source of removing the system, however inpastures and managed through its return organic waste and animal excretions cycleresults in a relatively closed. Due to the high degree of weathering, the tropical Oxisolsand Ultisols have low amounts of available P, with about 60-80% is in organic form.Furthermore, these soils have a high binding capacity of P. HPO4 ions that are releasedby mineralization of organic P or phosphate fertilizers are fixed in forms not readilyavailable or unavailable to plants. Due to the low calcium content and low pH, P mineralform of iron and aluminum phosphates relatively insoluble or soluble under anaerobicconditions (reduced soil). The two main procedures for setting soil P are: 1. Precipitationwith exchangeable Al. By applying the phosphate fertilizer basic cations containedtherein disperses aluminum exchangeable clays, which is hydrolyzed and reacted withHPO4 ions forming insoluble aluminum phosphate, 2. Adsorption of P in particulatesesquioxides. The higher content of oxides of iron and aluminum, the greater the bindingcapacity of P.P inputs to the system - the main source of P to pasture is the mineralization of soilorganic matter. The initial content of organic P, total P, moisture content of organicwaste, temperature and time are factors that determine the degree of net mineralizationof P contained in organic waste and animal. Approximately 3-30% of organic phosphoruscontained in the feces of sheep and 2-5% P contained in the organic waste can bevegetable mineralized. On average, about 77% of P from the litter and 79% of Pcontained in the dead roots, become available for plant growth in the year following itsdeposition. Of total P contained in the shoot of the plant is 60-80% soluble in water andmost are inorganic. In general, only the long-term return through animal manure P willsignificantly its recycling as a result of irregular distribution of feces and low mobility.The occurrence of beetle dung worms and increase the rate of mineralization of thefaeces through its burial in the soil. Phosphorus through the atmosphere (dust) or therain is small, being reported values from 0.04 to 0.6 kg P / ha / year. A similar situationoccurs with the processes of weathering of primary minerals from the soil.Another important mechanism for recycling or incorporation of P in plant-animal system isthe symbiotic association between roots and mycorrhiza. In general, the effects ofmycorrhiza on plant growth is manifested by increased surface area for absorption ofnutrients, and longevity of the root suckers and better use of some forms of nutrientsnot available for the roots colonized. Resaeches in Rondônia demonstrated thatinoculation of Scutellospora heterogama in Desmodium gyroides, Glomus etunicatum inStylosanthes capitata and Gigaspora margarita in Pueraria phaseoloides, provided forageyields similar or higher than those obtained with the application of 50 kg P2O5/ha in theabsence of inoculation. Moreover, the absorption of nitrogen and phosphorus weresignificantly enhanced with mycorrhizal inoculation.Outputs of the system - in well-drained arable land and P losses by leaching orvolatilization is minimal, estimated at 0.3 kg P / ha. No evidence of gas losses P, evenunder anaerobic conditions. Approximately 69-80% of total P plant vegetation can berecycled when it presents itself in a latent or decaying. The intensity and duration ofrainfall and the interval between the senescence of tissues and the first rain affect theamount of P returned to the soil or can be lost through runoff.The higher output of the system due to removal of fodder for the production of hay,silage or green biomass for direct supply to the animals. The removal means is smallanimal products, and reported values of 6.71, 6.76, 4.53 and 1.03 kg of animal product18/07/12 .:: Boletim Pecuário ::.2/2www.boletimpecuario.com.br/artigos/showartigo.php?arquivo=artigo1828.txt&tudo=simp/1000 kg respectively for calves, steers, sheep and cow's milk. In general, the lossesrange 1-10 kg P / ha / year depending on the yield load of pasture and animal used.Work undertaken in the Amazon found that the amount of P exported by cattle grazing,supplied with mineral salt in the trough, represented only 31.53% of the sum of nutrientsin the grass (Brachiaria humidicola) and mineral salt. For an animal productivity of 256 kgliveweight / ha / year, a total of 5.93 kg / ha / year of intake, was 60.88% of themineral and was only 39.12% of the grass, a , 87 kg / ha / year were stocked in theanimal and 4.06 kg / ha / year returned to the soil.Newton de Lucena Costa - Embrapa Roraima - 18 de Julho de 2012 -newton@cpafrr.embrapa.br      

Phosphorus cycling in pastures.

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Phosphorus cycling in pastures.

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