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Phosphorus status and cycling in native savanna and improved pastures on an acid low-P Colombian Oxisol

Oberson, A. ; Friesen, D.K. ; Tiessen, H. ; Morel, C. ; Stahel, W.

In: Nutrient Cycling in Agroecosystems, 1999, vol. 55, no. 1, p. 77-88

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    Titre
    • Phosphorus status and cycling in native savanna and improved pastures on an acid low-P Colombian Oxisol
    Auteur
    • Oberson, A.. Swiss Federal Institute of Technology (ETH), Institute of Plant Sciences, Plant Nutrition Group, Eschikon 33, 8315, Lindau, Switzerland
    • Friesen, D.K.. International Fertilizer Development Center, PO Box 2040, 35662, Muscle Shoals, AL, USA; and
    • Tiessen, H.. Department of Soil Science, University of Saskatchewan, S7N 0W0, Saskatoon, Canada
    • Morel, C.. Department of Soil Science, University of Saskatchewan, S7N 0W0, Saskatoon, Canada
    • Stahel, W.. Swiss Federal Institute of Technology (ETH), Statistics, 8092, Zürich, Switzerland
    Type de document
    • Postprint
    Langue
    • Anglais
    Publié dans
    • Nutrient Cycling in Agroecosystems, 1999, vol. 55, no. 1, p. 77-88. Kluwer Academic Publishers
    Autre version électronique
    Identifiant OAI-PMH
    • oai:doc.rero.ch:317082
    Summary
    On acid low-phosphorus (P) Colombian Oxisols, improved pastures with acid-soil-tolerant grass and legume varieties have increased beef production by a factor of 10 to 15 with only modest P fertilizer inputs. This indicates that the efficiency of P fertilization could be greater than is commonly expected on such strongly P-sorbing soils. To understand the effect of improved pastures on P cycling and availability, we estimated P budgets, and characterized soil P by sequential fractionation, isotopic exchange and biological activity measurements on soil samples from unfertilized native savanna, and fertilized improved grass-only (Brachiaria decumbens cv. Basilisk) and grass-legume (B. decumbens + Pueraria phaseoloides, Kudzu) pastures established in 1978 on a medium-textured isohyperthermic, tropeptic haplustox. Comparison of calculated P budgets, based on inputs and exports, with total soil P contents showed that fertilization, as part of the improved pasture management, had resulted in a measurable increase of total P in the surface 0-20 cm soil layer of nearly 30 mg kg-1 or about 20% over the savanna level. Sequential soil P fractionation of different seasonal samplings indicated that grass-legume maintained higher organic and available inorganic P levels with less temporal variation than the two other types. The linkage of organic P and available P was also reflected in soil biological activity. Estimates of P in microbial biomass and phosphatase activity were significantly higher in grass-legume than grass-only and savanna. The improvement in soil P availability, as measured by solution P concentration, P sorption and exchangeable P, was much greater in grass-legume than in grass-only. With comparable fertilizer inputs and greater product exports, improved P availability in grass-legume cannot be due to differences in budgets but can be attributed to changes in the overall biological activity in the soil-plant system caused by the presence of legumes in the vegetation cover. Total C, organic P content and macrofaunal activity were all significantly higher in grass-legume soils. Greater turnover of organic litter in grass-legume may provide for steadier organic P inputs and, therefore, higher P cycling and availability