Nutrient Cycling in Agroecosystems

, Volume 55, Issue 1, pp 77–88

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

  • A. Oberson
  • D.K. Friesen
  • H. Tiessen
  • C. Morel
  • W. Stahel
Article

DOI: 10.1023/A:1009813008445

Cite this article as:
Oberson, A., Friesen, D., Tiessen, H. et al. Nutrient Cycling in Agroecosystems (1999) 55: 77. doi:10.1023/A:1009813008445

Abstract

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.

acid low-P soilsimproved pasturesP budgetP cyclingsoil P fertility

Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • A. Oberson
    • 1
  • D.K. Friesen
    • 2
    • 3
  • H. Tiessen
    • 4
  • C. Morel
    • 4
  • W. Stahel
    • 5
  1. 1.Swiss Federal Institute of Technology (ETH)Institute of Plant Sciences, Plant Nutrition GroupLindauSwitzerland
  2. 2.International Fertilizer Development CenterMuscle ShoalsUSA; and
  3. 3.Centro Internacional de Agricultura Tropical CIAT, A.ACaliColombia (former address)
  4. 4.Department of Soil ScienceUniversity of SaskatchewanSaskatoonCanada
  5. 5.Swiss Federal Institute of Technology (ETH), StatisticsZürichSwitzerland