Akademik Veri Yönetim Sistemi
ACTA AGRICULTURAE SCANDINAVICA SECTION B-SOIL AND PLANT SCIENCE, cilt.57, sa.4, ss.357-364, 2007 (SCI-Expanded)
Soil phosphorus ( P) fractions can be used as indicators for short- and long-term P availability. The labile organic and inorganic P concentrations are critical sources of P in agroecosystems, representing an active reservoir ( source and sink) of P. The less available P pools ( other than residual P) may be better measures of potentially plant available P, since these pools represent the soil P reservoir that can re-supply labile pools over time. Little information exists on P pools in soil orders under indigenous vegetation in semi-arid climates in Turkey. Our objective was to assess short- and long-term plant availability of P over depth in the soil profile using chemical P fractionation. Soil samples were collected of different horizons in the profile from each of four major soil orders: Mollisol, Entisol, Inceptisol, and Aridisol. Samples were analysed using sequential fractionation to obtain seven P pools. In order of decreasing plant availability the seven pools are: resin extracted inorganic P ( resin-Pi), inorganic and organic P extracted by sodium bicarbonate (NaHCO3-Pi and NaHCO3-Po), inorganic and organic P extracted by sodium hydroxide ( NaOH-Pi and NaOH-Po), sulphuric acid extracted inorganic P (H2SO4-Pi), and P measured by a sulphuric/peroxide digestion (residual-P). Topsoil contained greater amounts than deeper layers for all P fractions except residual- P. Total P levels in Aridisol were considerably higher than in the Mollisol and Inceptisol and lowest in the Entisol. The Mollisol had the highest concentrations of labile inorganic P (sum of resin-Pi, NaHCO3-Pi). For the surface horizon, labile organic and inorganic P concentrations combined ( sum of resin-Pi, NaHCO3-Pi and NaHCO3Po) were highest in the Mollisol, followed by the Inceptisol and Aridisol with similar levels, and the Entisol with the lowest amount of labile P. Independent of soil order, higher concentrations of NaOH-Po and NaHCO3-Po occurred in the topsoil consistent with greater organic matter levels in the surface horizons. The largest pools of NaOH-Pi and H2SO4-Pi were found in the rooting zones of the Aridisol, followed by the Inceptisol, Mollisol and Entisol. Residual-P amounted to 19-26% of total P in the Mollisol, 32-51% of total P in Aridisol, 30-34% in the Inceptisol and 39-54% in the Entsiol with a higher percentage in the deepest horizons for each of the soil orders. Our results suggest that the readily plant available soil P pools of Mollisol are sufficiently large to support crop production. On the other hand, in the Aridisol, Inceptisol and Entisol the labile P pools are small. In the Aridisol, re-supply from more stable P fractions (NaOH and H2SO4-Pi) might contribute to P availability over time. However, in the Inceptisol and Entisol, re-supply of the labile P fraction from the more stable pools will not be sufficient given small pool sizes, and so regular P applications will be needed to sustain crop production for these soil orders.