Scand. J. For. Res. 14: 538–544, 1999 Phosphorus Solubility in an Acid Forest Soil as Inﬂuenced by Form of Applied Phosphorus and Liming ANN-MARI FRANSSON, BO BERGKVIST and GERMUND TYLER Lund Uniersity, Department of Ecology, Soil – Plant Research, Ecology Building, S -223 62 Lund, Sweden Fransson, A.-M., Bergkvist, B. and Tyler, G. (Lund University, Department of Ecology, Soil – Plant Research, Ecology Building, S-223 62 Lund, Sweden). Phosphorus solubility in an acid forest soil as inﬂuenced by form of applied phosphorus and liming. Received April 21, 1998. Accepted Oct. 26, 1998. Scand. J. For. Res. 14: 538–544, 1999. Sedimentary phosphorus, superphosphate, and wood-ash, as well as either sedimentary phosphorus, superphosphate or ash combined with lime, were distributed in selected plots in an 80-yr-old Norway spruce forest [Picea abies (L.) Karst]. After 2 yrs, the sedimentary phosphorus had increased the oxalate/oxalic acid-extractable P in the O-horizon, and the superphosphate had increased the oxalate/oxalic acid-extractable P in the E-horizon. At ﬁrst, the percolation water from the superphosphate treatment showed high P concentrations. It soon returned to control levels, however. The percolation water from the sedimentary phosphorus treatment gradually showed increased phosphate concentrations. The wood-ash increased neither the amount of extractable P nor the P concentration in the percolation water. The oxalate/oxalic acid-extractable P from the sedimentary P treatment was reduced by liming. The P concentration in the percolation water also tended to be reduced. This was perhaps due to formation of Ca phosphates in the vicinity of the lime particles. In addition, if the solubility rate was similar to the uptake rate, it could account for the decreased P concentration. Key words: extraction, fertilization, liming, percolation water, phosphorus, solu - bility, spruce. INTRODUCTION A high N concentration in soil may induce P deﬁ- ciency in plants (Mohren et al. 1986, Rosengren- Brink & Nihlga ˚rd 1994, Teng & Timmer 1995). Furthermore, the application of P and K may arrest nitrate leaching (Stevens et al. 1993, Harrison et al. 1995). In areas with a high N deposition, it may be necessary to fertilize forest soils with P and K to sustain growth and tree vitality and repress N leach- ing. Many of these areas are acid and subject to liming. However, fertilization or liming should be done in an economical manner, to make sure that the system is not disturbed more than necessary. The efﬁciency of P fertilization is not constant. In one study, fertilization of a forest stand only resulted in a 6% recovery of the added P in the vegetation. The remaining P was retained in the soil (de Visser & van Breemen 1995). As a consequence, the total amount of P is higher in fertilized than in unfertilized soils (Maggs 1988). In another study, however, 47% of the added P was taken up by the trees, although only a small share was easily soluble (Nilsson & Wiklund 1995). After fertilization, there was an im- mediate increase in the soil solution and the soluble inorganic P removed by resin bags (Aarnio et al. 1995), NaHCO 3 -extractable inorganic P (Steffens 1994, Tran & N’dayegamiye 1995) and double-acid- extractable P in the surface soil (Harding & Jokela 1994). This may simply be due to more inorganic P in the soil. However, no differences in the total bicar- bonate-extractable P between fertilized and non-fer- tilized forest soils have been measured after 20 yrs of repeated NPK fertilization (Clarholm 1994). It is also possible that organic P in the soil is affected by P fertilization. The NaHCO 3 -extractable organic P may decrease (Tran & N’dayegamiye 1995) or remain unchanged (Polgase et al. 1992a ). Indirect effects, such as an increased P mineralization or an altered composition of the organic residue, may arise (Polgase et al. 1992b ). If P is used as a fertilizer together with cellulose, the amount of organic P increases (Hedley et al. 1982). Fertilization may also change the P concentration in some organic matter fractions. Phosphorus concentrations in the humus of the Oe-horizon have been shown to increase (Harding & Jokela 1994). This may be due to an increased P content, either in the litter itself or in the microorganisms. Liming has two major implications to P chemistry in the soil: it increases the pH value and adds a large amount of Ca. The increased pH value affects the P availability, since it changes the solubility of the © 1999 Scandinavian University Press. ISSN 0282-7581