 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.plant-soil.com J. Plant Nutr. Soil Sci. 2013, 000, 1–9 DOI: 10.1002/jpln.201200334 1 Phosphorus pools in soil after land conversion from silvopasture to arable and grassland use Anna Slazak 1 *, Dirk Freese 1 , Eduardo S. Matos 2 , Seth Nii-Annang 1 , and Reinhard F. Hüttl 1,3 1 Chair of Soil Protection and Recultivation, Brandenburg University of Technology, P.O. Box 10 13 44, 03013 Cottbus, Germany 2 Embrapa Agrosilvopastoral, P.O. Box 343, 78550-970, Sinop–MT, Brazil 3 Helmholtz-Centre Potsdam – GFZ, German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany Abstract Differences in soil P among silvopasture, grassland, and arable lands have been well estab- lished. Nevertheless, most of the reports compare soil properties under long-term sites. Thus, there exists little information on the effect of the conversion of silvopasture to arable or grassland use on soil P pools. The objective of the study was to determine the impact of converting silvo- pasture system (SP) into arable cropping and grassland system on the distribution of P pools and potential P bioavailability. We compared the following systems: SP system, SP converted to arable cropland (SP-AL), SP converted to grassland (SP-GL), and for comparative purposes, a long-term arable cropland (AL). The P fractionation was performed by a sequential extraction scheme, using acid and alkaline extractants on samples collected from the 0–10 and 10–20 cm soil layers. It was assumed that the large variations in soil-P fractionations are caused by the dif- ferent management practices associated with land conversion. The results of P fractionation showed a dominance of calcium-bound P, HCl-extractable Pi constituted up to 36% of the soil total P (TP). However, the type of land use did not affect this P fraction. On the other hand, the reduction in labile-P i and NaOH-P i fractions observed at the SP-AL site may have led to the decline in readily available P. The soil total organic P (TP o ) content was 8% and 17% lower at SP-AL compared to SP and SP-GL site, respectively. Labile organic-P (labile-P o ) content was markedly higher at SP site compared to arable soils, and was ≈ 10% of TP o . The NaOH-P o con- stituted the highest fraction of the organic-P pool (55%–79% of TP o ) across all the study sys- tems, and was positively correlated with TP o (p < 0.01). The study indicates that conversion of SP system in temperate regions to arable cropping with conventional tillage seems to result in the reduction of P availability compared to SP, indicating SP as an important land-use practice. Key words: sequential P fractionation / P availability / agricultural soils / silvopastoral / land-use Accepted April 18, 2013 1 Introduction It is well known that agricultural practices and different soil management affects the distribution of soil P. Even though it is important to study the impact of changes in land-use prac- tices on the distribution of soil P, detailed knowledge on soil P fractions is necessary. The P-fractionation procedure deter- mines the various form of soil organic and inorganic P based on their solubility in different chemical reagents (Cross and Schlesinger, 1995; Bowman and Cole, 1978a). An aspect of different land-use practices on soil P characteristic has been discussed in several studies (Brookes et al., 1984; Condron et al., 2005; Cross and Schlesinger , 1995; Di et al., 1996; Khan and Joergensen, 2012; Martens et al., 2004; Michel et al., 2007; Sanyal and De Datta, 1991; Staley et al., 2008). Nevertheless, most of the studies that focused on inorganic and organic P in different ecosystems, examined the short- and long-term effects of land-use (Alt et al., 2011; Bowman and Cole, 1978a; Lilienfein et al., 2000; McKenzie et al., 1992; Sharpley and Smith, 1985; Song et al., 2007; Tiessen et al., 1983). These studies showed that cultivation without P fertilizer, led to depletion of most of the P fraction (mainly labile P pools); higher in continuous monocultures than in the crop rotations. McKenzie et al. (1992) reported less reduction in different P pools in crop rotations compared to continuous wheat monoculture. Nevertheless, studies on silvopastoral systems (SP) by Michel et al. (2007) and Nair et al. (2007) proved that the capacity of soil to store P is lower in treeless pasture compared to SP systems. These studies also showed that the presence of trees in pasture may reduce the likelihood of future additions of P being removed from the soil. For example, work of Magid (1993) in Denmark, Gug- genberger et al. (1996) in Germany, and Ellert and Gregorich (1996) in Australia revealed higher total organic P (TP o ) con- tents under pasture than under forest. Besides, Alt et al. (2011) in Germany and Turrion et al. (2001) in Spain reported higher TP o and P availability under grassland and pasture compared to forest. Also, depletion of TP o caused by land cultivation has been reported by several authors (Chen et al., 2000; Staley et al., 2008; Tiessen et al., 1982, 1983). How- ever, most of these studies concentrated on pastures, grass- land, and arable lands, and the conversion of pasture or silvo- * Correspondence: A. Slazak; e-mail: am.slazak@gmail.com