Effects of air-drying and freezing on phosphorus fractions in soils with different organic matter contents

Abstract

Little is known about the effects of air-drying and freezing on the transformation of phosphorus (P) fractions in soils. It is important that the way in which soils respond to such perturbations is better understood as there are implications for both P availability and loss to surface waters from soils. In this study, the effects of air-drying and freezing were investigated using two soils, one being a forest soil (FS) high in organic matter and the other being a sterile soil (SS) low in organic matter. Soil P was fractionated using a modified Hedley fractionation method to examine the changes of phosphorus fractions induced by air-drying and freezing. Generally, there were no significant differences of total phosphorus among the three treatments (CV% < 10%). Compared with field moist soils, freezing the soil evoked few changes on phosphorus fractions except that the resin-P increased in FS soil. On the contrary, air-drying significantly changed the distribution of phosphors fractions for both soils: increased the labile-P (especially resin-P) and organic-P (NaHCO 3 -Po, NaOH-Po and Con.HCl-Po) at the expense of NaOH-Pi and occlude-P (Dil.HCl-P and Con.HCl-Pi). Resin-P significantly increased by 31% for SS soil and by 121% for FS soil upon air-drying. The effect of air-drying seemed to be more pronounced in the FS soil with high organic matter content. These results indicated that drying seem to drive the P transformation form occlude-P to labile-P and organic-P and accelerated the weathering of stable P pool. This potentially could be significant for soil P supply to plants and P losses from soils to surface waters under changing patterns of rainfall and temperature as predicted by some climate change scenarios.

Spatial patterns in oxygen and redox sensitive biogeochemistry in tropical forest soils

“…However, these studies measured P from airdried soils, which can result in the formation of relatively insoluble Fe-P bonds associated with Fe oxidation (Chacon et al 2006, Wood andSilver 2012). The P concentrations from air-dried soils have been shown to differ from soils under field conditions (Xu et al 2011). …”

Air-Drying Effect on Soil Reaction and Phosphorus Extractability From Upland-Lowland Tropical Soils as Related to Their Colloidal Stability

“…Studies reporting increases in available phosphorus with airdrying (Gilliam and Richter, 1988 Xu et al, 2011), which in turn seem to outnumber those reporting decreases in extractable phosphorus with air-drying (Haynes and Swift, 1985). With the exception of the pilot studies by Ekpete (1976), Srivastava (1997) and Yongsong et al (1998) which were carried out on tropical soils and that by Gilliam and Richter (1988) in a sub-tropical environment, the rest of the studies just cited were carried out on soils from temperate locations.…”

Drying-induced changes in phosphorus status of soils with contrasting soil organic matter contents – Implications for laboratory approaches

“…However, drying as a soil preparation practice can affect the absolute amount of P extracted and the relative amounts of P in different P pools (Chepkwony et al, 2001;Condron and Newman, 2011;Sparling et al, 1985;Turner and Haygarth, 2001;Turner and Romero, 2010;Turner et al, 2003;Xu et al, 2011). Therefore, some authors recommend the use of fresh samples, with no pre-treatment (e.g.…”

“…more intense drying or freezing) than hitherto, and such perturbations and their effects on P fractions are likely to increase. Information about P transformation after laboratory soil drying could be a means of improving our understanding of P cycles and long-term changes in P pools due to global climate change (Xu et al, 2011).…”

“…The disruption and mineralization of soil organic matter (SOM) and lysis of microbial cells are the main mechanisms involved in P transformation during soil drying and subsequent rewetting (Chepkwony et al, 2001;Sparling et al, 1985;Turner, 2005;Turner et al, 2003;Wu and Brookes, 2005;Xu et al, 2011). Because P in 'dead' organic matter as well as microbial P are generally correlated with SOM (Achat et al, 2012), one can therefore assume that the effect of soil drying on P status increases with increasing SOM contents.…”