Changes in the chemistry of soil solution and acetic‐acid extractable P following different types of freeze/thaw episodes

Abstract

Freezing significantly influences the amount and chemical form of extractable soil phosphorus and, therefore, has important consequences regarding plant nutrient availability. Much of the current evidence relies on field-based observations and tends to be rather contradictory. The present work reports the specific effects various freezing episodes have on phosphorus availability. Experimental treatments included the freezing rate and the time soil remained frozen together with the number of freezelthaw cycles. These laboratory incubations used two soils, an iron humus podzol and a peaty podzol, sub-samples of which were equilibrated at three different soil-moisture contents. Concentrations of phosphorus in soil solutions and acetic acid extracts (Ac-P) were measured. Freezing had the greatest effect on the organic (Op) horizon of the peaty podzol, where the amounts of total dissolved phosphorus (TDP) and Ac-P increased from 0.58 to 3.21 and from 11.8 to 19.3 mg P kg-l, respectively. TDP in soil solution was subdivided into three broad categories, dissolved (molybdate) reactive (MRP), organic (DOP) and condensed (DCP). The rather variable effect that freezelthaw episodes had on these fractions highlighted the problems associated with attributing the 'freezing effect' to any single process.

Cold winter soils enhance dissolved organic carbon concentrations in soil and stream water

“…The studies which do exist report no, or inconclusive, effects on soil solution [DOC]. The strong influence of soil frost on [DOC] observed in our study is, however, similar to results obtained in laboratory-scale freezing experiments [Austnes and Vestgarden, 2008;Vaz et al, 1994;Wang and Bettany, 1993]. The great effect of soil frost on DOC, in contrast to previous field experiments, could be related to our long-term experimental design, which closely mirrors the natural variability occurring in the region [Öquist and Laudon, 2008].…”

Sample Pretreatment and Phosphorus Speciation in Wetland Soils

“…Similar changes occur after freezing (Ron Vaz et al, 1994) and can even continue during storage of air-dried samples (Turner, 2005). …”

Sampling, sample treatment and quality assurance issues for the determination of phosphorus species in natural waters and soils

“…Indeed, functional classification of water-extractable organic phosphorus from dry Australian pasture soils revealed similar proportions of microbially derived phosphate diesters and phytic acid from the non-biomass soil organic matter [59]. A similar mechanism probably occurs following freezing and thawing [60]. Such processes probably explain the increases in phosphorus extractable in bicarbonate following soil drying [61] Fig .…”