Seasonal and Soil‐Drying Effects on Runoff Phosphorus Relationships to Soil Phosphorus

Abstract

Controlling phosphorus levels in runoff is often recommended as the best way to minimize eutrophication of streams and lakes. Previous research has shown that increased concentrations of dissolved reactive P (DRP) in runoff from grassland are highly correlated to increased soil test P (STP) levels. We conducted an experiment to investigate the hypothesis that seasonal changes in field conditions (especially soil moisture) along with the practice of air‐drying soil samples prior to analysis may affect such correlations. Grass plots with a wide range of STP were randomly divided into two groups. In May (wet season), soil samples were taken from each plot in the first group, simulated rain was applied (75 mm h−1) to produce 30 min of runoff, and filtered runoff samples were analyzed for DRP. Each soil sample was analyzed for H2O content, sieved (2 mm), and split into two subsamples. One subsample from each plot was kept field‐moist at 4°C, and the other was air dried. Phosphorus saturation was determined only on air‐dry soil, but all soil subsamples were analyzed by Mehlich III and distilled H2O methods. In August (dry season), the second group of plots received the same treatment. All correlations of STP to runoff DRP were significant (P < 0.01), regardless of season or STP method. Water‐extractable STP from air‐dry soil and Mehlich III STP were not affected by season, but DRP concentration in August runoff was almost double that in May , so the resulting correlations were affected. Water‐extractable STP from field‐moist soil was higher in August than in May , and P saturation levels showed a similar trend. Runoff volumes were smaller in August, so season had little effect on mean DRP–mass loss.

Meteorological and management influences on seasonal variation in phosphorus fractions extracted from soils in western Ireland

“…Published literature has been somewhat limited regarding quantification of seasonal variation in soil phosphorus (P) characteristics, largely due to high field-scale soil-sample variability and the confounding effect of standard soil drying preparation prior to laboratory analyses (Pote et al, 1999). Diverging or conflicting seasonal patterns have been observed among different studies for soil test P (STP), especially Olsen P (e.g.…”

“…Perrott et al, 1990;Tate et al, 1991a;Magid and Nielsen, 1992;McDowell and Trudgill, 2000), and soil soluble P (e.g. Kuo and Jellum, 1987;Sharpley et al, 1995;Pote et al, 1999;Chen et al, 2003). Differences may be attributable to varying climates, soil types and land uses, but also the oft-used pre-analytical procedure of soil drying.…”

Grouping soils of the Montreal Lowlands (Quebec) according to fertility and P sorption and desorption characteristics

“…The combination of the P saturation index and Pw has been found useful in predicting the P solubility, P availability for crops or P desorption in soil and in determining the risk of the P transfer from these soils to the surface waters (Sharpley 1995;Beauchemin et al 1997;Pote et al 1999). The eight soil fertility subgroups can be rated by increasing order of P desorbability as determined from the Pw mean values: 2 ≤ 5 ≤ 4a < 4b ≤ 3a ≤ 1a < 1b ≤ 3b (Table 4).…”

Laboratory drying of organic-matter rich soils: Phosphorus solubility effects, influence of soil characteristics, and consequences for environmental interpretation

“…For convenience, soils are usually dried in preparation for laboratory analyses, despite evidence that drying and rewetting soils alters their physical and biological characteristics and releases soluble P ( Bartlett and James, 1980;Pote et al, 1999a;Turner and Haygarth, 2001;Styles et al, 2006). Large decreases in the number of viable microbial cells present in soils immediately after drying and rewetting (Stevenson, 1956;Sparling et al, 1985;Kieft et al, 1987;Van Gestel et al, 1991; have been attributed to cell lysis induced by osmotic shock upon rewetting with a low solute solution such as water (Kieft et al, 1987).…”

“…Some studies have found that acidic STP extraction methods are unaffected by drying soils (Pote et al, 1999a;Olde Venterink et al, 2002). Large drying effects on P solubility analyses could obscure relationships with STP and soil type, as used to develop soil soluble P loss indices.…”