Effects of Soil Drying on Soil pH and Nutrient Extractability

Abstract

A sample set from a field experiment conducted at two sites, a commercial organic potato farm and a conventionally managed experiment station farm, was used to compare the extractability of nutrients in field-moist and air-dried soils. Standard soil characterization methods of the Maine Soil Testing Service were used to determine soil pH and extractable nutrient content. The data were analyzed with Systat using paired t-tests. Air drying decreased soil pH and increased extractability of calcium, micronutrients, and metals. Many of the observed changes were probably a result of increasing surface acidity with drying. Drying increased the extractability of inorganic phosphorus, probably because of disruption of aluminophosphate complexes, particularly in conventionally managed soils, which had received high amounts of inorganic phosphorus fertilizer. Drying also increased the extractability of complexed phosphorus, probably both organically and inorganically complexed phosphorus, and decreased the extractability of potassium, probably by enhancing potassium fixation in clay interlayers.

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

“…Table 3 shows that, for both uplands and lowlands of the four locations, soil pH tended to be lower in air-dried samples compared to the field-moist samples, and that the only cases of significant differences were in the lowland soils -Akaeze for pH in both water and KCl, Omasi for pH in water and Nando for pH in KCl. The decrease in pH of some of the soils due to air-drying and the associated increase in surface acidity has similarly been reported elsewhere (Erich and Hoskins, 2011). The chemistry of drying mineral surfaces and its acidifying effect on soil surface can be found in Dowding et al (2005).…”

“…This is because air-drying allows soil samples to be stored for analyses even after a long time, since dried soil samples are perceived to undergo minimal changes caused by microbial and chemical reactions compared to field-moist samples (Erich and Hoskins, 2011). It equally increases the ease of handling of soil samples during analyses.…”

“…It equally increases the ease of handling of soil samples during analyses. However, air-drying soils before analysis often increases the concentration of solutes in soil solution which may later be precipitated or lead to an increased sorption on soil surfaces (Erich and Hoskins, 2011), and this may influence the results of soil analyses for easily sorbed soil chemical constituents. When solutes precipitate in air-dried soils, their complete solubility after rewetting such soils is unlikely.…”

“…When solutes precipitate in air-dried soils, their complete solubility after rewetting such soils is unlikely. It has been shown repeatedly that drying increases surface acidity, and that this phenomenon can affect the solubility and availability of many nutrients including phosphorus (Bartlett and James, 1980;Haynes and Swift, 1985;Erich and Hoskins, 2011).…”

Is air-drying of soil samples an appropriate step in determining plant available potassium for corn?

“…Most of the commercial soil testing labs and universities in the USA, with the exception of Iowa (Mallarino et al, 2013) include air drying the soil sample as a standard soil preparation step. Recommendations are based on extracting solutions, such as 1-nitrogen (N) ammonium acetate or Mehlich-3, added to the dried and ground soil sample (Erich and Hoskins, 2011;Nathan and NCERA-13 Soil Testing and Plant Analysis Committee, 2011). There is concern that air-drying soil samples for plant available soil potassium (K) status prediction may lead to over-or under-estimation of plant available K (Attoe, 1947;Luebs et al, 1956;Burns and Barber, 1961; Barbagelata and Mallarino, 2012).…”