The effects of freezing on soil phosphorus (P) chemistry are poorly understood, although freezing is habitual for many soils at middle and high latitudes. We studied the effects of various freezing treatments on the solubility and sorption of P in an incubation experiment on two coarse and two fine-textured cultivated surface soils in Finland. Air-drying was included in the experimental arrangement because freezing and drying have similar features. Compared with field-moist soils stored at þ5 C in the dark, freezing had few effects on P extractability by water or on sorption properties of P studied with a Q/I plot technique. Air-drying, by contrast, increased almost systematically the equilibrium concentration of P estimated with Q/I plots, water-soluble organic carbon, and the extractability of P, aluminium, iron and manganese in the soils. The results imply that drying destroys organomineral complexes. The breakdown of these complexes releases P, while simultaneously exposing new surfaces on which P could sorb. Because of the considerable impact of drying on the behaviour of P, air-drying of soil samples should be avoided in studies of the chemistry of P in soil. Freezing seems to be a safe way of storing mineral soil for such studies, but it may significantly alter the P conditions of soils rich in organic matter.

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We studied the effects of soil temperature (8 ºC and 15 ºC) on barley growth, barley phosphorus (P) uptake and soil P solubility. Barley was grown in a pot experiment in two soils with different P fertilization histories for 22 years. The availability of P was estimated by using 33P-labeled fertilizer and calculating L-values. After cultivation for 22 years at ambient soil temperature without P fertilization (-P), soil L-value had decreased compared to soil that received annual P fertilization (P+). Low soil temperature further reduced the L-values, more in the -P soil than in the +P soil. Our results demonstrated that P fertilization can only partially ameliorate poor growth at low soil temperatures. Thus, applying ample fertilization to compensate for poor growth at low soil temperatures would increase the P content and solubility in the soil, but plant uptake would remain inhibited by cold.

Sorption of phosphorus (P) in complete soil profiles in northern Europe is not adequately documented. I measured the sorption in genetic horizons of four cultivated soils (Inceptisols, Spodosol) in Finland using both field-moist and air-dried soil samples, fitted modified Freundlich equations (Q ¼ a  I b ÿ q) to the data, and presented the results in quantity/intensity (Q/I) graphs. Least-squares-estimates for the parameters of the modified Freundlich equation (a, b, q) were found to be imprecise measures of sorption. Values derived from the fitted equations (the amount of P sorbed at the P concentration of 2 mg litre ÿ1 and P buffering capacity at the same concentration) were more precise. Both were correlated with concentrations of oxalate-extractable iron and aluminium. In all soils, there was a distinct difference in sorption between the fertilized Ap horizons and the subsurface horizons, which retained P strongly. Most of the sorption capacity was located in the B horizons at depths between 0.3 and 0.7 m. The results demonstrate the effects of soil-forming processes and human impact on the sorption of P in the soils. Drying the samples prior to the sorption experiments altered the shape of the Q/I graphs. It increased dissolution of P at small P concentrations, sorption at large P concentrations, and the estimates for P buffering capacity. The effects of drying soil samples on the results and the imprecision of the parameters estimated with the modified Freundlich equation should be taken into account when interpreting results of Q/I experiments.

Sodium (Na) concentration of forage crops grown in Finland, particularly that of timothy, is much lower than is recommended in the feed of cattle. A pot experiment was carried out on clay, loam and organogenic soils to find out the effect of Na application (0, 200 or 400 mg dm 3 of soil, one application) on the concentration of Na, K, Ca and Mg of timothy and the effect of K fertilization (0, 100 and 200 mg dnr 3 for each three harvests) on the efficiency of Na application. Added Na elevated the Na concentration in all harvests on all soils. The magnitude of the effect (organogenic soils loam>clay) was opposite to the K supplying power of the soil. Potassium fertilization suppressed the effect of Na application substantially and Na concentration was elevated remarkably only when the K concentration of the plants fell to or below the deficiency level (approximately 15 g kg -1 ). According to a cation exchange experiment, nearly all added Na remained in the soil solution. Still, the apparent utilization of added Na remained below 4% on all soils, demonstrating the natrophobic nature of timothy. Sodium fertilization of timothy seems to be an ineffective way of increasing the Na content of forage at least on soils of a good K status or when applied with ample K fertilization.