Influence of sodium and potassium fertilization on the sodium concentration of timothy

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 dm-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