Selenium fertilizers and foliar application, Danish experiments.

In 1963 Se-deficiency was observed for the first time in Denmark in a few sheep in West Jutland. The sheep were cured by injection of "Tokosel", and a survey of the Se-status of Danish fodder crops was initiated. A comprehensive set of data was produced during the early 70's, using the fluorometric method. The survey showed a general Se-deficiency in the whole country, and series of experiments were carried out to elucidate the possibility of raising the selenium level in plants from the native 0.02-0.04 ppm to more than the desired minimum of 0.05 ppm. Three different methods of application were tested: seed pretreatment, fertilizer enrichment, and foliar application. Seed pre-treatment has some disadvantages while the two other methods proved to be efficient and safe in a series of experiments and in tests on a large number of farms all over Denmark. These experiments and tests are discussed in detail. It is concluded that about 120 g Se/ha as sodium selenite, 10 g Se/ha as sodium selenate - both added through PK- or NPK-fertilizers, or foliar application of about 5 g Se/ha are sufficient yearly treatments to raise the native Se content of the Danish crops to levels of 0.05-0.1 ppm.