The effect of catch crop species on selenium availability for succeeding crops

Selenium (Se) is an essential nutrient for humans and animals. In order to ensure an optimal concentration of Se in crops, Se fertilisers are applied. Catch crops may be an alternative way to increase Se concentrations in vegetables. Three experiments in Denmark between 2007-10 investigated the ability of catch crops (Italian ryegrass, fodder radish and hairy vetch) under different fertiliser regimes to reduce soil Se content in the autumn and to increase its availability in spring to the succeeding crop. The catch crops (Italian ryegrass and fodder radish) increased water-extractable Se content in the 0.25-0.75 m soil layer in only one of the experiments. Selenium uptake by the catch crops varied between 65 and 3263 mg ha(-1), depending on species, year and fertilisation treatment; this corresponded to 0.1-3.0% of the water-extractable soil Se content. The influence of catch crops on Se concentrations and uptake in onions and cabbage was low. There was a decrease in Se uptake and recovery of applied Se by onions following catch crops, which might indicate Se immobilisation during catch crop decomposition.