Many groundwaters used for irrigation contain elevated concentrations of F, but much remains unknown regarding how this F behaves within soils and plants. The present study investigated the adsorption and desorption of F from several soils in short- to medium-term irrigation systems and related foliar F concentrations in three forage plant species to the maximum tolerable level (MTL) in the diets of grazing animals (being 1.8 μmol/g for young cattle, for example). Although adsorption isotherms could be successfully used to predict the behavior (adsorption and desorption) of F within the soil, this was not related to the subsequent accumulation of F in plant foliage. In addition, the extent to which F accumulated in the foliage depended on the plant species. Regardless, F generally did not accumulate in plant foliage to levels exceeding the MTL when used at rates equivalent to irrigation for 25 years. In addition to uptake by roots, F may accumulate in foliar tissues directly due to retention from overhead irrigation. The data presented here regarding the behavior of F in soils and plants will assist in the rigorous regulation of F-containing irrigation water to ensure maximum plant growth while simultaneously minimizing potential harm.
Keywords: Rhodes grass; adsorption and desorption; fluoride toxicity; fluoride uptake; leucaena; lucerne.