Effect of fluoride supply on fluoride concentrations in five pasture species: Levels required to reach phytotoxic or potentially zootoxic concentrations in plant tissue

Recent findings have highlighted the possibility of increased fluoride (F) concentrations in herbage through F taken up from soil via the plant root. This paper aimed to assess the risk of F concentrations reaching phytotoxic or zootoxic concentrations in pasture plants. Five plant species commonly found in improved pastures in Australia, the sown species subterranean clov er (Trifolium subterranean) and cocksfoot ( Dactylis glomerata), and weeds barley grass (Hordeum leporinum), scotch thistle (Onopordum acanthium) and sorrel (Rumex acetosella) were grown in complete nutrient solutions with gr aded levels of added F to determine the effects of F- activity in solution on phytotoxicity and uptake of F by their roots. A model was developed usin g data from these solution culture experiments and data from the literature . The model assessed uptake of F by plants grown over a range of soil pH va lues and determined the risk of F taken up through the plant roots reaching phytotoxic concentrations, or concentrations potentially injurious to graz ing animals, in the plant shoots. Modelling data suggested that the plants studied would not accumulate phytotoxic concentrations of F in shoots or co ncentrations of F deleterious to grazing animals through root uptake in neu tral pH agricultural soils. The risks from F addition to soils in phosphati c fertilisers leading to reduction in pasture growth or animal health are t herefore low. However, in highly F-polluted soil, as the soil becomes more acidic or alkaline, the risk of zootoxic concentrations of F in shoots of p lants would increase.