The effects of pre-maturity desiccation with paraquat and leaching on the quality of dry Wimmera ryegrass

Abstract

The effects of pre-maturity desiccation with paraquat and post-maturity leaching with water on the quality of the dry residues of annual Wimmera ryegrass (Lolium rigidum) were examined under laboratory and field conditions. Paraquat applied at head emergence increased the levels of nitrogen, phosphorus, potassium and sulphur in mature ryegrass and, in some experiments, the levels of magnesium, calcium and water soluble carbohydrates (WSC), and increased the in vitro digestibility. Concentrations of nitrogen were changed little by leaching in either sprayed or naturally matured ryegrass. Concentrations of other mineral nutrients decreased following leaching to similar levels in sprayed and unsprayed tissue. The proportionate change in concentration of nutrients varied between experiments, with the nature of the nutrient, with the part of the plant, and with the period of leaching. Leaching removed WSC and, in one case, more was lost from paraquat-treated herbage. However, decreases in percentage digestibility in vitro were not significant. Changes in potassium and WSC contents were greater following multiple immersions than with a single immersion lasting the same total length of time, and this effect was not changed by spraying paraquat.