The effectiveness of autumn spray applications of cobalt sulphate, copper chelate and copper sulphate on Southland pastures

Abstract

Uptake of cobalt (Co) and copper (Cu) by ryegrass/ white clover based dairy pasture from autumn spray applications of cobalt sulphate (CoSO4) copper sulphate (CuSO4) and Cu chelate was measured at a site near Woodlands in Southland. The rates of application were 0, 12.6, 25.2, 50.5 g Co/ha (0, 60, 120 and 240 g CoSO4/ ha), and 0, 0.25, 0.5 and 1 kg Cu/ha. The concentration of Co in herbage was significantly increased initially by the two highest application rates (P<0.001). However, only the highest application rate of 50.5 g Co/ha (240g CoSO4/ha) gave increased herbage Co concentrations for the full 41 day duration of this study. In contrast the concentration of Cu in herbage at all rates of application for both forms was significantly higher (P<0.001) than that of the control even after 41 days, with the lowest rate of the sulphate form having concentrations similar to the highest rate of the chelate form. The herbage Cu concentrations from the treated plots, immediately following the application, exceeded 100 mg Cu/kg dry matter (DM) for all application rates and forms and dropped steadily until day 27 at which time they were in the range of 20-90 mg Cu/kg DM. Cu concentration remained relatively static from day 27 until the end of measurement at day 41. These levels should be sufficient to supply animal requirements, resulting in liver Cu levels which could remain adequate for the critical winter period. Hence when applied in liquid form, rates of Cu application lower than previously recommended may be sufficient. Despite this, care must still be taken in the first 5-10 days following application to avoid Cu toxicity to grazing animals. Keywords: copper chelate, cobalt sulphate, copper sulphate, pasture cobalt content, pasture copper content