THE EFFECTS OF TOPDRESSING DAIRY PASTURES IN THE WAIKATO WITH SODIUM CHLORIDE

Abstract

Recent dairy farm survey data suggest the sodium (Na) concentration in pastuies could be too low to maintain stock health on a number of farms. Trials have been established on three major soil groups in the Waikato to study: (a) the rates of NaCl rauired to raise Na concentrations in pasture; (b) the time required to do this; (c) the duration of the response; and (d) the effect of KCi on Na uptake. Na uptake in pasture was rapid initially, reaching a peak some 6 weeks after application. Thereafter the Na concentration in pasture declined gradually but after 30 weeks was still some 2 to 3 times the initial Na concentration. Soil Na levels followed a similar trend. Conclusions to date suggest an annual topdressing of NaCl at 100 kg/ha wll provide an adequate Na concentration in the pasture for animal health and production on a range of Walkato soils. In practice salt can be applied alone or mixed with other fertilisers. Where potassium is already high some replacement of NaCl for KCI in the fertiliser mixture can be considered. Regular monitormg by pasture analysts is recommended. Although salt applications will increase the Na content in the pasture, animal responses to Na supplementation have yet to be conclusively demonstrated. Research is planned with dairy cows in the Waikato to investigate this important aspect. Keywords: Salt, sodium chloride, pasture sodium, ryegrass, white clover pastures, topdressing, dairy cows