SOME EFFECTS OF TOPDRESSING PASTURE WITH SODIUM CHLORIDE ON PLANT AND ANIMAL NUTRITION

Abstract

A long term study is being made of the effects of replacing all or part of the fertiliser input of potassium chloride (muriate of potash - KCI) with sodium chloride (common salt - NaCI) on plant and beef animal nutrition. The ryegrass-white clover pasture which is growing on a sodium deficient pumice derived soil (Taupo sandy silt), had received heavy applications of KCI over the preceeding 10 years. Results from the first two years show that because of the already high potassium status of the pasture, neither KCI or NaCl had any effect on pasture dry matter production or species composition, but did effect the chemical composition. Topdressing with NaCl at rates of 100-200 kg/ha/vr significantly increased the herbage sodium concentrations, while similar rates of 'KC1 increased potassium concentrations but decreased sodium concentrations. However, the depressing affects of KC1 on sodium concentrations were offset by applying 50 kg/ha/yr of NaCI. increasing the sodium concenrrarron In me neruaye au"ve V, I 70 VI LIIG UIY IUU~LLXZI with NaCl had a beneficial effect on the growth of weaner beef animals. However, increasing the sodium intake of beef breeding cows grazing pastures high in potassium had a detrimental effect on the concentration of magnesium in the blood serum. Thus, as a relatively high intake of sodium may induce metabolic problems in breeding cows, topdressing pastures or direct supplementation of animals with NaCI, should not be undertaken without sound evidence of its necessity particularly in areas prone to grass staggers (hypomagnesaemic tetany). Key Words: animal nutrition, herbage sodium; plant nutrition; potassium chloride; ryegrass-white clover pasture, sodium chloride, serum magnesium.