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An extensive geographical survey was carried out to obtain information on the sodium and potassium content of topdressed grass-clover pastures in New Zealand. Results indicate that in many areas, especially away from the influence of sea spray, herbage sodium levels are below those estimated to be required by grazing animals. The associated potassium contents of these pastures, particulady in the North Island. are well in excess of animal needs and generally are more than adequate for plant nutrition. The possible effects on animal health of a low dietary intake of sodium coupled with excessive amounts of potassium are discussed. The importance of sources other than the plant in supplying sodium for animal needs is also pointed out. It is emphasised that there is an urgent need to assess fertiliser policy more in terms of the requirements of both plants and animals, by a plant analysis and balance sheet approach.

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The ability of the more important pasture and fodder plants grown in New Zealand to translocate sodium from their root systems into their leaf tissue was examined in a glasshouse pot experiment. Plants were classified into two distinct types: natrophilic plants, which have the capacity to accumulate large amounts of sodium in their shoots where adequate quilntities of sodium are present in the growth medium, but have low concentrations in their roots~ and natrophobic plants for which the converse is generally true. A further subdivision was made within both types, depending on the concentration of sodium in the lower stem or stubble tissue. The importance of this classification is discussed in relation to a nutritional problem which arises where natrophobic plants form a substantial part of the diet of grazing animals.