Magnesium uptake by herbage

Abstract

AbstractGround carboniferous limestone at 0, 5 and 10 t/ha was applied in all combinations with calcined magnesite at 0, 1.25 and 2.5 t/ha on perennial ryegrass/white clover swards at five sites. an extra treatment of ground magnesian limestone supplying magnesium equivalent to that in 1.25 tonne calcined magnesite was also applied at each site. cuts of herbage were taken over a period of 3 years and samples taken for magnesium and potassium analysis. at two of the sites the herbage samples were divided into grass and clover and analysed separately. calcined magnesite significantly increased the magnesium content of both grass and clover, and in both instances the higher dressing gave a further significant increase in magnesium content over the lower level of application. magnesian limestone was not as effective as calcined magnesite in the first 2 years after application, but had a similar effect on the magnesium content by the third year. 5 and 10 t/ha of ground carboniferous limestone had but a small effect on magnesium levels. this effect was probably of no practical significance. white clover contained, on average, about 25 % more magnesium than perennial ryegrass. the potassium content of clover was little affected by the magnesium and lime treatments, but calcined magnesite depressed the content in grass very slightly and magnesian limestone raised the % k value from 2.72 to 2.88.