The immediate and long-term value of some magnesium fertilizers for sugar beet

Abstract

SUMMARYNine 5-year field experiments between 1964 and 1971 tested the effect of kainit, kieserite, magnesium and calcium limestone, and farmyard manure on yield and magnesium uptake by sugar beet and on exchangeable soil magnesium. The experiments were in the main sugar beet growing areas on soils that contained little (12–24 ppm) exchangeable magnesium. The fertilizers were applied in the year before the first sugar-beet crop and fresh dressings of some were given to other plots each time sugar beet was grown. Kieserite increased sugar yield equally when applied in the sugarbeet seed bed or three years before the sugar beet. Magnesium limestone was effective only when the soil pH was less than 7·0. FYM greatly increased yield but the increase could not be explained entirely by the magnesium it supplied.On average, applying 100 kg/ha magnesium (as kieserite) to the seed bed increased the magnesium concentration in dried tops and roots by about 0·135 and 0·020% respectively and the total uptake by the crop in August by 9·0 kg/ha. The same treatment applied in the sugar-beet seed bed or 3 or 4 years previously increased exchangeable magnesium in the surface 25 cm of soil by 29·0, 7·6 and 1·8 ppm respectively. Thus much of the fertilizer given to the first sugar-beet crop was lost from the plough layer for the second sugar-beet crop but the yields indicated that some of it was available from depth.On alkaline soils, when exchangeable soil magnesium in the plough layer is 0–25, 26–50 or > 51 ppm, an initial application of 100, 50 or 0 kg/ha respectively of water-soluble magnesium is needed, applied either in the previous autumn or to the sugarbeet seed bed. If the exchangeable soil magnesium before the following or subsequent sugar-beet crop is 0–15, 16–25 or > 26 ppm, a further application of 100, 50 or 0 kg/ha respectively of magnesium should be given.