Field experiments on the magnesium requirement of cereals, potatoes and sugar beet in relation to nitrogen and potassium application

Abstract

Birch et al.: Magnesium Requirements of CropsAbsorbance was measured on a Unicam SP500 spectrophotometer. Chromatograms were repeated several times : the results are as follows : Extract Method 1 1 2 2 PC TLC PC TLC No. of chromatograms 5 5 4 4 Mean absorbance at 500mp 0.621 0.601 0.986 0,985 R.m.s. deviation 0.009 0.010 0.030 0.012 Coefficient of variation 1 . 5 1 . 6 3.1 1 . 3 %In a series of 14 assays, each performed in triplicate by TLC, the coefficient of variation was in the range 0.3-3.2 %, with a mean coefficient of variation for the 14 assays of 1 -6%.McKeown & Mark3 quote pairs of results of assays of annatto extract which differ by 0-4%, the mean difference for the six pairs being 1.6%. In our hands, thin layer chromatography has proved as suitable as paper chromatography for the separation of bixin before assay. Reproducible results can be obtained very rapidly.In 43 experiments on a range of soils there was little indication that magnesium sulphate applied to the seedbed increased yield of cereals, potatoes or sugar beet. In one experiment only, on potatoes, a very high rate of muriate of potash induced magnesium deficiency. Different rates of ammonium sulphate, compared on cereals only, did not affect crop response to magnesium.The magnesium content of barley foliage and the effects of magnesium sulphate and ammonium sulphate on this content were shown to be related to soil potassium and magnesium levels. 77 No. of Crop expts. Series I Spring oats Spring barley Series 11 Winter oats Spring barley Treatments compared" KzO rate: 40, 120 K2O method: broadcast on seedbed Mg rate and method: nil combine drilled 12 broadcast on seedbed 12 combine drilled N rate: 20, 60 K2O rate: 40, 120 Mg rate: 0, 24 Series lTI (a) Potatoes 4 K 2 0 rate: 120, 360 Potatoes 9 K20 rate: 120, 360 Mg rate: 0, 24 Mg rate: 0, 24 Mg rate 6: as foliar spray with K 2 0 rate 360" Ma rate: 0. 24 (b) Sugar beet 5 K 2 0 rate: 80,240

Effects of potassium and magnesium fertilizers on yield and size distribution of potatoes

“…There was a general lack of effect from applied Mg, confirming the findings of Holmes (1962), Birch et al (1966), Edwards (1967) and others.…”

“…Application of very high rates of potassium (300-350 kg K/ha) in the same experiments depressed yield compared with a normal rate (150 kg K/ha). Birch, Devine & Holmes (1966), in 14 experiments, found little effect of 29 kg Mg/ha applied to the seed bed on potato yield. Edwards (1967), Laughlin (1966) and Peeler & Heafield (1966) confirmed that there are negligible responses to applied magnesium sulphate.…”

Effect of added magnesium, potassium, lime and nitrogen on oats: II. Nutrient contents, cation ratios and magnesium uptake

“…Only a very low magnesium content in the growth base limited the yield (Jokinen 1977). In several experiments (Vigerust 1966, Birch et al 1966, Sorteberg 1975) the conclusion has been reached that magnesium fertilization does not affect the yield of cereals, but increases the magnesium content of the plants. In these experiments, carried out on mineral and peat soils, the magnesium content of the growth base was probably not so low as to retard the growth of the crop.…”