Field experiments comparing the effects of muriate and sulphate of potash on potato yield and quality

Abstract

1. Between 1955 and 1961 nineteen experiments were carried out on Majestic potatoes in various parts of England comparing muriate and sulphate of potash at three rates of application, in the range 75–336 lb./acre of K2O. Most of the experiments were on light soils.2. Total yield of tubers was on average the same from both sources at all rates of application, and this similarity was not affected by environmental conditions.3. Muriate of potash consistently gave a higher yield of large tubers than sulphate, with an average difference of 0·6 ton/acre. Conversely, muriate gave a lower yield of medium tubers than sulphate, again with a mean difference of 0·6 ton/acre.4. Muriate of potash significantly depressed tuber dry-matter content in eleven of the experiments, particularly at the higher rates, while sulphate had this effect in three experiments. Muriate gave a small increment in two experiments, at low rates only, while sulphate had this effect in five, most markedly at low rates. Sulphate gave a higher dry-matter content than muriate in most of the experiments. The mean difference was 1·0% at 300 and 336 lb./acre of K2O and 0·4 to 0·5% at lower rates.5. Sulphate of potash gave a more floury texture to the boiled tubers than muriate in three experiments, but otherwise no difference in texture was detected between the sources.6. The degree of off-flavour was not appreciably affected by rate or source of applied potash.7. After-cooking blackening was more marked at low than at high rates of applied potash in seven of the nineteen experiments. Muriate and sulphate of potash had similar effects.8. Farmyard manure ploughed down in winter was tested in three experiments and did not influence to any important extent the relative effects of muriate and sulphate of potash on tuber yield and quality.9. Application of the two sources on the flat before ridging and in the open drills was compared in the same three experiments, but did not alter the relative effects of the sources on yield or dry-matter content.