MANURING POTATOES AND BARLEY

New Zealand Mail, Issue 1536, 7 August 1901, Page 57

MANURING POTATOES AND BARLEY

The Department of Agriculture in Germany has issued a report on a series of potato manuring experiments which have extended over a period of seventeen years. In a comparison of farmyard and chemical manures, the yield was about the same on each, but the starch content of the tubers was -noticeably lower in .the former case, being only per cent., as against 16.15 per cent, in the latter. Farmyard manure was plainly unfavourable to the fullest development of starch. This conclusion, based on experiments in which the yard manure and artificials were applied to different plots, was confirmed by other experiments in which each was applied to the same plot in different 'seasons. In a comparison of sulphate of ammonia and nitrate of soda as sources of nitrogen for potatoes, the yield of tubers with the former was 7.3 per cent, less than with th e latter. J At the same time their starch content was less by 0.5 per cent. As a result, the amount of starch produced was 11 'per cent, less on sulphate of ammonia than on nitrate of soda. 1 This result is explained by the fact that nitrate of soda is a more readily available plant food. In a study of the influence of different kinds of manures on starch con. tent, a complete chemical manure was compared with other manures, identical except that either nitrogen or J phosphoric acid was omitted. The complete manure applied as a mixture at the rate of in all 2cwt per acre produced 15£ tons of tubers, with a 'starch content of 16.15 per cent. The fertiliser containing no phosphoric acid produced 14J tons of tubers, with a starch content of 16.15 per cent, and the fertiliser containing no nitrogen produced 132 tons, with a starch content of 16.45 per cent. It was proven either that phosphoric acid favours the formation of starch, or that nitrogen is unfavourable to it. It was shown by other experiments that both inferences are correct, but when the application of manure was 'doubled in each case the 'complete chemical manure produced a starch content of 19 per cent., the fertiliser containing no phosphoric acid 18.4 per cent., and that containing no nitrogen 18.6 per cent. —that is—nitrate of soda does not materially hinder the formation of gtarch, provided all other elements of T>lant food are present in sufficient quantities. Other experiments are reported which lead to the conclusion that a heavy application of potash neutralises the detrimental effect of farmyard manure on the formation of starch. Tn experiments on the effect of farmyard and chemical manures, reapectively, on succeeding crops of potatoes, the effect of an application of farmyard manure was almost as marked the second season as the‘first, but in the third season it was very much less, and in the fourth it had practically disappeared. ’The effect of artificial manures on succeeding

crops was much less marked, but when the application of artificials was double the amount usually applied the effect on the second crop was almost as great as in the case of yard manure. Potash is the most important ingredient of a potato manure. Nitrogen and phosphoric acid with potash gave only a small increase in yield 'over potash aione, and if potash is not included in the mixture there is almost no increase. Nevertheless, nitrogen and phosphoric acid are necessary complements of notash. though in small amounts of less frequent applications, for a continued application of potash "alone was found to result in a decreased yield. With regard to barley the experiments were made to ascertain the requirements of malting barley in potash, and the results showed that the use of potash manures only produce sensible effects on soils which are poor in potash, and in presence of u a sufficient supply of the other chief fertilising ingredients—phosphoric acid and nitrogen. Climatic conditions, especially those relating to rainfall, exercise a great influence on the 'action of potash manures. Provided, however, climatic conditions are favourable, and the soil is deficient in potash, the action of potash salts is at once shown by a 'sensible increase of yield, and by a considerable improvement in the quality of the grain, “especially in the following points:—l. Diminution of the amount of protein "(nitrogenous matter) and -“corresponding increase in the starch of the grain. 2. Increase in weight of the grain and decrease in the thickness of the husk. These modifications give to the grain the qualities sought for by brewers, and consequently increase its selling value. Potash manures, -it was found, give most satisfactory results on soils whose potash content is less than 1.5 per 1000. •In soils with a higher potash content, not only do potash manures produce no beneficial result, but they appear to increase the -requirements of the barley in respect to other fertilising ingredients—a result which is without profit to the crop.