Manuring for rich Crops of Turnips.
In Dr Aitken's own words: "In order to grow a large and at the same time a healthy and nutritious crop of turnips, such a system of manuring or treatment of the soil, by feeding or otherwise, should be practised as will result in the general enriching and raising of the condition of the land, so that the crop may grow naturally and gradually to maturity. For that purpose a larger application of slowly acting manures, of which bone-meal may be taken as the type, is much better suited than smaller applications of the more quickly acting kind. A certain amount of quickly acting manure is very beneficial to the crop, especially in its youth; but the great bulk of the nourishment which the crop requires should be of the slowly rotting or dissolving kind, as uniformly distributed through the soil as possible."
Experiments by the Author.
Experiments by the author on turnip-manuring, carried out in different parts of the South and West of Scotland, showed that while farmyard manure is valuable in giving the crop a good start and bringing it well forward during the period of germination and early growth, by supplying a certain amount of easily assimilable plant-food, and in the case of dry weather attracting a quantity of moisture, its application in quantities of 20 or even 10 tons per acre can scarcely be regarded as profitable, giving to farmyard manure a nominal value of a few shillings a ton. In these experiments slag proved itself a most valuable manure, indeed one of the most economical of all the manures experimented with. They further showed that heavy dressings with superphosphate, amounting to as much as 8 cwt. per acre, are, from an economical point of view, as a rule justifiable in Scotland; and that nitrate of soda and sulphate of ammonia possess practically equal value as a manure for turnips. In almost every one of the experiments the benefit of supplementing superphosphate with nitrogenous manure was shown. Potash was also found in many cases to be a thoroughly paying manure for the turnip crop, when it was applied along with nitrogen and phosphates; but when applied alone, far from exercising any appreciable benefit, it seemed to exert an injurious action.
Potatoes.
Potatoes are often classed along with the root crops, and in their manurial requirements they offer many points of similarity. Next to root crops, they may be said to make the most exhaustive demands on the soil, and therefore require a liberal general manuring. A point of importance in the manuring of potatoes is a good tilth in the soil, so as to enable a free expansion of the tubers to take place. They may be said to grow best on deep warm soils; but, like roots, if liberally manured, they may be successfully grown on any kind of soil. Farmyard manure has long been regarded as specially valuable for the potato crop. In many parts of Scotland it is applied in enormous quantities, ranging from 20 to even 40 tons per acre. There can be little doubt that the value of farmyard manure, as well as other bulky manures, for the potato crop, is partly due to their mechanical influence on the soil. Potatoes are surface-feeders, and require their food in a readily available condition. It is found desirable, therefore, to supplement farmyard manure by readily available artificial manures. Potatoes repay the application of a mixed manure containing all the fertilising ingredients—nitrogen, phosphoric acid, and potash—better than most crops.
Highland Society's Experiments on Potatoes.
The nitrogen is, according to the Highland Society's experiments, best applied in the form of nitrate of soda. Sulphate of ammonia does not seem, when farmyard manure is also applied, to have an equally valuable effect, as it influences the size of the tuber, producing an undue proportion of small potatoes. When no farmyard manure is applied, however, sulphate of ammonia seems to have a good effect, especially in wet seasons.
With regard to the nature of the phosphatic manure to be applied, superphosphate is to be preferred. Potatoes make large demands on potash, and consequently require potassic manures. In consequence of the fact that they receive large applications of farmyard manure, the necessity for adding potash in the form of artificial manures does not generally exist. Potash, if applied in too large quantities, has been found to exert a deleterious effect. We have already pointed out that muriate of potash tends to produce a waxy potato.
The Rothamsted Experiments with Potatoes.