THE USE OF MANURES.

Otago Witness, Issue 3148, 15 July 1914, Page 14

THE USE OF MANURES.

Modern agriculture is now recognised as an art based on a scientific study of the conditions under which plants live and grow and of the factors inducing fertility. Possibly science as applied to agriculture has not made such rapid progress as it has in relation to other branches of industry ; but nevertheless the success crowning the farmer’s efforts is in a large measure directly proportional to his understanding of the principles already established in so far as they affect his calling, and his ability to use the weapons which it has placed at his command. One of the features distinguishing modern agricultural practice from 'the old rule-of-thumb methods obtaining half a century ago is the increasing recognition of the value of artificials in assisting to maintain the soil in a state of fertility consistent with profitable crop production. The intelligent use of chemical fertilisers is now a recognised economy on all up-to-date farms. Until the advent of artificials, farmyard manure was almost wholly depended upon to keep the soil in good heart and' to supply the elements necessary to plant nutrition, and it should still form the basis of manurial treatment for soils showing signs of exhaustion. The problem with which the farmer is faced is not whether either chemical fertilisers or farmyard manure will satisfy the manurial requirements of his soil, but how best to make use of both, as it is now a generally admitted fact that the best results are obtained not by the use of either singly but by a judicious combination of the two. Each serves its own specific purpose—the farmyard manure supplying the humus necessary to the action of the nitrifying bacteria and at the same time improving the physical condition of the soil, while the artificials provide in a concentrated and comparatively quickly available form the elements necessary to plantgrowth. Of these latter elements those most likely to become temporarily exhausted owing to the demands made on the soil’s supply are nitrogen, phosphoric acid, and potash, and it is with the object of making up for the temporary deficiency of one or other, or all, of these ingredients that artificial fertilisers are applied. In referring to these deficiencies as temporary, the idea intended to be conveyed is that the elements are not present in an available form, although considerable quantities may be present in the soil in a dormant or insoluble condition. It is this dormant plant food which, by the action of the various chemical agencies in the soil, is ultimately rendered more or less soluble, and consequently available for succeeding generations of plants. It might here be noted that the chemical analysis of a soil is not of itself an accurate means of determining fertility, in that it only estimates the total amount of plant food in the soil, not distinguishing between the proportion of it which is available and that which is dormant. Chemical analysis has often shown soils to be abundantly supplied with all the elements necessary to plant ’ nutrition, and yet such _ soils fail to produce profitable crops, simply because this food was not in an .available condition. Other than indicating whether any elements are actually lacking in the soil, a chemical analysis may therefore prove of little practical value to the farmer. The only accurate method _of solving the problem of manurial requirements of a particular soil is by actual experiment on strips in the field. Taking as basis the constituents likely to be deficient —namely, phosphoric acid, potash, and nitrogen,—experiments should be conducted with the different fertilisers supplying these ingredients. By using the artificials in combination on one strip and then omitting one or other, or using each singly on succeeding strips, and comparing the results with those obtained on a control plot to which no manure has been applied, the manurial treatment to which the soil best responds can be accurately determined. Farmers will find such experiments profitable in the long run, often saving themselves the expense of providing fertilisers which are probably not required. This aspect of the question should commend itself to the_ thoughtful consideration of the progressive farmer. While there is no general rule, a number of factors must be considered in the economic selection and use of fertilisers. The food requirements of the different crops, their period of growth, the nature of the soil and its lime content are all important points. It is a matter of common knowledge that different plants require different amounts of plant food for their growth, and consequently derive different benefits from different manures. Some plants, for instance, particularly require nitrogen, others potash, while others favour phosphoric acid; so that even though an increase may be shown on the application of a complete manure (that is, one supplying all three plant foods) it is quite -possible that it may be directly due to only one of the elements provided by the fertiliser. The oftrepeated advice, “ Manure the crop, not the land,” should therefore be kept steadily in view. Then, again, the nature of the soil is an important factor in determining the choice of a fertiliser. To retentive soils readily soluble fertilisers are more suited, while to hungry, sandy soils, owing to the possibility of loss by leaching, the slower acting manures should be

applied. On land with a tendency to sourness acid manures, like sulphate of ammonia and superphosphate, should be replaced by those with an alkaline reaction like nitrate of soda and basic slag, thus minimising' the risk of exaggerating the acidity. The period of growth must also be considered. It is very evident that crops which mature quickly will require readily soluble food, while for those occupying the ground for a longer period, and consequently having more time to obtain their food, the slower acting materials would do as well. It will thus be seen that each soil and crop presents a separate manorial problem, and it is only by carefully-conducted experiments that the key to fertility can be accurately ascertained.