The question how far farmyard manure may be supplanted by artificials is one often discussed. We have already referred to this question in the chapter on Farmyard Manure. It is possible that, with our increasing knowledge of agricultural science, we may in the future be able to dispense with farmyard manure, and make shift to do with artificials alone. At present, however, all our experience points to the fact that the most satisfactory results are obtained from manures by using artificials in conjunction with farmyard manure. It is better both for farmyard manure and artificial manures to be applied together,[241] so that they may mutually act as supplementary the one to the other. While this is so, there may be circumstances in which it will be best to use artificials alone. Where, for example, fields, owing to their situation, are inaccessible, and where the expense of conveying the bulky farmyard manure would be very considerable, it may be found more economical to apply the more concentrated artificial manures. With few exceptions, however, it will be found most desirable to use artificial manures as supplementary to farmyard manure, and not as substitutes for it. _Farmyard Manure not favourable to certain Crops._ While the above is true, it may be well to point out one or two facts regarding the nature of the influence of farmyard manure on certain crops. For instance, it has long been recognised as inadvisable in strong rich soils to apply it directly to certain grain crops, such as barley and wheat, since such a practice is apt to encourage rankness of growth--an undue development of straw at the expense of the grain. It is consequently customary to apply farmyard manure to the preceding crop. The direct application of farmyard manure to wheat, however, according to Sir J. B. Lawes, is not fraught with unfavourable results where the soil is a light one; it is only when the soil is of a heavy nature that it is best to apply it to the preceding crop. Potatoes are another crop to which it is best not to apply it directly. On the other hand, many are of the opinion that mangels seem to be able to benefit from large applications of farmyard manure. _Conditions determining the Application of Artificial Manures._ In the application of artificial manures a large number of considerations have to be taken into account. Among these may be mentioned the nature of the manure itself, and its mechanical and chemical condition; the nature of the soil and its previous treatment with manures, as well as the nature of the climate, the nature of the crop, and the previous cropping. It may be well, therefore, to examine somewhat in detail some of these considerations. _Nature of the Manure._