The Feeding of Plants

I am asked to write on the broad subject of feeding plants and animals, but, to convey any precise ideas at all, I must employ the alphabet of science.

My Abc must be, on the one hand, Phosphates, Alkalies, and Nitrogenous salts; and, on the other hand, Proteids, Carbon- page 2 hydrates, and Fats. Take the simpler case first. What food does a plant need? Mainly air and water. Given these, an ordinary plant, with reasonable protection, will grow and flourish in the presence of sunshine, provided it has a suitable medium in which to push out its root system and to serve as a basis from which to rear the stem and leaves. Air, water, and sunshine are common property; and mere land, apart from the question of quality, is cheap enough. What, then, is there left for the farmer to supply when he has given his plant a suitable mechanical basis of support? What does a plant need to take out of the soil that land should vary so much in price? The common notion is that a plant builds most of its solid structure out of the solids it absorbs from the soil, though a moment's reflection over what remains after the burning of a tree or a field of ripe corn would point to the true conclusion, namely, that the whole plant—root, stem, leaves, and seed—is made out of mere air and water, with a trace only of solid mineral matter. But it is just this trace which it is important for the farmer to know about, because, while Nature has been liberal enough to supply him without charge with an inexhaustible stock of air and water, she has left it largely to himself to keep stored up in the soil with his own labour and money the proper proportion of mineral matter and nitrogen needed by the crops which he elects to grow.

Much can be done by systematic rotation and thorough tillage to keep the land in good heart—in other words, to induce Nature by means of sunshine, frost, rain, bacteria, etc., to keep on liberating from the upturned soil and subsoil year after year a sufficiency of the special salts needed for each succeeding crop. Proper rotation and tillage form the basis of all good agriculture, and really constitute the best means of manuring the land; but, when we desire to make specially paying crops take their turn more rapidly than Nature is able to renew her supplies, we must be prepared to make up the deficiency ourselves. In one soil the potash will tend to run short, in another the phosphates, in another the nitrogen; and this result will be much affected by the nature of the crops grown.

The purpose of the science of economic manuring is to learn to add each season for the particular crop we intend to grow just what is lacking in our soil, and nothing more. It requires no thought or knowledge to buy a manure labelled "Potato Manure" or "Turnip Manure," as the case may be; but this is mere wasteful empiricism, because such compounds can be specially adapted only for a ticular soil in a particular condition. They contain all the manurial constituents, where, perhaps, only one is markedly lacking. Attentive, accurate observation and experiment alone can determine what is really needed, and every farmer can find out this for himself without expense if he will take a little trouble.

Consider the case of a particular crop—the potato. At the present time this is especially important, on account of the "blight," which is Nature's messenger warning us that, if we do not keep our crops in robust health and vigor, she is going to back a lower form of life to destroy them. Our only response in the face of the enemy is the expensive one of arming ourselves with spraying pumps and page 3 poisons to kill the organisms as they come on year after year. The precaution is a proper one, but more essential things to do are (1) to grow only the hardiest and most resistive types of potatoes; (2) to procure good medium-sized seed from vigorous crops in other localities; (3) to keep the seed properly, so that it may not use up its strength by loss of first growth before planting; and, finally, to plant early in well-tilled ground containing the proper manurial constituents. We are fortunate if we happen to have a new bush clearing or a lea paddock which has not borne a potato crop for many years, but in the best potato districts such conditions are becoming rare. At Oamaru, for instance, I find farmers engaged in growing potatoes over and over again, almost without intermission, and with the addition of little or nothing in the way of manure. The steady decrease in the quantity and quality of the crops, which the farmers all admit and deplore, is inevitable.

Surely it would be worthwhile to find out precisely what is lacking. Nature contributes free everywhere at least 99 lbs. of the weight of every 100 lbs. of potatoes grown. We are called upon to supply only what she fails to make up, viz., at most, about one per cent of the weight of our crop. In other words, if we manage to increase a five-ton crop to a ten-ton crop by manuring, we shall have contributed to the tubers only about one cwt. per acre of pure phosphoric acid, potash, and nitrogen, at a cost of about £2 8s. 6d. This sum would provide a quarter of a ton of manure made up of 3 cwt. superphosphate, 1¼ cwt. of sulphate of potash, and ¾ cwt. of sulphate of ammonia, which allows a page 4 margin for impurity of commercial manures, for what is carried away by drainage, for what the plants fail to absorb, and for what they employ in building their roots, stems, and leaves. It will have cost us thus £2 8s. 6d. for the yield of an extra five tons of superior potatoes, and we shall have done much to render our crop vigorous and to save it from the ravages of disease. Such a compound manure as I have indicated would tend to largely increase the yield of potatoes on any land impoverished by cropping, because it contains all the necessary manurial constituents and is rich in potash, which is the special requirement of all the solanum tribe—potatoes, Cape gooseberries, tomatoes, native proper (bull-a-bull), etc.—which we know to revel in our bush clearings, rich in the potash of fallen leaves and burnt trees.

Some soils lack little but potash. In such cases why should we incur great expense in providing full proportions of nitrogen and phosphates? Usually all three constituents are beneficial, but they need to be supplied in proportions varying widely according to the soil. The problem of economic manuring can be solved in one way only, and it can be approximately solved very simply. When drilling a paddock for potatoes, mark out a small, even-looking patch for testing. Say the rows are 31 inches apart: select 10 drills and put pegs 15 feet apart in each drill. Each short row between the pegs will then represent 1-1120th of an acre, and will serve for 10 potatoes placed 18 inches apart. A quarter of a pound of manure to 15 feet is, then, equivalent to 2½ cwt. per acre. Treat the patch as follows:—

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Experimental patch of British Queen Potatoes planted at Seacliff in August of the present year with a view to ascertaining the advantage of keeping seed in shallow trays partially exposed to light and freely exposed to air, as compared with keeping the seed in bulk on a cellar floor or in pits.

The fore-ground area, below the white line, was planted with seed kept in the ordinary way, and procured from a first-class seedsman in Dunedin. It was an excellent sample, and had the advantage of coming from a district remote from Seacliff. The seed was picked and weighed, and the four rows were planted in succession from left to right with potatoes weighing respectively 2oz., 3oz., 4oz., and 5 to 7oz. The same order of weight was continued above the white line, but using potatoes grown at Seacliff. In this case, therefore, there was not the advantage of a change of seed. On the other hand, these potatoes had been stored, from the time of lifting the crop, in shallow trays, exposed to air and diffused light. The trays were essentially similar to those shown in the diagram to the left, but were made rather deeper and with skeleton frames, in order that there might be a free passage for light and air between the successive layers of potatoes when the trays were piled up to a height of four or five feet in a shed. The battens, &c., needed for making a thousand trays, cost £20. The labour of making was very little indeed, and could be done by any boy who has learned to use a hammer and saw. With reasonably careful usage, the trays should last ten years. A thousand trays suffice for storing about a hundred thousand tubers—say enough to plant about ten acres. The crop shown above is almost ready to dig, and, at the present high prices, would bring over £130 per acre. The three potatoes in each row between the lower transverse white line and the stakes higher up, were intentionally deprived of the shoots they had formed at the time of planting, and had to start in the same apparent condition as the potatoes planted below the white line. The seed planted with the sprouts intact came up with almost perfect regularity in September, a month sooner than similar seed deprived of shoots. The coming up of the seed kept in the ordinary way was extremely irregular, and was delayed from another month to two months; and in some instances the shoots are only appearing now, in the middle of December. This delay is partly due to the unusual wetness and backwardness of the season. Our neighbours' potato crops have in some cases failed almost completely, owing to the tubers rotting in the ground. It will be noted that one row of the seed kept in trays was cut. As this row runs right through the patch, it can be directly contrasted, in the fore-ground, with the comparatively feeble growth of the ordinary seed on either side. In further reference to the fore-ground patch, planted with ordinarily-kept seed, it may be noted that the potatoes between the transverse white line and the white pegs below were uncut, whereas those below the pegs were cut. The cutting, therefore, seems to have exerted comparatively little influence. The true test, however, will be the actual yield of potatoes. In the meantime it is interesting to study the diagram to the left, taken from a child's primer, published by Macmillan's twelve years ago, and to read what experience and observation had then taught on the other side of the world.

I would further point out that over half a century ago—after the potato disease had ruined Ireland—a London market gardener showed in a series of letters writtten to the Times, that while the potatoes all around him were a prey to the blight, his crops were unaffected, simply because he had taken the trouble to keep his seed exposed to light and air. Yet our New Zealand practice is still in the dark ages!

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At the end of a single season a farmer who carefully carries out this simple experiment with an equal sample of potatoes will have learned more about the science of economic manuring in relation to his own farm than any books or professors can tell him. I have supplied sets of weighed packets of manures, with directions, to two schools and to a number of persons interested in progressive farming, both in the North and South, this year, and shall be glad to do the same next season. Our object is to try to stimulate interest in farming as a profession, and to acquire and diffuse reliable practical information as to the special manurial requirements of various parts of the colony. We hope also to enforce attention to the great truth that the highest wisdom lies in sparing no pains to maintain the young organism throughout in the best possible condition. In plants, just as in the case of animals, the inroads of disease are best prevented by keeping the organism well nourished, vigorous, and healthy. It is better to be prepared to fight one's enemies rather than poison their wells. The potato plants which suffer most from various blights are those which have the least vital energy and resistiveness—the turnips attacked by aphides in a field are not, as one might expect, the healthiest and most appetising, but the weakest and least resistive; so also with human beings and consumption or any other disease. The broader principles of life apply equally to plants and animals. Such laws and principles ought to be conveyed to the rising generation, could be easily illustrated to children in schools, and would be appreciated by them.