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Wiltshire System.

(a.) Strong Land.	(b.) Light Land.
1. Wheat.	Wheat.
2. Beans (legumes).	Turnips.
3. Wheat.	Barley.
4. Vetches (legumes).	Beans or peas (legumes).
5. Wheat.	Wheat or oats.
6. Clover (legumes).	Clover (legumes).
7. Clover (legumes).	Clover (legumes).

These examples are not given as suited to any part of New Zealand, but are sufficient to illustrate the part that leguminous crops play in systems of rotation of crops.

In the case of (a)—heavy land, given above—we have four of these leguminous crops in a seven years' rotation, and always separating one wheat crop from another. There is no doubt about the part played by the beans, the vetches, and the clovers here. Wheat, like all the cereals, being a nitrogenous plant—requiring and removing from the soil a large proportion of nitrogen, which becomes stored up in the grain—impoverishes the soil so far as that element is concerned, and there will not be enough nitrogen left to grow another satisfactory grain-crop until the deficiency a supplied in some way. There is, however, quite enough of the other mineral food required by plants still left. Nitrogen becomes the "minimum"—the weakest link in the chain; consequently a leguminous crop—beans—is grown, which, while taking from the soil its due share of phosphoric acid, lime, potash, and magnesia, draws its nitrogen not from the soil (where there is not much to draw), but from the air (where there is an inexhaustible store of that most expensive of fertilisers). Not only, therefore, is there a big crop of beans got, but it is got at an expense (in phosphorus, potash, and lime) to the soil which is far more than covered by the enrichment of the soil in the nitrogen which is laid up there in the roots and other débris of the bean crop left after harvest. By these rat and other residual matters rich in nitrogen, the succeeding wheat will get the nitrogen required for its growth. This second crop of wheat is followed by vetches (another leguminous plant), which play the same part here that beans did in the other case. The vetches have again restored to the soil sufficient nitrogen for another crop of wheat, which is accordingly grown; this, having again used up the nitrogen, is succeeded by a two years' course of clover, which, like the beans and vetches, is leguminous, and restores the land, so far as nitrogen is concerned, to more than its original fertility. Of course, during this and all other rotations the necessary phosphates, potash, and lime must be kept up by the application of the proper manures. Provided these ingredients are supplied in sufficient quantity, the intervention of a leguminous crop may be always reckoned on for providing the nitrogen. It is an open question, however, in the case of clover, whether more nitrogen is supplied to the surface soil by eating the clover off as pasture or by cutting it off for clover hay. At first sight one would suppose that pasturing it would give the best results, because in that case most of the nitrogen and mineral nutrients (phosphorus, potash, lime, &c.) in the stems and leaves would be dropped on to the soil during pasturage; whereas, in the case of cropping clover—taking it off the ground as hay to be consumed else where—nitrogen, &c., will be removed. However, there is this consideration that must not be overlooked—namely, the leaves of the plant are its lungs, and also contain its stomata, or small mouths, by which it takes in its atom spheric food; and if these are kept small and weak by being closely eaten page 51 down by cattle or sheep the plants will not, for want of them, be able to grow to a large size, the nitrogen-and carbonic-acid-collecting apparatus will be defective, the whole plant will be kept in a starved, struggling condition, it will not develop far-reaching, enterprising roots, and therefore will not bring up from any considerable depth the mineral food-materials that may be there, and, in short, will neither require much nitrogen and other plant-food, nor would be able to use the same if they were offered, and the soil will be neither much the better nor much the worse for its presence. If, on the other hand, the clover be allowed to grow freely till it is worth cutting perhaps twice in the season, then the large leaves and the abundance of them will maintain a vigorous growth throughout; the plants will grow strong both above ground and under ground. The strong roots will support strong colonies of the nitrogen-microbe, and will penetrate far down (several feet in many cases), and draw thence phosphates, potash, and lime which would otherwise be dormant, and store these as well as the nitrogen in their large roots, and the lowest 2in. of the stem still left as stubble. The evaporation of moisture from the large leaves also will draw water from many feet under ground: this water has always a store of phosphates, potash, and lime in solution, which go with the water towards the plant, and some of which will be left behind in the surface soil when the moisture is drawn into the plants. All these nutrients—nitrogen (in the warty concretions on the large roots), phosphates, potash, and lime—will then be stored in the surface soil, and within easy reach of the following crop.

It might well happen, therefore, that the mineral food brought to the surface by the long roots would, on some soils, quite equal that taken away in the hay crop. Probably a combination of both kinds of treatment (pasturing off and haymaking) would suit some paddocks—cutting off once and pasturing afterwards. With a poor or hard subsoil that would not supply nourishment to clover roots, the surface soil would soon become impoverished with respect to its phosphates and lime, as clover requires a large supply of these, and, stimulated by the nitrogen-microbe, would rapidly take them up. In this case it would be a mistake to cut and remove the clover, as it would speedily scourge the land.

But it is not by red clover alone that this enrichment of the surface soil from below is effected. All long-rooted plants have the same effect, and among these may be classed lucerne, sainfoin, and probably all the clovers except white clover; also, though perhaps to a less degree, rape, mangels, and perhaps wheat itself, in a favourable soil. One of the functions of these in the rotation, therefore, will be to avail themselves of their long roots to tap nourishment beyond the reach of shallow-rooted plants, and to use up that nourishment, taken up by the terminals, or points of the roots, far down, and thus sparing the nutrients near the surface for the use of the following short-rooted crops. Not only so, but the roots and other débris of these long-rooted plants left in the ground will leave in the surface soil an accession of mineral food which they had rescued from below.

One could easily so impoverish the first 6in. of soil by a series of successive crops of oats that it could not carry oats again to advantage; and yet there might be an abundant store of the required phosphates and nitrogen at a depth of 9in. or 10in. A crop of rape or mangels or lucerne or red clover would tap this zone of nourishment, grow a big crop, and leave in its own débris sufficient nourishment at the surface for a succeeding good crop of oats.

Thistles and sorrel, an unmitigated evil though they be, perform this one useful function in the soil—namely, they bring up from below useful plant-food to the surface.

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Another and most important part performed by a change of crop in the rotation is the destruction of fungus and insect pests that infest some kinds of crop. Several of these are particularly attached to grain-crops, and cannot live on turnips or potatoes. When, by a series of grain-crops, such insects have become an intolerable nuisance, the remedy that suggests itself is to starve them out by growing for a season or two a crop on which they cannot live. So probably with finger-and-toe in turnips. The fungoid pest and its germs may have got possession of the land by a succession of turnip crops, and, in order to clear the soil of it, it may be necessary to grow a grain-crop, and perhaps to lay down in grass for a term. So with the disease in clover known as "clover-sickness," due, it is supposed by some authorities, to a very small longish worm that infests the plants but cannot live on any other plants than clover. It is quite useless, in this case, to persevere with the clover; no top-dressing or other manuring will eradicate the pest, and it may even take many years—five or six, or more—with other crops to starve the pest and qualify the land for clover again.

Then, there is that white grub (the larvæ of one of the ladybird beetles) which remains in the soil for two years eating up the roots of the oats and other corn, and common enough in Kurow and Duntroon and many other parts of Otago. The lecturer did not know whether that grub is very particular about its food; but, if it could not be rooted out by a change of crop from oats to turnips, then probably the best way to kill it would be to starve it out by a rigid bare fallow for a season, keeping the land quite bare of weeds and every other kind of plant.

Another service rendered by a root-crop (turnips or mangels) in a rotation is to thoroughly clear the land of the weeds that come with a grain-crop. The full advantage of this change of crop is got only when care is taken to keep the root-crop clean during the season. The after eating-off by sheep also goes to serve the same end by the perpetual and multitudinous trampling day after day for a few weeks in the cold winter weather. A change of crop, too, changes the kind of weed, or, rather, some weeds can thrive best with some kinds of crop, some with another; and, there-fore, when the crop is changed, the weeds that accompany that kind of crop, not being able to live with a different kind, are destroyed, and the new weeds that come in with the new seed will not have time to establish themselves permanently till in the course of the rotation the turn of another crop comes round. By a system of rotation weeds are thus kept under control and are not allowed to take possession of the land.

In rotations grass is often sown down with a grain-crop. Of course this saves a year, and in many cases may doubtless be of advantage, especially in strong land, and perhaps in a dry climate, where the young grass-plants require the shade of the grain-crop in hot dry weather. From another point of view, however, there is the objection that it is the same kinds of nourishment that grain and grass take out of the soil; and that therefore, on the one hand, the grain-crop has a competitor for the phosphates, lime, and potash and nitrogen of the soil, and suffers in consequence; and, on the other hand, the grass is impoverished at the outset of its career in life by having, as it were, to struggle for the means of subsistence with its sturdier companion, and thus has its natural development of both root and leaves impaired, and becomes, in this weak state, subject to the raids of insect and other pests, that may thus get a foothold in the soil, to the jeopardy and damage of the grass in its further growth.

Such are a few of the considerations that will suggest themselves to any one arranging for a system of rotation of crops; but of course there are many things to consider of more immediate and practical importance page 53 to the farmer, as for example: (1.) The market for his produce. There is no use in growing what you cannot sell to advantage. (2.) The nature of the soil. It may be quite good for certain crops, and quite unsuited for other crops that would be profitable on a different kind of soil. (3.) The climate must be taken into account—dry or wet, cold or warm. (4.) The relative price of produce. Cattle-feeding on pastures, turnips, &c., may be the most profitable in one place; grain-growing in another; dairying in a a third; cocksfoot-seed-growing in a fourth; potatoes in a fifth; and so on. He would be but a poor specimen of a farmer who would follow some hard-and-fast rules laid down by some one else, instead of thinking out for himself what would, on the whole, be the best system to follow on the land under his management. Changing prices would have to change the system. If the prices of all kinds of produce remained long in the same proportion to each other, it would be an easy enough matter to steer a safe course; but with wheat at 4s. one year and 2s. the next, or with potatoes varying between £6 a ton and £1 a ton from year to year, and similar variations in the price of other produce, it requires a very long-headed man to keep always on the safe side.