ROTATION OF CROPS.

Otago Witness, Issue 3882, 7 August 1928, Page 11

ROTATION OF CROPS.

NECESSARY IF SUCCESS IS TO BE OBTAINED. By John Fleming, F.R.H.S. Rotation is a system whereby crops are so arranged that a certain kind of plant is only grown in the same soil at regular intervals, and in which a certain rational order of cultivation is followed out. The advantages derived from a good rotation of crops are many. One particular plant demands different food ingredients from another, although it is generally found that plants of one order are much alike in that respect, by changing the crop every year: then, certain particular ingredients are not drawn upon in excess, and so a more economical balance is kept up in the soil, not a dearth of some things and an excess of others. Deeprooting plants remove much of the fertilising richness of the lower strata of soil, while a fibrous sur.face-rooting crop to follow would find the upper layer quite rich in plant foods. A full use of the yhole ground is thus made, and the soil is not so quickly exhausted. Now that

Insect, Fungoid, and- Bacterial Pests have become so powerful in the garden, everything must be done to see that they ar not allowed to secure a strong hold. Continuous cropping with the same plants, nurses diseases, and so they increase in virulence while the vigour of the plants decreases through the inability of the soi] to keep up supplies of food material. Variation of crops checks these pests, and diseases may, with careful work, disappear entirely. Some crops are thinleaved or of an erect habit of growth, and weeds are able to sprout up and usurp the light and food which should fall to the plant, but if a good succession of broad-leaved plants is kept up the weeks never cause much trouble. While rotational work may be based on rules and regulations, it must be perfectly obvious to everyone that conditions over which the gardener has little control may modify his system and bring about a dis tinct break in his chain of scientific work.

The Demands of the Kitchen often fix the year’s cropping, and it my be that large supplies of one or two particular plants upset the balanced system of work. Soil, too, determines the ultimate cropping, for one kind of land will not grow certain kinds of crops at all, or with such poor returns that the work is far from being economical. Rich soils stand exhausting rotations, while poor land requires careful nursing. Heavy land grows some plants well, while others fail entirely. The

Chemical Aspect of the Matter determines much of the practice—a limy or calcareous land may suit many crops yet others will not succeed there; peaty loam is too sour for some plants, while others grow there rampantly. Climate is a factor not to be neglected, and dry districts require different treatment from those having a heavy rainfall. Minor details occasionally spring up for consideration. Thus, weedy soils must have crops which will stifle these pests and clear the land. Want of drainage may* make a soil wet, sour, and cold, and therefore quite unsuitable for many a crop. Continuously grow ing a similar crop on the same land is highly deleterious to the fertility of the soil, and very scion the ground becomes “ sick ” of that particular plant—it will not give satisfactory returns so far as that one kind is concerned. Experience proves, too, that crops of the same botanical order are more or less alike in their demands, and so a change to another plant of the same order does not mean rotation at all. Brussels sprouts, cabbages, and cauliflowers are all alike from the point of view’ of rotation, hut they differ from peas and beans, or from carrot, lettuce, or potatoes. The Use of Manure may put off the need for rotation from year to year, but even this will not stay the advance of impoverishment, and no manure yet on the market is able to retain the fertility of soil unimpaired under continuous cropping with one kind of plant. Some crops bestow benefits on the land that are not to be despised, and advantage should be taken of that power. A few open .up the soil and help to render it friable. Leafy plants keep down weeds, and one or two—-for instance, those of the pea and bean family—enrich the soil by adding to the store of certain plant foods, and continue us cropping with

them would cause a wasteful excess, whereas by changing the crops these materials bestow benefits on future plants. Short rotations are scarcely of any advantage and most of the systems in general practice are founded on a

Four-course Rotation.

Longer rotations are occasionally carried out, but in small gardens the fourcourse rotation is found to be the best. Shallow-rooting plants should follow those that root deeply, loose growing or fineleaved crops succeed those that completely hide the ground with their foliage, plants of which the seeds or leaves are of value should come after those grown for the sake of their roots or tubers, and so on. These are points to remember. All members of the brassica family should always be grown on a fresh site each year, and when possible allow two seasons to elapse before cropping the same plot again with any of the family. This rotation with the cabbage family is most essential to keep down

That Dreaded Disease Club-root or finger and toe. This fungus thrives best in an acid soil: rresh organi manure, and certain acid artificial manures, ought therefore to be avoided if the fungus is feared. Lime should be used in large dressing, for it is the best antidote for acidity and for club-root. My advice is to dress the plot with lime for the cabbage family before putting out the young plants, and immediately after removing the ■ crop, whether the plants were attacked or not. Practise the rotation of crops, and never allow the disease to spread, by imagining that as only an odd plant is attacked the pest is not worth attention.

In the Flower Garden

rotation should be practised as far as possible, and no particular bed should contain the same kind of plant more often then once in four years. Herbaceous borders, which in som» gardens have never been anything else, do not permit of the usual kind of rotation, yet if some kind of scheme should be practised much enhanced results are obtained. The plants are improved by a change of position, and the soil is not exhausted in the same degree. Rose bushes are improved by being transplanted into a new border, or in the same hole amoi_; a supply of fresh, rich compost, in order to obtain the benefits of rotation. Manures ire quite unable to refresh the soil and give that vigorous action so essential to intensive gardening. One plan only succeeds, and that is the changing of the soil year after year, and so, when we find it inconvenient to change the p’ants "n any particular border we can change the soil instead, removing the old surface layer and adding an enriched compost to take its place, thus giving a new lease of ife to the plants and enhanced glory to the border.