SOME CROP ROTATION REASONS.

Otago Witness, Issue 3833, 30 August 1927, Page 12

SOME CROP ROTATION REASONS.

Not nearly sufficient consideration is given to the question of how best to maintain the fertility of the farm or pastoral area, and yet it is obvious that continuous cropping or the removing of meat, wool, ,or dairy produce must in course of time mean depletion of what constitutes a fertile soil. Some sort of rotation is essential for best results. Generally the reasons given for rotations is the necessity of cleaning the land, and other considerations are neglected. Rotations do give the farmer an opportunity of ridding his farm of weeds, but, in addition, the judicious alternative of different crops brings in its train the following advantages:—The control of insect and fungus pests, the fullest use of the food reserves of the soil, the storage of fertility, and convenience in farm operations. It is obvious that a grain crop such as oats offers less chance of killing weeds than a crop of mangels or turnips, where the individual plants are well spaced and it is easy to intercultivate with the horse hoe. If grain follows grain for any length of time we find usually an immense number of weed pests, which may take years of hard work to vanquish. Then if land is forced to grow certain plants year after year it becomes “sick,” and cannot support a remunerative crop of the particular plant. For instance, we may find neglected land become “ clover sick.” In a not dissimilar way we note that plants of the Brassica family are, after some years of growing, unable to produce healthy roots. In both these cases the “sickness ” is due to fungus pests, which are encouraged by the continual presence of certain kinds of plants, so that in the end they are able to ruin the complete crop. Consequently it is necessary in practice to alternate crops belonging to different families or natural orders, in order either to starve out the fungus which causes the sickness or to prevent it from becoming strong enough to do damage. Thus plants of the natural order Brassica?, such as cabbage, kale, swede, mustard, etc., should never occupy the same land two or at the very latest three years in succession. Of course, no hard and fast rule can be made, but one is courting failure if the requirements essential for the healthy growth of plants are not studied in due time.

The advantage of alternating crops can be readily observed if opportunity offers, as different plants explore different layers of soil. Shallow-rooted crops, like barley, if grown year after year rob the upper layers of soil, whilst the mineral elements available in the deeper parts are but lightly called upon.. Bj’ substituting' mangels (-which are' very ~eep rooted) for barley the fullest use can be made of the plant food available at varying depths, whilst deep-rooting plants will also promote the drainage and aeration of the lower layers of soil. A wise rotation system enables one to keep up the soil’s supply of the necessary organic matter. Under arable conditions, where the plough goes many times over the land, the humus is continually being used up, and thus does the soil’s fertility diminish. By ploughing under grass and clover roots we add to the stores of humus. Another advantage which accrues from the growing of clovers and grasses in a rotation is the storage of nitrogen due to the activities of bacteria which live in the nodules on the clover roots. Nitrogen is the most ■ expensive fertilising element required on the farm, but by using a rotation it. is possible to get nitrogen - added to the soil at a very cheap rate-.?- The Romans knew’ that clover benefited a •following ..wheat crop, and employed their knowledge in the form of rotations

which included leguminous crops like clover and beans. In a final word, it may be considered by some that arable farming will die out in course of time owing to the increasing costs of cultivation, implements, etc., and the great booin in fertilising pastures and the growing and fattening of stock; but arable farming is essential wherever good farming practices are followed, and will continue to the end. Experience has shown that by growing different kinds of crops in a particular order reliable results may be looked for, and hence we find that suitable rotations permit greater vigour in the crops; they arc more economical of manure, permit of an economical distribution of labour, and generally enable that variety of foodstuffs so essential where cattle and other live stock are kept to be grown.