ROTATION OF CROPS.

New Zealand Journal of Agriculture, Volume XVIII, Issue 2, 20 February 1919, Page 83

ROTATION OF CROPS.

By

A. McTAGGART,

M.Sc.Ag., Agriculturist.

All good farmers adopt a rotation of crops that suits the special conditions? of soil, climate, locality, and market with which they are associated. To do so is decidedly in the interests of productive agriculture and conservation of soil-fertility, upon which two important factors may be said to depend the perpetual welfare of a State'. Unfortunately, however, for some countries systematic crop-rotation is not universally adopted, and the result is the eventual abandonment o farms once the homes and means of sustenance, of prosperous families A standard example of this is to be found in the hundreds of abandoned farms m the New England district of the United States of -i America, fn certain districts of New 'Zealand, too, depletion of soil-fertility as gone • on apace for many years, due to the growing year after year of cereal crops and no attempt being made at crop-, rotation. It is to these districts especially that this article is directed.

SOME REASONS FOR CROP-ROTATION.

. There are many reasons why crops should be rotated. The following embrace the most important :—. ? ; (i.) Plant-food required.in abundance for one crop is. not- wanted in the same quantity , by another crop. Hence a rotation of crops utilizes stores of certain forms of available plant-food that would in Thn^+R 1 g ° unutlllzed Were 1 the Same cro grown year after year. Thus the natural food-supply, of the soil and the manures and tJnpJ required are economized. A proper balance is also maintained among the fertilizing constituents of the soil. rrnn 2 ’Lfi°-+~ fe r tlllty ls conserved. By growing continuously the same crop definite l Or T Of plant in the soil are more, or less rapidly exhausted, but where a rotation system embodying- a leguminous crop I clover ■P eaS? l &c.) is adopted fertility is conserved, for nitrogen, the fZJ of plant-food most readily (depleted from the. soil, is obtained . air ad stored for the use of subsequent crops. This assimilation of atmospheric mitrogen and its fixation is brought about by bacteria associated with the roots of legumes. This process of mutual sustenance of plant and bacteria, as the result of the activities both, is known, as symbiosis. The practice (of crop-rotation is made nrSr HS the / eSult + ° f this far-reaching discovery Scientific cropL.S 10n d ’ mamtena of soil-fertility are thereby rendered footing’ ’ mg PraCtlCe iS accordin S 1 y Placed upon a permanent

in the Sn ? crops, interchanged with (shallow-rooting n the rotation, draw upon the stores of plant-food existing in the lower portions of the soil and in the subsoil By so doing thev bring up to the surface, also to somejextent leave unassimilated in the upper

portion of the soil, nutrients that eventually become available for the shallow-rooted crop embodied in the system of rotation.

(4.) Production from the soil is increased, for, owing to the greater availability of plant-food in form suitable to the varying requirements of each crop in the rotation, more vigorous crops obtain, and hence high yields from the individual crops are secured as compared with the mediocre and gradually declining yields obtained from the same crop grown year after year -on the same area of land. The nitrogen accumulated in the soil as the result of the growth of the leguminous crop in the rotation,, whether alone or as clover in the pasture, plays an important part in promoting this increased production ; and to this important plant-food constituent, continuously augmented by the growth of the legume or legumes, is largely due the perpetuation of high or satisfactory crop-production and of a high degree of soil-fertility.

(5.) Weeds are eradicated or kept in check as the result of the •various methods of cultivation necessary for preparing the land for crops under rotation and for promoting a satisfactory growth of these crops. Prominent among the rotational crops valued from the point of view of cleaning the land is the hoed crop — roots, maize, or other crop calling for intercultivation. If more attention were paid to systematic crop-rotation in New Zealand there would be fewer weeds to contend with.

(6.) Pests, both insect and fungus, are kept in check to a large extent. The vigour of the crop grown in rotation is increased, and the crop is thereby fortified to a degree against the ravages of such pests, whereas a crop grown continuously on the same land suffers a loss of vigour and readily succumbs to attack by insect and fungus parasites when prevalent. The change of food provided by varying the crop under a rotation system does not suit the particular attacking pest, and the result is either the death of the pest or its transference to more congenial environment. 1 Notable examples of this phenomenon are to be found in the aphis being as a rule markedly numerous where turnip crops are grown on the same land for a few years in succession; in club-root being prevalent where cruciferous crops (turnips, swedes, &c.) are raised without lengthy intervals between the growing of members of this order, particularly when sown in a soil inclined to be sour and known to be affected by the club-root organism : and in rust being most marked, as a rule, where only a poor growth in a cereal crop obtains. In the latter case the crop is too weakly to resist attack- by the fungus parasite. Evidence of this phenomenon is to be found, in the comparative freedom from rust in a cereal crop grown on land where a good growth of clover had been ploughed under. The humus added to the soil thereby, also the moisture conserved and better distributed by this incorporation, results in a vigorous cereal crop, fortified to withstand invasion from the rust when the latter ultimately begins the attack under suitable conditions of temperature and moisture. A further example is that of the grass-grub often being decidedly bad in light porous soils where a short rotation of crops is not followed. Breaking up the land fairly frequently, rolling heavily, and substituting red clover for grass will greatly reduce this pest, if not rid the land of it. - -

(7.) A more even distribution of labour is promoted on the farm. As the crops under rotation are seeded and harvested at different times there is work for farm labour the year round ; hence the rush attendant upon the seeding and harvesting of one particular crop grown regardless of rotation is avoided, and the regular employment of satisfactory labour is assured where such is available. More stability is thus given to farming because of this regular employment of labour under a farm crop-rotation system.

(8.) A variety of crops for market and live-stock requirements is provided. Indeed, it is hard to conceive of live-stock being kept and satisfactorily fed without the'adoption of a system of crop-rotation, unless resort is made, * under favourable conditions, to pasture continuously as a means of feeding and finishing farm animals. . Diversity in crops grown on the farm means greater resource in the feeding of various classes of stock, also greater control of fluctuating conditions connected with the market prices of farm animals and their products and of farm crops subject to sale.

(9.) The location of live-stock used for feeding off farm crops is changed every year, thus improving the health of farm-animals as well as promoting increased production through the more vigorous cropgrowth, due to change of soil and to distribution of animal manure, and through the increased vigour of the stock fed on new ground.

(10.) Heavy loss, due - to failure or destruction of the crop grown repeatedly without regard for rotation, is avoided when a systematic rotation of crops is practised. In adhering to the latter the farmer “ has his eggs in more than one basket,’' and hence failure of one crop in the rotation system means only partial . loss of the product of the farm during a single year.

(11.) Seed is kept from deterioration under a rotation system because it is raised each year on a fresh area of land, whereas if grown regardless of rotation on the same land year after year it rapidly deteriorates. Of course, fresh seed could be obtained each year from off the farm, but this system has its inconveniences, and is a means of introducing weed-seeds periodically, and there is perpetually presented the defects ■due to growing the same crop on the same area annually. By these remarks it is not suggested that farmers should always save their own seed, but in most cases, and especially with certain crops and strains of seed thereof, it is decidedly advantageous.

The foregoing constitute the chief benefits derivable by the farmer from the adoption of a systematic rotation of crops suitable to his special conditions. In view of such benefits it is difficult to conceive of any tiller of the soil to-day refraining from practising a rotation of .some kind, much less his neglecting to ascertain the crop-sequence that best suits his special circumstances.

THE NORFOLK SYSTEM.

A type of rotation 'common to farming in various parts of the world, but particularly in England, is what is known as the Norfolk system. It is a four-year rotation consisting of wheat sown in the autumn on land ploughed out of lea a cleaning crop or crops, such as turnips, ■swedes, and potatoes ; barley or oats sown in spring ; and a leguminous

crop, such as clover (alone or in a mixture), peas, or beans. The wheat crop is sustained and encouraged by the nutrients (nitrogen principally) that accumulate as the result of the growing of clover or other legumes. The root crop is shallow-rooted, and hence feeds in the surface layer of the soil and not so deeply as the wheat crop. The following barley or oat crop profits by the residue from the phosphatic manuring of the root crop. The exhausting effect of the cereal crops, particularly as regards nitrogen, is offset by the growth of the succeeding leguminous crop. ' '

Many of the longer rotation systems are based upon the. Norfolk system. While it is the longer rotations that best suit New Zealand conditions, yet the short or four-year rotations are of decided value where the land is high-priced and limited, as usually obtains in the vicinity of our cities. Under such conditions the land needs must produce the most possible ; and the product has‘always a ready sale, or it can with profit be readily stored in the form of hay, ensilage, &c., for consumption during the period of least growth. A maximum production is required, and one of the following short rotations (chosen according to the conditions prevailing in a particular locality) will provide such :— -

No. i.— (i) Roots (swedes, mangolds) ; (ii) barley (iii) legumes

(clovers, peas, or clover in mixture) ; (iv) oats.

No. 2. — (i) Oats; (ii) legumes; (iii) maize (for ensiling) ;

(iv) roots.

No. 3. — (i) Wheat; (ii) roots ; (iii) oats ; (iv) legumes

Under such a rotation a liberal supply of artificial - fertilizer suited to the conditions of soil, climate, and crop is, as a rule, all that is required in the way of manure. The soil-renovating leguminous crop, together with proper and timely cultivation, do- all that is further required ' for keeping the crops growing satisfactorily- and ■ the soil always in good heart. -

SOME OTHER ROTATIONS. For purposes of intensive farming on high-priced land of limited area near a city, or on land that will not hold pastures for any length of time, the following . four-course five-year rotation of crops would also be suitable :

No. 4. —■ First year : (i) Oats ; (ii) green feed ; (iii) temporary pasture ;

(iv) temporary pasture

Second year: (i) Green feed; (ii) temporary pasture; (iii) temporary pasture ; (iv) roots.

Third year : (i) Temporary pasture ; (ii) temporary pasture ; (iii) roots ; (iv) oats.

Fourth year : (i) Temporary pasture ; (ii) roots ; (iii) oats ; (iv) green feed.

Fifth year : (i) Roots ; (ii) oats ; (iii) green feed ; (iv) temporary pasture.

In this rotation oats, green feed, and roots are each in turn missed every five years, thereby providing for the greater part o the time a

plentiful supply of temporary pasture, also green feed for feeding out to stock or for 'ensiling, and roots for feeding during winter with hay and ensilage. ' •

A longer rotation, suited for dairy farms and holdings suitable- for sheep- and cattle-fattening purposes, - especially for land that calls for breaking .up fairly frequently and not removed far from factory or market, is to be found in the following:— . ■

No. 5. — (i) Forage crops (rape or mixtures suitable for ensiling or feeding off) ; (ii) roots (mangolds, swedes, turnips) ; (iii) oats; (iv) grass and clovers ; (v) grass and clovers ;

(vi) grass and clovers.

No. 6. — (i) Oats ; (ii) grass and clovers ; (iii) grass and clovers ;

(iv) grass and clovers ; (v) roots ; (vi) forage crops.

No. 7. —(i) Forage crops ; (ii) grass and clovers ; (iii) grass and clovers ; (iv) grass and clovers ; (v) roots ; (vi) oats.

In No. 5 the grass-mixture is sown with the oat crop. The legumes grown in the pasture mixture, also in the . forage-crop mixtures (if grown), add nitrogen to the soil and so benefit the non-leguminous crops grown in these mixtures, also the succeeding root and oat crops. In No. 6 the root crop cleans and ameliorates the soil for subsequent satisfactory growth of the forage and oat crops. . Should it be preferred, owing to the nature of the soil or other cause, to sow the grass-mixture alone this can be done after the forage crop is. off, provided the weather and . seasonal conditions are favourable. No. 7 provides for such a contingency, as also for sowing the grass-mixture on rape land (unploughed) when fed off, if conditions suit such an economy.' Under average conditions of soil-fertility the only manure required for these six-year rotations is that applied—with the root crops, and with rape if grown as the forage crop. When the land does not carry a long grass lea, owing to lightness of soil or other deficiency, these six-year rotations are also adaptable. If desired, the length of grass lea could be slightly reduced. . - . '

For conditions such as remoteness from market, and difficulty or disinclination towards breaking up the lands owing to labour and other causes, the long rotations embodied in the following should be considered :— - -

No. 8. — (i) Oats; (ii) grass and clovers; (iii) grass and clovers

(iv) grass and clovers; (v) grass and clovers; (vi) roots (turnips) or rape. . ,

No. g. — (i) Roots or rape; (ii) grass and clovers; (iii) grass and clovers; (iv) grass and clovers; (v) grass and clovers;

(vi) oats.

No. 10. — (i) Wheat; (ii) roots or rape; (iii) grass and clovers ;

(iv) grass and clovers; (v) grass and clovers; (vi) grass and clovers; (vii) grass and clovers.

No. 11. — (i) Roots or rape ; (ii) wheat; (iii) grass and clovers ;

(iv) grass and clovers; (v) grass and clovers; (vi) grass and clovers ; (vii) grass and clovers.

In each case the grass lea can be varied (lengthened or shortened) according to the conditions associated with the farmer. In No. 8 provision is made for so wing, the grass - mixture with the oats if soil

and climate permit, while No. 9 provides for seeding the mixture on rape ground or the ground properly prepared by the growing of a turnip crop liberally manured. This latter provision is also found in No. 10, designed for wheat areas not handily situated. In No. 11 the wheat crop is grown on land well prepared by the previous growing of turnips or rape. In these latter six- or seven-year rotations the manure required for maintaining the soil in good heart is also supplied liberally with the turnip or rape crop.

CONCLUSION.

The foregoing discussion of definite rotations suitable for New Zealand conditions is, of course, not to be regarded in the light of finality, for local differences in conditions sometimes cause marked variation in the required rotation. Nevertheless, these rotation systems embody the principles of rotation viewed from the standpoint of the general conditions prevailing in New Zealand in respect to arable land.

Finally, the writer would emphasize the fact that rotation of crops is the foundation of modern farming. The responsibility of maintaining that foundation rests upon present-day farmers individually and collectively.