Production and Trade Potato Cultivation

Seed.

Good seed is true to name, high yielding, free from disease, and well adapted to the region in which it is to be used. Much effort is usually necessary to get and keep seed of such qual ity in America. Growers in the South buy nearly all of their seed from producers in the North and the maritime provinces of Can ada. This is necessary because southern-grown potatoes are seriously devitalized by heat and virus diseases. An extensive in dustry in the production of certified seed has developed in the northern States and Canada to meet this need. Approximately 13,000,000 bu. of certified seed were produced in the United States and Canada in 1927. Most of this was of the varieties Green Mountain, Irish Cobbler, Rural and Bliss Triumph. Certification is done by governmental or State institution agencies after due inspection of plants and tubers made during the growing season. In the South, where the growing season is long enough to produce two crops, a second crop is grown during the cooler months of fall. This is used to some extent as seed to plant the main crop.

Seed potatoes should be kept in a dormant condition during storage by placing them under conditions of medium humidity, darkness, and low temperature. Immediately after harvest, po tatoes are in a resting condition and cannot be made to germi nate at once. This rest period lasts about six to eight weeks after which the tubers will sprout if conditions are favourable. Storage experiments have shown that dormancy can be maintained for six to eight months at temperatures ranging from 32° to 4o° Fahrenheit. When higher temperatures foster sprout development, the tubers become shrunken, lose vitality and each successive gen eration of sprouts is weaker than the preceding one. In fact, seed vigour in stored tubers can be measured, to a degree, by noting the character of the sprouts; if small, and originating from many eyes, the seed may be adjudged weak. Long storage sprouts should not be allowed to develop and where present must be removed before treating and preparation of the seed for planting. It is a common procedure to disinfect uncut seed potatoes against such tuber borne diseases as common scab, rhizoctonia (black scurf), and black-leg. This is done at any time up to planting date, pref erably when the tubers are in a clean, dormant condition. Various disinfectants and methods are used. Corrosive sublimate (mer curic bichloride) and formaldehyde have been most used. More recently, organic mercury compounds have become popular be cause they are more rapid in their effect. The two first mentioned chemicals are applied either in hot or cold solution, the time of immersion of tubers being dependent on the temperature of the solution used. Detailed directions for treatment should be ob tained and observed for each method used. Treatment of uncut rather than cut tubers is advised.

It is good practice to green-sprout seed potatoes after disin fection. This is essentially a germination test which results in more perfect stands of plants, less disease, and usually in increased earliness. The method is to expose the seed tubers to subdued

sunlight for three to four weeks before planting. The tubers should be spread on a smooth, dry floor in a layer not over two or three tubers deep. This permits the development of short, thick, tough, green sprouts which are resistant to adverse soil conditions after planting. Green-sprouting also permits the elimination of diseased, weak-sprouting and dormant tubers. Both cut and uncut tubers are planted depending on the size of the tubers, the cost of seed, quality of seed and cost of labour. About 20 bu. of seed can be cut by hand in a day. Some mechanical cutters permit of greater speed, but more seed is wasted and less accuracy results. Large tubers must be cut for the sake of economy. Whole tubers smaller than one ounce in weight should not be used. Small whole tubers may be as good for seed as large whole seed cut provided they contain no more disease and originate from high yielding plants. Seed pieces should be cut large enough to insure at least one vig orous healthy sprout. Pieces weighing less than one ounce are subject to drying out when planted in hot dry soil and may result in weak plants or missing hills. Blocky-shaped seed pieces with a minimum of cut surface are preferred. Experiments have proved that the eyes from the basal and the apical end of the tuber are of equal value for seed. It is well to store cut seed for a day or two to allow the cut surface properly to suberize or cork over. This corking-over is best accomplished by storing the cut tubers in an atmosphere of relatively high humidity and high temperature. The use of such drying materials as hydrated lime, gypsum and sulphur to cause rapid drying is no longer recommended.

Fertilization

of the potato is a very important factor in pro duction. In the Eastern and Southern States chemical fertilizers make up nearly one-third of the total cost of production. On the sandier soils along the Atlantic seaboard, a ton to one and one-half tons of a complete analysis fertilizer is commonly applied. West ward and on heavier soils, a less quantity of an analysis contain ing less nitrogen and potash is used. In the first mentioned regions, a 5-8-7 analysis is recommended while on the newer and heavier soil types 4-12-4, 5-10-5 or these same analyses in double strength are the general rule. When stable manure is applied lib erally, as in the dairy regions, commercial nitrogen may not be needed. In using a ton or more of fertilizer to the acre, half is commonly broadcast just before planting, the other half being ap plied in the drill row at planting time. Modern potato planters are equipped to distribute fertilizer on each side of the seed piece and well mixed with the soil to avoid possible burning of the potato sprouts. In recent years, there has been a rapidly increas ing tendency to use double strength fertilizers in correspondingly decreased acre applications.