The method of soil preparation will depend mainly upon the character of the soil, and the crops previously grown. Fall plowing is often an advantage, especially for pastures, heavy sods, muck lands and clay loams. A favorite practice before planting any field in onions for the first time is to grow the previous year a crop, such as potatoes or corn, which requires thorough cultivation. Coarse stable manures may also be used the year before planting onions. Such a course of treatment will rid the land of troublesome weeds and increase the supply of humus. Rotation is highly desirable, as it is a means of reducing loss from fungous diseases and insect pests and of maintaining proper soil conditions. Other vegetables, as spinach, celery, beans, lettuce, etc., may be used with profit. The selection of the other crops in the rotation must be determined by market, soil, moisture, climate and labor conditions.
Whatever crops are grown previous to planting onions, the soil preparation must be thorough. If plowing is deferred until spring, this operation should be attended to as soon as the ground is sufficiently dry, followed by repeated harrowing, to prevent the escape of soil moisture and to prepare a fine seed bed. The usual forms of disk harrows, followed with the Meeker Disk Smoothing Harrow and finished with a plank drag should leave the land fine, even and smooth.
Muck soils, to be used for the first time, require special preparation. They must be cleared, drained and thrown up to the exposure of winter freezing. Although analyzing high in plant foods (401), large amounts are not available. Lime will help to release the needed plant food and to correct any soil acidity that may exist. It is generally desirable to grow other crops for a season or * more until proper soil conditions have been secured.
An analysis of the Southport White Globe onion shows that 2,000 pounds of the mature bulbs contain 2.70 pounds of nitrogen, 0.92 pounds of phosphoric acid and 2.09 pounds of potash. The average legal weight of a bushel in the United States is about 56 pounds. A yield of 500 bushels an acre would, therefore, make a total of 28,000 pounds, and would require 37.80 pounds of nitrogen, 12.88 pounds of phosphoric acid and 29.26 pounds of potash. Although these figures have some value in indicating the need of the onion, it is generally recognized that the amounts used should be considerably in excess of that shown by chemical analysis. The fact is, that no other vegetable requires higher fertility than the onion. The plants must have a bountiful supply of available food until the bulbs are formed.
Stable manures are universally preferred to commercial fertilizers because of their influence on the physical properties of the soil. Poultry droppings, on account of their fineness and high percentage of nitrogen, possess the greatest value. When gardeners keep large flocks of chickens it will pay to collect the droppings at regular intervals and to preserve them so that there will be a minimum loss of nitrogen. All manures, however, are prized for this crop. Composting the coarser manures is regarded as essential to reduce them to the proper physical condition, to prevent excessive top growth at the sacrifice of bulb formation and to destroy weed seeds. Fresh manures may be applied to other crops the year before or spread in the fall before or after plowing. An excellent plan is to plow first and then apply and disk in the manure. Rotten or composted manure is used to the best advantage in the spring after plowing, thoroughly incorporating with the soil before sowing or planting the onion crop.
Hundreds of successful growers cultivating lands remote from supplies of manure must resort to the use of commercial fertilizers. The greatest differences prevail in regard to formulas and amounts used an acre. Voor-hees ("Fertilizers," p. 280) recommends, for sets, "50 pounds to the acre of nitrogen in organic forms, as dried blood, cottonseed meal or tankage; 60 of phosphoric acid, which may be partly in organic forms, as bone or tankage; and 100 of actual potash, derived from a muriate. The application of a fertilizer containing nitrogen 5 per cent, phosphoric acid 6 per cent and potash 10 per cent, at the rate of 1,000 pounds an acre, and well worked into the soil previous to planting, would furnish these amounts." He further recommends applications of nitrate of soda or sulphate of ammonia at intervals of about three weeks. The fertilizers usually employed range from 4 to 6 per cent of nitrogen, 5 to 8 per cent of phosphoric acid and 8 to 10 per cent of potash.
For use in southern states. Beattie (U. S. D. A. Farmers' Bulletin 354, p. 13) recommends:
Nitrate of soda, 14 to 16 per cent nitrogen...,
Acid phosphate, 16 per cent
Muriate of potash, 50 per cent
For use in sections where cottonseed meal cannot readily be obtained:
Nitrate of soda, 14 to 16 per cent nitrogen
Muriate of potash, 50 per cent
When early maturity of large bulbs or bunching onions are desired, nitrate of soda should be used more freely. It is in general use among onion growers, the amount for dressing varying from 50 to 200 pounds an acre. The early applications are most valuable.
The total amount of commercial fertilizer an acre has a wide range among commercial growers. A very successful Massachusetts specialist never uses less than two tons. The application, however, usually varies from one-half to one ton an acre.
The great bulk of the onions grown in the United States is produced from seed sown in the open ground where the crop matures. This system is especially well adapted to conditions known to be highly favorable to the production of onions. Practically all of the American varieties, as Yellow Danvers, Yellow Globe, Southport Red Globe and Red Weathers-field, are grown from open ground seedlings..
Early seeding is regarded as of the greatest importance. As soon as the ground is fully prepared, the drills should be started. When wheel hoes are to be used it is customary to allow 12 to 14 inches between rows. When horse tools are employed in cultivating, the rows are made 24 to 30 inches apart. If the ground has been properly fitted for this crop, close planting and wheel hoe tillage will secure the largest profits. A small, well-trained mule can be used to draw the cultivator when the rows are only 18 inches apart.