Earliness, high quality and large size are the factors that count for the most in securing remunerative prices, and liberal and intelligent feeding bear a direct relation to each of these requisites. The gardener expects a great deal of his asparagus plants; he wants them to produce salable shoots for two months or more and then recuperate sufficiently to yield a good crop the next year.
When starting a new field the plants should have all the food they can utilize. Soon after setting, 800 pounds of a 5-8-10 fertilizer should be applied along the rows, and a top-dressing of nitrate of soda used at intervals of three or four weeks. Rotten manure can be used profitably before planting. A similar treatment should be given the second year. The plants should then be well established and a different course of treatment given.
The supply of vegetable matter must be maintained. This may be done by applying annually 10 to 15 tons of stable manure to the acre. Much larger amounts were used some years ago, but more economical results have been attained by reducing the application of stable manure and increasing the amount of commercial fertilizers.
Manure may be applied in the fall, early in the spring or at the close of the cutting season. It is doubtful, however, whether application should ever be made in the fall, and there is a growing inclination to make such applications after the cutting season, rather than in the spring. All kinds of stable manures are satisfactory for asparagus. They should be applied between rather than directly over the rows. It is believed that mulching with manure over the rows is objectionable because of the tendency of the manure to draw,the crowns of the plants nearer and nearer the surface. Furrows are often opened with a one-horse plow to receive the manure. This practice is questionable, because the plow necessarily breaks and mutilates a great many roots. The better practice is to broadcast the manure as evenly as possible between the rows, and to mix it with the soil, by the use of a disk or a cutaway harrow.
Very few garden crops can be fertilized as heavily as asparagus and a profit be made on every dollar expended for plant food. Many of the most successful growers believe that the largest net returns cannot be realized without an annual investment for plant food of $60 to $80 an acre. Stable manures have been practically abandoned by some growers, but the safer practice is to apply them liberally enough to maintain the supply of humus. From one to three tons of commercial fertilizer an acre may be employed advantageously on established beds.
There has been much discussion as to the character of the fertilizer adapted to this crop. According to analyses made by Wolff, a ton of fresh sprouts contains 6.4 pounds of nitrogen, 1.8 pounds of phosphoric acid and 2.4 pounds of potash. The best fields produce at the rate of three tons an acre, and this would require 19.2 pounds of nitrogen, 5.4 pounds of phosphoric acid and 7.2 pounds of potash. It is very evident that the shoots themselves do not abstract large amounts of plant food. To meet these needs it would take only 128 pounds of nitrate of soda, 38 pounds of 14 per cent rock phosphate and 14 pounds of muriate of potash. Now, why do expert growers feed their plants with such great liberality? Because other factors besides the mere production of shoots must be taken into account. The enormous root system and the tons of tops renewed every year must be supported. Again, growth of both shoots and tops must be very rapid, and consequently there must be no shortage in the supply of quickly available plant food.
Nearly all growers agree that nitrogen is the most important element of plant food for asparagus, and while the majority of them believe that it should be applied in the form of nitrate of soda, some growers prefer organic material, as dried blood, tankage, fish scrap or cottonseed meal. As to the best commercial fertilizer to use, investigators and practical growers differ widely in their recommendations. Voorhees suggests the basic fertilizer, 4-8-10, supplementing with heavy applications of nitrate. Rolfs recommends 4-5-7. An expert New Jersey grower uses a 6-7-5 formula. Many practical growers prefer 5 or 6 per cent of nitrogen.
The proper time of application is a much disputed question. As the leaves or elaborating organs are not permitted to develop until after the cutting season, it is argued by some that the proper time to apply nearly all of the plant food, both stable manure and commercial fertilizer, is after the cutting season, when the leaves are formed. Voorhees and others believe that the plants are benefited by early spring applications, especially if green shoots are produced. On the other hand, we must not lose sight of the fact that next year's crop is mainly dependent upon this year's top and root development. Large tops and strong roots mean heavy shoots next year.
If seeds and plants have been selected intelligently and all cultural conditions are favorable, the following treatment should give excellent results: Apply 10 to 15 tons of fine manure early in the spring, or probably with as much benefit immediately after the cutting season; one and one-half tons of a 4-8-10 mixture, half applied in early spring and half immediately after the last cutting; 150 pounds of nitrate of soda by broadcasting as soon as growth begins in the spring; 150 pounds of nitrate of soda when the cutting season is half over; 150 pounds of nitrate of soda at the close of the cutting season and the same quantity one month later.
Common salt was used in large amounts on asparagus beds until quite recently. It possesses no fertilizing value, and although it draws some moisture and is injurious to weeds, its use is no longer considered an advantage by successful commercial growers.