The soybean seems to profit by the addition of nitrogenous fertilizers, but these should not be needed after the soil heroines thoroughly inocu lated. If nitrogen be used it may well be in the form of nitrate of soda and in small quantities, chiefly to stimulate very young plants.
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Time to must not be planted until all danger of frost is past and the soil has become warm. In the northern part of the United States the planting of this crop occurs just after corn-planting. In the Gulf states the best time is from the beginning of May to the middle of June. Planting may continue to the middle of July, but germination and early growth and yield are less satisfactory from this delay. From Kansas southward it is practicable under favorable con ditions to mature soybeans grown as a catch-crop after wheat or, in the Gulf states, after oats.
Cultivation should be shallow and level, and similar to that given corn.
soybean plant is doing its best work for the farmer unless its roots bear a number of tubercles or root nodules. On this plant, the root tubercles are roundish enlargements that when fully developed are about the size of peas (Fig. 590). On any soil in which root tubercles fail to develop spontaneously, it is advisable to effect artificial inoculation by the introduction into the soil or on the seed of the nitrogen-fixing germs appropriate to soybeans. This may be done by moistening the seed with a dilution of pure cultures of the germ, directions for which accom pany each package; or, more certainly, by the use of soil from a field where soybeans have recently produced abundant tubercles.
If this soil be drilled in with the seed, in a dry, finely powdered condition, GOO to 1,000 pounds per acre may suffice, but if applied broadcast, and not in immediate contact with the seed, at least one ton will be required. If only a very small quantity of soil is available, a peck of it may be stirred in about ten gallons of water, and the same day the seed moistened with this liquid. By this process, apparently a smaller number of plants become inoculated than by the use of larger quantities of dry soil. It has been found that it is less easy to cause a sufficient number of germs to adhere to soybeans than to cowpeas, for the reason that soy beans are so smooth and free from indentation or cracking. Hopkins prefers not to attempt thorough inoculation the first year, but to use only about 100 pounds of inoculating soil per acre, reseeding the land to soybeans the second year and relying on the natural spread of the germs from the decay ing tubercles produced by this partial inoculation.
In Kansas, Connecticut, Illinois, and apparently in most states, the soybean when first grown developed no tubercles, but when grown for several years in succession in the same land, inoculation gradually increased. On lime soil at Lexington, Kentucky, tubercles were abundant the second year, but not the first; in experiments in Connecti cut, there were no tubercles for at least three years. The gradual self-inoculation of soils is probably due to germs carried on the seed in such small numbers as to produce an insignificant num ber of tubercles the first year, which few would constitute the parent stock of a far larger number the second year, and so on. On medium and poor soils, inoculation may greatly increase the yield of seed or forage and the extent of soil-impove ment. On rich land, soybean plants without tuber cles are sometimes as thrifty and productive as plants bearing nodules. But even here inocu lation is beneficial in decreasing the draft on the soil and in the enrichment of the land for future crops.