Cyril G. Hopkins

“ The tubercles are, of course, easily seen with the eye, but the tubercle is only the home of the bacteria, somewhat as the ball upon the willow twig is the home of the insects within. The bacteria themselves are far too small to be seen with the unaided eye, although they can be seen by means of the most powerful microscope. ”

“ It is believed that 100 pounds of infected soy bean soil per acre will be sufficient to produce a thorough infection the second year, and it is improbable that one ton of infected soil per acre would produce a thorough inoculation the first season. One ton is only twenty times 100 pounds, while one tubercle which will be produced during a single season from a single bacterium may contain many million bacteria, thus it will be seen that it will be more economical to inoculate rather lightly and allow the bacteria to multiply themselves rather than to inoculate heavily at great expense. ”

“ Calcium, magnesium, iron, and sulfur have no market value as elements of plant food because they are present in practically all soils in abundance as compared with the amounts required in plant growth. The three elements nitrogen, phosphorus, and potassium, do have market values, because they are required by plants in very considerable quantities, and they are present in most soils in rather limited amounts, and when the available supply of any one of these elements becomes too much reduced in a soil the crop yield also becomes reduced. ”

“ While the failure of clover may often be due to drouth, and in some places due to soil acidity (lack of lime) , and sometimes even due to an insufficient supply of available phosphorus or of potassium, we now know with certainty that it sometimes fails because of the absence of the nitrogen-gathering bacteria, especially on land which has never grown clover, and probably also on land which has not grown it recently. We should always remember that the bacteria do not thrive in strongly acid soils. ”

“ In general agriculture in Illinois, whether it be grain farming or ordinary livestock farming, the growing of legumes is absolutely essential as a part of any economic system which shall maintain the fertility of the soil; and for the successful growing of legumes the presence and assistance of the proper species of nitrogen-gathering bacteria are also absolutely essential. ”

“ One of the reasons for applying ground limestone to soils which are deficient in lime is to furnish the element calcium in suitable form for the formation of nitrates in the process of nitrification. Ground limestone is calcium carbonate (CaCO3) , a compound containing one atom of calcium (Ca) , one atom of carbon (C) and three atoms of oxygen (O3) . This is the same form of lime which is contained naturally in limestone soils—soils which are noted for their great productiveness—and it is generally the most economical form of lime to use for correcting soil acidity and promoting nitrification. ”

“ The cowpea bacteria are already quite widely distributed in southern Illinois, especially where this crop has been grown for several years, but they are not common in the soils of other parts of the state. It is doubtful, however, if it is necessary or even worth while to take the trouble to inoculate soil for cowpeas. Some few tubercles almost invariably develop on cowpea roots the first year they are seeded, even where they have never been grown before, and if seeded the second year on the same land the plants are usually abundantly provided with root tubercles. ”

“ Like many other biennial plants, it probably often lives more than two years if not allowed to produce seed. Alfalfa is a perennial plant, and it is said that there are alfalfa fields which have been cut annually for more than fifty years without reseeding. The similarity of alfalfa and sweet clover when young, and also the similarity of the tubercles formed on the roots of each have long been noticed, and the possibility of the same bacteria living upon both plants has already been suggested in the agricultural press. ”

“ It now seems absurd to suppose that there were red clover bacteria in Illinois soil before red clover itself was grown on Illinois soil, unless the same bacteria live also upon some other legume which was native to our soils. There is some evidence that the vetch bacteria are native to our soil, possibly living upon the native wild vetches. At any rate, tubercles commonly develop on vetch roots without artificial inoculation. ”

“ Of course if sweet clover should get into the field and persist in growing, and if it were found to injure the alfalfa appreciably or markedly, we can always resort to plowing the ground up and growing corn or other crops, thus obtaining some benefit from the leguminous crop for its fertilizing value, and at the same time completely eradicating the sweet clover, but leaving the soil well infected with alfalfa bacteria ready to serve in case alfalfa should be again seeded within a few years. ”

“ It may be that the same bacteria also live on some other leguminous plant which is more or less widely distributed over the state, but it seems more likely that the bacteria are brought with the seed. As a matter of fact, the cowpea harvest is usually dirty. This is an annual plant, and consequently the crop is grown on recently plowed land and is sometimes cultivated during the season. Cowpeas are commonly harvested with a mowing machine and then raked up on the loose ground. When they are threshed more or less dirt remains with the seed. ”

“ In some cases a relationship exists which is not parasitic but symbiotic. The term symbiosis, which is commonly used by biologists to define this relationship, means living together in mutual helpfulness. ”

“ When clover is cut for seed, it is frequently left to lie upon the ground until the straw becomes half rotten and very dirty; and, consequently when it is threshed, it practically always happens that there is at least some small amount of dust and dirt taken with the seed. This dirt is almost sure to carry with it some bacteria from the soil. ”

“ In these young and rapidly growing plants the tubercles are much richer in nitrogen than any other part of the plant. It should be stated that as the plants approach maturity the nitrogen is largely absorbed from the tubercles and stored in the tops and roots. At the time these plants were taken up the tubercles actually contained more nitrogen than the roots. The infected plants contained nearly four times as much nitrogen as the plants not infected, and about three-fourths of the total nitrogen in the infected plants was obtained from the air. ”

“ The soy bean seed is nearly round and smooth, and the seed coat is not commonly cracked. These facts may explain why the soy bean seed carry so few bacteria as compared with cowpeas.
On one of the soil experiment fields on the university farm at Urbana, where soy beams have been grown for three years, no tubercles could be found on the plants either the first or second year, and only an occasional plant with tubercles could be found the third year. ”

“ It should be remembered that there are ten essential elements of plant food each of which is of equal importance to the plant, for if the plant is deprived of any one of the ten essential elements it is impossible for it to develop and mature. ”

“ Nitrogen is removed from the soil not only in the crops grown, but also, and frequently in larger amounts per annum, in the drainage waters, and in some other ways, as by denitrification and by the blowing and washing of the surface soil. ”

“ The infected soil need not be applied with any high degree of uniformity, but special care should be taken that the higher places and watersheds are not missed in scattering it over the field. If a few square yards, or even square rods, should be missed on the slopes or lower land, it would make but little difference, as the bacteria will be washed over such places from the higher land. ”

“ If these few bacteria are scattered with the clover seed when it is sowed they will inoculate at least a few plants, and if they are allowed to multiply on these plants, and especially if the same field is repeatedly seeded with clover, the soil will ultimately become thoroughly infected with the clover bacteria. ”

“ The alfalfa commonly grows about two and a half feet high, with many stems growing from the crown of the root, especially after it is two or three years old. It bears purple flowers and peculiar spiral-shaped seed pods. Sweet clover is a biennial plant, dying after reaching maturity, which commonly occurs the second year of its growth. ”

“ This is the general process of nitrification in which the nitrifying bacteria transform or transfer the nitrogen from insoluble organic compounds into soluble compounds in which it may serve as available plant food. The nitrate which is thus formed may be calcium nitrate or magnesium nitrate or potassium nitrate or even sodium nitrate, depending upon which of these alkaline elements is present in the must suitable form. If no alkaline element is present in available form then no nitrates can be made in the soil. ”

“ Thus the bees obtain their food from the flowers and, in turn, the flowers, many of them, are incapable of producing seed or fruit unless the pollen is carried from the male flower to the female flower by bees or other agencies. ”

“ Just how long the bacteria will live in a soil without a leguminous crop upon which they can feed is not definitely known. Certainly they live for two or three years, but probably not more than five or six years. Further investigation is needed to establish the length of time the different kinds of bacteria may remain in the soil under different conditions. ”

“ Even though they may sometimes live in such soils and perhaps produce some tubercles upon the roots of certain hardy, strong growing legumes, like cowpeas, nevertheless we are obtaining some strong evidence that in such acid soils they have but little power to gather nitrogen from the air. ”

“ The tree is injured rather than benefited by the mistletoe. Dodder is also a parasitic plant, living upon other plants, except during the early part of its growth. Ticks and lice are common examples of animal parasites living upon other animals. ”