Modern improvements in agriculture will probably be, in the main, such as are based upon fundamental processes unknown to the ancients. By the word "processes" it is intended to indicate not those methods the scientific reasons for which were understood--for these in ancient times were very few--but simply those which from long experience were noticed to be beneficial. Good husbandry was in olden times clearly understood to include the practice of the rotation of crops, and the beneficial results to be expected from the introduction of those crops which are now discovered to act as hosts to the microbes which fix atmospheric nitrogen were not only observed, but insisted upon.
From a scientific point of view this concurrence of the results of ancient and of modern observation may only serve to render the bacteriology of the soil more interesting; but, from the standpoint of an estimate of the practical openings for agriculture improvements in the near future, it greatly dwarfs the prospect of any epoch-making change actually founded upon the principle of the rotation of crops. It is, indeed, conceivable that fresh light on the life habits of the minute organisms of the soil may lead to practical results quite new; but hardly any such light is yet within the inventor's field of vision.
This view of the limited prospects of practical microbiology for the fixing of nitrogen in plant-food was corroborated by Sir William Crookes in the Presidential Address already cited. He said that "practice has for a very long time been ahead of science in respect of this department of husbandry". For ages what is known as the four course rotation had been practised, the crops following one another in this order--turnips, barley, clover and wheat--a sequence which was popular more than two thousand years ago. His summing up of the position was to the effect that "our present knowledge leads to the conclusion that the much more frequent growth of clover on the same land, even with successful microbe-seeding and proper mineral supplies, would be attended with uncertainties and difficulties, because the land soon becomes what is called clover-sick, and turns barren".
In regard to any practical application of microbe-seeding, the farmers of the United Kingdom at the end of the nineteenth century had not, in the opinion of this eminent chemist, reached even the experimental stage, although on the Continent there had been some extension of microbe cultivation. To this it may fairly be added that some of the attention attracted to the subject on the Continent has been due to the natural tendency of the German mind to discover fine differences between things which are not radically distinct. Under the title of "microbe-cultivation" the long-familiar practice of the rotation of crops may to some continental enthusiasts seem to be quite an innovation!
