How Crops Feed: a Treatise on the Atmosphere and the Soil as related to the Nutrition of Agricultural Plants

Abstract

MR. JOHNSON'S earlier treatise, “How Crops Grow,” has been rendered familiar to the English public through Messrs. Church and Dyer's admirable edition, and forms a complete manual of the structure and physiology of the plant, treated in a manner specially adapted for agricultural students. The present work is intended as a companion treatise on everything connected with the nutrition of plants. The subject divides itself naturally into two sections, the first relating to the atmosphere, and the second to the soil, as sources of the food of plants. The question whether plants derive their nitrogen direct from the free element in the atmosphere was long a vexed one among physiologists. Mr. Johnson details the experiments which were thought to favour the argument on both sides, giving the preference, and we think rightly, to the later researches of Boussingault, and those of Lawes, Gilbert, and Pugh, which appear to demonstrate that the enormous quantity of free nitrogen in the air is not available for the food of plants; but that they draw their supply of it from the extremely minute quantities of ammonia and other nitrogenous compounds that form an essential ingredient of the atmosphere. Under the head of water as an element in plant-food, we miss any reference to the recent important researches of Dehérain, which show that the evaporation of water from leaves is determined entirely by light, and by those rays only which are efficacious in the decomposition of carbonic acid, and that it may proceed in a perfectly saturated atmosphere. This omission will probably be supplied should an English edition be published. The second portion of the work relates to the soil as a source of food for plants, and is the one which will be of special interest and value to practical agriculturists. Here we find treated in an exhaustive manner the origin and formation of soils, the kinds of soil, their definition and classification, their physical characters, and the soil as a source of food to crops, including those ingredients whose elements are of atmospheric origin, and those whose elements are derived from rocks. We can do no more than recommend to the notice of those interested in agriculture a work which we believe will be found a reliable handbook to that scientific knowledge in which the bulk of English agriculturists are at present so lamentably deficient. The most scientific of all manual occupations is actually conducted on a system which is a mixture of complete empiricism and unscientific theory.