The phenomena attending the absorption of oxygen by soils have been investigated by Déherain and Demoussy, and also by Wollny. An account of the work of the French chemists can be found in the Annales Agronomiques. Their method was to place the soils under examination in a closed tube holding about 100 c.c. and kept at constant temperature, then after a certain time to extract the gases and determine the carbon dioxide present. This was taken to be a measure of the amount of oxidation. The general results they obtained are as follows:

1. The quantity of carbon dioxide produced increases with the temperature to about 65°C., and then decreases. At higher temperatures (above 90°) it increases again.

The object of the present communication is to collect together and compare the data obtained in the principal investigations which have been carried out in this country during the past five years into the variations in composition of the milk of the cow. The results of many of these experiments have been published only in annual reports or as special bulletins with limited and more or less exclusively local circulation.

During the last sixty years numerous percolation and evaporation experiments have been made in this country and elsewhere. The method employed has been that originally used by Dalton, which has the advantage that the chemical and physical properties of the soil may, if desired, be thoroughly investigated. In addition to these experiments in which the evaporation from the soil, or from the soil with vegetation, is estimated by deducting the amount of drainage from the rainfall of the same period, numerous determinations of soil moisture have been made in the United States, from which evaporation may be directly determined. The difference between the estimated evaporation and the rainfall gives of course the amount of percolation.

The Ixodidae have received so little consideration at the hands of British naturalists that there does not exist amongst our literature any classification of the family having pretension to accuracy or completeness. This may be sufficient to account for the fact that in 1900 when inviting correspondence through the columns of Science-Gossip, I did not receive any reply from a fellow-countryman who had made a serious attempt to study the British ticks, though I have been favoured with much kindly assistance from correspondents who had turned their attention to foreign species.

Below is a brief summary of the chief points of interest which our investigations appear to have suggested so far:

That the most convenient method of sampling roots for analysis is to remove a core from each root, and that when using this method at least 50 roots must be cored in order to obtain a sample representing the composition of the bulk of roots grown on a field.

That a large proportion of the commonly grown strains of mangels may be assigned to one or other of five types.

That of these types, four have their cropping power and percentage of dry matter so nearly in inverse proportion that they yield practically the same weight of dry matter per acre.

That the fifth type, Long Bed, yields considerably more dry matter per acre than the other four varieties.

That large roots on the average contain more water and less dry matter than smaller ones.

That there is a considerable variation in the composition of mangels from year to year, probably depending on such conditions as rainfall and sunshine at particular periods of growth.

That manurial treatment causes distinct variations in composition, the most noticeable point being that excessive applications of nitrogen delay ripening and decrease the percentage of dry matter.

That different farms grow roots of different composition.

That there is very great variation among individual roots of the same variety grown side by side, in content of dry matter, sugar, and nitrogen, and in size, shape, colour; in fact, in all the characters which we have been able to observe.

That there is so little correlation between the different characters that it is possible to pick out for seed-mothers large roots containing high percentages of dry matter rich in any desired constituent, and it is suggested that, from analogy with the sugar beet, continuous selection carried out in this manner may result in improvement in any desired direction.

That since colour, shape, and specific gravity of root or of juice are shown not to be correlated with percentage of dry matter, sugar, or nitrogen, selection for these characters is not likely to lead to any improvement.

The investigations to be described below are the outcome of some experiments started in 1900 which had in view the improvement of English-grown wheat. The necessity of such work may not be evident to all, so at the outset I will sketch in broad outlines the state of affairs which led me to undertake the task. The fact is generally recognized that the wheats of this country are characterized by their high yields per acre and by the shapeliness of their grain. We can grow on the average over 30 bushels to the acre where the United States grow 14, Russia 10, and the Argentine 7. Yet the acreage under wheat in this country has fallen from three and a-half million acres in 1876 to one and a-half million in 1903, and we now grow approximately only one-fifth of the wheat we consume. Further than this there is good evidence to show that the quality of the grain now grown is inferior to that of twenty years ago. It has been sacrificed to yield, and many of the better class varieties, such as Chiddam, Red Lammas and Rough Chaff, have been more or less driven out of the field by varieties such as Square Head and Rivet, which are capable of giving slightly larger crops of grain and straw. These inferior varieties have now to compete with wheat imported from Canada, the United States, Russia and other countries. The seriousness of the position becomes evident when one finds English wheat selling at 28s. 6d. a quarter when Manitoba Hard is selling at 35s.

At the time of the commencement of the Rothamsted experiments very little was known as to the amounts of combined nitrogen and other substances present in rain-water.

Marggraf (74) found nitric acid, chlorine and lime in rain-water collected during the winter of 1749–50, and, subsequently, in snow. These analyses, which are probably the earliest, were followed by those of Bergman (15) who detected the same substances both in rain and snow; whilst somewhat later de Saussure (99) noticed the presence of ammonia in the atmosphere. Between 1820 and 1825 several analyses of rain-water were made.

The present communication is intended as a contribution to the study of the capacity of soils to retain moisture in equilibrium with the atmosphere. The experimental material with which it deals consists in part of the analytical data obtained in the investigation of one hundred soils of the county of Dorset, which has been carried out for the County Council, and in part of a series of determinations made for the purpose of elucidating this problem.

An agricultural problem to which little attention has been directed is the relation of the supply of combined sulphuric acid in the soil to the growth of crops. Field experiments upon the value of gypsum and sulphate of iron have been made, and artificial manures containing sulphates are constantly being used, but the specific effect of the combined sulphuric acid in these materials seems never to have been sufficiently investigated. Indeed, any useful effect produced by gypsum has been ascribed to indirect action, e.g., the liberation of other constituents from insoluble soil compounds.

With such conflicting results it is difficult to draw definite conclusions. The data are not put forward with that object, but it was felt that there is sufficient interest in the figures themselves to warrant publication. This communication is intended as an interim report on investigations which will be continued as time and occasion permit. However, the general features most worthy of note are as follows:—

(1) The order of the solvent power of the three solutions of each of the two classes remains the same throughout. In the citrate solutions the order is (descending), (1) neutral, (2) acid, (3) alkaline solution, with only two exceptions, viz., the raw bone meals No. 7 and No. 9, discussed under Table III.

With the free acid the solubilities are in the order of the strength of solution without exception.

In general the hop is diœcious. Sometimes, however, in gardens of the Bramling variety, hills are met with from which bines arise bearing both male and female flowers. Such monœcious plants are rare.

At the beginning of 1902 I was asked to investigate the nature and causation of a disease of sheep, locally termed “struck,” with the hope of finding some suitable form of preventive treatment.

The experiments described in the following pages were made with a view to discover how far purely physical and chemical processes, known to take place in the soil, may be expected to give rise to nitrites and nitrates. Scattered throughout the extensive literature on nitrification are occasional papers tending to show, what might also be expected on theoretical grounds, that non-bacterial processes may be important sources of nitrates. Formerly these processes were considered to be the only sources, then came the brilliant researches of Schloesing and Muntz, Warington, Winogradsky, and others on nitrifying organisms, and non-bacterial processes were forced into the background. Now that a full knowledge of the various sources of nitrogen compounds in the soil has become so indispensable to the agriculturist, it seemed desirable to make a careful examination of the various chemical and physical processes known to take place in the soil, and to ascertain whether they make any direct or indirect contribution to its stores of nitrates. To this end we have repeated and extended such of the recorded observations bearing on the subject as seemed to merit repetition; we have also devised other experiments to make the examination as complete as possible.

The methods usually employed for estimating calcium carbonate in soil are all subject to more or less serious practical difficulties when the percentage of lime falls below 0.5.

In gravimetric methods, in which the carbon dioxide set free by acid has first to be boiled out of solution and then perfectly dried before absorption by potash, a very small weight of carbon dioxide is estimated by the gain in weight of a comparatively heavy absorption apparatus.

For nearly eighteen years the problem of the fixation of nitrogen by the root nodules of leguminous plants has been the subject of investigation by numbers of workers in many parts of the world, and steady progress has been made towards realising the conditions under which the organism works in the nodule. Artificial nutrient media have been prepared closely resembling the food supplied by the plant, and the organism itself has in recent years been induced to grow in artificial culture in the characteristic “bacteroid” forms approximating to those which are found in nature.

It is well known that the fertility of “virgin” soils is due to the accumulation of the débris of a natural vegetation which has been in occupation of the soil for a long epoch previously. Only when the climate and rainfall are suitable to the growth of the plants and the partial preservation of their residues does a virgin soil of any richness arise; on the one hand, virgin soil may be as poverty stricken as the most worn-out European field because it has never carried any vegetation; on the other hand, as in the tropics, the débris of an extensive vegetation may decay with such rapidity that no reserve of fertility accumulates.

In a stretch of arable lands like those of the Ganges Valley, although damage may be caused by occasional floods, which are sudden and of short duration, the more general, and by far the most serious loss is due to deficiency of moisture of the soil: thus the relation of the soil to soil moisture becomes of more than ordinary importance. Dr Voelcker, in his Report on Indian Agriculture, remarks: “In India the relation of soils to moisture acquires a greater significance than almost anywhere else.......” This relation is fundamental, for on it depends the methods for the conservation of soil moisture, for the economical application of irrigation water, and for the treatment of barren and salt lands—all problems of direct interest to agriculturists in the plains of Northern India. The methods for dealing with these problems must be largely—if not entirely—empirical until such time as the behaviour of the soil in its relation to moisture is investigated. The problem in all its various branches is enormous, and in a country in which the seasons follow each other with such rapidity, and vary the one from the other in so marked a manner, it frequently happens that a particular point, if not determined within a period of a few days, must await solution until the following year.

One of the main problems placed before the agricultural chemist is the estimation of the requirements of a given soil for specific manures, or the interpretation, by means of data obtained in the laboratory, of the behaviour of the soil towards these manures, as seen in properly arranged field experiments. For various reasons the obvious method of determining the proportions of Nitrogen, Phosphoric Acid, and Potash in the soil fails in many cases to give the required information; even the more modern methods of measuring only the quantities of these materials which are attacked by weak acid solvents, and in consequence regarded as available to the plant, by no means always accord with the results of experience. Hence from time to time attempts have been made to attack the problem from another side and to use the living plant as an analytical agent. The scheme is to take a particular plant grown upon the soil in question, and determine in its ash the proportions of constituents like phosphoric acid and potash. Any deviations from the normal in these proportions may then be taken as indicating deficiency or excess of the same constituent in the soil and therefore the need or otherwise of specific manuring in that direction. The theory rests on two assumptions, first that each plant has a typical ash composition, constant when the plant is grown under similar conditions; secondly that the variations in the proportion of such a constituent as phosphoric acid will reflect the amount of that plant food available in the soil, as measured by the response of the crop to phosphatic manuring. From this point of view a number of investigations have already been made: Hellriegel discussed the relative variations of the proportion of potash in the ash of barley straw and of the soil in which it was grown; Heinrich analysed the roots of oats and fixed certain minima, below which the need for specific manuring was indicated.

Since its inception in 1894 the American Soil Bureau has investigated many important problems and obtained results which are now common knowledge in this country, but its earlier Bulletins are altogether eclipsed in interest and far-reaching significance by a series recently published. In presenting an account of these it will be most convenient to set out first the purely scientific part of the work, and then the practical applications. This is the logical order and also the order in which the results were actually obtained.