Accounts have already been published by this department of investigations made as to the origin, nature and properties of the glacial drift soils of the north-east of Scotland; in particular, the soil as found at the Experimental Farm of Craibstone, near Aberdeen, has been studied by means of mechanical analysis and the determination of the chemical composition of the fractions resulting therefrom (4). The results obtained have brought out some characteristic features of the Craibstone soil, and have indicated that important differences may exist between a glacial drift soil, derived mainly from rocks of granitic nature, and such a soil as that of Rothamsted, arising from the “Clay with flints” formation.

In 1914 the result of a study of the evaporation of water from soil was published by B. A. Keen, who distinguished two factors governing the rate of evaporation. One factor was that the available surface from which evaporation takes place decreases as the moisture content decreases. Keen deduced an equation that expressed the operation of this factor, viz.

in which D is a constant, w = percentage of water by weight and s = the real specific gravity of the soil. He showed that this equation agreed with his experimental results with a reasonable degree of accuracy.

1. Attention is drawn to Mason's modification of Livingston's soilpoint method of directly estimating the water-supplying power of a soil in situ. Mason used ordinary lead writing pencils as soil-points.

2. This method, heretofore tested only in the laboratory, has been employed by the writer in an ecological field study. Details of the procedure adopted are described, and the reliability of the method is indicated by the presentation of a series of mean results with their corresponding probable errors.

3. It is concluded that the method is practicable; it should prove of considerable usefulness to workers in ecology.

1. The investigation described is a continuation of the researches of certain workers in the British West Indies on the significance of the shrinkage coefficient of clays and soils. A brief outline of these researches and their results is given.

2. Tempany's hypothesis, which explains shrinkage as due to contraction consequent on loss of water by evaporation from the saturated gel-skeleton that ramifies throughout a mass of soil at its point of maximum plasticity, is criticised on the grounds that it does not completely fit the facts. In particular, it fails to account for the abnormally low shrinkage coefficients exhibited by lateritic soils, notably the red upland soil of Barbados. Mason explained this abnormality by assuming that kneading does not entirely destroy aggregation of soil particles, which is especially well marked in the Barbados red soil. The writer demonstrated, however, that soils of similar colloid content, and belonging to one and the same geological type, but exhibiting different degrees of aggregation, possess similar shrinkage coefficients. A different hypothesis to explain soil shrinkage was therefore sought.

3. The hypothesis finally accepted is based on the belief that colloidal gels possess a reticulate structure. At the point of saturation, a hydrogel probably contains water in two phases. The first of these is adsorbed in the walls of the gel; it has been shown by Wilsdon, in the case of soil colloids, to represent the moisture content at the hygroscopic coefficient stage. The second phase fills the vesicles of the gel, and is a crystalline phase.

1. The use of a positive air pressure on closely packed soils decreases the time of recovery and increases the yield of solution obtained by water displacement.

2. Equipment and technique for the recovery of displaced solutions is described.

3. Data from three sandy loams and two silty clay loams are reported.

4. Successive displaced solutions of equal electrical conductivity were obtained from each soil. The concentration thus measured was in each case the same as that of the liquid obtained without the use of displacing water.

5. Concentrations of individual ions in successive portions of displaced solution are uniform in soils at optimum and this also appears to be true at half optimum.

6. There is an inverse proportion between total moisture content of soil and concentration of displaced solution as indicated by measurements of specific resistance.

7. When the solution displaced by water from a given mass of soil was used as displacing agent on another portion of the same soil, the newly displaced solution had the same concentration of electrolytes as the displacing solution. The opinion is expressed that this result indicates that the displaced solution has the same concentration as the solution with which it came in contact in the soil.

8. Typical differences in behaviour of the various solutes in displaced solutions are discussed.

9. The significance and limitations of water extractions of soils are discussed in the light of the results from displaced solutions.

1. Further confirmation is presented in support of the relationship between the presence of vitamin A in the milk and its supply in the food.

2. The influence of the supply of the vitamin A in the food on the quantity or fat content of the milk is uncertain, in any case it appears to be much less than that produced by turning the cows out to grass.

3. The increase of the vitamin A-content of the milk produced by feeding cod liver oil is not accompanied by a rise in the lipochrome pigments as is the case when the cows are turned out to grass.

4. Up to 4 ounces per day of a good quality cod liver oil produced no fishy flavour in the milk or butter of one cow, but further experiments appear desirable.

5. Stall feeding even when ensilage was used causes the winter milk to be lower in vitamin-content than summer milk; this is mitigated by such restricted grass feeding as is possible in the south of England.

The work undertaken in 1922 was in the main a continuation of that done in 1920 and 1921, the results of which have already been published, and the object of which had been to determine the relation between the size of the seed tuber-sets and their resultant crop, and the further relation between the amount of heavy ware in the crop and the size of the seed.

1. The usual shaking methods have been examined and found unsatisfactory.

2. A method has been evolved for the estimation of the number of soil organisms by a direct count, and the numbers found to be very much higher than any previously reported.

3. A method for the disintegration and dispersion of the soil particles and bacteria has been devised, by means of which plate counts were made which were comparable with direct counts.

4. The dispersive actions of shaking and of vibrating have been compared. The former was found to give results which depended on the moisture content of the soil, whereas the trembling motion gave results in which the effect due to the moisture content was not apparent.

5. High counts made by previous observers can usually be correlated with one or more of the following factors:

(i) Greater dispersion of the soil as a result of the action of frost, etc.

(ii) An alkaline reaction, e.g. presence of ammonia, magnesia, etc.

(iii) Presence of a protective colloid, e.g. the effect of the addition of large quantities of straw, or traces of gelatine.

(iv) Absence of a flocculating agent, especially calcium compounds.

In conclusion the author wishes to express his gratitude to Dr G. S. Graham-Smith, F.R.S. at whose suggestion the investigation was started and under whose guidance and direction the bacteriological work was carried out in the Pathological Laboratory, Medical Schools, Cambridge; to Professor T. B. Wood, C.B.E., M.A., F.I.C., F.R.S., for facilities for carrying out the physico-chemical investigation at the School of Agriculture; to Messrs L. F. Newman, M.A., F.I.C., W. B. Hardy, M.A., F.R.S., W. H. Harvey, M.D., E. K. Rideal, M.B.E., M.A., G. Udny Yule, M.A., F.R.S., F. W. Foreman, M.A., F.I.C., and to the late Professor Sir German Sims Woodhead for their kindly advice and encouragement; to Messrs E. G. Staples, B.A., W. M. Davies, B.A., B.Sc, A.I.C. and A. W. R. Joachim, B.Sc. for assistance in the execution of the physico-chemical experiment; and to Mr W. A. Mitchell of the Medical School for his assistance in fitting up apparatus.

It is unlikely that as a formulated problem any consideration of settled crop-husbandry is of greater antiquity than the cereal yield problem. In its broad form it embraces all the possible means of increasing the output of grain per unit area. The earliest civilizations of Mesopotamia and Egypt must have been compelled to explore these means as soon as they began to encounter the limitations to cultivable area which dwelling in fixed communities imposed. Wheat and barley were their principal food stuffs so that the cereal yield problem, the most comprehensive concern of present-day agriculture, goes back to the remotest antiquity. It must have evoked incessant effort along divers lines and the cumulative result is appreciable from a comparison of the best cereal races of to-day and the forms which like Hordeum spontaneum and Triticum dicoccum dicoccoides have been regarded as the progenitor types. Unfortunately it is not possible to trace back very far the sequence of the solution of the problem as constituted by improvements in husbandry and the utilization of better cereal forms. Fragments of information may be culled from the writings of various periods but they are of doubtful value. The author's reliability is often in question, the unit of measure uncertain, and even the identity of the crop a matter of doubt. Herodotus' well-known story, passed on from another, of increases of 200 and even 300 fold yielded by barley in Mesopotamia in 500 B.c. is possibly the oldest fragment. It is difficult to interpret but it gains colour from the further statement that the leaves of the plant were of the width of four fingers. Concerning progress in England, while reasonably precise information goes back no further than forty years, there are widely separated records of sufficient worth to indicate the historical trend. It has been deduced from the Manorial Records that at the time when that system had become established there was a flat rate of about ten bushels per acre for wheat. Much later, when Sir Charles Davenant compiled An Essay upon the Probable Methods of making a People Gainers in the Ballance of Trade (published 1699), he computed the “neat produce” of eight million acres of arable land to be 79 million bushels of grain.

(1) A new and simple method of measuring the shrinkage of moist soil on drying is described, which at the same time gives values for the pore space and specific gravity of the soil.

(2) Diagrams for a number of diverse soils are given, illustrating the character of soil shrinkage.

(3) The shrinkage is shown to take place in two stages in both of which there is a linear relationship to the moisture content.

(4) Tentative explanations of these two stages are advanced, based on the well-known colloidal-coating hypothesis, and confirmatory experiments described.

(5) By means of the method the effect of alternate wetting and drying of soil in producing a good tilth is illustrated.

(1) The moisture equivalent of a normal soil diminishes as the weight of soil taken for the determination increases.

(2) Some soils are particularly impermeable to water in thick layers: in these cases the moisture equivalent increases with the weight of soil taken and may become very large owing to waterlogging. A soil may, however, have a very high moisture equivalent without showing waterlogging.

(3) Dilute solutions of flocculating salts such as calcium sulphate, or ammonium nitrate or sulphate, reduce the moisture equivalent, and sodium carbonate increases it.

(4) The effect of sodium carbonate is complicated: with gradually increasing concentration, the moisture equivalent first diminishes and then increases to a maximum, after which there is further diminution.

(5) The soil samples which easily showed waterlogging in the Briggs-McLane apparatus had a higher concentration of hydroxyl-ions (pH) than those which did not.

(6) Whilst the colloidal content of a clay seems related to its moisture equivalent, no such connection appears to exist for substances such as kaolin or aluminium hydroxide.

In an empirical manner cod liver oil has been used for many years as an occasional food for farm animals. Generally speaking, its use has been chiefly confined to the rearing of calves and to improving the condition of horses. It is difficult to glean from the literature of animal husbandry information about the use of this oil, but it would appear that whilst the majority of authorities favour its employment in small amounts in special cases others are inclined to regard the oil with suspicion. Thus, Campbell (1900) (i) recommends cod liver oil as an efficient substitute for cream in the rearing of calves; a conclusion that was confirmed in a later publication from the Leeds Station (Seton, 1901) (2). These reports warn users against the inferior grades of oil and show that if good preparations are used there is no detrimental effect on the flesh when animals are afterwards slaughtered as bullocks.

So many papers on the use of the phenol disulphonic acid method for estimating nitrates in soils have been published in this country and in America in the last few years, that some apology seems needed for adding yet another note to the literature of the subject. The method possesses great advantages as regards rapidity and convenience over the methods involving distillation and yet in the writers' experience, in spite of the numerous studies already made, it has failed to give entirely satisfactory results; in particular when small quantities of nitrate have to be estimated in soils containing much organic matter, the strong sulphuric acid in the reagent chars the organic matter and makes it exceedingly difficult to match exactly the tints from the soil extracts with those given by the standard nitrate solutions.

One of the main problems confronting the advocates of silage in this country is the selection of crops suitable for being grown for ensilage purposes, particularly in view of the fact that attempts to produce maize silage in this country have frequently been unsuccessful. It has been demonstrated, in trials extending over a number of years at Cambridge, that the mixed oat and tare crop can be used for the production of silage with success. The silage from oats and tares, when made under favourable circumstances, is possessed of great palatability and excellent nutritive value, and moreover, the process, considered from the point of view of losses of ingredients as a result of silo fermentation, is, if anything, more economical than that by which maize forage is converted into silage (1).

It is not infrequently assumed that varieties of cultivated plants differ not only in their suitability to different climatic and soil conditions, but in their response to different manures. Since the experimental error of field experiments is often underestimated, this supposition affords a means of explaining discrepancies between the results of manurial experiments conducted with different varieties; in the absence of experimental evidence adequate to prove or disprove the supposed differences between varieties in their response to manures such explanations cannot be definitely set aside, although we very often suspect that the discrepancies are in reality due to the normal errors of field experiments.

In my previous paper on the electrical determination of moisture in soils (1) I reserved the question of possible effects of soil salt movement in vitiating the conclusions therein reached as to the usefulness of the electrical method in practice. The present communication contains an account of some experiments carried out with a view to settling this point.

In the study of animal nutrition valuable information has been obtained from feeding experiments, the results of which depend upon the liveweight test. These results, however, deal only with the relative values of different foodstuffs and methods of feeding, and the accumulated data are, on the whole, not of such a nature that general physiological laws can be deduced from them. For the elucidation of such laws, it is necessary to carry out metabolic experiments by which the transformation of energy and material within the body can be studied with some degree of precision.

Several methods for estimating nitrates by reduction to ammonia were examined. The error involved in the use of acid reducing agents in presence of amino groups was emphasised.

A method based on the use of Devarda's alloy and magnesia is recommended.

In the estimation of nitrates in plant extracts, etc., by this method an equal volume of rectified spirit is first added to the solution to precipitate colloidal matter. The precipitate is filtered off and an aliquot part of the filtrate containing the equivalent in nitrate nitrogen of about 0.1 gm. of KNO3 is distilled with steam for 45 minutes with 1 gm. of Devarda's alloy and ½ gm. of freshly ignited magnesia. A blank determination is essential, in which the same volume of filtrate is distilled for the same length of time with ½ gm. of magnesia.

In Kjeldahl estimations in presence of nitrates, where the separate estimation of nitrates is not required, 2 c.c. of 25 per cent. NaOH may be substituted for the magnesia. Relatively this is very much less soda than Devarda recommends. The mixture in this case may be distilled directly for half-an-hour. The nitrates are thus reduced and the ammonia produced is collected before beginning the digestion with sulphuric acid.

This work was carried out under the supervision of Mr F. W. Foreman to whom the author's best thanks are due for much valuable criticism and advice.

(1) The ratio of the total lactation yield to the maximum yield, divided by the mean ratio (in the particular district) for the month of calving in which the lactation commenced, has been selected to represent the shape of each individual cow's lactation curve, and has been called the shape figure (S.F.).

(2) The variation of individual S.F.'s was found to be less than that of all cows taken together—i.e. the shape of the curve, though largely determined by environmental factors, is due partly to a genetic characteristic of the cow.

(3) The S.F.'s of 1st calvers are high (about 11 per cent, above those of subsequent lactations); i.e. heifers give a small maximum relative to their total yield.

(4) No significant relation was found between the length of the dry period preceding calving, and the ratio of the total to the maximum yield in the subsequent lactation.

(5) S.F.'s rise markedly and definitely as we pass from low to moderate, and from moderate to high, yielders; i.e. in good milkers the maximum is lower relative to the total yield than in bad milkers. Though there is variation from herd to herd (due probably to the system of management), this rise was shown between bad and good cows within the same herd, and seems to be a definite genetic character.

(1) The colorimetric method is unsuited to the examination of heavy, alkaline soils owing to the turbidity of the suspension.

(2) Where the nature of the suspension permits of colorimetric determinations being made, they agree with those obtained electrometrically: with the latter method practically identical results are obtained using soil-water mixtures or moderately clear extracts.

(3) No disturbing effect is likely to be introduced by amounts of nitrate up to 500 parts per million of soil.

(4) Owing to the effect on the pH of a soil suspension caused by varying the proportion of water and time of extraction, these conditions should be fixed for routine work. We have found 1 hour's extraction with 5 parts of water satisfactory.

(5) On account of the amphoteric or buffer nature of clay, soil shifts the reaction of acids and alkalis in the direction of neutrality.

(6) The effect of sodium salts on a soil is to displace aluminium and so reduce alkalinity: the residual soil after leaching is found to be more alkaline.

(7) The effect of drying alkaline soil is to cause the pH of the extract to be lower than that obtained from the undried soil. If however the time of extraction is prolonged, the differences disappear almost entirely.