In the course of determinations of organic carbon in soils, some unexpectedly high figures suggested the possibility that free carbon in the form of fragments of coal or cinder might affect appreciably the results obtained. The soils in question were from the Coal Measure district of Flintshire, and the presence of notable amounts of coal was not surprising. Even in soils from other districts, however, it is not unusual to find small carbonaceous fragments, which are generally noticeable in the coarse sand separated in mechanical analysis. Their presence is not difficult to explain, for domestic ashes containing unburnt coal or cinders are often thrown on to the manure heap, and thus get carted on to the soil where they persist unaltered. The highest proportions of elementary carbon may be expected in heavily manured soils such as those of gardens.

1. The average carbon-nitrogen ratio for fifty British soils from widely distributed areas approximates to the figure 10: 1 given by other investigators. The range of variation is from 6·5 to 13·5: 1. Sixteen foreign samples gave C/N ratios varying from 2·0 to 23·0: 1.

2. Soils from limited areas, whether high or low in organic carbon, give approximately constant ratios, but these ratios vary from place to place according to soil, climate, etc. It is suggested that the C/N ratios may be specific.

3. The C/N ratios of arable soils do not differ appreciably from those of grassland soils. The percentages of carbon and nitrogen are somewhat higher in the grassland samples than in the arable samples.

1. The application of the zinc uranyl acetate method to the determination of exchangeable sodium in soils is discussed.

2. Using this method of determination, good agreement was found between the exchangeable sodium extracted by 0·5 N acetic acid and that extracted by N ammonium chloride.

3. The procedure for estimating sodium in acetic acid extracts is described, and the results for a number of typical non-saline Welsh soils are given.

The heavy wastage occurring in many dairy herds adds importance to the question of sex ratio in cattle, and it becomes an important factor in herds where it is desired to use only home bred cattle, as in herds free from tuberculosis and contagious abortion. The information required for the present investigation was obtained from Private Herd Books, particulars being taken as to sex of calf, month of birth and whether or not it was a first calf. Herds ravaged by contagious abortion were excluded, and also others if it was considered that there might have been neglect in entering births in the private herd book.

Experiments extending over the four years, 1926–9 inclusive, have been carried out on a heavy and stony loam soil to compare rotary cultivation with normal methods for the production of a seed-bed. The work has been confined to spring-sown crops—swedes and barley—and to spring cultivations.

Rotary cultivation gives earlier and better germination of seed, followed by better early growth.

In every experiment, however, the final yield has either been no better, or else significantly below that obtained from the plots cultivated in the usual way. The barley crop gives equally good yields under the various soil cultivation treatments; although there is better germination under rotary cultivation, the plants on the remaining plots, having greater root range, throw out more tillers and thus level up the yield. The swede crop did not do so well under rotary cultivation, in spite of better early growth. In the 1926 experiments this was due to an extensive hardening or “capping” of the soil on the rotary cultivation plots but, although this effect was absent in the 1928 experiments, a reduced yield was still obtained.

Keratin, prepared from horn meal, was added to moist field and garden soil and allowed to decompose in the laboratory. The keratin was found to undergo a decomposition resulting in a slow, but steady accumulation of ammonia and nitrate. 35–40 per cent, of its nitrogen was transformed into nitrate after 120 days. The addition of keratin produced little or no increase in the number of bacterial colonies on agar platings, but markedly increased the number of actinomycete colonies, especially in garden soil. Two strains of actinomycetes were isolated and found capable of thriving on keratin in pure culture, decomposing the keratin with the formation of ammonia. One of the strains could be recognised as Actinomyces citreus Krainsky, as described by Waksman. The other strain could not be named, but corresponded closely to the description of Waksman's Actinomyces 145.

In cases of field experiments when one plot is missing, a method has been developed for furnishing an estimate of the yield of the missing plot, based on all the other values. The calculation is given for (a) a Randomised Block experiment, and (b) a Latin Square arrangement. In both cases the actual arithmetic is very simple.

The steps in the procedure are:

(1) Determine the desired value by an application of the equation (A) or (B) according as the experiment was arranged in Randomised Blocks or in a Latin Square.

(2) Proceed as usual with the analysis of variance, using the estimated figure for the missing yield, and remembering to deduct one from the number of degrees of freedom ascribable to error.

A modified technique for the Keen-Raczkowski box experiment is described; it is believed that this new method is as accurate as, and is more convenient than, the one employed earlier.

The results obtained for pore space by the new method are very nearly the same as those obtained by the old method. The old and new results obtained for water retention and swelling are not the same, but are related to one another by simple linear expressions, and correlations with other soil properties deduced from the old data are applicable also to the new.

One of the previous papers by Coutts(1) in this series has directed attention to the value of the data obtained from what is now generally referred to as the perforated box experiment devised by the present writer and Raczkowski(3). In a further paper Coutts(2) has described an improved and simplified technique, which gives results that are either identical with the old method (pore space) or else related to them by simple linear expressions (water retention; volume expansion or “swelling”). As Coutts’ procedure is now being followed at Rothamsted, and is likely to be taken up by other workers, it appears desirable to record some hitherto unpublished data bearing on the technique of the method, obtained at Rothamsted some years ago by Prof. Ohga (S.M. Educational Institute, Mukden, Manchuria) and dealing with the effect on the results of the degree of packing to which the soil is subjected. The original method, followed by Coutts in its essential details, is to add the soil in small quantities, tapping the box on the bench after each addition, until the box is nearly full, at which stage the filling is completed in the manner described in the original communication.

The conclusions of an earlier study of the yield of dressed grain from Hoos Field over the period 1852–1921 are recalled, and the method of conducting an examination of the influence of rainfall on the yield is described. The method yields a series of curves showing at any given period of the year the benefit or loss to the final yield in bushels per acre due to an additional inch of rain over the average at that period. Thirteen plots are considered, and the curves are found to fall roughly into groups corresponding to the system of manuring adopted. The main effects noted are these: (1) Excess of rain is beneficial to the barley crop for a short period in summer, and, in the case of certain plots, over the autumn and winter period. This is in contrast to the corresponding result for wheat on Broadbalk, where excess of rain was found to be beneficial only on a few plots and over a very limited period. (2) Rainfall over the six months when the barley is not in the ground is just as important as rainfall in spring and summer, and the time at which the rain falls in winter is important. Excess of rain in autumn benefits plots 1–A, 3–A and 7–2, and in winter continues to benefit 1–A and 3–A. (3) The curves for 2–O and 2–A are essentially different in character from those of the other plots, and point to the important effect of excess of winter rain in reducing the yield of the plots having phosphate but no alkali salts (i.e. no potash, soda, magnesia). (4) Excess of rain at time of sowing is harmful in all cases. (5) The curves of the “O” series (without nitrogen) are much flatter than those of the “A” series, which have a nitrogenous dressing in addition. (6) The indication of summer benefit is not inconsistent with the conclusions of Hooker that a cool summer is desirable for barley. (7) The farmyard manure plot 7–2 bears certain resemblances to the curve for the corresponding plot 2 b on Broadbalk.

The table of results given in the last section shows that for all experiments for which the Resistance Formula has been fitted the values of the constants are consistent, bearing in mind the standard errors to which these values are subject. The constants for nitrogen may be held to have been determined with some approach to precision, but those for potash are not so well determined. We find at Rothamsted, for example, that the crop responds to a moderate dressing of potash, but higher dressings do not usually improve the yields any further. This fact limits the precision of the formula. The reader is asked to refer at this point to the full descriptions as to the meaning to be attached to the constants of the formula given by Bh. Balmukand in the earlier paper(1). The constants an and ak, called the importance factors, are interpreted as determining the capacity of the crop to recover the particular nutrient out of the soil. The chemical analysis of the tubers grown under nitrogen and potash starvation conditions should, therefore, furnish us with values which should be of the same order of magnitude as obtained by the formula. The minimum nitrogen percentage figure is 0·204, which when reduced to our units is equivalent to 4·57 lb. of nitrogen per ton of potato. The values obtained from the Resistance Formula are as close as the standard errors allow us to expect, and are also of the same order of magnitude as the chemical composition of the tubers demands.

The organic matter of the soil has engaged the attention of soil investigators ever since the latter part of the eighteenth century. The volume of literature on the subject is enormous, and perhaps in a greater degree than in any other branch of soil work we find here examples of the tendency to draw definite conclusions from inconclusive evidence. This is not surprising when it is remembered that perhaps the most important part of the soil organic matter, the humic matter, is a high molecular organic colloid, the investigation of which takes us at once into the most difficult fields of organic and of physical chemistry—fields in which the worker often needs to use special methods of experimentation which have become available only during recent years. Moreover, the study of humic matter is rendered particularly difficult, since it is a secondary product derived from the complex organic constituents of plant residues, themselves of unknown or little-known constitution, and since it is not known from which of these plant constituents it is derived.

The alkali extraction of the organic matter from the soils of certain plots of the classical permanent experiments on Barnfield and Broadbalk at Rothamsted, receiving respectively organic manure, artificial fertilisers and no manurial treatment, has been studied, together with a colorimetric examination of the extracts for the comparison of the content of humic matter.

It is shown that, in spite of the different cultural and manurial treatments which the different plots have received, there is a marked similarity in the properties of the organic matter of these soils, with regard to its behaviour on extraction with cold and hot dilute caustic soda, and the colour intensity of the organic matter in the extracts.

The methods used for the determination of organic carbon in the soils and their extracts are noted in an Appendix.

The results discussed in this paper are further considered, along with those in the two next following Parts (III and IV), in Part V of this series, in their bearings on the origin of the humic matter of the soil.

Experiments are described in which the decomposition of various plant materials and of purified preparations of plant constituents, during rotting under neutral aerobic conditions in the presence of soil organisms, has been studied in relation to the formation of humic matter.

The formation of humic matter was more closely related to the change in the lignin content than to the change in content of the other groups of plant constituents estimated.

1. The fungicidal properties of solutions containing sulphur in polysulphide form, viz. sodium, potassium, calcium and barium polysulphides, were tested by application to the conidial stage of Sphaerotheca Humuli growing upon young hop leaves in the greenhouse.

2. Four samples of sodium polysulphide solutions, two prepared in the laboratory and two commercial products, were examined. When applied with 1 per cent. soft soap as the spreader, solutions containing 0·5 per cent. polysulphide sulphur proved fungicidal. With 0·5 per cent. gelatine as the spreader, fungicidal strength did not begin to be attained until the concentration of polysulphide sulphur reached 0·11 per cent. The results suggest that the nature of the spreader may influence the fungicidal properties of polysulphide sulphur.