TABLE XIII.—INFLUENCE OF SOIL TREATMENT UPON THE NUMBERS OF FUNGI AS DETERMINED BY THE PLATE METHOD—(AFTER WAKSMAN).
| Soil Fertilisation. | Reaction. | Numbers of Fungi per Gram of Soil. |
|---|---|---|
| P.H. | ||
| Minerals only | 5·6 | 37,300 |
| Heavily manured | 5·8 | 73,000 |
| Sodium nitrate | 5·8 | 46,000 |
| Ammonium sulphate | 4·0 | 110,000 |
| Minerals and lime | 6·6 | 26,200 |
| Ammonium sulphate and lime | 6·2 | 39,100 |
The type of soil and its treatment exercise a great influence over the number of fungi present. Fischer[6] found that farmyard manure increased the number of fungi in uncultivated “Hochmoor,” cultivated “Grunlandmoor,” and a clay soil by two, three, and five times respectively. Waksman’s results[25] indicate that the more fertile soils contain more fungi, both in number and species, than the less fertile ones, and if one averages his results, the following figures are obtained: garden soil, 525,000 per gram; orchard soil, 250,000; meadow soil, 750,000; and forest soil, 151,000. Recently Waksman[25e] has found that manure and acid fertilisers increase the numbers of fungi in the soil, whereas the addition of lime decreases them ([Table XIII.]).
Jones and Murdock[10] examined surface and sub-surface samples of forty-six soils representing seventeen soil types in eastern Ontario. Molds were fairly uniform in numbers in all soils except a sandy clay loam and sandy clay shale, in which they were absent.
It has also frequently been pointed out that acid and water-logged soils are richer in fungus content than normal agricultural soils. On the other hand, Brown and Halversen[2] found, examining six plots receiving different treatment and studied through a complete year, that the numbers of fungi were unaffected by moisture, temperature, or soil treatment. Against this, however, must be set the work of Coleman[3] who studied the activities of fungi in sterile soils and found such factors as temperature, aeration and food supply to exercise a deciding control.
Investigations at Rothamsted show that Broadbalk plot 13, receiving double ammonium salts, superphosphate and sulphate of potash and yielding 31 bushels per acre, and plot 2, receiving farmyard manure and yielding 35·2 bushels, contain approximately equal numbers of fungi. This figure is about half as high again as that for plot 3, which is unmanured and yields 12·6 bushels, plot 10, with double ammonium salts alone and yielding 20 bushels, and plot 11, with double ammonium salts and superphosphate and yielding 22·9 bushels per acre. A primary factor, however, in all considerations such as these is the equality of distribution of fungi laterally in any particular soil. There are probably few soils so homogeneous as the Broadbalk plots at Rothamsted, and on plot 2 (farmyard manure since 1852) samples taken from the lower and upper ends and the middle region gave average numbers of colonies per plate of 24, 23, and 25 respectively. On the other hand, soil samples taken only a few yards apart in the middle region of the plot gave average plate counts of 33·7 and 56·8.
Conclusion.
Surveying generally the field covered in this chapter, one can only be impressed with the fragmentary character of our knowledge and with the fact that, owing to the selective nature of the technique, the data we possess, if assumed to be representative, give an entirely partial and erroneous picture of the soil fungi. From the qualitative aspect, the chief impediment is the impossibility of obtaining reliable specific determinations of very many of the soil fungi. Lists of doubtfully-named forms from particular soils or geographic regions are useless or a positive evil, and there is imperative need for the systematising of selected genera by physiological criteria, such as has been partially done for Penicillium, Fusarium, and Aspergillus. Furthermore, until a standardised and non-selective technique has been devised, or a number of standardised selective methods for particular groups, comparative investigations into specific distribution can give little of value. This latter criticism is also very applicable if regard be paid to the quantitative aspect of soil work, for progress here largely depends upon the elaboration of a standardised fractionation technique. Every single factor in these methods needs exact analysis, for each gives opportunity for great error, and each error is magnified many thousand times in the final results. Much has been done in this direction at Rothamsted, but more remains to do. Finally, working with single species in sterilised soil under standardised conditions, there is fundamental work to be done on the relation of plate colony to soil “individual.”
[1] Adametz, I., “Untersuchungen über die niederen Pilze der Ackerkrume,” Inaug. Diss., Leipzig, 1886.
[2] Brown, P. E., and Halversen, W. V., “Effect of Seasonal Conditions and Soil Treatment on Bacteria and Molds in Soil,” Iowa Agric. Expt. Sta. 1921, Res. Bull., 56.