50 



THE AGRICULTURAL NEWS. 



February 12, 1916. 



in certain circumstances, lime also. A soil in good tilth 

 has a characteristically crumbly and slightly sticky 

 feel, and its resistance to the pressure of one's heel can 

 best be described by the English farmer's term of 

 'kindly'. 



Obviously such a complex condition must be 

 difficult to measure. We can determine the water- 

 content of the soil, the proportion of particles of 

 different sizes, the content of organic matter and so on: 

 but tilth is more complex — a sort of resultant in fact, 

 of these different determinations. What seems to 

 us to be the most likely way of obtaining a useful 

 index of tilth is by means of an appliance described 

 after the conclusion of this article. It has been used 

 originally to determine the degree of compactness of 

 soils, which, of course, must be closely related to what 

 we understand by tilth. The device works on the 

 principle that the number of drops of a ram on to 

 a metal spike nece.s.sary to make the spike penetrate 

 the soil to a certain depth, is a measure of the relative 

 compactness of the soil. 



The appliance is easy to construct, as will be seen 

 from the illustration, and its trial in experiment 

 stations and on estates is to be recommended. The 

 first thing to which attention should be given is the 

 appliance itself. That is to say, before it can be 

 employed to serve a useful purpose in agriculture, the 

 exact significance of the observation it furnishes must 

 be enquired into. To what extent does water-content 

 of the soil affect the instrument:" It would probably 

 be found necessary, in comparing two soils, to do so 

 when their water-contents are practically the same, or 

 at least, if they are not, to make determinations and 

 correct the mechanical observations accordingly. Then 

 again the establishment of correlations would be 

 valuable. The dynamometer observations in plough- 

 ing a field, which would be an index of relative hori- 

 zontal resistance in the soil, would probably vary- 

 directly with the observations taken with the appliance 

 referred to above in a vertical direction. 



The great advantage of being able to measure 

 tilth would lie in the direction of facilitating the 

 making of comparisions. To be able to .say that the 

 tilth of one estate is, on the average, so many units 

 bettor than another would be of distinct advantage: 

 and the same thing would apjjl}' to individual fields on 

 the same estate. In a general way such tilth observa- 

 tions would be very useful in -soil surveys, and would 

 tend to enhance the practical value of physical analyses. 



In manipulating the mechanical 

 device, auger plate E is placed 

 squarely on the ground and pin 1) 

 is set in the aperture. Sheath F 

 is then slipped over pin D, and 

 ram (J is dropped on the pin until 

 it is driven into the soil sufficiently 

 deep for mark b on the ram to be 

 even with the top of sheath F. The 

 ram is raised each time to the mark 

 and then dropped freelj' by its 

 own weight (7,445 gm.). This 

 operation is repeated, recording 

 eacli drop, until mark c on the ram 

 is even with the top of sheath F. 

 Thus, the pin is driven a distance 

 of 4i inches in the ground each 

 time a test was made. The 

 number of drops necessary to 

 produce this effect is the measure 

 of the relative compactness of .soil 

 in the various plots. 



Fig. 5. Device for testing the 

 compactness of the soil. (After 

 C. A. Le Clair, in the Journal 

 of Agricultural Research, Vol. V, 

 No. 10.) 



THE SPIRIT OF THE SOIL. 



This is the title of a book by G. D. Knos embodying ihe 

 results of Professor Bottomloy's attempt to prepare a new 

 fertilizer from peat. The book is reviewed by Professor 

 Keeble, F.R.S., I)irector of the Royal Horticultural Society'.^ 

 Experiment Station, and editor of the Girdener's Chronicle, 

 in the issue of Nature for December 9, 1915. 



The successful results obtained with plants in pots after 

 the application of fertilized peat has been recorded already in 

 this .Journal. An explanation of how the material produces 

 its effects has not. Consequently the brief account given by 

 Professor Keeble in his review will be of interest. Certain 

 bacteria possess the power of liberating from peat large 

 quantities of soluble humates. These .soluble humates are in 

 themselves of service to plants as sources of food. They 

 serve, moreover, as a culture medium in which nitro£jen-fixing 

 h&c\.ev\a. —Azotoh'icter chroococcum, etc., — multiply rapidly. 

 Hence by adding cultures of nitrogen fixers to sterilized 

 humated peat, the amount of nitrogen in the latter is 

 increased. 



At first the remarkable results which were undoubtedly 

 obtained from the application of fertilized peat were attributed 

 to this large nitrogen content: but the fact that growth was 

 not only increa.sed but the habit became sturdier and the 

 root development greater, led to the suggestion that the 

 virtues of bacterized peat are to be .sought el.sewhere than in 

 the nitrogen content. Professor Rottomley was led to the 

 very interesting conclusion that the growth of plants is 

 conditioned not oidy by the well-known substance- producing 

 food materials, but also V>y hitherto unknown growth 

 stinuilators. The.se .substances, which he claims have been 

 isolated from jicat, Profe=.sor Bottomley has called auxi- 

 inones: while Mr. Knox refers to them under the more 

 poetical title of the spirit of the soil. Professor Bottomley 



