100 TYPICAL ANALYSES 



attention has been and is being given to a study of the mechanical 

 composition of soils, especially in America, but, so far, it is not exactly 

 clear how the results are to be co-ordinated with fertility. 



Summary. In considering the results of a chemical analysis of a 

 soil, the most important data are : 



1. The nitrogen and organic matter. 



2. The total phosphoric acid, lime and potash. 



3. The "available " phosphoric acid and potash. 



4. The presence or absence of injurious ingredients (" alkali " ferrous 

 compounds, etc.). 



The first two afford the best means of gauging the potential fertility, 

 i.e., the actual amounts of plant food which the soil can supply, and 

 which therefore determine the limit of the number of crops which the 

 soil can carry without manure. The third affords the best criteria as 

 to a soil's requirements with respect to phosphatic and potash manures, 

 or gives the best means of estimating the actual present fertility of the 

 soil. In this connection, the limits to be taken as indicating need of 

 manuring are somewhat uncertain, and the best and most reliable 

 method would be to compare the figures for the soil in question with 

 those obtained from the analysis of similar soils of known fertility. 



In all cases it is well to keep in mind Liebig's " law of minimum," 

 viz., that the limits of fertility are fixed by the amount of the parti- 

 cular constituent of plant food which is most deficient in the soil under 

 consideration. For example, if a soil be lacking in phosphates, ap- 

 plications of potash or nitrogenous manures will not enable it to give 

 a full crop. 



Examples of Actual Analyses. This chapter may conclude with 

 a few examples of analyses of soils, in order to illustrate the points dis- 

 cussed. The following table gives the figures derived from analyses, 

 made in most cases by the writer, of a few typical English and Trans- 

 vaal soils, and will serve to show some of the main points of difference 

 between soils of various classes and particularly between those of tropical 

 and temperate countries : 



A is a good English pasture soil, a sandy loam, from the coal 

 measures. 



B is an arable sandy loam also from the coal measures. 



C is a sandy soil, poor in plant food. 



D gives the median values from analysis of 100 soils of the county 

 of Dorset. 1 



E is a "black turf" a peaty clay soil of the Transvaal. 



F is a red clay soil of the Transvaal. 



G is a chocolate-coloured clay soil of the Transvaal. 



H is a chocolate loam. 



I is typical of red and brown loams. 



J is typical of red sandy soils. 



K is a brown sandy soil. 



L is a representative of grey and yellow sandy soils. 



The most noticeable feature in the above table is the comparative 



1 The Soils of Dorset, Dr. Luxmoore, Aug., 1907. 



