SOIL ANALYSIS AND ITS INTERPRETATION 335 



or with a soil where the conditions are so unfavourable that 

 organic debris does not decompose {e.g-. acid soils), or only 

 forms accumulations of peat. On the other hand, some of the 

 best loams, where the conditions are most favourable to rapid 

 decomposition and nitrification, contain but little nitrogen. 

 A few typical examples are given in Table LXXXVIII. 



Table LXXXVIII. — Nitrogen and Loss on Ignition. 



Loss on ignition 



Nitrogen . 



Loss on ignition 

 in subsoil 



Nitrogen in sub- 

 soil 



Soils containing much calcium carbonate are as a rule 

 rich in nitrogen, partly no doubt because of the rather high 

 nitrogen content of the rock and partly also because they are 

 folded, green manured, cropped with leguminous plants like 

 sainfoin, lucerne, etc., all of which tend to increase the nitrogen 

 supply. The nitrogen in some chalk soils is given in Table 

 LXXXIX. ; all are arable soils, excepting the last, which is 

 open downland. 



Table LXXXIX. — Nitrogen Content of Certain Chalk Soils. 



Carbonates. — The analyst is often asked whether or not 

 a particular soil contains sufficient calcium carbonate, and in 

 endeavouring to answer this question he must bear in mind 

 the twofold function of this substance, to prevent "sourness" 

 (p. 118), and to flocculate the clay. Where only a small 

 amount of clay — say 8 per cent, or less — is present the floccu- 

 lating action is less needed and a smaller amount of calcium 



