142 



SOIL CONDITIONS AND PLANT GROWTH 



with a rich soil containing abundance of valuable non-acid organic 

 matter, or with a soil where the conditions are so unfavourable that 

 organic debris does not decompose, 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 LVII. 



TABLE LVII. NITROGEN AND Loss ON IGNITION. 



Soils containing much calcium carbonate are as a rule rich in nit- 

 rogen, 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 as follows : 



All are arable soils, excepting the last, which is open downland. 



Carbonates. The analyst is often asked whether or not a particular 

 soil contains sufficient calcium carbonate, and in endeavouring to an- 

 swer this question he must bear in mind the twofold function of this 

 substance, to prevent "sourness" (p. 62), and to flocculate the clay. 

 Where only a small amount of clay say 8 per cent, or less is present 

 the flocculating action is less needed and a smaller amount of calcium 

 carbonate suffices. The Stedham soil (Table LIV.) is an example ; it 

 is near the bottom of a slope along which water containing calcium 

 bicarbonate in solution is drifting, and therefore shows no tendency 

 to become sour. The 0^03 per cent, of calcium carbonate present, 

 hopelessly inadequate as it appears, suffices for its needs and no increase 

 in crop is obtained by applying lime. The Lydd soil (Table LV.) con- 

 tains only 'O2 per cent., but is also well supplied with calcareous water 

 from below and shows no sign of sourness. Similar soils that have not 



