THE SOIL AND ITS EFFECT ON PLANT GROWTH. 27 



acre was not regarded as important, but these conditions do not 

 prevail to-day, and we need to know exactly how sour a soil 

 really is and what is required to put it right. An acid condition 

 of soil indicates either an already low or else a declining supply 

 of available lime. Lime is not only used by all growing plants, 

 but it also acts as a great regulator of soil fertility. It may not 

 always be advisable to lime all acid soils under all conditions, but 

 it is very important to know whether a soil is acid, and how acid 

 it is, in order that if lime is not used, crops may be grown which 

 are best adapted to the conditions. Further, the degree of 

 acidity alone is not necessarily an index to the lime requirement 

 of a soil, which may be influenced by other factors, such as the 

 amount of organic matter present. The present position is well 

 illustrated by a recent report of the work of the Advisory Chemist 

 attached to the University College of North Wales, Bangor. This 

 officer has paid special attention to the soils of North Wales, and 

 has made an extensive survey which is now nearing' completion 

 and should be of great value for advisorj^ purposes. In particular 

 he has examined the question of the lime requirements of soils 

 in his area. He finds that he can divide the soils into three 

 broad groups. In the first, there are those which contain com- 

 paratively large amounts of calcium carbonate, and are therefore 

 presumably not in need of lime. Secondly, there are soils, 

 which, although they contain little or no calcium carbonate, and 

 give mdications of lime requirement by certain recognised 

 laboratory methods, do not show lime requirement by more 

 modem tests. Thirdly, there are soils which show lime require- 

 ment by all tests. Generally, the calcium carbonate content of 

 the soils is very small, and according to the older laboratory tests 

 it would appear that liming is an urgent necessity. For various 

 reasons liming has been much neglected in North Wales, and yet 

 no large apparent disadvantage can be noticed. 



The question of liming cannot, of course, be dealt with in the 

 laboratory alone, and there is urgent need for an extensive 

 series of field trials throughout the country. There is some ground 

 for hoping that these will be arranged at no very distant date. 

 At the same time, we want much more precise laboratory tests 

 for lime requirement than exist at present. This need was felt, 

 for example, by the Department of Agricultural Chemistrj^ of the 

 University of Leeds in the extensive investigations which they 

 have been conducting for some years into the liming of Yorkshire 

 soils. An endeavour was made to devise some simple laboratory 

 test which would help to get over the difficulty, and it was found 

 that a certain chemical solution invariably became red when mixed 

 with the liquid extracts from soils that were known to be sour, 



