ROOT SYSTEM AND SALTS 



41 



and apart from salt content the soils had probably very 

 similar properties ; the results therefore clearly indicate a 

 direct beneficial action of the salts. In most investigations, 

 however, comparison can be made only between the systems 

 of different individuals. The effects of the addition of 

 certain salts to an exhausted Rothamstead soil studied by 

 Brenchley and Jackson (1921) are shown in Table VII. 



TABLE VII 



Development of Roots and Shoots of Wheat (16 weeks old). 



Weight in Grammes 



Dry 



The increase in root development is marked with phos- 

 phate as compared with nitrate, and the diminution in the 

 shoot/root ratio shows that it is not wholly due to a secondary 

 effect through the shoot. Gericke (1921) found that wheat 

 seedlings grown in culture solutions lacking nitrogen showed 

 a remarkable root development though the shoots were 

 stunted. 



The effect of phosphates in promoting root growth 

 has long been recognised in agricultural practice. It is of 

 importance not only in promoting the swelling of such 

 " roots " as the turnip or mangold, but in causing increased 

 development of the branches of the absorbing system. 

 Russell sums up : " Dressings of phosphates are particularly 

 effective wherever greater root development is required 

 than the soil conditions normally bring about. They are 

 invaluable in clay soils, where the roots do not naturally 

 form well. . . . They are used for all root crops like 

 swedes, turnips, potatoes, mangolds. . . . Phosphates are 

 needed for shallow-rooted crops with a short period of 

 growth like barley. Further, they are beneficial where- 

 ever drought is likely to set in, because they induce the young 



