DIVISION OF SOILS. 137 



proportion of normal carbonate to bicarbonate is so small that the 

 solutions for most practical purposes may be considered as solutions 

 of the bicarbonate alone. But for the salts of magnesium, potassium, 

 and sodium this is far from being the case. In all cases, the propor- 

 tion of normal carbonate to bicarbonate increases with the tempera- 

 ture and with the concentration. These results are of great signifi- 

 cance in explaining the conditions observed in various areas of the 

 arid regions containing soluble carbonates, and which at first appeared 

 hopelessly anomalous. It is believed that the results will have value 

 not only in soil studies, geological investigations, etc., but also in cer- 

 tain technical operations involving the preparation and handling of 

 alkaline carbonates. 



CLASSIFICATION OF ALKALI SOILS. 



The present classification of alkali soils into those containing white 

 alkali and black alkali, each of which presents an infinite number of 

 problems,* is not in keeping with the advance in our knowledge con- 

 cerning such soils. As a result of the investigations of this Division, 

 a new classification has been proposed, as it indicates that the vast 

 array of problems which the alkali soils have apparently presented 

 hitherto can be grouped into a very few general classes. 



It has been shown that alkali does occur in the soils of humid areas 

 under certain conditions, and that these conditions are not unusual. 

 Indeed, it seems probable that the formation of temporary alkali in 

 soils of the humid regions is much more common than generally sup- 

 posed, and this may account for certain phenomena of plant disease. 



ALKALI VEGETATION AND SOILS. 



The relation of the natural vegetation of a soil to the inherent 

 characteristics of the soil itself, while a matter of great importance 

 and worthy of the closest attention everywhere, is especially so in 

 alkaline areas. A study of the effect of the growth of certain plants 

 in forming soluble carbonates, better known as black alkali, in soils 

 where this substance had not previously existed, has been continued 

 during the past year. It has been shown that this factor must be 

 considered in the introduction of such plants for forage purposes, as 

 the final condition of the soil may be made worse by the formation of 

 the very harmful black alkali from the white alkali originally present. 



A study has been made of certain native plants which have been 

 found to grow on soils containing excessive amounts of sodium car- 

 bonate or black alkali, in which no other vegetation will grow. It was 

 found that these particular plants were able to excrete soluble organic 

 acids on their leaves and stems, and these acids are sufficiently strong 

 to decompose carbonates, and thus form neutral salts, less injurious to 

 vegetation. It seems probable that the plants protect themselves from 

 the caustic action of the carbonates by the formation of these acids. 

 The further study of this subject and the possible economic value of 

 these plants is in the province of plant physiology. 



The amount of soluble salts which may be present in a soil and yet 

 not prohibit growth has been found with a close degree of accuracy 

 for the various areas in which the field parties have worked. But as 

 the character of the alkali varies in different areas, quite an extended 

 investigation was carried on, in cooperation with the Division of 

 Vegetable Physiology and Pathology, to determine the toxic limit (or 



