74 DRY LAND FARMING 



it the white color which characterizes it. It is a mix- 

 ture of the sulphates and chlorides of soda and mag- 

 nesia. The most harmful effect from the presence of 

 white alkali is that it retards or entirely prevents ger- 

 mination in the seeds. Some crops, however, will stand 

 as much as one-tenth of one per cent, of white alkali. 



Black alkali is due to the presence of carbonate of 

 soda along with the aforementioned salts. It dissolves 

 the vegetable matter in the soil and gives it its dark 

 color. It tends to consolidate the soil in proportion as 

 it is present. In some instances, because of the previous 

 nature of the soil, the black appearance may not come 

 to the surface and yet there may be much carbonate of 

 soda in the subsoil. When it is present in any consider- 

 able quantity, the soils which contain it are practically 

 untillable during the dry portions of the year. One- 

 tenth of one per cent, of black alkali will prevent the 

 growth of useful plants. Nevertheless in small amounts 

 the alkalies are quite helpful in promoting vegetation. 

 Plants will be much stimulated in their growth because 

 of their presence. It is when they are present in excess 

 that they become injurious. They are more injurious 

 in seasons which have fairly good spring rains followed 

 by a shortage in the summer rainfall. The salts are 

 thus brought into the root zone by the excessive evapo- 

 ration which follows, and the plaryts then fail because 

 of drought. Unwise or excessive irrigation brings the 

 alkali to the surface, and to the extent in some instances 

 of rendering land unfruitful which previously may have 

 produced good crops. Alkali is most liable to accumu- 

 late where the land is depressed and where the drainage 

 is not good. In humid areas the excess of these salts is 

 washed out from time to time, so that in these their 

 presence is not usually harmful. Both classes of alkali 

 tend to destroy the soil texture. They destroy its granu- 

 lar condition, causing it to become impervious to water. 



