“Buack AukaiT’ in the San Luis Vauuey 7 
that when it is plowed it breaks up in hard cakes or lumps. This 
effect is so marked on some soils that the carbonate formed, due 
to the application of Chile saltpetre, cakes the ground so badly that 
anyone can tell just where the saltpetre was applied. This was 
so noticeable in a field in which I had made some fertilizer ex¬ 
periments that the plowman who was sent to do the fall plowing 
picked out of the 48 plots into which the field was divided, the 12 
plots to which the Chile saltpetre had been added. The smallest 
amount added was 62.5 pounds to one million pounds of the soil. 
This would give rise to about 75 pounds of carbonate to each 
million pounds of soil, provided the largest possible amount of 
carbonate was formed, and yet this actually sufficed to puddle 
and cake the land to the extent that I have indicated. This amount 
expressed in percentage is seventy-five ten thousandths of 1 per¬ 
cent. This amount is very much less than is necessary to Injure 
plants by directly eating off the roots or to poison them. The 
amount necessary to do this is from four to five one hundredths of 
1 percent, or from 400 to 500 pounds in each million pounds of 
soil. This “black alkali” is really very poisonous to plants and 
its effect on the physical or mechanical condition of the soil is 
very bad. 
NITRATES DESTRUCTIVE IF PRESENT IN SUFFICIENT 
QUANTITIES 
There are still other salts that occur in our soils of which we 
must take some note, for they may easily become so abundant as 
to be injurious, or even to be fatal, to all vegetation. In bulletins 
Nos. 155, 160, 178, 183 and 186 of this Station I have described in 
some detail, the occurrence of these salts, nitrates, in some of our 
Colorado soils in such quantities as to kill vegetation, even old, 
well established apple trees. One of the very first occurrences 
of this sort that I recognized was in the San Luis Valley. The 
occurrence of these salts may have two effects. A small amount 
of them, 10 to 20 parts to a million parts of the soil, may produce 
big crops of oats or other farm products, whereas, too much of 
them will burn and kill the crop. At this time I wish only to call 
attention to the fact that this question exists in the agriculture of 
the San Luis Valley. I may state that I saw in Rio Grande County 
in the season of 1916, a quarter section that had been planted to 
peas, on which no peas were grown. The grasshoppers were 
blamed for the destruction of the crop, but no grasshoppers were 
to be found on the quarter section. Nitrates, however, were pres¬ 
ent in this soil in fatal quantities. These statements are made 
simply to impress upon the minds of interested parties that there 
