48 Transactions Texas Academy of Science. — 1908-1909. 
DEFICIENCY OF SOILS. 
The weight of the crop without phosphoric acid divided by the 
weight with phosphoric acid, gives the extent of deficiency. If the 
unfertilized crop is 50 per cent or less of the fertilized crop, the 
soil is regarded as very deficient (DD) ; and if more than 90 per 
cent, not deficient (S). 
Several crops were sometimes grown on the same soil. In finally 
deciding on the deficiencies for soils, all crops grown upon the soil 
were considered, and also any other circumstances which may have 
affected the conclusions. 
We have divided the soils into groups, according to their content 
of active phosphoric acid. Group 1 contains soils having less than 
10 parts active phosphoric acid per million; group 2, less than 20; 
group 3, less than 30 and so on. 
The results of our pot tests are combined in table I, in which 
the number of soils decided to be very deficient, deficient and not 
deficient, are given. Also the percentages of the total number in 
the group is given. 
Of the 38 soils containing less than 20 parts per million of active 
phosphoric acid, we find 32 highly deficient, five deficient, and one 
sufficient. The sufficient soil had only one pot experiment made on 
it, with mustard, and the results might very possibly have been de- 
ficient had more tests been made. 
Soils containing 20 parts per million, or less, , of active phosphoric 
acid are highly deficient in phosphoric acid. 
Considering the table further, we find that the percentage of very 
deficient soils decreases rapidly from 87 per cent in the first group 
to 14 per cent in the fourth, after which it decreases slowly to the 
11-19 group, after which there is a sudden increase. One soil, how- 
ever, makes a great difference in the percentage in these groups. 
Table I. — Number and Percentage of Deficient Soils Grouped Accord- 
ing to Content of Active Phosphoric Acid. 
Number of Soils. Percentage of Soils in Group 
DD D S DD D S 
No. 1 13 2 .. 87 13 
2 19 3 1 83 12 4 
3 7 10 1 39 55 6 
4 1 5 1 14 71 15 
5-6 ’ 1 4 2 14 57 28 
7-8 2 13 . . 13 87 
