ula Fe 
In such cases one always turns to the admirable work at Rothamsted 
for help and the constantly increasing difference between the yields of 
plots 11 and 13 Broadbalk Field seem to show that the indirect effects are 
decreasing. ‘The gypsum alone on plot 11 would theoretically release 90 
pounds per acre of potash annually while the total annual application of 
potash on plot 13 is 100 pounds. The theoretical amount of potash that 
could be released by the bases in the minerals used on the fully fertilized 
plots at Rothamsted amounts to about 400 pounds of potash per acre an- 
nually while the potash applied in sulphate amounts to 100 pounds. While 
Director Hall has clearly pointed out the difference between the early 
years and the later, too many who use Rothamsted results to fortify their 
arguments simply take the average for the whole period and neglect to 
consider the results by decades. 
Especially when we wish to secure indication of soil needs as promptly 
as possible should we take pains to use materials that will exert as little 
indirect effect as possible. By using blood as a source of nitrogen and 
gypsum free precipitated phosphates as the source of phosphoric acid we 
can remove most of these indirect effects and at the same time use ma- 
teriais easily secured and of high availability. 
Another point that is never considered in planning the plot tests in 
the section under consideration is the marked difference in the fixing 
power of soils for plant foods and the firmness with which they hold them. 
This is roughly recognized in providing for an excess of phosphoric acid 
in commercial formulas but is seldom considered in plot tests. 
The plot tests in most cases have simply been copied from plans made 
before the nitrogen gathering power of bacteria associated with legumes 
was understood and sometimes altered because of the injurious effect of 
the excessive nitrogen applications or too often abandoned altogether be- 
cause the growth of the institution demanded the land for other purposes. 
The frequent changes in the staff of workers has also interfered seriously 
with both the conduct of the work and the interpretation of the results. 
The conditions in the winter wheat section of the United States are 
such that large crops must be produced in order to realize a suitable re- 
turn on the selling value of the land and the money spent for farm labor. 
The small grain crops are so related culturally with the clover crop that 
they are almost necessary in a rotation if we expect to utilize our most 
widely distributed legume as a source of nitregen. 
