117 



In such cases one always (urns 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 ns possible. By using blood as a source of nitrogen aud 

 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- 

 terials 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 lie- 

 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 lie 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 arc so related culturally with the clover crop that 

 they arc almost necessary in a rotation if we expec.1 to utilize our nnst 

 widely distributed legume as a source of nitrogen. 



