716 IOWA DEPARTMENT OF AGRICULTURE 



plication of kainit, potassium chloride or potassium sulphate is to be ad- 

 vocated. 



PhospJiorus. — Phosphorus is the element which is most apt to be de- 

 ficient in soils, not only in available form but also in insoluble com- 

 pounds. According to many analyses there is less than 2,000 pounds of 

 phosphorous per acre to a depth of 62/3 inches in Iowa soils. Comparing 

 this with over 30,000 pounds of potassium per acre to the same depth, 

 it is evident that there is more danger of a phosphorous deficiency in the 

 soils of the state. 



This deficiency may be remedied by applying phosphorous to the soil 

 in one of three forms: as fine ground natural rock phosphate, as steamed 

 bone meal, or as acid phosphate. The latter material carries the phos- 

 phorous in a form immediately available for plant food, while in the 

 other cases it occurs in an insoluble form and must be transformed to 

 be available. The advocates of rock phosphate recommend, however, 

 that it be applied with barnyard manure or green manure In order that 

 bacterial activities may be enhanced by the latter materials and a 

 more rapid transformation of the phosphorous compounds may occur. 

 They contend also that as the soluble phosphates are transformed into 

 an insoluble form in the soil, when not immediately assimilated, it is 

 of no particular value to use the soluble form. While this change of the 

 soluble form into insoluble does occur in the soil, one important point 

 should not be overlooked — when the soluble material is added to the soil 

 it is immediately dissolved and uniformly diffused through the soil. 



Thus, after the change into insoluble form occurs the phosphate is 

 in such physical shape that the bacterial action reproducing the soluble 

 material is considerably greater than it is on the insoluble rock itself. 



The rock is much cheaper and hence its use may seem advisable for 

 financial reasons, but it is still a mooted question whether it is not 

 more profitable to apply a soluble phosphate which unquestionably gives 

 quicker returns and probably larger yields even although perhaps not 

 as great percentage returns for the money invested, than to bury 

 a large quantity of rock phosphate in the soil where it becomes slowly 

 available. 



The Station is not prepared to make definite recommendations on 

 this point, and if they desire, farmers may test and compare the use 

 of soluble and insoluble phosphorous fertilizers. 



FIELD TESTS TO DETERMINE FERTILIZER REQUIREMENTS OF SOIL. 



Farmers generally recognize the fact that soils differ in productive 

 power. Sometimes soils which differ markedly from each other are 

 found on the same farm or even in the same field. 



In many cases the best soil on the farm is not as fertile as it should 

 be, or some portion of the farm is notably unproductive. The farmer may 

 desire, therefore, to test his soils in v. practical manner in order to de- 

 termine the effect of nitrogen phosphorus, lime or some other fertilizing 

 material on the crop yields. 



A fertility test that has been thoroughly tried out and that includes 

 the application of substances supplying the elements of plant food which 



