486 Journal of Agricultural Research voi.xv. no. 9 



As a source for the necessary nutrient salts a formula of culture solu- 

 tion worked out by Shive ^ for wheat was made use of. Since no simi- 

 larly tested formula for clover culture was available, the same solution 

 was used for the clover experiments. Shive's solution (R5C2) was made 

 up on the following basis : 



Potassium phosphate (KH2PO4) 0.0180 mole in i liter of solution. 



Calcium nitrate [Ca(N03)2] 0052 mole in i liter of solution. 



Magnesium sulphate (MgSO^) 0150 mole in i liter of solution. 



All salts are calculated as water-free. 



In this solution we should expect to have whatever mineral materials 

 are necessary for wheat plants in proportion and concentration found by 

 culture test to be most fitting. 



To get a standard with which to compare the results obtained with the 

 marls, a series of culture solutions was made up on the basis of Shive's 

 solution so modified as to supply the potassium in the form of the com- 

 mon salts of commerce. These in very impure form have furnished a 

 large part of the potassium present in the commercial fertilizers of the 

 past and should give results up to which marls should measure if they 

 are to be substituted for these salts as equally satisfactory sources of 

 agricultural potassium. 



It is well known that potassium absorption is greatest during the time 

 when increase in volume is the predominant feature of plant develop- 

 ment; hence, chiefly during the earlier stages of the life of the plants. 

 The experiments, therefore, were not continued to maturity, the crop 

 being harvested and dried for comparison after a growth period of eight 

 weeks from the planting of the seed. 



The pots, nearly filled with sand, were well watered with the desired 

 culture solutions in case all constituents were soluble, and the seeds of 

 wheat or red clover were immediately planted. The use of a surplus of 

 solution was avoided in order that materials might not be washed down 

 into the saucers and beyond the reach of the plants. 



In the case of the slowly soluble greensands the quantity of material 

 needed was weighed out and thoroughly mixed with the dry sand. These 

 mixtures were put into the pots and irrigated with culture solutions from 

 which all sources of potassium were omitted. It was hoped in this way 

 to find out whether the greensand materials could yield useful potassium 

 rapidly enough to permit the plants to make growth. Control cultures 

 in which all nutrients but potassium were present gave a measure of the 

 gain resulting from the presence of the salt or of the greensand. Other 

 controls with complete culture solutions, which would be expected to 

 yield the most favorable results were provided. 



' SmvE, John W. A THREE-SALT NUTRIENT SOLUTION FOR PLANTS. In Amer. Jour. Bot., V. 2, no. 4, 



p. 159. 1915. (p. 157-160.) 



A STUDY OF PHYSIOLOGICAL BALANCE. IN NUTRIENT MEDIA. In Physiol. Researches, v. i, no. 7, 



P- 327-397. IS fig- 1915- 



