iQio] CURRENT LITERATURE 



175 



1 . 75 atmospheres. Analyses of the soil extract of the poor soil showed it to 

 be proportionally low in K^O and PA- Also addition of KH2PO4 to the poor 

 soil at the rate of 150-300 pounds to the acre greatly increases the growth of 

 wheat. A similar analysis of the soil extract of the good soil showed it to be 

 as poor in nitrates, nitrites, and ammonium salts as the extract from the poor 

 soil, but with a relatively high calcium magnesium ratio. Addition of 

 Ca(N03)2 to the good soil at the rate of 200-400 pounds to the acre greatly 

 improved the growth of the plants. Hibbard concludes that the soil is 

 deficient in calcium and perhaps nitrates. If, as Hibbard's results seem to 

 indicate, one can tell the fertilizer needs of a soil by such a study of the soil 

 extracts, he has given us a new practical method of great significance. He has 

 also hinged the fertilizer question largely on the balance between nutrient ions. 



Hibbard worked only on the early stage of the growth of wheat. It would 

 be of interest to know whether the same ratios apply to the middle and late 

 stages. It will also be interesting to see the nature of these ratios when plants 

 with high sulphur demands (alfalfa, cabbage, etc.), those with high potash 

 demands (potato, tobacco, etc.), or those with high general nutrient demands 

 (squash, cucumber, etc.) are used. These stand in contrast with the wheat 

 with its moderate demands. The method also needs the test of a great range 

 of soil types of various degrees of fertility. Considering all of these variables, 

 the application of the method may become rather complex. The work is 

 sure to stimulate a great amount of investigation. 



The use of a 3-salt nutrient solution requires that the variation in concen- 

 tration of the several nutrients shall always be in pairs. In Shive's solution 

 a change in concentration of sulphur is always accompanied by a correspond- 

 ing change in the concentration of magnesium, potassium by phosphorus, 

 and calcium by nitrogen. There is no reason for thinking that the magnesium 

 demands of a plant are thus tied up with the sulphur demands; in fact, in 

 soils we think of the sulphur as existing mainly as calcium sulphate, and in 

 fertilizer practice it is more generally added in this form. This is not an 

 adverse criticism of the use of 3-salt nutrient solutions; it is rather an acknowl- 

 edgment of the complexity and innate difficulties of the problem. Since so 

 many variations in proportions of nutrients are possible, the investigator must 

 study only a portion of these, if he completes his investigations within a reason- 

 able time. 



Livingston and Tottingham* recognize this shortcoming of the 3-salt 

 nutrient solution when they mention the 6 possible combinations of salts and 

 proceed to investigate the best proportions in the second combination. The 

 possible combinations are: 



I II in IV V VI 



Ca(N03). Ca(N03)a Ca(H.P04). CaCH.PO^)^ CaSO^ CaSO^ 



KH.PO^ K.SO4 KNO3 K.SO4 KNOj KH.PO4 



MgS04 Mg(H.P04). MgS04 Mg(N03)a Mg(H.P04). Mg(N03). 



« LiviNXSTOx, B. E., and Tottingham, W. R., A new 3-saIt nutrient solution for 

 plant cultures. Amer. Jour. Bot. 5:337-346. 1918. 



