108 



FUNDAMENTALS OF FRUIT PRODUCTION 



however, tend to increase solubility. "The result of solubility of these singly 

 salt treated soils goes to indicate that a salt or fertilizer treatment leaves a resid- 

 ual effect upon the soil and this residual effect continues to be manifested in in- 

 creased solubility and in increased crop-producing power." 



Availability of Phosphorus. — It has been stated that phosphorus 

 is available to the plant only when present as a phosphate and that sul- 

 phur is absorbed only as sulphate. However, all phosphates and sulphates 

 are not equally available; furthermore, a phosphate that is highly avail- 

 able for the plants of one species may be much less available to those of 

 another. This principle is well illustrated by the data presented in 

 Table 10 showing the percentage of normal growth made by plants grown 

 in nutrient solutions that were uniform except for the form in which 

 phosphorus was presented. 



Table 10. — Comparative Growth of Various Plants with Different 

 Phosphates 

 (After Truog^^^) 

 (Growth on acid phosphate represented by 100) 



In commenting on these data Truog'*^ remarks: "The great differences 

 exhibited by the various plants in their growths on the different phosphates 

 indicate tliat plant characteristics play an important role in this connection. 

 The fact that rape made a better growth on rock phosphate than on ferric 

 phosphate, while in the case of oats the opposite was true, indicates that solu- 

 biUty alone is not the only factor involved in the utilization of these phosphates 

 by plants. The remarkably vigorous growth of the barley with ferric phos- 

 phate is another indication that aside from solubility or availabiUty, some 

 phosphates seem to serve the needs of certain plants better than others. The 

 remarkable adaptability of certain soils to certain crops may partly be due to 

 causes of this nature." 



Availability Varies According to Kind of Plant. — In general the avail- 

 ability of inorganic soil constituents is increased by the activity of the 



