RELATION OF MOISTURE IN SOLID SUBSTRATA TO 

 PHYSIOLOGICAL SALT BALANCE FOR PLANTS AND 

 TO THE RELATIVE PLANT-PRODUCING VALUE OF 

 VARIOUS SALT PROPORTIONS 



By John W. Shive 



Plant Physiologist, New Jersey Agricultural Experiment Station 



INTRODUCTION 



Soil moisture is perhaps the most important single factor affecting crop 

 production, and the relation of soil moisture to plant growth in general 

 has been the subject of much investigation. Not so much attention has 

 been given, however, to the relation of moisture in soils or other solid 

 substrata to physiological salt balance or to the plant-producing value 

 of complete fertilizer rations for plants, for the reason perhaps that ade- 

 quate methods for quantitative studies were not available. 



The need of some method by which the effects of nutrient solutions of 

 known composition upon the growth of plants may be studied in the 

 presence of some solid substratum resembling soil, but without so many 

 of the biological and chemical complications always encountered in soil 

 cultures, has practically been realized in the new sand-culture method 

 recently developed by McCall {8)} By this method plants may be grown 

 in sand supplied with nutrient solutions of any desired composition, 

 which may be renewed or modified almost as readily as water cultures. 

 This method makes it possible to study quantitatively the influence of 

 various degrees of moisture in solid substrata uoon the physiological 

 salt balance, so far as this affects plant growth. 



Harris (5) has pointed out that the effect of a fertilizer upon the growth 

 of wheat is largely dependent upon the amount of soil moisture and em- 

 phasizes the point that fertilizer experiments, in order to be of any value, 

 must be made under widely varying moisture conditions. It has 

 been shown by Gile (5), McCool {10), Tottingham (75), McCall (9), 

 Ayres (/), and others that the physiological value of any set of salt pro- 

 portions varies, in general, with the total concentration of the medium; 

 but as yet no general rule has been formulated to express the manner of 

 this variation. It thus appears that physiological salt balance in nutrient 

 solutions is largely dependent upon total concentration. 



' Reference is made by number (italic) to " Literature cited," p. 377-378. 



Journal of Asricultural Research, Vol. XVIII.No. 7 



Washington, D. C. Jan. 2, 1920 



tf (357) KeyNo.N.J.-a 



