238 



SOIL CONDITIONS AND PLANT GROWTH 



There has been much controversy as to the effect of con- 

 centration of the nutrient solution on plant growth. The 

 relationship is curiously elusive : at first sight it appears a 

 most simple thing to ascertain. The difficulty is to change 

 the solutions sufficiently often to prevent complications due to 

 exhaustion of essential nutrient substances. 



Breazeale (5i<2) concluded from his experiments that 

 small variations in concentration of the nutrient medium are 

 without effect on plant growth ; this view is accepted by 

 Whitney and Cameron and in this country by Stiles.^ It is 

 vigorously controverted by Hall, Brenchley, and Underwood 

 (i2ic: see also $4c), who maintain that within certain limits 

 the plant growth is affected by and increases with the con- 

 centration, although recognising that the differences become 

 less as the solutions are more frequently changed. Hoagland 

 and Sharp (i36<r) also find that growth increases with increas- 

 ing concentration up to a point, beyond which no further 

 growth is obtained : absorption of nutrient salts still continues, 

 however. Some of their results with barley, after two days 

 growth, are given in Table LXIII. 



Table LXIII. — Transpiration and Growth of Barley in Solutions of 

 Different Concentrations. Hoagland and Sharp, 136c. 



Adequate concentration of nutrients is of great importance 

 in the early stages of plant growth : in later stages high 

 concentration is less necessary and may be undesirable.^ 



^Annals of Botany, 1915, 29, 8g. 



^Se3 also J. S. Burd, yourn. Ag. Research, 1919, 18, 51-72. 



