SOIL CONDITIONS AND PLANT GROWTH 



where potash food is deficient, while very little more leaf, 8508 lb., 

 give rise to nearly three times as much root, 40,128 lb., where more 

 potassium salts are supplied. The harmful effect of potash starvation 

 on carbohydrate production does not seem to be the result of a patho- 

 logical condition of the chloroplastids. Reed found that they remained 

 normal for two months and even increased in numbers in potash-starved 

 algae. 



A second effect is on the formation of grain ; unlike phosphates and 

 nitrates, potassium compounds have a very marked effect on the weight 

 of the individual grains, as may be seen by comparing Table XVII. 

 with the corresponding Tables IX. (p. 32) and XIV. (p. 38); indeed to 

 withhold potash is the surest way of producing stunted grain. These 

 stunted grains are often sterile on the potash-starved grass plots at 

 Rothamsted. 



TABLE XVII. EFFECT OF POTASSIUM SALTS ON THE DEVELOPMENT OF BARLEY. 



HELLRIEGEL (131). 



Lastly, the tone and vigour of the plant are very dependent on the 

 potassium supply ; potash-starved plants are the first to suffer in a bad 

 season, or to succumb to disease. The Broadbalk wheat plots receiving 

 potassium salts give conspicuously better results than the others when- 

 ever the year is unfavourable to plant growth ; taking the yield on 

 the unmanured plot as an index of the character of the season, we 

 obtain the following results for a series of good and of bad years 

 respectively : 



TABLE XVIII. YIELD OF WHEAT IN THOUSAND POUNDS PER ACRE. ROTHAMSTED. 



J The bad years were 1867, '71, '72, '75, '76, '77, '79, '86, '88; the good years were 

 !868, '69, '70, '81, '83, '85, '87, '89, '91. 



