SOIL CONDITIONS AFFECTING PLANT' GROWTH 71 



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 XXII. YIELD OF WHEAT IN THOUSAND POUNDS PER ACRE. 



ROTHAMSTED. 



In the bad years the average rainfall was 32*55 inches 

 (harvest years, September-August), while in the good years 

 it was 27-10 inches ; the badness of the season may be 

 connected with the high rainfall and corresponding low tem- 

 perature. Similar results are obtained, however, if other un- 

 favourable conditions set in. 



The improvement in healthiness is well exemplified by the 

 power of resisting disease. At Rothamsted the potash-starved 

 wheat and mangolds are liable to be attacked by disease, 

 especially where there is excess of nitrogen, while the sur- 

 rounding plots, equally liable to infection, remain healthy. 

 FlaXjgrowers in the north of Ireland have found that potassic 

 fertilisers increase the resistance of the plant to the attacks of 

 the wilt organism. 



At the Cheshunt Experimental Station liberal treatment 

 with potassic fertilisers makes the tomato plant more resistant 



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

 years were 1868, '69, '70, '81, '83, '85, '87, '89, '91. 



