CHAPTER XXIX 



CRITICAL PERIODS IN PLANT LIFE 



IN this connection we may well consider another cause of 

 differences in crop yields quite out of proportion to the difference 

 in soil treatment. There may be, and often are, critical periods in 

 the life of plants, when some small measure of assistance may 

 change prospective failure into marked success. Thus, it is not 

 infrequently a question of life or death with the clover plant when 

 the nurse crop is removed; and, while most of the plants may die 

 at that time on untreated land, a good stand of clover may be saved 

 where a very light application had been made of manure, fertilizer, 

 or soil stimulant. The nutrient value of the application may not 

 be sufficient for half a ton of clover, but the difference in yield may 

 amount to one or two tons; and from the larger crop larger resi- 

 dues are left on and in the soil, resulting in a larger crop of grain 

 the following year. Thus, enormous credit may be given, which is 

 not at all deserved, on the basis of total plant food concerned. 



One of the most critical periods in the life of the corn plant is 

 at the time the ears are forming, and an ample supply of moisture 

 appears to be especially necessary at that time. If a severe sum- 

 mer drouth is coincident with this critical period, the yield of 

 grain is likely to be small; and any soil treatment which has the 

 effect either of hastening or retarding the development of the plant, 

 and thus of bringing the earing time either before or after the 

 drouth, may very markedly affect the crop yield. 



The farmer is usually most anxious for conditions under which 

 his wheat will " fill " well, and since this is influenced very appre- 

 ciably by the temperature during this critical period, it follows that 

 very marked effects upon both yield and quality may sometimes 

 result from any soil treatment that causes the wheat to " fill " 

 either a few days earlier or a few days later than on the untreated 

 land. On the other hand, the treatment, whether applied as a crop 



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