CHAPTER V 



THE RESPONSE OF FRUIT PLANTS TO VARYING CONDITIONS 

 OF SOIL MOISTURE AND HUMIDITY 



Water as a factor in growth thus far has been discussed only in its 

 general importance in the development of the plant as a whole. There 

 are, in addition, certain specific responses made by the plant to a varying 

 water supply. 



Influence of Soil Moisture on Vegetative Growth. — One of the most 

 important of these specific responses is in new tissue formation, an in- 

 crease in size or bulk. Data have been presented in Table 19 showing 

 the influence that various methods of culture, such as tillage, tillage and 

 cover crops and artificial mulches, have upon vegetative growth measured 

 by trunk circumference. 



New Shoots and Their Leaves. — Table 33 gives certain averages found 

 by Hedrick in sod-mulched and cultivated plots in a New York apple 

 orchard. Every phase of vegetative growth measured showed a gain 

 from tillage. Moreover the tillage plot averaged considerably higher 

 in moisture during the growing season. Probably much of the influence 

 of tiflage was due to the increased moisture available in the soil, yet it is 

 difficult to say how much is to be attributed to this factor and how much 

 to the influence of the tillage on plant nutrients, particularly nitrates. 



More direct evidence of the effect of water on vegetative growth is 

 furnished by certain orchard irrigation experiments. The following 

 quotations from a report on an investigation in Utah bear on this point. 

 "Frequent applications of irrigation water applied to peaches on a 

 gravel loam (about 15 feet deep) at intervals of 7 or 8 days produced a 

 more continuous and greater total twig growth than the same total 

 amount of water applied with larger applications at intervals of every 

 10 to 12 days. The more porous the soil the more frequently the trees 



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