22 FUNDAMENTALS OF FRUIT PRODUCTION 



Though water absorption is greatly reduced at low temperatures many 

 plants are able to take up water when the soil temperature is below 0°C., 

 for even at —3 or — 4°C,, much of the soil water is not frozen and the soil 

 is still capable of delivering water to the root surface. ^^ 



The amount of oxygen in the soil air has a marked effect on root 

 absorption; if for any reason the supply of oxygen is inadequate, absorp- 

 tion ceases. It should be remembered, however, that oxygen dissolved 

 in the soil water is available to the root system. In fact, the oxygen 

 absorbed by the living cells of the root must be dissolved in water before 

 it can be taken up. The susceptibility of the roots to differences in the 

 oxygen supply varies markedly with different plants. Thus roots of 

 Coleus Blumei and Heliotropium peruvianum showed injury after three 

 days' exposure to a soil atmosphere mixed with 25 per cent, nitrogen 

 gas, while roots of Salix sp. grew freely in pure nitrogen. ^^ There is some 

 indication that roots of deeper penetration are less responsive to changes 

 in aeration and temperature than the more superficial roots. 



The effect upon top growth of reduced absorption by the roots occasioned 

 by poor aeration incident to a condition of the soil approaching saturation, is 

 strikingly illustrated by the behavior of established trees of certain kinds in 

 portions of India. Howard and Howard^^ record that these trees naturally 

 have a short resting period during midwinter, a period often accompanied or 

 preceded by leaf fall. With a rise in temperature during February, new leaves, 

 shoots and flowers are formed and rapid growth continues until hot weather 

 checks it. A second period of rapid vegetative growth is inaugurated with the 

 advent of the monsoon, but when the soil approaches saturation, growth slows 

 down again or nearly ceases. There is a third period of vegetative activity at 

 the and of the monsoon when, with the drying out of the soil, the attendant 

 aeration makes increased root activity possible. This third period of growth is 

 finally checked by the low temperature of the winter season. 



Transpiration (and hence absorption) is decreased by the addition of small 

 amounts of tartaric, oxalic, nitric, or carbonic acid to the soil and is increased 

 by alkalies, such as potash, soda, or ammonia, though under field conditions 

 these factors are apt to be of minor importance. ^^ An increase in the concen- 

 tration of the soil solution likewise decreases water absorption by its effect on 

 the osmotic process. Such effects probably vary greatly with different plants. 



Submergence and Root Killing. — The effects of submergence on decidu- 

 ous fruit plants are due primarily to the diminished aeration of the roots 

 which this ordinarily involves. It has been found that certain land plants 

 with submerged roots absorb water more rapidly at first but that later 

 the rate of absorption falls off to a marked degree, the plants wilt and 

 after a few days the leaves become yellow and drop.^^ After prolonged 

 submergence the roots below the surface die and no new roots develop; 

 eventually the entire plant succumbs. All of these effects, however, 

 were alleviated or eliminated when the roots were submerged in aerated 



