Salt tolerance may affect the marketable por- 

 tion of the plant. In some instances, vegetative 

 growth is more affected than fruiting and vice 

 versa (8,75,95). 



A 50-percent yield decrement may be within 

 the profitable production range for field and forage 

 crops in certain cases; but a yield decrement as 

 little as 1 5 percent, or a normal yield accompanied 

 by a deterioration of quality, might be sufficient 

 to eliminate most of the profits from fruit and 

 vegetable enterprises having a narrow margin of 

 income over costs. 



Nutritional Effects 



Plants require a balanced nutrient content in 

 the soil solution to maintain optimum growth. Use 

 of saline water for irrigation may or may not 

 significantly upset this nutritional balance depend- 

 ing upon the composition, concentration, and vol- 

 ume of irrigation water applied. 



Some of the possible nutritional effects were 

 summarized by Bernstein (14) as follows: 



High concentrations of calcium ions in the soil solu- 

 tion may prevent the plant from absorbing enough 

 potassium, or high concentrations of other ions may af- 

 fect the uptake of sufficient calcium. 



Different crops vary widely in their requirements for 

 given nutrients and in their ability to absorb them. Nu- 

 tritional effects of salinity, therefore, appear only in 

 certain crops and only when a particular type of saline 

 condition exists. 



Some varieties of a particular crop may be immune to 

 nutritional disturbances while other varieties are severely 

 affected. High levels of soluble sulfate cause internal 

 browning (a calcium deficiency symptom) in some let- 

 tuce varieties, but not in others. Similarly, high levels of 

 calcium cause greater nutritional disturbances in some 

 carrot varieties than in others. Chemical analysis of the 

 plant is useful in diagnosing these effects. 



At a given level of salinity, growth and yield are de- 

 pressed more when nutrition is disturbed than when nu- 

 trition is normal. Nutritional effects, fortunately, are not 

 important is most crops under most saline conditions; 

 when they do occur, the use of better adapted varieties 

 may be advisable. 



Many variables are involved and each adverse 

 condition must be diagnosed and treated accord- 

 ingly. 



Piiytotoxic Substances and Specific Ion Effects 



In addition to the effect of total salinity on os- 

 motic soil-plant relations, individual ions may have 

 varying effects on plant growth. These ions include 

 both common and trace elements occurring natu- 

 rally in irrigation water, those introduced by man's 

 activities, and those which enter the soil solution 

 through a reaction between the soil and the irri- 



gation water. Considerable information is avail- 

 able regarding the effects of nutritional balance of 

 the major plant nutrients. Although complicated 

 by interactive effects of soil and plant character- 

 istics, these nutritional effects are not as serious as 

 phytotoxicity which may be caused by trace ele- 

 ments or specific ions. 



Trace elements are those which normally occur 

 in water or soil in very small quantities. Some 

 may be essential for plant growth in very small 

 amounts while others are nonessential. Some of 

 these elements do not occur naturally in most 

 waters or soils, but will be discussed here since 

 they may enter water supplies as a result of in- 

 dustrial pollution. 



When an element is added to the soil in toxic 

 amounts, it may combine with it to give either of 

 two results. First, it may decrease in concentra- 

 tions so that it is no longer toxic. Second, it may 

 increase the store of that element in the soil. If 

 the process of adding irrigation water containing 

 a toxic level of the element continues, a steady 

 state will be approached with time in which the 

 amount of the element leaving the soil in the 

 drainage water will equal the amount added with 

 the irrigation water, and no further change in 

 concentration in the soil will occur. 



In many cases, these elements are held very 

 strongly by soils and in some cases, they may 

 be toxic in relatively low concentrations. There- 

 fore, irrigation water containing toxic levels of 

 trace elements may be added for many years 

 before steady state is approached. A situation ex- 

 ists then where toxicities may develop in years, 

 decades, or even centuries from the continued ad- 

 dition of polluted irrigation waters. The time would 

 depend on factors apart from properties of the 

 water itself. Changes in technology and economy 

 could easily alter circumstances significantly in 

 such a long time. 



Genetic differences in tolerance of plants to 

 different elements or ions has been mentioned. 

 Variability among species is well recognized. Re- 

 cent investigations by Foy (58), working with 

 soluble aluminum in soils, has demonstrated that 

 there is also variability among varieties within 

 a given species. This suggests the possibility of 

 breeding varieties to minimize phytotoxicity which 

 may result from a constituent in irrigation water. 



Research dealing with effects of trace elements 

 on plant growth does not permit, in general, any 

 conclusions regarding threshold values beyond 

 which specific plants will react unfavorably. Most 

 studies have been carried out with several plant 

 species in sand or solution cultures under a wide 

 variety of environmental conditions. It is difficult 



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