Certain fruit crops are, however, sensitive to 

 chlorides. Bernstein (16) has indicated (table IV- 

 17) that maximum permissible chloride contents 

 in the soil solution range from 10 to 50 me/1 for 



TABLE IV-17. Maximum Permissible Chloride 

 Contents in Soil Solution for Various 

 Fruit-Crop Varieties and Rootstocks (16) 



Limit of 

 tolerance to 

 chloride in soil 

 Crop Rootstock or variety solution me/I 



ROOTSTOCKS 



Citrus Rangpur lime, Cleopatra 50 



mandarin 



Rough lemon, tangelo, sour_ 30 

 orange 



Sweet orange, citrange 20 



Stone fruit Marianna 50 



Lovell, Shalil 20 



Yunnan 14 



Avocado West Indian 16 



Mexican 10 



VARIETIES 



Grape Thompson seedless, Perlette 50 



Cardinal, Black Rose 20 



Berries Boysenberry 20 



Olallie blackberry 20 



Indian summer raspberry 10 



Strawberry Lassen 16 



Shasta 10 



certain sensitive fruit crops. In terms of permissible 

 chloride concentrations in irrigation water, values 

 up to 20 me/1 may be used, depending upon en- 

 vironmental conditions, crops, and irrigation man- 

 agement practices. 



Foliar absorption of chlorides can be of impor- 

 tance in sprinkler irrigation (48, 50). The adverse 

 effects vary between day and night (varying 

 evaporative conditions) and the amount of evapo- 

 ration that can occur between successive wettings; 

 i.e., time after each pass with a slowly revolving 

 sprinkler. There is less effect with nighttime sprin- 

 kUng and less effect with fixed sprinklers (applying 

 water at a rapid rate) as contrasted with slowly 

 revolving sprinklers (required to apply water at a 

 low rate). Concentrations as low as 3 me/1 of 

 chloride- in the irrigation water have been found 

 harmful when used on citrus, stone fruits, and 

 almonds (16). 



High Bicarbonate water may induce iron chlo- 

 rosis by making the iron unavailable to plants 

 (26). Problems have been noted with apples and 



pears (134) and with some ornamentals (98). Al- 

 though concentrations of 10 to 20 me/1 of bicar- 

 bonate will cause chlorosis in some plants, it is of 

 little concern in the field where precipitation of 

 calcium carbonate minimizes this hazard. It is 

 difficult to set up specific criteria for such indirect 

 effects. 



Pesticides: Insecticides, fungicides, rodenti- 

 cides, and herbicides, as a group, include both 

 organic and inorganic compounds, all of which 

 can directly or indirectiy have a bearing upon the 

 irrigation water in which they are found. The 

 effects of some of these can be detrimental to 

 crops, livestock, wildlife, and man. Some are easily 

 broken down and disappear quickly while others 

 are persistent. Some are only sparingly soluble in 

 water, but all cause problems if accidental spillage 

 produces high concentrations in water or if they 

 become adsorbed on colloidal particles subse- 

 quently dispersed in water. 



Compounds derived from petroleum are used 

 direcdy for pest control or are involved in formu- 

 lation and synthesizing other pesticides. Many of 

 these substances produce no serious pollution haz- 

 ards because they break down rapidly. Synthetic 

 materials developed within the last 20 years pro- 

 duce most of the hazard potential. There are sev- 

 eral types such as halogenated hydrocarbons, 

 organophosphates, carbamates, phenoxys, thio- 

 cyanates, substituted ureas, and triazines. Many 

 of the halogenated hydrocarbons appear to be 

 quite persistent in the environment. Aldrin and 

 dieldrin, chlorinated hydrocarbon insecticides, 

 have been found to be absorbed by vegetable crops 

 from contaminated soil. DDT, a widely used in- 

 secticide for many years, has been found to be very 

 persistent and can be transported in runoff from 

 agricultural areas as well as being transported by 

 air currents (193). 



Herbicides are used widely in agriculture di- 

 rectly on the crop and on the soil, on cropped and 

 noncrop areas in the vicinity of agricultural areas, 

 and for aquatic weed control. Petroleum solvents 

 are effective aquatic weed killers which are rapidly 

 dissipated and degraded. These aromatic solvents 

 are widely used for keeping irrigation canals clear 

 of weeds and are not harmful to crops (29). 

 Copper sulfate is also widely used in irrigation for 

 algae and other aquatic weed control. The copper 

 concentration is maintained at a low level and has 

 little or no history of producing harmful effects on 

 crops. The fate of copper applied for weed control 

 in irrigation canals is being studied in cooperative 

 aquatic weed research programs by the U.S. 

 Bureau of Reclamation and Agricultural Research 

 Service. 



156 



