The phenoxy acid herbicides 2,4-D and 2,4, 5-T 

 have become suspect as contaminants of irrigation 

 water. Some research has been initiated by various 

 groups. These materials are known to be subject to 

 rapid biological degradation in soils, but their fate 

 in irrigation water and runoff water is still not well 

 understood. Recent findings indicate that water 

 temperature and dissolved oxygen content may 

 influence the rate of biological decomposition of 

 these herbicides in impounded water (40). 



Millions of acres of farm, range, and forest lands 

 are treated annually with millions of pounds of 

 pesticides. It has been predicted that present use 

 of pesticides will increase tenfold in the next 20 

 years. There is too litde known about the ultimate 

 fate of the many compounds and their influence on 

 irrigated agriculture as well as the total environ- 

 ment. This stresses the need for further work to 

 determine the potendal effect of the many pesti- 

 cides in irrigation water. Some work is currently 

 underway by industry, universities, and Federal 

 agencies to study the fate of these pesticides in 

 irrigated agriculture; but as yet the state of science 

 is very incomplete. 



There is little evidence to indicate that under 

 normal use insecticide contamination of irrigation 

 water would be detrimental to plant growth or 

 accumulate in or on plants in toxic concentrations. 

 Herbicides, on the other hand, could be harmful 

 to crop growth if misused. Since many herbicides 

 break down in water, permissible limits should be 

 established for the point of application to crops. 

 Suggested permissible levels are shown in table 

 IV-18 along with information on treatment rates 

 of application and estimated concentrations in 

 water reaching the field or crop. These levels are 

 tentative and subject to change as indicated by 

 future research. 



Temperature: Excessively high or low tempera- 

 tures in irrigation water can deter plant growth. It 

 is not the temperature of the water per se that 

 affects plant growth, but the resultant temperature 

 of soil to which it is applied. Numerous investiga- 

 tions have been carried out relating the tempera- 

 ture of the substrate to plant growth; but few, 

 regarding the direct effects of irrigation water tem- 

 perature. Adverse soil temperature conditions can 

 affect seedling emergence, growth rate, time of 

 maturity, and yields of various crops. Here again, 

 the effect on the plant is governed by specific soil 

 characteristics and the genetic characteristics of 

 specific plants. Furthermore, the temperature of 

 the root zone and effects are governed by tempera- 

 ture changes occurring between irrigations. 



In greenhouse studies with the Calora variety 



of rice, Raney (138) allowed the soil solution 

 temperature to drop from 70 to 50 F for a period 

 of 4 days. He found that if this were done in the 

 stage between emergence and tillering, or 30 to 

 60 days after planting, the yield was depressed by 

 approximately 10 percent. He also found a com- 

 parable critical period during the flowering period, 

 about 100 days after planting. 



Other water temperature effects were noted by 

 Wieringa (194) on kidney beans. In greenhouse 

 experiments, he found that yields would increase 

 with soil temperature increasing from 70 to 86 F. 

 With temperatures of 50 F, no germination oc- 

 curred. By decreasing the temperature from 77 to 

 50 F for a period of 3 days, a 17-percent decrease 

 in root and foliar growth occurred if the tempera- 

 ture decrease was made at the three-leaf stage. The 

 same process produced a 40-percent decrease in 

 root and foliar growth at the six-leaf stage and the 

 yield itself decreased 1 5 percent when the process 

 was carried out at the nine-leaf stage. 



In regard to tomatoes, Martin and Wilcox 

 (102) in greenhouse studies found minimum tem- 

 peratures for satisfactory growth at 56 to 58 F. 

 Increasing temperatures produced increased yields. 



Holekamp and others (69) studied the effects 

 of water temperatures upon cotton in the green- 

 house. For emergence, best results were obtained 

 in the 60 to 70 F range. With temperatures less 

 than 60 F average minimum soil temperature, only 

 40 percent of the plantings produced seedlings. 

 They concluded that there was a 1.7-percent de- 

 crease in percentage of emergence for each degree 

 less than the 60 F average minimum. 



The adverse effects of cold water on the 

 growth of rice were suddenly brought to the atten- 

 tion of rice growers when cold water was first re- 

 leased from Shasta Reservoir in California (138). 

 Summer water temperatures were suddenly 

 dropped from about 61 F down to 45 F. Research 

 is still proceeding and some of the available in- 

 formation was recently reviewed by Raney and 

 Mihara (140). Dams such as the Oroville Dam 

 are now being planned so that water can be with- 

 drawn from any reservoir depth to avoid the cold- 

 water problem. Warming basins have been used 

 (139). There are opportunities in future planning 

 to separate waters — the warm waters for recrea- 

 tion and agriculture; the cold waters for cold- 

 water fish, salmon spawning, etc. 



Review of research accomplishments does not 

 offer guidelines for establishing temperature cri- 

 teria for irrigation waters. Aside from the other 

 complicating variables previously mentioned, the 

 manner in which irrigation water is applied, sur- 

 face or sprinkler, could influence changes in the 

 resultant soil temperature. Assuming that the soil 



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