WASTES IX RELATION TO AGRICULTURE AND FORESTRY 



97 



gation and livestock. Agricultural and forestry 

 leaders planning and developing upstream water- 

 sheds for optimal social benefits need far better in- 

 formation on possible measures for coping with 

 these seriously harmful mineral additions to 

 streams. 



A number of metallic salts and related materials 

 have been added to soils over the years as (a) in- 

 secticides or fungicides, (b) micronutrient supple- 

 ments, or (c) inadvertently as impurities in 

 fertilizer. Lead arsenate was the main insecticide 

 used to control codling moth in fruit trees for 

 many years. This metal salt accumulated to rela- 

 tively high levels in soils of apple orchards of the 

 Northwest. On orchard removal, succeeding crops 

 have been injured. Calcium arsenate used to con- 

 trol cotton insects accumulated to toxic levels in 

 some cotton soils. Copper compounds, for example, 

 bordeaux mixture, have long been prime fungi- 

 cides. Copper may be found in some vineyard soils 

 at relatively high levels. Copper or zinc salts need 

 to be added as supplemental minor elements in 

 some soils. Evidence from a few areas suggests 

 that the practice may be overdone. Some ores used 

 for fertilizer production may carry undue quan- 

 tities of boron, arsenic, zinc, or fluorine. These im- 

 purities are usually not harmful. 



Serious losses from soil contamination by min- 

 eral salts have not occurred. Enough warning 

 lights are on the horizon, however, to signal the 

 need for more adequate information on the action 

 of these contaminants in soils and the availability 

 of counteractive measures. 



The heavy salting of highways to facilitate 

 t raffic movement following snowstorms has cause* I 

 serious damage to right-of-way vegetation and lias 

 increased silt damage to streams when erosion fol- 

 lowed killing of the vegetation. This type of dam- 

 age has been felt by adjacent property owners — 

 both rural and urban. It has been particularly 

 serious in part of New England. In humid areas, 

 rainfall eventually remedies the damage. 



Research is needed to assess the problem and 

 adjust findings of saline soil and water research for 

 irrigated lands to solution of the highway salinity 

 problems. 



Mineral salts have long been serious contami- 

 nants in the soils and associated waters of irrigated 

 areas in arid regions. With competition for water 

 increasing in the water-short sections of this coun- 



try, one can expect that the needs of irrigation 

 agriculture will not rank high. If waters of vary- 

 ing quality are available, agriculture will un- 

 doubtedly have to get along with that which is less 

 than the best. All indications the world over point 

 to greater need for information on the evaluation 

 and management of salt-affected soils and waters. 



Water available for irrigation use varies widely 

 in quality. Previous use or treatment (softening) 

 of the water can affect its quality for irrigation. 

 More elastic criteria are needed to characterize 

 water quality for this use as modified by climate, 

 soil characteristics, management practices, drain- 

 age, quantity of water available, and kind of crops 

 grown. 



Advances in atomic power plants for general ion 

 of electricity and in processes for desalting sea 

 water have prompted feasibility studies of plants 

 to produce both low-cost power and water. Cost 

 estimates for the water imply a level currently ac- 

 ceptable to irrigation users. Advancing technology 

 should in time provide water well within the eco- 

 nomic reach of many irrigation users. As this 

 water is essentially free from any dissolved chem- 

 icals, its use on saline and sodic soil may present 

 problems of water intake and leaching of salts al- 

 ready in the soil. Research must be conducted on 

 the use of such water for irrigation in area- now 

 successfully irrigated with water containing rela- 

 tively high amounts of salts, such as the Imperial 

 Valley where each acre-foot of Colorado River 

 water imports 1.2 tons of dissolved salts. The 

 use of the pure water may be as a dilul ur- 



rent supplies or particularly for the high-salt- 

 content flows leaving irrigated fields as tile drain 

 effluents. 



Salts in. or previously in, soils affect their pi 

 cal and chemical characteristics. The interrelation- 

 ships are complex. An increasing body of knowl- 

 edge is needed on the chemistry, mineralogy, and 

 microbiology of the hundreds of different k : 

 of -oils affected by salinity. Retter means of assay- 

 ing these salty-soil problems are needed as 

 to their irrigation by waters varying widely in 

 chemical characteristics. 



Salts move in soil- only with water a< the ve- 

 hicle. Information on the physical state of wn 

 in these soils is fundamental to understanding 

 principles of salinizat ion and desal W 



recent breakthroughs on techniques (o- 



