WASTES IX RELATION TO AGRICULTURE AXD FORESTRY 



9 



15 million tons of salt. Three thousand freight 

 trains, 100 cars long, would be needed to carry 

 this much salt. Much of it comes from geological 

 deposits or accumulations in arid lands. It means 

 that a farmer in the Imperial Valley of California 

 who applies 5 acre-feet of irrigation water to his 

 crops, also applies 6 tons of salt per acre. Hence, 

 he must remove at least 6 tons of salt per acre in 

 the drainage water from his farm. 



Salinity is a hazard on about half the irrigated 

 acreage in the "Western States. Crop production 

 on one-quarter of this acreage is already impaired 

 by salt-affected soils. Production is threatened hi 

 irrigated projects the world over. 



Over the past couple of decades, research has 

 enhanced the capability of coping with salt prob- 

 lems affecting agriculture. 



Improved procedures for evaluating water 

 quality for irrigation have been developed, using 

 electrical conductivity as the primary criterion 

 and sodium-absorption-ratio as the secondary 

 criterion. 



Far better standards have been developed for 

 leaching procedures in the reclamation of soils and 

 for leaching requirements during continued man- 

 agement. 



Much advancement has been attained in under- 

 standing the physico-chemical behavior of salt- 

 affected soils. 



Since water is the vehicle by which salt moves 

 in soil, an understanding of the physical princi- 

 ples of water movement is absolutely essential. 

 Excellent progress has been made in measuring 

 the energetics of water retention and movement in 

 soils. 



Good progress has been made in characterizing 

 the salt tolerance of important crop plants. 



There is a real need to develop better means of 

 assaying salty-soil problems as related to char- 

 acteristics of irrigation waters. The relationships 

 are von- complex, and oversimplification can lead 

 to poor technical guidance. 



Recent advancements in making key measure- 

 ments on the physical forces involved in soil water 

 must be exploited towards far better appraisal of 

 field conditions related to water. 



There is an increasing need to attain an under- 

 standing of the biochemical and physiological 

 mechanism in plants that determine their toler 

 ance to various salt-affected soils. The role of cli- 



matic conditions in modifying these mechanisms 

 also needs clarification. There is an urgent need 

 to develop crop varieties higher in salt tolerance. 

 An understanding of basic mechanisms in each 

 important species would obviate the present 

 superficial approach of cut-and-try testing. 



The management practices followed in an irri- 

 gated field that is subject to salinization need far 

 better quantitative characterization. 



Hard experience in the Western States has 

 shown that successful irrigation requires effective 

 drainage. Accumulating salts must be continually 

 leached out. Excessive leaching wastes water and 

 nutrients. There is an urgent need to develop and 

 test better mathematical expressions for the cal- 

 culation of leaching requirements, drainage re- 

 quirements, and the proper salt balance that ought 

 to be maintained. 



One of the pressing needs for information in 

 irrigation agriculture is the development and 

 evaluation of alternative procedures for the dis- 

 posal or reclamation of return flow — procedures 

 that seek to maximize beneficial use of total water 

 available, while minimizing contamination for 

 downstream users. 



The heavy salting of highways in Northern 

 States to facilitate traffic movement following 

 snowstorms has caused serious damage to right-of- 

 way vegetation and has increased silt damage to 

 streams when erosion followed killing of the vege- 

 tation. The consequences of highway salting need 

 far better evaluation. 



The Federal Council of Science and Technology 

 has recommended that agricultural research in- 

 volved in this general area should increase four- 

 fold during the current 5-year period. 



Organic Wastes 



This category includes material such as sewage, 

 animal wastes, crop residues, forest trash, and food 

 and fiber processing wastes. When these substances 

 arc carried in water, they incur a high biochemical 

 oxygen demand. When dry upon the land, some 

 arc combustilc. some produce odors, and some at- 

 tract flics and vermin. 



Sewage 



About I acre- feet of water flows from 



municipal sewage facilities on the average day. 

 Some of this could be used for irrigation even 



