WASTES IN RELATION TO AGRICULTURE AND FORESTRY 



63 



offers an unusual opportunity to study complete 

 soil profiles through which nitrate transfer can be 

 traced from soils to underlying water tables. The 

 highly permeable subsoils of this basin facilitate 

 nitrate transmissions from uncultivated soils 

 downward to the ground water table within two or 

 three seasons under natural rainfall. Nitrification 

 occurs very rapidly in soils that have received 

 sewage effluent devoid of nitrate. Concentrations 

 of 90 to 130 p.p.m. of nitrate have been found in 

 water percolating to the underground reservoir 

 from well-aerated permeable soils. This important 

 research is being continued. 



The U.S. Department of Agriculture has in- 

 itiated cooperative research with the Colorado 

 agricultural experiment station toward gaining 

 information on the deep percolation of nitrate 

 under various land uses in the valley of the South 

 Platte Kiver. Analyses have been made on 129 

 cores varying in depth from 10 to 65 feet, as lim- 

 ited by bedrock or water table depth. Quantity of 

 nitrate in transit to the water table is emphasized, 

 but other water contaminants are also measured. 

 Cores from beneath native rangeland and irri- 

 gated alfalfa contain insignificant amounts of 

 nitrate. Those from cultivated dryland fields con- 

 tain significant amounts of nitrate below the 

 root zone even though rainfall in the area averages 

 only 15 inches a year. Slightly larger amounts of 

 nitrare are found under irrigated fields of corn 

 and sugar beets. Preliminary evidence indicates 

 that about 20 to 30 pounds of nitrogen as nitrate 

 per acre are lost to the water table during the 

 average year. 



Highly variable amounts of nitrate are being 

 found under cattle corrals. The amount appears to 

 depend on the corral management, corral age, and 

 the water content of the profile, which affects 

 denitrification. As much as 5,000 pounds of nitrate 

 nitrogen per acre has been found in a 20-foot 

 profile. Nitrite is detected in the cores from some 

 corrals. Nitrate was not found in cores where 

 reducing conditions predominate, indicating that 

 nitrate is destroyed in profiles under corrals lack- 

 ing oxygen because of high microbial activity. 

 Corrals with good manure management from the 

 esthetic, "public nuisance,' ; and animal health 

 standpoint appear to be the worst in relation to 

 subsurface contamination with nitrate (108). 



Samples from water tables beneath corrals 



frequently contained nitrite, ammonia, organic 

 carbon, and phosphorous. Samples were redolent 

 with a very offensive odor. 



Inorganic Salts and Minerals 



Problems in agriculture related to the accum- 

 ulation of salts in soils, surface waters, and ground 

 water are as old as the arts of irrigation that 

 apparently began some 7,000 years ago in the 

 valleys of the Tigris and Euphrates (18. 60) . 



When earth materials weather, small amounts 

 of soluble salts are released. Under humid climates, 

 such solubles are leached away ; under arid or semi- 

 arid climates these solubles tend to accumulate 

 at the surface as a result of evaporation. Water 

 transports solubles from one part of the landscape 

 to another. For example, a desert storm abets such 

 salt accumulation in a play a basin. Irrigation 

 water brings solubles from miles away and abets 

 their accumulation in the irrigated fields unless 

 they are leached away through a proper drainage 

 system. 



Following the transfer of E. W. Hilgard from 

 the University of Michigan to the University of 

 California in 1875, a real beginning occurred in 

 the United States on research on salinity problems. 

 Hilgard's work in California (1875-1906) on the 

 kinds of salts that prevail in salted soils and 

 waters, their distribution in the soil profile, and 

 the relative tolerance of different vegetative spe- 

 cies to salts still stands as a monumental contribu- 

 tion. 



By the turn of the century, or soon thereafter, 

 most of the agricultural experiment stations in 

 the Western States had initiated research pertain- 

 ing to the salinity or "alkali" problem associated 

 with irrigation agriculture. The U.S. Department 

 of Agriculture si ailed investigations in this area 

 with the establishment of the Office of Western 

 Irrigation Agriculture in 1! 



W. P. Kelley of the University of Calif, 

 was one of numerous leaders in salinity research 

 during early decades of this century. Based on his 

 research. Kelley set forth in 1934 five primary 

 points that must be considered in the management 

 of salt-affected soils: 



1. The adequacy of the drau ige ldi- 

 tions. 



