WASTES EST RELATION TO AGRICULTURE AXD FORESTRY 



61 



pounds per acre of P 2 5 at the beginning of the 

 study, lost an average of 1.42 pounds of P 2 5 per 

 acre for the 5-year period. This study on a soil 

 which was amenable to maximum leaching pro- 

 vides little evidence that phosphorus enters into 

 drainage water as a result of field application of 

 phosphate fertilizer. 



The excellent experiments on soil loss from ero- 

 sion carried on by the Missouri agricultural ex- 

 periment station (84) were very significant in re- 

 vealing the large losses in phosphorus that would 

 take place from fields by soil erosion. An experi- 

 ment was carried out on a Shelby loam soil with 

 plots 90 feet long, having a 3.86-percent slope. 

 Where corn was grown continuously, the loss of 

 phosphorus by erosion was 18 pounds a year. That 

 is, more phosphorus was lost by erosion in 1 year 

 than would be absorbed by corn plants producing a 

 75-bushel crop. Even where a good rotation was 

 practiced, the loss of phosphorus by erosion was 

 found to be 6.2 pounds per acre. However, under 

 continuous bluegrass, only 0.1 pound of phos- 

 phorus per acre was lest by erosion simply because 

 grass cover provides such excellent protection 

 against soil losses. This early research presented 

 clear evidence that if phosphate is getting into 

 streams from farmers' fields, it is getting there by 

 soil erosion. However, such phosphorus riding on 

 soil particles is highly insoluble in the water of 

 the stream. 



Other studies have shown similar results. Studies 

 (98) at the Alabama agricultural experiment sta- 

 tion indicated that 82 percent of the phosphate 

 applied to a fine sandy loam soil in Alabama over 

 a period of 26 years was lost by erosion, amount- 

 ing to a total loss of 1,430 pounds per acre. Ee- 

 search at the Virginia agricultural experiment sta- 

 tion measured nutrient losses by erosion from a silt 

 loam soil on different slopes (94). During a 5-year 

 rotation of corn, wheat, and clover, 610 pounds of 

 phosphorus per acre were lost from a 5-percent 

 slope. The loss of phosphorus was twice as great 

 on a 15-percent slope. Direct measurement of the 

 amount of soil eroded showed that most of this 

 loss took place during the growth of the corn. 



The U.S. Department of Agriculture has long- 

 term studies underway to measure the soluble 

 unadsorbed phosphate in water from the runoff of 

 variously treated watersheds in the Appalachian 

 foothills. This study will provide some information 



that is urgently needed on the sources of phos- 

 phorus in the streams of a watershed. 



Nitrate 



Eesearch in the U.S. Department of Agricul- 

 ture has not ignored the movement of nitrate from 

 fields into surface and ground waters. Nitrate salts 

 are extremely soluble, and are readily transferred 

 by water movement. However, this simple rational- 

 ization by no means implies that the nitrogenous 

 fertilizers applied to farmers' fields are the source 

 of nitrate found in surface and ground waters. 



Nitrate salts have accumulated to high levels 

 under natural conditions. The high level of ni- 

 trate salts in the vast accumulation of "caliche"' 

 that took place in geologic times on what is now 

 the Plateau of Tarabaca in northern Chile stands 

 as stark testimony to the enormous level to which 

 natural nitrate accumulation can occur. 



Hilgard (55) discovered during his studies on 

 salinity at the University of California during the 

 latter part of the 19th century that there were a 

 number of locations in California and Nevada 

 where nitrate accumulated in the caliche. He re- 

 ported that a sample of caliche from the Colorado 

 Desert of southern California contained 80 per- 

 cent sodium nitrate, and that a caliche deposit near 

 White Plains. Nev., contained 50 percent sodium 

 nitrate. 



Headden (53) studied the naturally occurring 

 "nitre" spots of eastern Colorado during the early 

 years of this century. He even found nitrate in 

 ground water 80 feet below the surface. In 1910. 

 when he first reported this observation, virtually no 

 chemical nitrogen fertilizer was used in Colorado. 

 Headden concluded that nitrate was being formed 

 currently by the biological oxidation of nitrogen 

 fixed in those spots by nonsymbiotic micro- 

 nanisms. Seliakov (101) came to a comparable 

 conclusion to explain nitrate accumulation in the 

 saline soils of Russia. 



Nitrate formed in soils by natural pv- 

 humid climates would be leached out by rain, 

 whereas they would accumulate near the surface 

 under arid climates. It is important to recognize 

 these early studies showing that nitrate may be 

 formed naturally and may move in the direction 

 of soil moisture movement, including percolation 

 to ground water. 



The previously mentioned cooperative res 

 (9) between the U.S. Department of Agriculture 



