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In many arid sections of Western America there have been reported marked accumulations of nitrates in the cultivated soil. Hilgard,(1) who was the first to observe these accumulations, believed that the nitrates are being formed at the present time by the rapid nitrification of the organic matter contained in the soil. In Colorado there has been considerable trouble with orchards dying; the death of the trees in some cases has been attributed to the excessive accumulations of nitrates in the cultivated soil. These accumulations are due, according to Dr. Headden,(2) to the fixation of atmospheric nitrogen by bacteria now at work; the organic nitrogen thus formed by the nonsymbiotic bacteria being at the same time converted into nitrates.

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