Retention by soils of the nitrogen of urea and some related phenomena
1940
Conrad, J.P. | Adams, C.N.
1. In preliminary studies in which urea solutions were percolated through columns of dry soil and then the columns subsequently sectioned, the response of milo was used to indicate the final distribution of the nitrogen applied in the urea. Untreated soils progressively removed at least some of the nitrogen of urea and of CaCN2 from solutions as they percolated through them. This property of the untreated soils was largely lost by percolating urea at 90 degrees C, but persisted at 2 degrees, 11 degrees, and 40 degrees C. 2. Though a small amount of adsorption and unusually great microbial activities might account for these data, an alternate explanation is a catalytic hydrolysis (independent of micro-organisms) of urea to ammonium carbonate during percolation with the subsequent strong retention of the latter. 3. To test the possibility of catalysis in the hydrolysis of urea, percolations were conducted with various soil treatments. No significant differences in the growth responses between the untreated soils and those percolated under toluene were disclosed. Significantly smaller amounts penetrated to the lowest pots of the columns with these two treatments than with soil preheated in a moistened condition to about 85 degrees C and subsequently dried before percolation. A slower rate of percolation significantly decreased the amount of nitrogen reaching the lowest pots with the untreated and toluened soils, but not with the preheated soil. 4. The growth results as well as the analyses of the small amount of percolates from the columns are in agreement with the hypothesis that adsorption and a thermolabile catalysis were perhaps largely responsible for the retention of the nitrogen of urea by the untreated soil.
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