Recovery of 15N-Labeled Fertilizers in Field Experiments
1972
Westerman, R. L. | Kurtz, L. T. | Hauck, R. D.
Urea and oxamide, each labeled with ¹⁵N, were compared as fertilizers in two field experiments in adjacent locations in successive years with ‘Sudax SX11’ Sorghum-sudan hybrid (Sorghum sudanense) as the test crop. Four cuttings were harvested during the first experiment and three during the second. Patterns of uptake of fertilizer N were in accord with the characteristics of the two carriers. In the first harvests in both experiments the amounts of N taken up from urea were markedly greater than from oxamide; but by the third harvests, yield responses and N uptake from oxamide were greater than from urea. Total recoveries of fertilizer N from the two carriers during the entire growing season were similar as greater recoveries of urea-N in the early summer were compensated for by greater recoveries of oxamide-N in the late summer. Of the N added in urea in the first experiment, 51% was recovered in the crops and 28% was still in the soil (0–25cm) at the end of the growing season. Corresponding figures for oxamide were 52% in the crops and 31% in the soil. In the second experiment, when fertilizer applications and planting operations were delayed until more favorable growing weather, 93% and 99% of the urea- and oxamide-N, respectively, were estimated as recovered in the crops, and measurements of the amounts of fertilizer remaining in the soil were not attempted.
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