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Availability Characteristics Of and Plant Response to Nitrogen Sources

The relative availability characteristics of nitrogen in urea, cottonseed meal, a commercial urea-formaldehyde product, and an experimental urea-wax material were studied through successive leachings in model lysimeters in the laboratory and by leaching and plant growth in the greenhouse. The effects of the nitrogen sources on yield and chemical composition of field-grown tobacco were studied under different moisture regimes.

The total release of nitrogen from the urea-wax source was comparable to that from urea but significantly higher than from urea-formaldehyde or cottonseed meal sources. The rate of N release during the first 21 days was not different among the urea-wax, urea-formaldehyde, and cottonseed meal sources; thereafter, it was higher from urea-wax. When differences in crop response occurred among the different sources, the yield and quality index were higher from urea-wax than from cottonseed meal or urea-formaldehyde. These results and data from other research suggest that the probability of practical contributions of slow release fertilizers in the commercial production of annum field crops is quite small.

Key Words: Controlled release fertilizers • Nitrogen sources • Nitrogen availability • Plant response to nitrogen • Leaching effect

² Professor of Soil Science, North Carolina State University at Raleigh.

Received for publication August 8, 1968.