SLOW RELEASE N FERTILIZERS APPLIED IN FALL FOR CORN

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Abstract
Slow release N fertilizers were considered as efficient sources of N for fall application to corn (Zea mays L.). Accordingly, sulfur-coated urea (SCU) and crotonylidene di-urea (CDU) were compared with urea in several field experiments. Neither SCU nor CDU were shown to be advantageous over urea in terms of grain yield. Similarly, the N content of the leaf opposite and below the ear did not show a greater availability of N from SCU and CDU than from urea applied in the fall. Response to residual N from previous applications of urea, SCU, and CDU was obtained for 2 yr after application. There was a tendency for a greater response to residual SCU. The concentration of NO−3 in the 0- to 18- and 18- to 36-cm soil layers was usually less with slow release N fertilizers than urea at early May sampling times. By mid-June, the NO−3 concentration had increased substantially with both urea and the slow release N fertilizers. In 2 yr when urea was also applied in the spring, the NO−3 concentration with spring-applied urea was higher than with fall-applied urea. This reflects the greater loss of N during the winter months with fall-applied urea. After growth terminated in the fall, NO−3 apparently continued to be released from urea and slow release N fertilizers at similar rates. Thus slow release N fertilizers also have potential to contribute significantly to the NO−3 concentration in drainage and groundwaters. In general, there was no noteworthy difference between SCU and CDU in this study. Also, slow release N fertilizers did not show any agronomic advantage over urea when applied in the fall.