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Greenhouse Evaluation of Nitrogen Fertilizers for Rice¹

ABSTRACT

As part of a research program to improve the efficiency of N fertilizers for lowland rice (Oryza sativa, L. var. IR38) in developing countries, a number of modified urea products have been evaluated in a greenhouse experiment. Fertilizers were applied to rice grown in two soils subjected to continuous or intermittent flooding. The results demonstrate the advantages of split application, deep placement, and controlled release in increasing fertilizer efficiency. However, the major finding was that a combination of deep placement and controlled release results in a substantial increase in fertilizer N recovery by the plant. This combination, in the form of sulfur-coated supergranules of urea, gave a mean apparent recovery of fertilizer N by rice of approximately 84% compared with only 28% for urea applied in a single dose at transplanting.

By using ¹⁵N-labelling, losses of applied N were measured for selected treatments. Extensive losses (30% for Decatur soil, 50% for Crowley soil) were measured for urea applied at transplanting. Much less (6% and 14–24%, respectively) was lost of ammonium sulfate applied similarly. Point application of the urea as a supergranule at the 8-cm depth reduced losses to < 4%. The intermittent flooding did not promote losses. Losses of broadcast fertilizers were greater from the Crowley soil (pH 6.2) than from the Decatur soil (pH 5.0).

¹ Contribution from the Agro-Economic Division of the International Fertilizer Development Center (IFDC), Muscle Shoals, Alabama 35660.

² Soil Scientists.

Received for publication March 14, 1979. Accepted for publication June 27, 1979.