A better understanding of the efficacy of various nitrogen (N) forms on pecan tree production would help growers make more sound decisions regarding the fertilization of their orchards. The following treatments were evaluated for their effect on pecan leaf tissue nutrient concentration, leaf chlorophyll index, trunk circumference growth, pecan yield, nut weight, percent kernel, pecan tree yield efficiency, and alternate bearing: 1) ammonium nitrate (AN; 34N–0P–0K) at 1.8 kg N per tree (AN1.8); 2) AN (34N–0P–0K) at 3.6 kg N per tree (AN3.6); 3) ammonium sulfate (AS) at 1.8 kg N per tree (AS1.8); 4) AS at 3.6 kg N per tree (AS3.6); 5) urea at 1.8 kg N per tree (U1.8); 6) urea at 3.6 kg per tree (U3.6); and 7) untreated control (C). Leaf elemental tissue analysis, pecan tree trunk growth, pecan yield, quality, and alternate bearing intensity (I) suggest that pecan trees are unaffected by differences in the fertilizer sources used in this study on the acidic soils of the Southeastern U.S. Coastal Plain. N rate also had little influence on measured variables. Based on these results and, perhaps more directly, upon agronomic N use efficiency (AEN), it appears that pecans can be more efficiently fertilized at N rates of 108 kg N/ha compared with 215 kg N/ha under Southeastern U.S. Coastal Plain conditions regardless of N source.
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