Proceedings of the 16th Central Hardwoods Forest Conference GTR-NRS-P-24 580 GROWTH AND FOLIAR NITROGEN CONCENTRATIONS OF INTERPLANTED NATIVE WOODY LEGUMES AND PECAN

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A study on nurse cropping nut trees with leguminous plants and trees. Results were not very telling.

Abstract.—
The interplanting and underplanting of nodulated nitrogen-fixing plants in tree
plantings can increase early growth and foliage nitrogen content of hardwoods, especially black walnut and pecan. Recent studies have demonstrated that some non-nodulated woody legumes may be capable of fixing significant levels of atmospheric nitrogen. The following nine nurse crop treatments were established with and without interplanted northern pecan: the nodulated legumes black locust, false indigo, and smooth false indigo; non-nodulated thornless honeylocust, Kentucky coffeetree, and redbud; non-leguminous buttonbush; 16N-8P-8K tree food spikes; and a control without shrubs or fertilizer. Average foliage nitrogen
content of the nurse trees ranged from 3.3 percent for black locust, false wild indigo, and smooth wild indigo, and 2.1 percent for honeylocust and Kentucky coffeetree, to 1.8 percent for redbud and buttonbush. In the fourth growing season, pecan foliage nitrogen was similar across all treatments (1.8 to 2.0 percent); however, black locust had increased pecan foliage nitrogen to 2.2 percent in the sixth growing season. Pecan growth is similar across all treatments except when interplanted with black locust that overtopped the pecan and is suppressing its growth. Interpretations include the possibilities that soil nitrogen was adequate to preclude any benefits from biologically fixed nitrogen, that nurse plants did not release sufficient fixed nitrogen to increase pecan growth, and foliage nitrogen in non-suppressed saplings, or that other soil factors are limiting pecan development.

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