Effect of understory management on phenological responses of eastern black walnut on an alluvial Arkansas soil

Authors: Burner, David; Brauer, David; Pote, Daniel; SNIDER, J - Former ARS Employee

Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2014
Publication Date: 1/15/2015
Citation: Burner, D.M., Brauer, D.K., Pote, D.H., Snider, J.L. 2015. Effect of understory management on phenological responses of eastern black walnut on an alluvial Arkansas soil. Agroforestry Systems. 89:135-147.

Interpretive Summary: Black walnut produces nuts and high-valued timber for income and wildlife benefits. Plant types (nut vs. timber) are suspected to have different management inputs throughout the life of the plantation; however these inputs are poorly defined. Landowners need information on how plant type responds to management of perennial understory grasses, and if this affects timing of periodic tree growth phenomena (phenology). ARS scientists at the Dale Bumpers Small Farms Research Center near Booneville, Arkansas measured phenology of various leaf and trunk characteristics of the two main plant types when understory grasses were treated with two levels of nitrogen fertilization and three levels of grass control on a bottomland soil. Fertilization increased grass yield which delayed tree budbreak, but tree phenology was generally insensitive to grass treatment. This might have been because the trees had been well established and maintained, the deep soil might have had adequate nitrogen, and the trees were too mature to respond quickly to grass management. Instead, tree phenology was affected more by plant type than grass management. The overriding importance of plant type suggested that land managers focus on the long-term goal, nuts or timber, from the inception of the black walnut plantation.

Technical Abstract: Black walnut (Juglans nigra L.) is commonly grown in agroforestry practices for nuts and/or timber with little knowledge of how understory herbage management might affect tree phenology. We compared black walnut plant type (variety and wild-type) for phenological response in date of budburst, leaf area index (LAI), quantum yield of photosystem II (Fv/Fm), radial stem growth, and total chlorophyll concentration in response to understory herbage N fertilization and herbage suppression in an agroforestry practice on an alluvial soil. Herbage treatments generally had little impact on phenological responses, although N fertilization increased herbage yield that delayed budburst. Radial stem growth commenced at about budburst (mid-April) and virtually ceased in late October, about 30 d before leaf drop. Early-season radial stem growth was greater for the wild-type than the variety, while the variety had more rapid late-season growth. The wild-type had consistently greater LAI than the variety at any given day-of-year (DOY), and usually had greater LAI than the variety regardless of herbage treatment. Leaves of both plant types maintained a high Fv/Fm during most of the growing season, but total chlorophyll concentration decreased across DOY regardless of plant type. N fertilizer should be applied with understory herbage suppression to avoid delay of budburst. Further study is needed of phenological responses during longer growth periods, or as affected by latitude, soil water, and soil fertility.