|Brauer, David - Dave|
Submitted to: Journal of American Pomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2009
Publication Date: 4/30/2009
Citation: Brauer, D.K., Ares, A., Thomas, A. 2009. At similar trunk diameters varieties of eastern black walnut have greater nut yields than native trees. Journal of American Pomological Society. 63:42-50. Interpretive Summary: Many landowners in the United States have limited access to knowledge of the potential economics returns from eastern black walnut agroforestry practices and this lack of knowledge may be limit the establishment of walnut plantings. There are indications that varieties of eastern black walnut selected for improved nut quality may produce more nuts; however data are lacking to fully support this hypothesis. ARS scientists from Booneville AR and a cooperating scientist from the University of Missouri-Southwest Research Center compared nut yields from stands of trees consisting of native and named varieties across a range of tree sizes. Results from this study clearly demonstrated that grafted trees of named varieties produced more nuts than native trees of the same size. Landowners planting eastern black walnuts for nut production will interested in these results because they identify a management option that promotes higher nut yields. Nursery producers who produce grafted seedling trees will be interested in these results also because they demonstrate a beneficial characteristic of grafted seedlings trees warranting their higher retail prices.
Technical Abstract: Many landowners in the United States have little access to information on economic returns from agroforestry practices. Despite the existence of agroforestry economic simulators, data bases are lacking to predict returns from nuts produced by eastern black walnut (EBW), Julgans nigra L., a hardwood species with potential for agroforestry in the central United States. The objective of this study was to determine the effects of tree stock type (native versus named genotypes selected for higher nut quality) on the relationship between tree diameter at 1.3 m above ground (DBH) and nut yields in EBW. Nut yields and DBH measurements were collected from five stands of native stock trees and seven stands of grafted named genotypes of EBW in the central United States for two consecutive years (2002-2003). Ten of the 12 stands were selected as paired sets in which stands of the two tree stock types had similar DBH and were located within a 25 km distance. Trees from grafted named genotypes had significantly greater 2-year means for nut yields in four of five paired stands. In the fifth set of paired stands, the DBH of the native-tree stand averaged twice that for the named genotype stand. Relationships between 2-year mean DBH and nut yields were highly significant for both tree stock types. However, the slope for the regression equation for predicting nut yields from DBH for named genotype trees was twice as great as that for native trees. DBH and nut yield relationships were utilized to predict nut production 25 years after planting at 4 site indexes from 6.1 to 15.2 m for an EBW alley cropping practice in which bermudagrass hay was the companion crop. These analyses indicated that: 1) predicted income from hay sales added significantly to the economic returns of the alley cropping practice; and 2) predicted income was greater when grafted named genotypes were planted because of greater nut yields and higher nut prices.