Characterization of black walnut (Juglans nigra) cultivars for agroforestry systems
Authors:   , Bishop Benjamin 
Published: September 2022

The identification of complementary species combinations will accelerate the expansion of temperate agroforestry. Since the mid-19th century, European timber plantations have taken advantage of the late-leafing habit of walnut (Juglans spp.) to grow a spring grain crop between the tree rows. A parallel but underutilized opportunity in North American involves incorporating eastern black walnut (Juglans nigra L.) cultivars into alley cropping systems. Eastern black walnut is native to North America and exhibits architectural and phenological characters for reduced competition with winter alley crops. Black walnut also produces nutritious nuts, and cultivars with improved kernel percentage and mass offer potential to cultivate the species as a domesticated orchard crop, as opposed to just the high-quality timber for which it is well-known. However, field observations suggest significant variation in tree architecture and phenology amongst cultivars, which is likely to influence complementarity with winter grains. Comprehensive characterization of trait genetic diversity is needed to best leverage germplasm into productive systems. FirstHere, we review literatureliterature is reviewed related to implementing alley cropping systems (ACS) with consideration of cultivar-dependent traits that may reduce interspecific competition. In additionIn addition, an experiment was performed characterizing black walnut cultivars for their aboveground compatibility for light inwith alley cropping systems. A population of 11 cultivars with replicates in New Franklin, MO was measured for understory light infiltration from April-June of 2021. Results showed over a two-fold difference in light infiltration between the most contrasting cultivars during the second week of May. Tree architecture and phenological event timing were also measured to determine potential causative factors of differences observed. The impact of this research may help growers interested in walnut alley cropping with cultivar selection and management practices for effective agroforestry systems. While the compatibility between tree and crops is an important factor in agroforestry design, cultivars must also be commercially productive for robust adoption by growers. An additional study was performed on the performance of 7 selections from the UMCA Black Walnut Breeding Program. A replicated population of these selections were observed in 2017 and 2021 for key traits for improving the commercial production quality of black walnut such as yield, kernel percentage and kernel mass. Results showed selections were able to significantly outperform the parental generation in these traits by as much as 135 percent. Additional years of harvest data as well as replication sites for this trial will help refine the understanding of the commercial performance of selections and allow for broader recommendations to growers at large. While the focus in this thesis is directed toward black walnut, broad characterization of other underutilized fruit/nut species will allow for robust diversification of ACS.