Black walnut occurs on open, non-crop land in the Tennessee Valley region. Trees grow around the farmstead, along fence rows, and in pastures on most farms. In recent years harvesting of walnuts for market from these trees has increased significantly. Looking forward to a fuller utilization of the wild black walnut crop, knowledge on the bearing habits of these open-grown black walnut trees was required. To supply this information a study of tree growth, nut yield, and nut quality was undertaken in 1940. Results on nut yield available from this study after six years are summarized in this report.
[Footnote 12: Contribution from TVA Forestry Relations Department,
Forestry Investigations Division on a project conducted in the Forest
Products Section.]
This study was initiated with the selection of representative open-grown walnut trees throughout the Tennessee Valley. In 1940, 96 sample trees were selected and 36 trees were added to the study in 1942. These 132 trees are located in 42 counties and afford a good representation of age, size, and growth quality of open-grown black walnut. Each sample tree has been visited annually. Entire crops were collected, carefully weighed and sampled: tree diameters and other measurements were taken for the tree growth phase of the study. When convenient, nuts were hulled in the field with a corn sheller, but more often they were brought to Norris and run through a hulling machine. After hulling, the nuts were dried until cured, then a sample for each tree was tested for percentage of filled nuts, nut weight, and cracking quality.
Yield
Results on nut yield and nut quality for the 132 sample trees have been condensed to the presentation in Table 1. For the six-year period the average tree in this study had a diameter of 13.3 inches and yielded 33 pounds of hulled, dry nuts a year. The yield of common black walnut trees in the Tennessee Valley is characterized by extreme variation. Tree size, of course, influences nut yield. One-half of the yields from a 6-inch diameter tree ranged from no crop to 4 pounds of hulled, dry nuts; whereas half the yields from a 22-inch tree ranged from 40 to 100 pounds. A yield of less than one-half pound of hulled, dry walnuts was considered "no crop". Some individual trees had unusually high or low yields. The outstanding bearer was tree 117. It had the highest average yield for the six-year period, and the heaviest crop of hulled, dry nuts for any single year. During the six years this tree yielded 953 pounds of dry, hulled nuts and 194 pounds of kernels—truly outstanding production for a common black walnut tree. Another notable bearer, tree 100, yielded 916 pounds of nuts and 189 pounds of kernels. However, this tree was almost 11 inches larger in diameter than tree 117. The exceptional bearers in each diameter class also had the highest single nut crops. The other extreme is characterized by low yields. Crops were lacking or insignificant for trees 60, 63, 211, and 221. Tree 37, with a 19.7-inch diameter, bore only one crop of 31 pounds during the entire six-year period. This tree has no value for nut production but would yield a good sawlog.
Variation of yield by seasons and locality was examined by grouping the 132 sample trees into six localities of 22 trees each. Greater variation in averages by crop years existed than averages by tree location groups. However, some variation was found between the eastern and western portions of the Tennessee Valley.
Indications on bearing habits were obtained for a six-year period on 96 trees, Nos. 1 through 140 (Table 1). Crop records for each of these trees were examined for relatively high and low yield by seasons. Convincing evidence on the alternation of bearing has accumulated during this six-year period with 46 percent of the trees having lighter crops every other year. Of these, 28 trees bore lighter crops in the odd years and 16 trees bore lighter crops in the even years. Tree 117, previously mentioned as outstanding in regard to yield, produced lighter crops in 1940, 1942, and 1944. This tree is located in west Tennessee.
Walnut trees bearing lighter crops in 1941, 1943, and 1945 are more abundant in the eastern than in the western portion of the Tennessee Valley. This occurrence undoubtedly accounts for much of the variation found between the eastern and western portions.
Four other yield patterns were recognized in 30 per cent of the trees. These indicate the existence of uniform annual crops and three-year cyclic bearing of black walnut. The bearing habits of the remaining 24 per cent of the trees is considered merely irregular, since definite patterns cannot be recognized until bearing records cover a longer period of years.
Nut Quality