Black walnuts

With the exception of peanuts, most of the important nuts from around the world are home on trees, many of them from native seedlings. Among the latter group are the beechnut, Bra2il nut, butternut, chestnut, filbert, hickory nut, pecan, pine nut, and black walnut. The pecan, Knglish walnut, filbert, and almond are the four principal edible tree nuts produced in the United States, where the term Knglish walnut is used synonymously with the Persian or Carpathian walnut (2). 

Table 8. Seasonal Change in Composition of Black Walnut Kernels ...

Various methods of home-dyeing cotton and wool materials using natural dyes made from hulls of butternut, hickory nut, pecan, eastern black walnut, and Knglish walnut have been described (149). As far back as during the Civil War, butternut hulls have been used to furnish the yellow dye for uniforms of the Confederate troops. More recent attempts have been made to manufacture yellow and brown dyes from filbert shells on a commercial scale. The hulls are treated with copper sulfate and concentrated nitric acid to produce a yellow color, with ferrous sulfate to produce oHve-green, or with ammonia to produce mby-red (150) (see Dyes AND DYE INTERMEDIATES Dyes, natural). 

Although nuts have been a staple food in many countries for generations, their status in the United States as a chief food crop is relatively recent. The main suppher of Knglish walnuts, filberts, and almonds had been Europe. However, pecans and black walnuts are indigenous to North America, and the United States is the principal producer of pecans. Other U.S. nuts, such as beech, butternut, white walnut, American chestnut, chinquapins, hickory, picon, and northern California black walnut, are utilized mainly for local consumption. Chestnuts and chinquapins are susceptible to the chestnut blight fungus, Endothiaparasitica which has virtually destroyed the American chestnut (152). 

Eor practical purposes, the sapwood of all species may be considered to be susceptible to biodeterioration. The heartwood of some species, however, contains toxic extractives that protect it against biological attack. Among the native species that have decay-resistant or highly decay-resistant heartwood are bald cypress, redwood, cedars, white oak, black locust, and black walnut (60). Douglas-fir, several of the pines, the larches, and honey locust... 

Juglone [481-39-0] (Cl Natural Brown 7 Cl 75500) was isolated from the husks of walnuts in 1856 (50). Juglone belongs to the Juglandaceae family of which there are a number of species Jug/ans cinerea (butter nuts), J. regia (Persian walnuts), and J. nigra (black walnuts). Persian walnuts were known to the ancient Romans who brought them over from Asia Minor to Europe. As early as 1664, the American colonists knew how to extract the brown dye from the nuts of the black walnut and butternut trees, both native to eastern North America (51). 

Oak-hickory 23 -10 70%, diluted by hickory, maple black walnut... 

The toxic influence exerted by Juglans nigra (black walnut) on other plants has been attributed to 5-hydroxy-1,4-naphthoquinone (juglone) (11,31). Hydrojuglone is present in the root bark, leaves, and fruit husks. This compound is not considered toxic, but it is oxidized to the toxic juglone upon exposure to air (51). Rainfall... 

It is known that black walnut trees produce a substance that inhibits growth and causes wilting of many plants. Avoid planting vegetables, especially tomatoes, near black walnut trees. 

Allelopathic Interference of Black Walnut Trees with Nitrogen-Fixing Plants in Mixed Plantings... 

Early evidence of black walnut allelopathy. As early as 77 A.D., the Juglans genus was cited as having a poisonous effect on other plants. An even earlier account was recorded by Pliny the Elder in... 

European alder has been observed to decline at age 8 years in plantings when mixed with black walnut. It has been surmised that black walnut allelopathy was the most likely cause for the black alder decline (25). 

To gain more understanding of the European alder decline and because of our concern about the future growth of black walnut planted with nitrogen-fixing species, a study was initiated to measure soil juglone concentration and to estimate the number of Nitrobacter and Nltrosomonas bacteria in a black walnut plantation containing plots of black walnut alone and in mixture with European alder and autumn-olive. 

The mean juglone concentration in soil beneath plots of autumn-olive/ black walnut was significantly lower than in soil beneath European alder/black walnut and black walnut-alone plots (Table I). Juglone concentrations also differed with sampled depth (Table I). Significantly higher concentrations were present at the 0-8 cm depth than at lower depths. 

Soil beneath European alder/black walnut plots had higher nitrate nitrogen levels than soils beneath autumn-ollve/black walnut or walnut-alone plots (Table III). Mean total nitrogen did not differ significantly between treatments. 

Mean organic matter was greatest in the European alder/black walnut treatment, followed by the walnut-alone and autumn-olive/black walnut treatments (Table III). The mean pH was lowest in the autumn-olive/black walnut treatment, followed by the European alder/black walnut and walnut-alone treatments. 

Table I. Juglone Concentration in Soil According to Depth and Treatment in a Mixed Planting of Black Walnut and Nitrogen-fixing Species...

Table III. Mean Total and Nitrate Nitrogen, Organic Matter, and pH in Soil Beneath Black Walnut Planted in Mixture with Nitrogen-fixing Species...

Treatment means for pH and organic matter varied significantly between treatments, except for the pH between European alder/black walnut and walnut-alone. According to Alexander (32), nitrification is almost negligible at pH 5.0. Nitrification in soil beneath red alder (Alnus rubra Bong.) was reported at a pH as low as 3.5 (33). Obviously nitrification has not been eliminated in soil beneath treatment plots in our study. 

The almost bare to sparsely covered understory under autumn-olive in autumn-olive/black walnut plots has been attributed to reduced light intensity caused by the dense shade. The understory conditions rapidly approach those of a hardwood "forest" compared to the open European alder/black walnut and walnut-alone plots (38). Thus, the autumn-olive shorten the time it would normally take old-field conditions to disappear (37). The overall height of autumn-olive and the understory plot conditions have not changed in the last 4 or 5 years, while growth of the black walnut has continued at an improved rate (39). 

In summary, there is little reason to be concerned about allelopathy in mixed plantations where walnut is grown for timber as the harvested crop. Allelopathy does appear to be a factor to consider before planting European alder as a nurse crop with black walnut. Black walnut has had no apparent effect on the autumn-olive but is probably responsible for the decline and mortality of the European alder. These results present interesting possibilities for future research on the plant/soil/microbial relationships related to the metabolism of aromatics. 

Brooks, M. G. "Effects of Black Walnut Trees and Their Products on Other Vegetation" West Va. Univ. Agric. Exp. Stn. Bull. 347, 1951, p. 31. 

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