AGRONOMY NOTES



Vol. 29, No. 5, 1996

 Differential Black Walnut Growth on a Recommended Soil Map Unit:
  Investigation of Related Soil Chemical and Physical Properties

 D.C. Ditsch, J. Stringer and D. McIntosh


     Black walnut (Juglans nigra L.) is one of the best known and
most valuable trees in Kentucky.  However, due to its high value,
the species has been aggressively harvested from natural stands,
creating a limited supply of quality black walnut trees.  Many
landowners recognize this as an investment opportunity and have
placed small tracts of unused land into black walnut production.
      Production of high-value black walnut is a long-term
investment (50+ years), the success of which is highly dependent
upon proper soil site selection. Soils best suited for black
walnut production are well drained, more than 40 inches deep,
have a pH ranging from 5.0-8.4 and contain less than 35% coarse
fragments (% by volume greater than 2 mm). Proper soil-site
selection will increase seedling survival and growth, and reduce
the length of time between establishment and harvest. Landowners
must be aware that planting and cultural practices (i.e.
competition control, pruning and thinning) are labor intensive,
therefore, rapid growth is of economic importance.  Soil site
selection should begin by consulting a USDA-NRCS county soil
survey report to indentify the soil map unit of an area and
describe its suitability for black walnut production. Soil map
units that are deliniated on soil maps identify the soil type
that dominates the area within each delineated map unit. Although
the scale of mapping soils for county soil survey reports is not
likely to delineate mapping units smaller than 2-3 acres, it is
not uncommon for several kinds of soil to occupy areas smaller
than two acres in size in patterns not practical to be shown
separately on the soils map. Therefore, small areas should be
examined in greater detail in order to more precisley determine
soil-site suitability.
     A black walnut demonstration planting was established at the
Robinson Substation in Quicksand, Kentucky on a soil map unit
shown to be suitable for black walnut growth. Over time, however,
a distinct differential in growth pattern developed across this
uniform appearing site that suggested unsuitable soil conditions
were present. The objective of this study was to measure soil
chemical and physical characteristics, and relate them to walnut
tree growth at this site.

                      MATERIALS AND METHODS

     In 1983, black walnut seedlings were planted on a 12' x 12'
spacing on a uniform appearing site (230' x 100') delineated on a
soil map of the area as being a Nolin-Grigsby (Ng) complex (fine
silty, mixed mesic, dystric, fluventic, eutrochrepts and coarse
loamy, mixed mesic, dystric, fluventic, eutrochrepts,
respectively) (Figure 1).  Tree height was used as an index of
growth and measured in 1995 using a Criterion 400 measuring
laser.  Soil was sampled within the planted area at 40 individual
sites on a 24' x 24' grid pattern.  Soil samples from each
sampling point were collected in 12 inch increments to a 4 ft.
depth using a truck mounted hydraulic probe.  Each soil sample
was analyzed for pH, organic carbon (OC), soil test levels of
phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc
(Zn), and particle size distribution. A more detailed soils map
within the planted area was prepared by close examination of soil
morphological characterisitics at the individual sampling sites.
Soil bulk density was measured at the center 4 inch section of
each 12 inch core sample.  Linear regression analysis was used to
determine the relationship between tree height and individual
soil characterisitics.

                      RESULTS AND DISCUSSION

     Twelve years after planting, black walnut tree height ranged
from 2.5 - 37 ft., resulting in a distinct differential in growth
pattern across the study site (Figure 2).  Differences in the
soil chemical properties measured at the various soil depths did
not relate to differences in tree height (Table 1), as indicated
by non-significant correlation coefficients.
     Intensive sampling of the planted area showed that there
were five different soil types contained within what was shown on
the soils map to be one map unit.  These were: Barbourville loam,
eroded; Barbourville loam; Barbourville silty clay loam;
Allegheny silt loam; and Shelbiana silt loam.  A generalized
description of the three soil series is as follows:

Barbourville Series:consist of deep well drained soils on
footslopes and alluvial fans.  They formed in colluvial and
alluvial material. Typcially, these soils have a dark brown loam
surface layer, 12 inches thick.  The subsoil, from 12 to 14
inches, is brown loam and from 18 to 23 inches, is dark yellowish
brown gravelly loam. The mottled substratum, from 33 to 50
inches, is yellowish brown gravelly loam.  Slopes range from 0 to
20 percent.

Allegheny Series:consist of deep well drained soils on terraces,
footslopes and alluvial fans.  They formed in old alluvial
material. These soils have a dark yellowish brown loam surface
layer 9 inches thick.  The subsoil from 9 to 28 inches is strong
brown clay loam and from 28 to 42 inches is yellowish brown loam.
The substratum from 42 to 65 inches is yellowish brown loam.
Slopes range from 0 to 25 percent.

Shelbiana Series: consist of very deep, well drained soils on
terraces. They formed in mixed alluvium from sandstone, siltstone
and shale.  The surface layer is very dark grayish brown loam
10 inches thick.  The subsurface from 10 to 18 inches is dark
brown loam.  The subsoil from 18 to 65 inches is dark yellowish
brown loam.  The substratum from 65 to 80 inches is dark
yellowish brown loam with common grayish brown mottles. Slopes
range from 0 to 20 percent.

     Differences in tree height appeared to be related to the
occurrence of the five soil types indentified, despite all soil
types being recommended as suitable for black walnut production.
Greatest average tree height (Av.=29.4') was measured on the
eroded Barbourville loam while the least amount of growth was
measured on the Shelbiana silt loam (Av.= 10.9').  Table 2 shows
the textural class for each sampling depth of the five soil types
identified.  These data show that the Barbourville soil types are
loamier in texture to a depth of 4 ft than Allegheny and
Shelbiana, suggesting that a difference in soil porosity or
drainage might be responsible for the differential tree growth.
However, no visable signs of restricted drainage (gray color
and/or mottling) were observed.
     Prior to soil sampling, several of the smaller black walnut
trees were hand excavated to observe root growth.  The root
systems of these trees were poorly developed and exhibted
predominately shallow lateral growth suggesting a soil compaction
problem.  Table 3 shows the average soil bulk density for each
sampling depth.  As expected, soil bulk density increased with
increasing soil depth (range 1.35 - 1.79 g/cm3).  However, these
data indicate that tree growth on the study site was greatest in
areas where soil bulk density was the highest. While these
results are difficult to explain based on our general
understanding of root growth and soil compaction, work reported
by Daddow and Warrington (1993), suggest that soil texture is a
major factor to be considered when determining "growth-limiting"
bulk density (GLBD). For example: soil with a large amount of
fine particles (silt and clay) will have smaller pore diameters
and a higher penetration resistance at a lower bulk density than
a soil with a large amount of coarse particles. Daddow and
Warrington concluded that coarse-textured soils will usually have
higher GLBD than fine-textured soils.

                           CONCLUSION

     Black walnut production is a long-term investment that
requires proper soil/site selection for maximum tree growth. The
results from this study clearly demonstrate the soil
heterogeneity that can occur on small, yet uniform appearing
tracks of land, and the effect this variability can have on
growth of black walnut. Due to the scale of mapping used in
published soil surveys, intensive soil sampling should be done on
areas to be used, in order to identify small scale differences in
soils which may be present. The Nolin-Grigsby complex soil map
unit shown on the NRCS soils map actually contained five
different soil-types in the 0.5 acre study area. Black walnut
tree height was greatest on the loamy textured Barbourville soils
as compared to the slightly heavier textured Allegheny and
Shelbiana soils, suggesting that differences in soil texture
across the study site had a greater influence on tree height than
differences in soil pH, OC, P, K, Mg, Ca, and Zn levels measured
to a depth of 4 ft.

                            REFERENCES

Daddow, R.L. and G.E. Warrington. 1993. Growth-limiting soil bulk
densities as influenced by soil texture.  WSDG-TN-00005, USDA
Forest Service, Fort Collins, CO.

USDA-NRSC. Breathitt County Soil Survey.  (Mapping completed, but
report currently unpublished).

USDA-SCS. 1983. Soil Suitability for black walnut. Technical
Publication Number 5, Lexington, Ky.


Table 1. The relationship between black walnut tree height and
various soil chemical characterisitics as indicated by regression
coefficient of determination.

_________________________________________________________________

                                       R2
                    _____________________________________________

                               Soil Depth (inches)
                    _____________________________________________

Chemical              0-12      12-24       24-36       36-48
Characteristic
_________________________________________________________________

Organic Carbon       0.008     0.00009      0.02        0.166

Phosphorus           0.08      0.017        0.02        0.0005

Potassium            0.15      0.02         0.06        0.227

Calcium              0.10      0.07         0.11        0.20

Magnesium            0.14      0.08         0.005       0.024

Zinc                 0.04      0.01         0.04        0.021

water pH             0.24      0.18         0.21        0.30

buffer pH            0.29      0.19         0.09        0.11
_________________________________________________________________

All R2 values shown are not significant.


Table 2. Textural class of samples taken by depth for the five
soil types identified.
________________________________________________________________


                             Map Unit
             ____________________________________________________
Soil Depth          Barbourville
             __________________________________
             l,eroded   l   sil    Allegheny sil   Shelbiana sil
_________________________________________________________________
  inches.............Texture Class....................

  0-12          sl     l    l         sicl               sicl

 12-24          sl     l    l          cl                sicl

 24-36          sl     l    l          sl                 cl

 36-48          l      sl   sl         sl                  l
_________________________________________________________________

  sl=sandy loam; l=loam; sicl=silty clay loam; cl=clay loam.




Table 3. Soil type, bulk density at various depths and
coresponding tree height.
_________________________________________________________________


                              Soil Depth
              ______________________________________
  Soil Type         0-12"   12-24"   24-36"   36-48"   Tree
                                                      Height
_________________________________________________________________
             ..........bulk density (g/cm3).........    ft


Barbourville l,   1.59a+    1.74 a  1.78 a   1.79 a   19-37
    eroded

Barbourville l    1.51 ab   1.57 bc 1.66 ab  1.69 ab  10.5-32.5

Barbourville sil  1.52 ab   1.67 b  1.67 ab  1.69 ab  12-34.5

Allegheny sil     1.48 b    1.66 b  1.61 b   1.71 ab  2.5-17

Shelbiana sil     1.35 c    1.54 c  1.63 ab  1.61 b   5.5-28
_________________________________________________________________
+ Values within a column for each sampling depth followed by the
same letter are not significantly different at the 95% level of
probability.