Mature nut trees are usually large trees, and large trees demand space.
Young nut trees, therefore, must be planted relatively far apart from
each other and for the first few years, at least, there is an abundance
of unused land between the trees, which may be used for intercropping.
The choice of just what crop or plants to use is often perplexing and
should be considered for several aspects.
The economic factors are of prime importance. The cost of growing the
crop, the specialized farm machinery and equipment needed, the
availability of labor, the distribution of the seasonal labor demand,
the time of the critical cultural practices or of harvesting, the
potential market, and the expected price of the saleable product must
all be considered.
The staple farm crops of the region are often preferable to specialty
crops, particularly from the labor standpoint. Corn, wheat, oats,
potatoes, and legumes can all be grown with a minimum of labor and the
use of power machinery. There is less risk involved with farm crops than
with specialities, both in securing an adequate crop and in the price
received for the product. Fruit, vegetables and ornamentals often have
very critical requirements. They must be sprayed, harvested, and shipped
at exactly the right time or all the proceeds will be lost. Staple crops
are not so demanding in either culture or harvesting.
The labor distribution throughout the season or even throughout the year
must be considered and well planned in advance. No two crops should
require exact and demanding attention at the same time. They should be
chosen and planted so that a regular, even distribution of labor can be
maintained with as little of a rush period as possible and yet with a
minimum of idle time.
The general agricultural pattern of the region must be considered. In a
sparsely settled grain and livestock region it would be quite
inadvisable to grow strawberries or other crops which require a maximum
of hand labor during a very brief period. Berries, however, may be
perfectly well suited to sections where either transient workers or city
children can be secured with little effort.
The crop should suit from the ecological viewpoint. It must not compete
with the young, growing trees for mineral food and water, particularly
during spring and early summer when the trees make most of their annual
growth. On the other hand, if planted too close to the trees, some
intercrops may be shaded too severely to produce a normal yield.
Success in intercropping is usually found between plants which are quite
dissimilar in form and habit. Black walnuts and pasture grasses furnish
a typical example. The long taproots of the walnuts penetrate deeply
into the soil, while the grass roots are shallow and fibrous and feed
in the soil surface layer. The aerial portions of these plants are
likewise quite different, the walnuts tower high in the air, while the
grasses form their crowns on the very surface of the ground. The light
shade cast by the walnuts does not interfere with the photosynthetic
activity of the grasses, but it is sufficient to discourage growth of
broad-leaved weeds which have a higher light requirement than that of
grass. This light shade also tends to provide a greater supply of
available moisture for the grass, in that it reduces temperature and,
consequently, water loss from the grass and soil by keeping down both
transpiration and evaporation.
Experiments in both Tennessee and Ohio have shown that the quantity of
grass produced from beneath walnut trees is greater than on equal areas
in the open and that the quality, as represented by a larger protein
content, is also higher. For this reason, one may well consider
livestock as the income-producing portion of a walnut-pasture planting.
Over one fourth of the agricultural land of the United States is devoted
to pasture and much of the land is suitable for interplanting to
walnuts, butternuts, and other pasture trees, as honey locusts and black
locusts, all of which are known to improve the pasture grasses to some
extent. The potential income which may be derived from such plantings
over this vast acreage is enormous and is the more striking in that
these pasture trees occupy a plane that is now idle and unproductive,
that is, the area lying above the grass tops. The nuts produced on this
"upper story" will represent almost all "clear profit" in that very
little care need be given these walnut trees after they have been
properly planted. Livestock guards will need to be placed about the
trees at planting time and kept there until the trees have grown to the
point where they may no longer be harmed by straddling and browsing.
Pastures are excellent sites from another angle. The closely grazed sod
furnishes an ideal place to rake the nuts together at harvest time.
Anyone who has hunted for nuts in a dense ground cover will appreciate
this factor.
While the walnut responds best to the deep, fertile soil of the river
bottoms and flood plains, it will grow well on the lower portions of
slopes if water is available and the site is not too exposed to the
force of drying winds. Contour strips should be prepared by plowing
several furrows downhill, each a little less in depth than the
preceding, and the walnuts planted thereon. The walnut is a spreading
tree and plenty of space should be allowed. Perhaps it may be wise to
plant the walnuts at extended intervals and fill up the contour row with
black locusts, for post wood, and honey locusts to produce succulent
pods for cattle feed. In any event, it is better to allow too much,
rather than too little space, as walnuts are long-lived trees and will
thrive best where there is least competition. In Iowa, black walnuts are
responding well to "basin culture" in sites which were prepared by
"scalping" the sod from the upper portion of a slope and depositing it
on a lower portion in order to catch and retain more water.
Nut trees are like all other trees in that they react favorably to good
horticultural practice. Fertilizer, particularly nitrogen, is usually
always helpful. The addition of lime when the soil is acid and of
organic matter when humus becomes depleted will aid in better soil
aeration and an increased moisture supply. This, in turn, will be
reflected in more vigorous tree growth and greater nut production.
Occasional spraying may be necessary to control the Datana caterpillar
in the summer.
Chinese chestnuts seem to be admirably adapted for interplanting with
mulberries, cherries, pears, and the like in poultry runs and hog lots
where the pigs and chickens will control the weevils by gleaning the
prematurely dropped and overlooked chestnuts which contain the grubs of
the weevil. The fruit portion of the integrated planting will maintain a
high carbohydrate ration during the season for the use of the livestock.
Here, again, plenty of space should be allowed between trees to allow
each its full measure of water, food, air and sunlight.
Careful and thorough research is needed to determine the full
requirements of nut trees and to work out the interplanting
relationships. In view of the vast potentialities for their use,
investigational programs may soon be under way and much more definite
information be made available to the farmer and landowner.