Fall, 1992 (v5n1)
Prichard, T.L., L. Hendricks
and J. Caprile
Report to the California
State Water Resources Control Board. 1992
In this demonstration project,
conducted in Farmington, California, cover crops and soil disturbance
were evaluated for their effect on water infiltration in a walnut orchard.
The study was begun in the fall of 1990, and initially involved both walnuts
and almonds. Due to poor cover crop stands, how-ever, the almond study
was discontinued. In addition, the legume cover crops in the walnut study
did not survive the combined effect of the 1990-91 drought and freeze.
Therefore, researchers consolidated their efforts in walnuts and all cover
crops were replanted and became established in the fall of 1991.
The study contrasted three
annual legumes and three perennial grass covers:
Legumes
- Berseem/crimson clover mix
- Subdover mix
- Wild flower mix (trefoil, alyssum, and California poppy)
Grasses
- Prairie home mix (perennial rye grass and creeping red fescue)
- Tall fescue
- Hard fescue
Each species or mix was planted
in the aisle on both sides of an entire tree row, and each treatment was
replicated three times.
Stand Establishment
During the winter, broadleaf
weed species were quite competitive with the grasses. After mowing in
late March, both the fescues thrived and easily out-competed the weeds,
while the prairie home mix was somewhat patchy. The clovers competed well
before mowing, and were quite dominant after mowing. The wildflower mix
grew poorly, and became established only in the very few areas where no
other vegetation grew.
Water Infiltration
Water infiltration characteristics
were measured using a portable, rainfall simulator-type infiltrometer.
Water infiltration was first measured under three soil surface conditions-undisturbed,
disturbed (raked), and disturbed re-crusted. The results indicated that
mechanical stirring of both silty clay and sandy loam soils broke up a
crust and improved infiltration characteristics (figure 1). Also, the
presence of a crust decreased infiltration on both sites below both the
raked and undisturbed treatments.
A previous study showed that
infiltration into sandy soils was limited by a crust for an entire irrigation,
resulting in a 50% reduced infiltrated water volume compared to undisturbed
soils. Crusted clay soils were only influenced for the first 2 hours of
an irrigation, after which infiltration was limited only by the soil's
clay texture.
Water infiltration characteristics
were measured under perennial grass compared to a soil maintained free
of weeds by herbicides for an entire season. For comparison, gypsum (used
to improve water infiltration) applied both through the soil and through
the water was also evaluated.
A huge increase in initial
infiltration rate occurred in the cover crop treatment compared to
all other treatments (figure 2). However, the steady state, or the sustained
infiltration rate, of the cover was not significantly greater. Therefore,
only an irrigation system which provides water at the maximum rate of
intake, such as furrow or flood irrigation, can benefit. Orchards irrigated
with sprinkler systems, which apply a constant precipitation rate, will
not experience increased infiltration over a typical 12 to 36 hour irrigation.
The improvement in water
infiltration is a result of soil surface protection from the mixing and
sorting action of water flow or water drop impact. Also, improvements
are a result of an increase in soil organic matter, which improves soil
structure. The net effect is a reduction in soil crust development.
For more information write
to: Terry Prichard, UC Cooperative Extension, 420 5. Wilson Way, Stockton,
CA 95205.
(CJ-FMCC.O74)
Contributed by Chuck Ingels
Figure 1. Accumulated
infiltration of water under three different levels of soil disturbance.
(not available)
Figure 2. Accumulated infiltration of water into soil under different
management regimes. (not available)
[ Back | Search | Feedback ]