AGRONOMY NOTES
VOL. 30, NO. 3, 1997
EFFECTIVENESS OF TILE DRAINAGE ON A FRAGIPAN SOIL IN AN ORCHARD SITE
Gerald R. Brown, Dwight Wolfe, and Lloyd Murdock
INTRODUCTION
Orchards require a well-drained soil in order for roots to
have good aeration and to function properly. The soil is
unsatisfactory for orchard purposes if the water table remains
within six inches to a foot of the soil surface for a week after a
heavy spring rain, or within three feet of the surface for several
weeks after growth starts. Poor internal water drainage is a
limiting factor for many sites. In Kentucky, many orchards are on
soils with a fragipan which result in perched water tables near the
surface during winter and spring months. Perched water tables
exist above the fragipan only during months when precipitation
exceeds evapotranspiration. This often results in extended periods
of water saturation of the top two to three feet of the soil. For
good growth and optimum production, internal water drainage needs
to be improved.
This can be done by ridging the site or by installing tile drain
lines. However, ridging changes the soil profile, makes it more
difficult to operate equipment, and may be of limited value because
it can lead to ponding of water and/or soil erosion. Traditional
tile drainage with a crushed rock (aggregate) back fill is
effective although expensive. A method of installing tile without
rock aggregate by mixing the soil and staying above the fragipan is
reported to be effective.
The purpose of this study was to determine the effect six
years after installation of this method of installing tile on soil
moisture in an orchard site that is wetter than desired through
much of the dormant season.
MATERIALS AND METHODS
An orchard site on a Tilsit silt loam soil and a 0 to 2 percent
slope was selected at the University of Kentucky Research and
Education Center, Princeton, KY. USDA-NRCS personnel determined
that the fragipan depth was at approximately 20 inches and was
typical for this soil type. The Tilsit soil is classified as
moderately well drained, but rainfall usually exceeds drainage
during winter and early spring. As a result, the site is usually
waterlogged in the rooting zone from December through April.
Although the USDA-NRCS recommends setting tile lines 30 ft apart
for high value crops, lines were set 40 ft apart due to existing
trees planted on 20 ft row spacing. A 2 ft-wide backhoe bucket was
used to dig trenches that followed the slope of the fragipan. Tile
was installed immediately overlying the fragipan in the bottom of
these trenches. After removal, the soil was thoroughly mixed and
replaced.
To serve as a control, an undisturbed and untiled site with
similar topography, elevation, sod cover, and management history
was examined and determined to be of the same soil type and
classification as the tiled site described above. This untiled
site was located about 150 feet from the tiled site. Water table
levels in the piezometers at the two sites were compared to
determine the effectiveness of the tile.
Piezometers were installed for use in monitoring ground water
levels at each site. Six different tile lines were monitored and
thirty-four piezometers were dug, twelve in the untiled site,
twelve within 3 ft of the tile lines, and ten within 20 ft of the
tile lines (Fig. 1). Thus, piezometers were nested within each of
the three treatments. Each piezometer was dug with a 1 ft diameter
auger to a depth of 40 inches penetrating into but not through the
fragipan. A 40 inch long, 3 inch diameter pvc pipe was placed in
each hole to a depth of 26 inches below the soil surface and
backfilled around the pipe. The remaining 14 inches of pvc pipe
that extended above the soil surface was covered with an inverted
coffee can.
The distance from the soil surface to the water level in each
piezometer was measured 3 to 5 times per week from 4 January 1993
to 17 May 1993, for a total of 87 measurements. Rainfall during
this period was only 0.33 inches below normal. Analysis of
variance and mean separation by the least significant difference
(LSD.05) were performed on these data.
RESULTS AND DISCUSSION
Six years after installation, tile effectively reduced perched
water table levels. Significantly higher water table levels were
observed at the untiled site compared to the average of both 3 ft
and 20 ft from the tile for 63 of the 87 days, 72.4 percent of the
time. The environment in the area close to the tile line was
improved significantly. Water table levels in the untiled site
were significantly higher than the levels 3 ft from the tile 85% of
the time (74 of the 87 measured days). The area 20 ft from the
tile was also improved but not as much as the area 3 ft from the
tile. The water levels in the untiled site were significantly
higher than levels 20 ft from the tile 54% of the time (47 of the
87 measured days).
One of the wettest months in this study was January, with 4.75
inches of precipitation (0.95 inches above normal). During this
month, the water table levels in the untiled site were
significantly higher than the levels 3 feet from the tile 17 of the
18 measured days (Fig. 2). At 20 ft from the tile, the same was
true for only 6 of the 18 measured days (Fig. 2).
There were 21 days in this experiment during which the
recorded water table levels averaged higher than their previous
measurements. Such rising water levels are indicative of water
infiltration exceeding internal drainage and evapotranspiration.
The tile seemed to be most effective in this situation.
Significantly higher water table levels were observed at the
untiled site compared to the tiled site (average of both 3 ft from
the tile and 20 ft from the tile) for 19 of the 21 days (or 90 % of
the time) that water table levels were rising. However, areas
close to the tile were most affected as indicated by the fact that
water levels at the untiled site and 20 ft from the tile were
significantly higher than those 3 ft from the tile for 18 of the 21
days water table levels were rising.
These results are summarized in terms of the percent of the
days that the water table level was within 6, 12, and 18 inches of
the soil surface (Table 1). Free water within 6 inches of the soil
surface was observed at 3 ft from the tile less often than at the
untiled site or for 20 ft from the tile (Table 1). The percent of
days that water table levels were within 12 or 18 inches of the
soil surface were not significantly different between the 20 ft
from the tile and the other two sites (untiled site and 3 ft from
the tile), but were significantly different between the untiled
site and 3 ft from the tile (Table 1). Thus, 20 ft away from the
tile, water table levels do not differ significantly from those of
the untiled site at either the 15, 30, or 45 cm depth.
SUMMARY
The results of this experiment suggest that tile installed
without an aggregate backfill significantly lowers the water table
levels near the tile on a Tilsit loam soil with a fragipan at 20
inches. Six years after installation, there was less free water at
3 ft from the tile than either 20 ft from the tile or at the
untiled site, the primary benefit being within 6 inches of the soil
surface. To improve a site for orchard use similar to the one in
this study and utilizing the tile installation method that was
used, it is suggested that tile be installed no more than 10 feet
from the trees.
ACKNOWLEDGEMENTS
The authors express appreciation to June Johnston for her technical
assistance.
Table 1. Percent of days(z) the water table was within 6, 12, and 18
inches of the soil surface.
Site 6 in 12 in 18 in
3 ft from tiley 2 bx 12 b 26 b
20 ft from tile 25 a 37 ab 53 ab
untiled 31 a 51 a 64 a
z Data recorded on 87 of the 137 days from 4 January through 17 May
1993, at UK, REC, Princeton, KY.
y Installed Fall 1987.
x Mean separation by LSD0.05. Means with the same letter are not
significantly different.