Vol.2, No.4, 533-535 (2011) Agricultural Sciences
opyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Effects of soil moisture and length of irrigation on soil
wetting to deliver fumigants through microirrigation
lines in sandy spodosols
Bielinski M. Santos*, James P. Gilreath
Gulf Coast Research and Education Center, IFAS, University of Florida, Wimauma, USA;
*Corresponding Author: bmsantos@ufl.edu
Received 24 August 2011; revised 22 September 2011; accepted 13 October 2011.
Soil fumigant delivery through microirrigation
(drip) lines has the potential to replace direct
soil injection into planting beds. However, wet-
ting coverage in these Spodosols must be im-
proved to increase soilborne pest and weed
control. Field trials were carried out to deter-
mine the imp a ct of soil m oisture on the exte nt of
wetting cross-sectional areas through varying
irrigation times. Soil moisture contents w ere: 1)
7% moisture (field capacity), and 2) 20% (satu-
ration), along with 2, 4, 6, 8, and 10 h of irrigati on .
Pressed beds had 70 cm tops. Drip lines had
emitters spaced 30 cm apart delivering 0.056
L·min–1 per m of row at 55 kPa, and two drip
lines were buried at 2.5 cm below the surface
and 30 cm apart from each other. Water was
mixed with a blue marking dye to analyze the
water distribution patterns. Beds were opened
at the emitters and high-resolution digital pic-
tures were taken for each treatment. Resulting
images were adjusted using photographic soft-
ware and covered areas across the beds were
determined. Regression analysis showed sig-
nificant quadratic equations for both soil mois-
ture situations, with saturated soils obtaining
the highest cross section coverage (90 and 94%
after 8 and 10 h). In field capacity beds, the ma-
ximum cross section coverage obtained was
82%. Within each soil moisture situation, there
were no differences between 8 and 10 h of irri-
Keywords: Methyl Bromide; Drip Irrigation;
Soilborne Pests; Water Management
The loss of methyl bromide (MBr) as soil fumigant
has prompted a great deal of research to identify an al-
ternative to use in horticultural crops. Thus far, combi-
nations of broad-spectrum fungicides and nematicides
followed by herbicides have been shown to be suitable
options to reduce the impact of soilborne diseases,
nematodes and weeds in vegetable crops. The conven-
tional procedure to apply chemicals such as 1,3-di-
chloropropene + chloropicrin (1,3-D + Pic) and metam
sodium (MNa) has been either in-bed injections with
chisels or pretransplant broadcast applications with spe-
cialized equipment [1]. However, the cost of the equip-
ment and the risk of personnel poisoning are some of the
concerns about these application techniques.
Application of any MBr alternative requires the
maximum possible coverage of soil volume in order to
contact the target pest in sufficient quantity and time
duration to achieve acceptable control. Unfortunately,
this is not always possible, thus pest control gaps are
frequently observed. Therefore, more efficient delivery
systems need to be developed. Some recent reports have
indicated that strawberry yields obtained with MBr were
comparable with those of Telone C-35 (1,3-D + Pic
65:35; Dow AgroSciences LLC, Indianapolis, Indiana,
USA), Inline (1,3-D + Pic 61:33; Dow AgroSciences
LLC, Indianapolis, Indiana, USA), liquid and granulated
MNa, Pic, methyl iodide, and methyl iodide + Pic
(60:40). Other trials indicated that Inline® + MNa, Te-
lone-C35® + MNa, Telone II® (98% 1,3-D; Dow Agro-
Sciences) + MNa, and Telone-C35® + MNa + Bacilus-
subtilis were equivalent to MBr [2]. However, no much
research has been conducted under Florida conditions on
this subject and it needs to be further expanded.
The benefits of developing a soil fumigation system
for light sandy soils, such as are present in Florida, could
transcend current boundaries, allowing scientists to gain
a better understanding of how fumigants move in the soil
and their relationship with crop yields. Likewise, it
would impact on the feasibility of vegetable crop set-
B. M. Santos et al. / Agricultural Sciences 2 (2011) 533-535
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
tings, since costly injection machinery would not be
needed for soil fumigation, because the same irrigation
system used for delivery of water and fertilizer would be
utilized. One of the biggest obstacles to many alterna-
tives has been the onerous requirement for personal pro-
tective equipment (PPE). This PPE makes application
even more difficult in subtropical climates because of
the impact on workers. The possibilities of reducing soil
and water pollution and personnel poisoning/exposure
could be additional benefits derived from alternative
delivery procedures.
Soil texture has a close relationship with waterfront
movement in the soil profile. Heavy to loamy soils usu-
ally have slow vertical infiltration, providing greater
opportunities for liquid formulations to move laterally,
thus increasing coverage. However, in sandy soils, lat-
eral movement of water is restricted by the large amount
of macropores [3]. This has been the case for wetting
pattern trials in Georgia, where distances of 45.7 cm
between drip emitters provided the least bed width cov-
erage, with the most occurring with 30 cm between
emitters. The lowest uniformity of wetting took place
with 40.6 and 45.7 cm between emitters, and a maxi-
mum wetting of 60% of the bed volume was obtained [4].
In Florida, irrigation duration trials resulted in 45% of
the soil volume in the bed wetted after 12 h with a single
drip tube, and 85% coverage after 10 h with two lines [5].
Likewise, irrigation volumes were tested and indicated
that the use of two drip tubes only reduced the time of
flooding, even though two drip tubes increased spatial
distribution. The most bed wetting achieved with a sin-
gle tube was 50% to 60%, using 1135 L per 30 m of row
[6,7]. Huckaba et al. [8] found that bed wetting with a
single drip tape resulted in 50% coverage after 8 h, while
use of two tapes yielded 90% coverage.
To avoid erratic soilborne disease control with mi-
croirrigation, water application has to be studied consid-
ering the internal water movement in the soil profile.
Research needs to be conducted to determine the opti-
mum parameters for fumigant application through mi-
croirrigation systems in sandy soils. Distribution of irri-
gation water containing soil-active pesticides throughout
the raised soil bed may be necessary to obtain adequate
control of soilborne pests with microirrigation-applied
chemicals. The objective of this research was to deter-
mine the impact of soil moisture on the extent of water
coverage obtained through varying irrigation times.
Two field trials were conducted during January and
March 2003 at the Gulf Coast Research and Education
Center (GCREC) of the University of Florida. The soils
were classified as EauGallie fine sand (AlficHaplaquods,
sandy, siliceous, hyperthermic) with 1.0% organic matter
and pH 7.3. Raised beds were pressed with a bedder and
covered with low-density plastic mulch. Bed dimensions
were 0.71 m wide on top by 0.81 cm wide on the bottom
by 0.20 m high, giving an approximate cross sectional
area of 0.15 m2. Two drip irrigation lines (T-Tape Sys-
tems, San Diego, California, USA) will emitters spaced
30 cm apart were placed on bed tops before plastic
mulch placement. Each emitter delivered 0.056 L·m1
per minute at 0.55 bars. Drip lines were buried 2.5 cm
below the surface and 30 cm apart.
Treatments were arranged in a split-plot design with
three and six replications for January and March trials,
respectively. Soil water contents were the main plots,
while lengths of irrigation were the subplots. Water con-
tents were 7% (field capacity) and 20% (saturation).
Lengths of irrigation were 2, 4, 6, 8, and 10 h. Water
table was maintained 0.45 m below bed surface by con-
tinuously providing seepage irrigation. Each experimen-
tal unit was 6 m long. Soil moisture levels were meas-
ured by weight at the beginning of each trial. Soil sam-
ples were collected at random from three places within
each block and dried for 48 h at 120˚C.
Distribution of microirrigation water was evaluated by
using a water-soluble blue marking dye. The 0.95 L of
dye was mixed in a 208-L tank and was introduced into
every tankful of water during the various irrigation cy-
cles. This methodology has previously being tested and
provides a quick, inexpensive, and readily visible me-
thod for evaluating patterns of microirrigation water dis-
tribution [4,5]. One week after dye application, plastic
mulch was removed in two places within each experi-
mental unit and cross sections were exposed at the emit-
ters. In order to obtain darker cross sections, each cut
was allowed to dry for 2 h. Afterwards, high resolution
digital pictures were taken of each section. Resulting
images were transferred to photographic software and
covered areas were analyzed and calculated. During pre-
liminary trials, this digital methodology was adjusted to
reduce image distortion. Also, this method was validated
against a manual technique used previously, in which a
Plexiglas grid is placed against the cross sections and the
dye-marked contour is drawn [5]. The digital methodol-
ogy proved to be more accurate and less time-consuming.
The relationship between irrigation time and covered
area was examined with regression analysis. Standard
errors were used to measure differences among treatment
There was no significant interaction between treat-
ments and trial (P > 0.05). Therefore, data from the two
trials were combined. Irrigation times significantly (P <
0.05) affected cross-sectional covered areas (Figure 1).
B. M. Santos et al. / Agricultural Sciences 2 (2011) 533-535
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Figure 1. Effects of irrigation time on cross-sectional covered
area of beds under two soil moisture contents. Regression
equations are y = 39.6 + 34.6x – 1.6x2, r2 = 0.91 for 20%
moisture; and y = 55.0 + 27.6x–1.3x2, r2 = 0.94 for 7% mois-
Quadratic regression equations characterized the re-
sponses of each soil moisture status (y = 39.6 + 34.6x
1.6x2, r2 = 0.91 for 20% moisture; and y = 55.0 + 27.6x –
1.3x2, r2 = 0.94 for 7% moisture).
When irrigation was applied for 2 h, no differences
were observed in the wetted areas for either soil mois-
ture, with less than 45% of total area wetting. However,
significant changes were observed beginning with 4 h of
irrigation. In those cases, beds with 20% moisture
reached larger wetted areas at the emitters than those
with 7% moisture. When 20% moisture was present,
there were increments of 7%, 6%, 9%, and 8% at 4, 6, 8,
and 10 h of irrigation, respectively. With the soil at field
capacity and 10 h of irrigation, 82% wetting was obtained,
whereas a maximum coverage of 94% was obtained in the
saturated soil during the same period (Figure 1).
Previous reports on Florida Spodosols have indicated
that the largest covered area obtained with two irrigation
lines was 85% [5]. That finding was confirmed by these
trials, where 82% wetting area was obtained under simi-
lar conditions. However, coverage was further improved
by raising soil moisture prior to the irrigation. Therefore,
soil water status has an influence on water distribution
patterns throughout planting beds, increasing bed wet-
ting as soil moisture increases.
This finding might allow scientists to redesign strate-
gies for drip-applied fumigants in Florida Spodosols.
Further studies should be conducted to determine if dif-
ferences in wetting areas reflect positively on yields or
soilborne pest and weed control. Also, the research
should be conducted to assess the effect of increased
wetting on fumigant diffusion beyond waterfronts.
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