Figure 1: Irrigation amounts for 2002 and 2003.
Progress Report on Microirrigation in Guam, 2003.
UNIVERSITY OF GUAM
COLLEGE OF NATURAL AND APPLIED SCIENCES
AGRICULTURAL EXPERIMENT STATION
Western Regional Research Project W-128
Progress Report - 2003
Project Title: Microirrigation Technologies for Protection of Natural Resources and Optimum Production.
Principal Investigators: P. Singh
PROGRESS OF WORK AND PRINCIPAL ACCOMPLISHMENTS:
Objective 1. To evaluate and refine microirrigation management strategies to promote natural resource protection and optimal crop production.
Objective 2. To improve, modify, and evaluate microirrigation system design and components for natural resources protection and optimal crop production.
Experiment 1.
Field experiment to evaluate the susceptibility
to clogging for five popular drip lines was setup in February of 2003 at
Yigo Agricultural Experiment Station, Guam. Delta T-Tape from Toro, Typhoon
20 from Netafim, Turbulent Twinwall 9” and 24” from Chapin, and Submatic
24” from Submatic were selected for evaluation. The design setup
consisted of a set of three drip lines 50 feet long and 3 feet apart for
each type. Each set was connected to a submain. Each submain
was connected to the main via an electronic water meter and a solenoid
valve. A filter and pressure regulator were installed on the mainline.
A datalogger was programmed to activate irrigation twice a day for 10 minutes
each time. The pressure regulator was set at 10 psi. Ten emitters
were randomly selected from each type of drip line and emitter flow was
measured once every month. Water samples were also collected for
chemical analysis.
The mean flow rate, standard deviation,
and percent decrease in flow rate of each set of ten emitters for each
drip line type are presented in table 1 and graph 1 for the duration February,
2003 to September, 2003. The Toro Delta T-Tape had the lowest clogging
at 6.6% while the Chapin Turbulent Twin 24” had the highest clogging at
51.7%. Finally, extreme drops in flow rate and high standard deviations
for the Netafim, Submatic, and Chapin 24” drip lines are the result of
a some or most of the ten sample emitters clogging considerably (50 to
100 percent drop in flow rate). Table 2 lists the dates and number
of emitters with over a 50% decrease in flow for each drip line type.
Usefulness of Findings:
1. Drip lines from the same manufacturer
may clog at a different rate.
2. The information will provide another
evaluation parameter for farmers to consider while choosing a drip line.
Future Plan of Work:
1. Continue to evaluate drip lines from different manufacturers in terms of clogging potential.
Publications: None
Table 1: Mean emitter flow rate, standard deviation, and percent decrease in flow.
Graph 1: Mean Emitter flow rate with percent decrease in flow
Table 2: Total number of emitters out of
10 sample emitters with 50% or greater flow
rate decrease
Experiment 2.
Field studies were conducted over two seasons to determine the Optimal Wetted Soil Volume (OWSV) for growing watermelon in the shallow (19.6cm average soil depth), high pH Guam Cobbly Clay soil of Northern Guam. Watermelon (Citrullus lanutus) variety China Baby was transplanted on March 4, 2002 and again on April 8, 2003 in a random block design with twelve rows, three replications and four treatments. Treatment numbers reflect drip line per row configurations of 1, 2, 3, and 4 drip lines. Drip line spacing - based on soil wetting pattern field tests – of 20.32 cm was use. Plant spacing was 1.22m in rows 3.05m apart. Pre-plant soil analysis showed a mean pH of 7.32 in 2002 and 7.80 in 2003. For 2002, organic matter was 6.25%, phosphorous 6.31 ppm, and potassium 20.23 ppm. In 2003 organic matter was 5%, phosphorous 24 ppm, and Potassium 14 ppm. switching tensiometers were used to maintain a -20 cb soil moisture tension for all treatments. Phosphorous was banded at a rate of 280 kg/ha for both experiments. nitrogen and potassium was applied based on soil analysis, extension recommendation , and plant petiole sampling. Total amounts of N and K were kept equal for all treatments. Potassium amounts for 2002 and 2003 were 225 kg/ha while Nitrogen amounts for 2002 and 2003 were 140 kg/ha and 168 kg/ha respectively. Black polyethylene plastic mulch was used to control weeds, provide a uniform soil moisture level between irrigations, and to prevent leaching of N and K nutrients during heavy rains. Row covers were used until flowering to reduce pesticide use. Twelve stainless steel drainage lysimeters were installed in the middle of each row prior to the first experiment.
Irrigation amount, leachate amount, leachate N-P-K concentrations, plant petiole N and K concentrations, soil salinity, soil moisture tension, plant canopy area, diseased/deformed fruit types and amounts, and fresh harvest weight were all measured. Irrigation amounts for both years are shown in figure 1. Use of one drip line per row required a significantly higher number of irrigation events and a higher number of fertigation events to deliver the desired amount of fertilizer. The average number of irrigation and fertigation events for both seasons are given in figure 2. Yield amounts, which show no significant differences between treatments or between seasons are given in figure 3. Treatment 1 had the highest water use efficiency for both seasons as shown in figure 4. The tensiometer set-up and numbering configurations used is shown in schematic 1 while measurements for treatments one and three are shown in figures 5 and 6, and reflect soil moisture uptake patterns in the early and later stages of crop development.
Acknowledgement: Funding for the 2002 and 2003 OWSV experiments were from a USDA special grant (T-STAR).
Usefulness of Findings
1. Yields for one, two, three, or four
drip line configurations under black plastic mulch are the same, while
water use efficiency is best when using one drip line.
2. The number of irrigation and fertigation
events for 1 drip is higher than for 2, 3, or 4 drip lines and results
in higher man hours for irrigation management. Also, the fertilizer need
amounts for the one drip line treatment were difficult to meet, especially
early in plant development, because of the soil wetting pattern and slower
rate of irrigation amount.
3. We are recommending a two drip line
configuration to farmers in Northern Guam and are in the process of producing
and irrigation/fertigation schedule Technical Bulletin.
Future Plan of Work
1. Evaluate four drip line irrigation schedules
to determine the optimal schedule
for growing
watermelon in the shallow fast draining soils of Northern Guam.
2. Evaluate nitrogen fertigation rates
with respect to optimal watermelon production.
Publications/Presentations:
1. Singh, P., Brown, R.W., Matanane,
F. 2002. Guam Agricultural Climatic Data System: 1999 Climatic Data and
Summaries. Guam Agriculture Experiment Station Technical Bulletin 389.
2. Singh, P., Schlub, R., Cruz,
F. 2002. Irrigation, Fertigation, and Drainage chapter in Eggplant, Pepper,
and Tomato Production Guide for Guam, Guam Cooperative Extension, pp. 36-39.
3. Singh, P., Brown, R.W. 2003.
Evaluation of a Microirrigation System Design Parameter for Watermelon
in Tropical Shallow Soils. The 24th CAS Conference, March 2003. Abstract.
Workshop/Training:
1. Farmers Workshop. June, 2003.
This workshop was held for microirrigation technology transfer and information
dissemination for watermelon production.
2. Summer internship program for high school students. July 2003. Trained one student in microirrigation.
Figure 1: Irrigation amounts
for 2002 and 2003.
Figure 2: Average number of irrigation
and fertigation events for 2002 and 2003 for all treatments.
Figure 3: Total yield for 2002 and
2003 for all treatments.
Figure 4: Water use efficiency for
2002 and 2003 for all treatments.
Schematic 1: Tensiometer configuration.
Figure 5: Moisture uptake pattern
for one and three drip line treatment, two weeks after transplanting.
Figure 6: Moisture uptake pattern
for one and three drip line treatment, two weeks after transplanting.