Progress Report on Microirrigation
in Iowa, 2003.
Title: Microirrigation: Technologies for protection of natural resources and optimum production.
Personnel: Henry G. Taber
Vince Lawson
Department of Horticulture Department of
Outlying Farms
Iowa State University, Ames, IA 50011
Objectives:
Iowa research was carried out on the following 2 objectives of the four in the project.
1. To evaluate and refine microirrigation management strategies to promote natural resource protection and optimal crop production.
4. To promote appropriate microirrigation technologies through formal and informal educational activities.
Progress of Work and Accomplishments:
Objective 1
The research was conducted at the Muscatine Research Farm (eastern Iowa along the Mississippi river). This site is an excessively drained coarse sand (sandy, mesic Entic Hapludoll) with 93% sand, 1-5% clay, organic matter of 1-3% and AWC of 0.5-0.7 inch/foot.
Sweet bell peppers grown in twin-rows on
black plastic mulch was the test crop to evaluate 3 irrigation scheduling
methods using 2 in-line emitter spacings. The irrigation methods
were:
1. Soil tension = irrigation event triggered
when daily readings of a 6-inch tensiometer reached 10-12 cbars.
Water amount to apply determined as 50% depletion of AWC and brought back
to field capacity.
2. Smittle crop coefficient = daily ET
(modified Penman equation) X Smittle crop coef. (developed in GA under
similar soil type and planting arrangements) determined daily amounts of
water to apply.
3. Crop canopy = daily ET X crop canopy
cover (never < 40%).
The 2 in-line emitter spacings were 6-inch and 12-inch Chapin twin wall cane tubing that delivered 0.3 gpm/100 ft. The water amount called for by the methods was applied twice daily, at 8 am and 2 pm.
Results
Table 1. Water applied and pepper
fruit produced for the growing season of June 17 to August 9. Yield
results are the sum of two harvests, Aug. 1 and Aug. 11, 2003.
| Irrigation method | Water used, gal/plot | Total
bu/acre |
Marketable
bu/acre |
Cull
bu/acre |
| Tensiometer | 1021 | 700 A | 287 A | 413 |
| Crop canopy | 903 | 607 AB | 170 B | 437 |
| Smittle | 978 | 528 B | 135 B | 385 |
Table 1 indicates that watering via the 6-inch tensiometer setting of 10 to 12 cbars resulted in 32.6% more total fruit produced compared with the Smittle crop coefficient method. Further, the marketable yield was doubled. But cull fruit accounted for 67% of total fruit indicating none of the watering methods were suitable for commercial production. Cull fruit were mostly small and misshapened. By the second harvest significant root plugging of emitters was evident.
Tensiometer readings in all plots reflected the water amounts applied, i.e. the Smittle and crop canopy methods (both based on ET measurement) tended to run drier than the tensiometer based method. The reference ET for the period was 12.24 inches. The crop ET for the crop canopy treatment was 9.6 inches and the Smittle method 10.88 inches. Even though total water quantity was similar among treatments, the tensiometer method applied 383 gallons/plot more water prior to July 8, compared to 270 gals/plot for the crop canopy and Smittle methods, which resulted in more branching and flower development. There was no difference in yield between the two emitter tape spacings. Marketable fruit size and fruit shape was similar in all treatments at 5.7 ounces each and a 0.99 length/diameter ratio, respectively.
Objective 4
A tensiometer demonstration trial was conducted with 4 Amish growers (under-represented clients, small farmers) of greenhouse tomatoes in SE Iowa. Their growing medium was field soil which was previously cropped with alfalfa. Although they installed microirrigation tubing they did not know when to water or how much to apply. Two equipment stations, each containing a 6-inch and 12-inch tensiometer, were established in each greenhouse and growers instructed on their use. Results indicated considerable soil moisture tension variability within a greenhouse. Also, acceptance of this water scheduling method differed among growers.
Impact of Work
The field day and grower demonstrations
offered participants the opportunity to observe microirrigation in a field
setting. Growers were able to gain ‘hands-on’ experience with the
system that, in some cases, improved tomato yield and quality.
Publications, Extension Presentations, Student Involvement
Taber, H. G. (Ed.). Annual Fruit/Vegetable Progress Report. 2002. Iowa State Univ. Coop. Ext. FG-601, pp.65.
Muscatine Island Summer Field Day and Tour, July 14, 2002. Participants visited a 200 acre microirrigation melon farm.
-- Presentation at field day by H. G. Taber, Title: Irrigation scheduling techniques for pepper production.
Student involvement: Darin Enderton, undergraduate horticulture student.