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Iowa State University

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2001 Annual Report

Title:    Micro irrigation: 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 micro irrigation management strategies to promote natural resource protection and optimal crop production.

2.       To promote appropriate micro irrigation technologies through formal and informal educational activities.

 

Progress of Work and Accomplishments:

The research was conducted at the Muscatine Research Farm (eastern Iowa along the Mississippi river).This site is 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. The work on comparison of the tensiometer and watermark sensors in finer textured soils was completed in 2000, but the evaluation of irrigation scheduling methods continues.

 

Objective 1

 

Sweet bell pepper was the test crop to evaluate irrigation scheduling methods. Ammonium nitrate at 250 lbs/acre was banded over the row and rotovated in on May 8, 2001.After rainfall produced field capacity black plastic and trickle tubing was laid over the beds on May 14.

 

The trickle tubing was placed in the bed center approximately 2 inches deep. The trickle line was Chapin, turbulent twin-wall, 10ml with 9-inch openings to give a flow rate of 0.65 gpm/100 feet at 10 psi. Water source was a deep well.

 

Five-week old 'Brigadier' pepper transplants were set May 18, about one week after the frost-free date (25% chance).Planting arrangement was twin rows, 14 inches apart, on 4-foot wide plastic, with plants spaced 21 inches in-row.

 

Weather data collection included daily max/min temperature, wind speed, solar radiation, and relative humidity.

 

Tensiometers (Irrometer Co., Riverside, CA) were set at 6-inch, 12-inch, and 18-inch depth in each plot. Their position was between 2 plants and 6-8 inches from the trickle tubing. Readings were taken almost daily at 8 am.

 

Irrigation treatments were designed to compare four scheduling methods:

1) Soil moisture tension with a 6-inch tensiometer target of 10 cbars;

2) A target of 15 cbars;

3) ET * Kc, where ET calculated from the modified Penman equation through the ISU Ag Climate Station program, and Kc determined by percent crop canopy closure. The Kc value was never below 0.4; and

4) AzSched model using chili pepper as the bell pepper crop was not available. The AzSched irrigation efficiency was 85% and allowable depletion before irrigation set at 30%.

 

For treatments 1 & 2 the volume of water applied when the cbar target was reached was 0.12 inch, based on the following criteria: effective pepper rooting depth of 12 inches, wetting diameter of 12 inches, and 0.5-inch/foot AWC.

 

Water was applied twice daily, if needed, at 8 am and 2 pm. Normal crop culture and pest management practices for the area were followed. Additional N, as 32% uran, was applied through the irrigation at 10 lbs N/acre/week starting July 7 and ending July 16.

 

Harvest began July 30, 72 days after transplanting, and occurred weekly for three pickings ending August 14.

 

The irrigation-scheduling program was not initiated until June 25 or when the age of the transplants were 40 days and flower clusters were present. The Muscatine automated weather station and the AzSched calculated identical ETr values of 11.6 inches, from June 25 to August 14, 2001 (Table 1).

 

The AzSched calculated ETc at 4.92 inches while our trt. #3 calculated ETc at 5.72 inches. We used 3 levels of Kc, 0.32, 0.40, and 0.64 (Table 1).The AzSched program for chili peppers used similar values, except during rapid fruit enlargement where the AzSched Kc did not increase appreciably. Irrigation amounts for trt. #3 (ETc) were 5.2 inches and AzSched calculation was 3.40, but 4.08 inches was applied. More was applied than the schedule called for to prevent plant wilting. Volume of water applied to trts. 1 and 2 were similar at 7.30 inches. Tensiometer 6-inch depth readings fluctuated greatly in this coarse sand so that the 5 cbar differential between the two treatments was difficult to maintain. Rainfall for the period was 3.30 inches, which was not considered in trts. 1, 2 or 3.

 

Obviously, the AzSched chili pepper program cannot be used for bell pepper, but it allowed us to gain familiarity with the program.

 

Total fruit harvest was lowest for the AzSched treatment (Table 2).This effect was the result of low fruit number. However, there was no significance among treatments for marketable yield. There was a high incidence of cull fruit (small, severely misshapen), about 45%, in this trial because of unusually high night temperature during fruit development. Marketable fruit size was lowest for the Etc and AzSched treatments, at 4.6 ounces (Table 3).The L/D ratio, a measure of fruit quality or blocky appearance, was closest to 1.0 for the AzSched treatment, but not different from 10 cbars or the ETc treatment (trt. 3).

 

Soil water tension somewhat reflected the volumes of water added (Fig. 1).This was more noticeable at the 12-inch depth where ETc and AzSched treatments were significantly drier than the cbar target treatments. There was a high standard deviation for the 6-inch tensiometer readings among the reps, probably due to inaccurate placement and water channeling in this coarse sand. July 8 to 19 was a high evaporative demand period with ETr averaging 0.25 inch/day. The 6-inch tensiometer indicated we did not maintain the 10 or 15 cbar target even though 0.12-inch of water was added twice per day (Fig. 1). However, the 12-inch placement soil moisture tension was consistent at 10-12 cbars.

 

For treatments 1-3, similar total yield, water use efficiency was highest for the ETc treatment at 3592 lbs of fruit/inch, compared with 3041 lbs/inch for the cbar treatments. At the 12-inch depth the 10 cbar treatment remained near field capacity most of the season (Fig. 1).The ETc and AzSched were > 40 cbars several days after July 8 - a period of fruit set and enlargement. At 50 cbar, this coarse sandy soil has < 65% of the water held at field capacity. Even at the 18 inch depth the AzSched treatment soil moisture tension was high for this soil type.

 

Undoubtedly, the Kc factor was too low in both the ETc and AzSched treatments. (Smittle et al. (1994)) developed daily ET/ETp factor values for bell pepper grown on similar coarse sand soils in Georgia. Utilizing their regression equations based on plant age and employing a conversion for Esp. as suggested by Brady et al. (1995) the corresponding Kc values would be almost double (Table 1). The calculated crop use would be 9.67 inches or 84% of ETr, a value that seems high. The 10 cbar treatment crop use of 7.3 inches represents 63% of ETr.

 

Objective 4

 

A presentation, with handouts, was given at the Great Plains Vegetable Conference, St. Joseph, MO with > 300 grower attendance. Also, proper placement of tensiometers for micro irrigation was emphasized at a summer field day.

 

Work Planned for 2002

Continue the evaluation of tensiometer set points for high pepper yields and efficient water use. Varieties will be evaluated for adaptability to the region.

 

 

 

 

Literature Cited

 

Bracy, R. P., R. J. Edling, and E. B. Moser.1995.Drip-irrigation management and fertilization of ell pepper in a humid area. Micro irrigation for a Changing World: Conserving Resources/Preserving the Environment, Ed. F. R. Lamm, pp. 181-186.

 

Smittle, D. A., W. L. Dickens, and J. R. Stansell.1994.Irrigation regimes affect yield and water use by bell pepper. J. Amer. Hort. Soc. 119:936-939.

 

Publications

Taber, H. G. (Ed.).Annual Fruit/Vegetable Progress Report.2000.Iowa State Univ. Coop. Ext. FG-601. pp. 27-29 and p. 58.

 

Taber, H. G.2001.Petiole sap nitrate sufficiency values for fresh market tomato production. J. Plant Nutr.24: 945-959.

 

Table 1.Crop coefficient and ETc for pepper irrigation models, Muscatine, IA.

 

                                    ETr 1    Trt. 3, Selected 2          Trt. 4, AzSched          Plant Age, GA 3
 

Time Period

inches

Kc

inches

Kc

inches

Kc

inches

Jun 25 to Jul 8

3.41

.32

1.11

.34

1.00

.72

2.46

Jul 8 to Jul 18

2.49

.40

1.00

.43

0.98

.82

2.17

Jul 19 to Aug 14

5.68

.64

3.61

.48

2.92

.91

5.17

Total

11.58

 

5.72

 

4.92

 

9.67

1 ET calculation was identical for AzSched and the ISU climate station program.

2 Crop canopy coverage.

3 Smittle et al. (1994) ET/ETp values for a bell pepper crop grown on a similar coarse sand. Converted to Kc as used by Bracy et al. (1995).

 

 

 

Table 2.Effect of irrigation scheduling on yield of bell peppers, coarse sandy soil, Fruitland, IA, 2001

                                    ------- Yield, cwt/acre -------
 

Treatment

Total

Marketable

Cull1

Total No. 2

Cull, %

1.10 cbars

223 A 3

121

102

126 A

46

2.15 cbars

221 A

121

99

122 AB

45

3.Etc

185 AB

101

84

105 AB

45

4.AzSched

154 B

92

62

99 B

40

1 Cull = very small, severely misshapen - pointed, curved, bent, C shaped, indentation

2 Total No. = number of fruit over 3 harvest on a per plot basis

3 Mean separation by Waller-Duncan k-ratio test.

Table 3.Marketable fruit size and shape of 'Brigadier' bell pepper as affected by irrigation treatment at the 1st and 2nd harvests.

 

 

 

                                    -- July 30---                 --- August 8----
 

Treatment

Size, oz.

L/D

Size, oz.

L/D

1.10 cbars

5.3 A 1

1.04

5.0 AB

1.07 AB

2.15 cbars

5.2 A

1.04

5.2 A

1.11 A

3.ETc

4.6 A

1.03

4.2 B

1.05 AB

4.AzSched

4.7 AB

1.07

4.5 AB

1.03 B

1 Mean separation by Waller-Duncan k-ratio test

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