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«By BEE LING POH A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF ...»

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REDUCING DRIP IRRIGATION OPERATING PRESSURE FOR REDUCING EMITTER

FLOW RATE AND IMPROVING IRRIGATION MANAGEMENT

By

BEE LING POH

A THESIS PRESENTED TO THE GRADUATE SCHOOL

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2010 1 © 2010 Bee Ling Poh 2 To my family 3

ACKNOWLEDGMENTS

I would like to express my deep respect and sincere gratitude to my major professor, Dr. Eric Simonne, for his guidance, and patience (through numerous working lunches and manuscript revisions) to see me through the M.S. program. He has taught by example what it is to be a teacher and a researcher and I have picked up lifeskills that, I believe, would benefit me wherever I go. My heartfelt thanks to my advisory committee members, Dr. Xin Zhao and Dr. Danielle Treadwell, who were looking out for me in Fifield Hall and provided me with timely administrative support and words of encouragement. I would also like to thank my other committee members, Dr. Craig Stanley and Dr. Stephen Olson, for their technical support and advice.

My irrigation system would not work so well without the technical expertise of Mike Alligood. He constantly amazes me with his resourcefulness and perseverance to solve any problem on the farm. My thanks also to the crew in Live Oak who provided maintenance of my research plants.

I am indebted to my friends, Dr. Aparna Gazula, Dr. Francesco Di Gioia, Desire Djidonou, Sherry Kao and Pei-wen Huang, who provided that extra pair of hands to make my research work that much easier. My life has been much enriched by our friendships. I want also to thank Dr. Amy Simonne for opening and accepting me into her home when I first arrived and easing me into life in the U.S.

I would not be doing the MS program if not for the funding of Agri-Food and Veterinary Authority (AVA) of Singapore, and the support of my colleagues in AVA.

Special thanks to Lam-Chan Lee Tiang, Renee Chou and Leslie Cheong for their confidence and support of me, and to Fadhlina Suhaimi, Tay Jwee Boon and Thomas Tan, for covering my duties while I am away.

4 Finally, my deepest appreciation of my family who were constantly encouraging and backing me up, and had made my stay in the U.S. that much easier.

5

TABLE OF CONTENTS

page ACKNOWLEDGMENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF ABBREVIATIONS

Abstract

CHAPTER 1 INTRODUCTION

2 REVIEW OF LITERATURE

Units to Express Drip Irrigation Volumes

Soil Water Flow and Water Holding Capacity

Rootzone Water Holding Capacity

Water Movement in Sandy Soils

Keeping Water and Nutrients in the Crop Rootzone

Visualizing Soil Water Movement

Goal and Objectives of Project

3 EFFECT OF REDUCED IRRIGATION SYSTEM OPERATING PRESSURE ON

DRIP-TAPE FLOW RATE, WATER APPLICATION UNIFORMITY AND SOIL

WETTING PATTERN ON A SANDY SOIL

Background

Materials and Methods

Flow Rates and Uniformity Trials

Dye Tests to Visualize Wetted Zones

Results and Discussion

Flow Rates and Uniformity

Movement of Waterfront

Summary of Findings

4 EFFECT OF OPERATING PRESSURE, IRRIGATION RATE AND NITROGEN

RATE ON DRIP-IRRIGATED FRESH MARKET TOMATO NUTRITIONAL

STATUS AND YIELDS: IMPLICATIONS ON IRRIGATION AND

FERTILIZATION MANAGEMENT

Background

6 Results and Discussion

Crop Cycle and Weather Conditions

Flow Rates and Irrigation Volumes

Tomato Plant Petiole Sap NO 3 --N and K+ Concentration

Fresh Market Tomato Yields

Using Low OP for Early Crop Season

Summary of Findings

5 MOVEMENT OF THE WETTED FRONT UNDER DRIP-IRRIGATED

TOMATOES GROWN ON A SANDY SOIL

Background

Materials and Methods

Results and Discussion

6 CONCLUSION

LIST OF REFERENCES

BIOGRAPHICAL SKETCH

–  –  –

1-1 Production and value of fresh market tomato in the United States, 2007Comparison of drip irrigation characteristics for application of water, nutrients or fumigants.

2-1 Amount of water for a drip-irrigated acre at different bed spacings and wetted widths assuming an evapotranspiration of 0.10 inches per day.

2-2 Research showing decreased wetted depth and increased wetted width at low emitter flow rates

2-3 Research showing increased wetted depth and decreased wetted width at low emitter flow rates

2-4 Example of pressure losses due to friction in the components of a drip irrigation system.

2-5 Research carried out in Florida on effect of various irrigation volumes and durations on soil wetted depth and width.





3-1 Theoretical and measured flow rates for three drip tapes at 6 and 12 psi operating pressure and two lengths of 100 and 300 ft.

3-2 Emitter flow variation (q var ), coefficient of variation (CV), and uniformity coefficient (UC), and their ratings (Rt) for three drip tapes

4-1 Treatment combinations of nitrogen rate, operating pressure and irrigation rate for Spring 2008 and 2009 ‘Florida 47’ fresh market tomato production....... 78 4-2 Nitrate-nitrogen concentration in tomato petiole sap at selected growth stages in 2008 and 2009 for ‘Florida 47’ fresh market tomato production.......... 79 4-3 Potassium concentration in tomato petiole sap at selected growth stages in 2008 (A) and 2009 (B) for ‘Florida 47’ fresh market tomato production.............. 80 4-4 Seasonal fresh market tomato yields in number of 25-lbs cartons per acre for 2008 and 2009

–  –  –

1-1 Seepage irrigation used for fall tomato production with plastic mulched raised beds in a commercial farm in central Florida.

1-2 Overhead sprinkler irrigation mounted on a linear moving system in an experimental field in central Florida..

1-3 Drip irrigation used for spring tomato production with plastic mulched raised beds in an experimental field in north Florida.

2-1 Changes in hourly crop water requirement and crop evapotranspiration (ETc) within a 24-h period for open-field production of drip irrigated tomato................ 44 2-2 Longitudinal section of an Alpin-Blanton-Foxworth sandy soil beneath five emitters showing circular dye pattern after a single irrigation event................... 45 2-3 Calculated depth (A) and width (B) of water movement for a single emitter in response to increasing irrigation volumes

2-4 Theoretical changes in flow rate as irrigation operating pressure increases for a typical drip emitter.

2-5 Triple-compacted raised beds for strawberry production using a single drip tape in southern Florida.

3-1 Schematic diagram of treatment plots showing drip tape with shut-off valves to create irrigation treatment durations of 45, 90, 180 and 240 min

3-2 Transverse section of an Alpin-Blanton-Foxworth sandy soil beneath one emitter showing elliptical dye pattern after irrigating for 4 hours

3-3 Effect of irrigation volume on depth (A) and width (B) of wetted zone at operating pressure of 6 and 12 psi.

4-1 Target weekly irrigation schedule for Spring 2008 and 2009 ‘Florida 47’ fresh market tomato production with raised bed plasticulture system

4-2 Cumulative growing degree day during the growing seasons for Spring 2008 (30 Apr. to 8 July) and 2009 (8 Apr. to 1 July) in Live Oak, FL

4-3 Actual cumulative irrigation applied for Spring 2008 (A) and 2009 (B) ‘Florida 47’ fresh market tomato production with raised bed plasticulture system........... 84 5-1 Transverse section of an Alpin-Blanton-Foxworth fine sand showing a quasihorizontal blue dye pattern

–  –  –

5-3 Depth response of the waterfront to total volume of water applied on an Alpin-Blanton-Foxworth fine sand.

–  –  –

Chair: Eric H. Simonne Major: Horticultural Science The goal of this project is to determine if reducing irrigation system operating pressure (OP) could improve drip irrigation management and be specified as a UF/IFAS recommendation for irrigation scheduling. This was assessed through three objectives to compare a reduced OP of 6 psi to the standard OP of 12 psi. In the first objective to determine the effect on emitter flow rates, water application uniformity and soil water movement, flow rates for three commercial drip tapes were found to decrease to 0.13gph at 6 psi compared to 0.19-0.25 gph at 12 psi without affecting uniformity of irrigation at 100 and 300 ft lateral lengths. Using soluble dye as a tracer, depth (D) of the waterfront response to irrigated volume (V) was quadratic D = 4.42 + 0.21V –

0.001V2 (P 0.01, R2 = 0.72) at 6 psi, with a similar response at 12 psi, suggesting that depth of the wetted zone was more affected by water volume applied rather than by OP itself. The depth of wetted zone went below 12 inches when V was about 45 gal/100ft, which represented about 3 hours of irrigation at 6 psi and 1.8 hours of irrigation at 12 psi for a typical drip tape with flow rate of 0.24 gph at 12 psi. This implies that, for the same volume of water applied, reduced OP allowed extended irrigation without increasing the wetted depth. OP also did not affect the width (W) of the wetted front, which was

–  –  –

wetted width at reduced OP was 53% of the 28-inch wide bed, reduced OP should be used for two-row planting or drip-injected fumigation only if two drip tapes were used to ensure good coverage and uniform application. Reducing OP therefore offers growers a simple method to reduce flow rate and apply water at rates that match more closely the hourly evapotranspiration to minimize the risk of drainage and leaching losses.

The second objective studied the possibility of growing a tomato crop with reduced water (100% irrigation rate of 1000 gal/acre/day/string vs 75%) and nitrogen (N) fertilizer (100% N rate of 200 lb/acre N vs 80% and 60%) inputs at reduced OP. In one year, marketable yields were greater at 6 psi than at 12 psi (753 vs 598 25-lb cartons/acre, P 0.01) with no significant difference among N rate treatments. But in another year, marketable yields were greater at 12 psi (1703 vs 1563 25-lb cartons/acre at 6 psi, P = 0.05) and 100% N rate (1761 vs 1586 25-lb cartons/acre at 60% N rate, P = 0.04).

Irrigation rate did not have any significant effect (P = 0.59) on tomato marketable yields in either year with no interaction between irrigation rate and N or OP treatments. These results suggest that reduced OP may not be able to provide enough water to meet the needs of a fully growing crop and instead could be more appropriate for use with young plants when water demand is low.

For the third objective to determine soil water movement after a cropping cycle, it was found that response to OP was significant (P = 0.01) with maximum average wetted depths of 52 and 63 inches at 6 psi, and 64 and 67 inches at 12 psi, for the respective years of study. In the presence of plants, water moved in the soil at a lower rate of 0.09 inch/10gal/100ft compared to 0.9 inch/10gal/100ft without plants. However, the

–  –  –

reduced OP alone was not able to keep irrigated water within the crop rootzone of 12 inches. Overall, reducing OP using a commercially available pressure regulator is a simple, practical and inexpensive method to obtain low emitter flow rates that may help to reduce water and fertilizer inputs without compromising uniformity in small fields.

Based on these results, we propose that UF/IFAS irrigation recommendation specify reducing OP as a practice in irrigation scheduling to improve on-farm water and nutrient management.

–  –  –

Shrinking world water supplies and increased environmental conservation have put agriculture under intense pressure to reduce water use and minimize risks of pollution by fertilizers and pesticides. Agriculture is the principal user of all water resources, accounting for 70% of water withdrawals worldwide, with industry using nearly 21% and domestic use amounting to 9% (FAO, 2003). Irrigated agriculture produces 40% of the world’s food crops on 20% of arable land. To accommodate the food and fiber needs of the increasing world population, agriculture is expected to increasingly improve its water utilization to satisfy a 67% increase in food demand from 2000 to 2030 at a projected water usage increase of only 14% (FAO, 2006).

Common irrigation systems include seepage (or flood), overhead and drip irrigation (Locascio, 2006). Important attributes of irrigation systems are uniformity of water application, water use efficiency (defined as the ratio of water delivered to the crop to water pumped), and cost of installation and maintenance. In seepage irrigation (Figure 1-1), the presence of an impervious soil layer at 20 to 36 inch depth allows the establishment of a perched water table that supplies water to the rootzone by capillarity.

Although large amounts of water are required and water use efficiency is only 33%, seepage systems are used on 45% of irrigated crops in the U.S. as they are inexpensive to set up, easy to maintain and continuously supply water to the crop. In overhead irrigation (Figure 1-2), where water is applied to crops by solid set sprinklers, linear moves or center pivots, a much improved water use efficiency of about 75% is achieved. It is used on 50% of irrigated crops in the U.S. despite higher installation and maintenance costs than seepage systems.

–  –  –



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