Lettuce and Lemons
Low Desert Irrigating and Fertilizing

Automated fertilizer injection system.Yuma produces a major portion of the nation’s winter lettuce and lemons. At the same time, growing these crops in the desert’s warm climate requires a lot of water. Production agriculture in general used 81% of the total water consumed in Arizona, according to a 1990 figure.

How can growers use less water and still produce high quality vegetables and citrus in the desert? Two series of experiments in progress at the Yuma Agricultural Center (YAC) are testing ways to improve water efficiency.

“The objective of this multidisciplinary project is to evaluate and develop efficient irrigation practices for vegetables and citrus in the low desert regions of Arizona,” says Charles Sanchez, soil scientist and director of the YAC.

“We’re being challenged to use resources more effectively, both water and fertilizer,” he explains. “Water conservation is of paramount importance not only to save water but to enhance the efficient use of fertilizer as well. When you use water efficiently, it enables you to use fertlizer more effectively, particularly nitrogen.”

Inefficient irrigation contributes to nitrogen losses from soils. As growers add more nitrogen, the excess may leach into the groundwater. Irrigation practices in some areas of Yuma also contribute to salt loading in drainage water flowing from Arizona to farmland in Mexico, according to Sanchez. Properly managed irrigation can reduce these losses, and research in progress may identify methods and strategies that can produce crops of the highest yield and quality at the lowest cost to both the grower and the environment.

UA faculty have designed a series of experiments in Yuma to test different types of irrigation in a field setting. The research analyzes and compares pressurized irrigation systems, such as microsprinklers and buried drip, with traditional furrow and flood irrigation. Yuma growers commonly furrow irrigate lettuce and flood irrigate lemons.

UA faculty involved in the project along with Sanchez include John Palumbo, entomologist; Mike Matheron, plant pathologist; Paul Brown, soil scientist; David Still; plant scientist, Mark Wilcox, agricultural and natural resources Extension faculty; and Glenn Wright, plant scientist.

“Pressurized irrigation is not big in this part of the state, but it’s very big in California and Florida, so we know that some growers may eventually want to try it,” Sanchez says. “We want to assist them in choosing the best tools for it when they do.” Previous research conducted on citrus at the Yuma Agricultural Center showed that trickle, spray and bubbler irrigation systems improved irrigation effficiency substantially over the traditional flood irrigation.

“There is a tendency for growers to apply generous amounts of water to produce because of anxiety about crop quality and lack of sufficient information to do otherwise,” Sanchez notes. Growers need to produce a crop of both high yield and quality to make a profit. The project specialists plan to research and develop efficient scheduling and water management techniques and then offer this information to growers through education and training outreach programs.

Lettuce Research

Although pressurized irrigation, such as trickle methods, can help save the amount and the cost of water, Sanchez recognizes that these systems are expensive to install. In addition, growers in the area practice complex crop rotations and multiple cropping patterns such as vegetables to cotton, alfalfa or wheat, making it difficult to establish a permanent or semi-permanent drip system.

The iceberg lettuce research, sponsored by the Arizona Iceberg Lettuce Research Council, involves five acres of different experiments with the following objectives:

  1. Compare lettuce grown with buried drip to lettuce grown by furrow irrigation
  2. Evaluate irrigation regimes for furrow-irrigated lettuce
  3. Evaluate combinations of water and nitrogen for lettuce produced by buried drip.

“If growers are going to switch to buried drip, we’d like to help them decide the best way to do it,” Sanchez says. “Last year we put in a new system in the valley for irrigating lettuce. We had two experiments; the first was buried drip arranged in statistically valid experimental design with various combinations of water and nitrogen.

“However, recognizing that many growers don’t want to go to a drip system because of cost, hassles and complicated rotations in Yuma, we also have a second experiment.” This uses a furrow irrigation system to find the best way to irrigate efficiently, using different moisture management tools such as tensiometers, neutron probes, and AZMET (computerized weather ) data.

Differing amounts of water are applied to the lettuce during the growing season, using both drip and furrow systems. Throughout the experiments, researchers sample whole lettuce plants to determine plant growth and development.

Lemon Research

Arizona citrus grows on sandy soils in the low desert, where water evaporates faster. This is the first study to examine the impact of irrigation frequencies on fruit sizing of ‘Lisbon’ lemons. The research is funded by the Arizona Citrus Research Council, and encompasses four acres of water and microjet experiments on ‘Lisbon’ lemons, and flood irrigation efficiency on five acres of lemons. Objectives include the following:

  1. Determine the impact of different flood irrigation regimes on earliness, quality and yield of ‘Lisbon’ lemons on sandy soil.
  2. Evaluate the response of young lemon trees to water and N combinations under spray irrigation.

“We recognize the reality that many growers continue to use flood irrigation because of the higher cost and high technology aspects of pressurized flow,” Sanchez admits. “So we have a flood irrigation project on lemons. We want to find the ideal moisture regime for lemons: what produces the most significant yield, quality and size.”

The researchers are irrigating the orchards at different moisture regimes of 25%, 40%, 55%, and 70% moisture water depletion. For example, this means that for the first regime, they will irrigate the trees when the soil is depleted of 25% of its moisture, as measured with a neutron probe or other moisture measuring device.

For the other experiment, they will feed varying concentrations of nitrogen through the spray irrigation system to find out which is best for the tree and leaches least into the ground, depending on the amount of water applied to the crop.

Selected preliminary results include the following:

  1. Optimal fruit growth and yield was obtained at approximately 40% soil moisture depletion.
  2. Tree-growth for the highest micro-spray irrigation regime was greater than for flood irrigation.

Article Written by Susan McGinley, ECAT, College of Agriculture
This is part of the 1996 Arizona Experiment Station Research Report
This document is located at http://ag.arizona.edu/pubs/general/resrpt1996/lettuce.html
Return to index for 1996 report

Researcher:

Charles Sanchez, Yuma Agricultural Center
Phone: (520) 782-3836