Progress 07/01/11 to 06/30/16

Outputs
Target Audience:The audience for this project is professionals working in landscape irrigation management and water policy, and anyone irrigating landscape trees in the low desert Southwest. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?One undergraduate student each year studying Plant Sciences was employed to assist in data collection in the field, analyze tree ring growth, enter data, and prepare summary graphs. This student received training in research methodologies, preparation of tree samples for analysis, measuring growth rings, and summarizing data in graphs. Two field days in fall 2013 and 2014 were attended by about 200 participants including green industry personnel, municipal employees, and some Master Gardeners. They learned about the study in a lecture followed by the opportunity to rate plant quality in the field without knowing the irrigation treatments, which we revealed later. Participants were often surprised about the growth and some quality issues of trees based on the irrigation treatments. Ongoing and final results of the study were reported at conferences, tree health workshops, and seminars attended by arborists, landscapers, nursery personnel, horticulture industry representatives, and landscape designers and architects. In total U. Schuch presented at 10 such events in Arizona and the Southwest region to over 850 attendees. She also presented results as posters or oral presentation at two national and one international horticulture conference to other academics. Attendees at the regional and local presentations were usually offered continuing education credits for arborist certification. How have the results been disseminated to communities of interest?Results were disseminated at field days, conferences, workshops, seminars as described above to over 850 attendees. Several articles were published about the study in trade magazines with a circulation of over 4,000 directed to green industry personnel throughout the Southwest. A brief summary was provided to the Arizona Forestry Department for one of their blogs. In addition to green industry personnel, Master Gardeners and representatives from home owner associations attended some of the presentations. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Water is essential for irrigating landscape plants in the desert Southwest. Trees provide many benefits including shade and cooling. Plants vary in their water requirements and it is important to estimate the minimum and optimum amount of water necessary to maintain plants while conserving water. The actual water use or need of plants has rarely been quantified. Knowing how much water a tree needs to survive or to grow to its mature size will be helpful in applying irrigation water more judiciously. The study reported here was conducted after trees were well established. They were watered with three different levels of irrigation for four years followed by one year without irrigation to simulate drought conditions. Plant growth and health of the nine types of trees (species) was monitored during the five years of study. After 4 years of irrigation treatments, trees of similar size were grown with half the amount of water applied to the wet treatment for mesquite, palo verde thornless hybrid, 'Red Push' pistache, Desert willow 'Art's Seedless', Texas ebony, and Southern live oak. All species increased in size with fewdifferences for the same species receiving different irrigation treatments. Severe symptoms of deficit irrigation including leaf or branch damage, dieback, or plant death started to develop on Arizona cypress, Afghan pine, and Rio Grande ash, especially under the dry and sometimes medium irrigation treatment, even before the onset of drought. After one growing season of simulated drought without supplemental irrigation mesquite, desert willow, palo verde, and pistache maintained good quality.Overall quality of Afghan pine, Arizona cypress, and Rio Grande ash was unacceptable and plant health deteriorated rapidly with some trees dying.Texas ebony could not tolerate an abrupt lack of irrigation once accustomed to regular irrigation. Irrigation recommendations for each tree species were developed and will result in significant water savings if adopted by landscapers and anyone irrigating trees. Using the minimum amount of water necessary to irrigate the five species with extremely low water requirements in this studywill allow the growth of twice as much green canopy compared to tree species that require the high amount of water such as pine and cypress. Green industry personnel, municipalities, city planners, and homeowners can use this information to select trees for urban plantings, keeping in mind the water required to allow them to develop into mature, healthy specimens. Trees growing in #15 containers were transplanted into a field January 2007 at the Maricopa Agricultural Center in Arizona. From May 2010 until March 2014, three different irrigation treatments were applied to determine how tree growth and quality are affected by different irrigation regimes. Irrigation treatments were applied as a percentage of the reference evapotranspiration (ETo) at the site. The bubbler irrigation system delivered the wet, medium, and dry treatment consisting of 80%, 60%, or 40% of ETo from May until October and 40%, 30%, or 20% of ETo from November to April. Trees in the wet treatment receiving a total of about 1,000 gallons of water per year while those in the medium and dry treatment received three quarter or half of that amount per year. In April 2014 the irrigation system was removed to determine how trees respond when they are suddenly left to rely only on natural rainfall. In January 2015 trees were cut close to the ground and tree rings were analyzed. Data collection included measurements of plant height, trunk diameter, and canopy diameter twice each year. Monthly quality ratings evaluated foliage appearance and density, health problems, and overall appearance. The experimental site was located in the arid climate of the Sonoran Desert at an elevation of 1180 feet in Arizona where summer temperatures exceed often 100°F up to several weeks and freezing temperatures occur in December and January. ETo at the experimental site ranged from 2 inches/month in December to 11 inches/month in June, the month with the highest ETo demand. Rainfall is almost equally divided between the summer rains from July to September and during the winter months. The frequency of irrigation differed substantially between treatments resulting in about 10 irrigation events for the dry and 21 events for the wet treatments per year. Irrigation during the summer was applied more than once per week for the wet and only every other week for the dry treatment. Winter irrigation for the wet treatment was applied about every three weeks, whereas trees under the dry treatment went without irrigation for over four months. The three irrigation treatments had no effect on height, canopy area, and trunk diameter over a period of four growing seasons. The one exception was the Southern live oak where the dry treatment had a smaller canopy area than the wet treatment. Representative trees of each species at the beginning of the irrigation treatments were healthy and well established. By March 2014, all plants had significantly increased in size, particularly in canopy area. Palo verde grew fastest, followed by mesquite, pistache, and desert willow, while the other trees grew at a slower rate. Canopy area increase from the beginning of irrigation treatments until the onset of drought increased 520% for palo verde, 270% for mesquite, about 100% for pistache and desert willow, and around 30% for live oak, pine, and ash. At the end of the experiment palo verde trees were about 20 feet tall, and had a trunk diameter of almost 10 inches. The smallest trees, Texas ebony and live oak were 8 and 9.5 feet tall with trunks of 3.6 inches diameter. Tree ring growth after five years of study showed no difference between irrigation treatments for each species. All plants were in good condition in 2010 when the irrigation treatments started. Their ratings were between 4 and 5 (5 being the highest) for overall plant quality, indicating that they had foliage, flowers, and fruit as would be expected of a healthy tree, and there was no evidence of insect, disease, or abiotic stress. Quality ratings of palo verde, mesquite, pistache, desert willow and Texas ebony never dropped below 4.0 (high quality, good appearance) for any treatment from May 2010 until March 2014. Although all plants continued to increase in size, overall quality of Afghan pine, Arizona cypress, Rio Grande ash, and live oak under the dry or medium irrigation treatment started to decline in quality below the minimum acceptable rating of 3.0. Many of the stressed trees showed some recovery during early spring, but then continued to decline again as temperatures increased. During the simulated drought that started in March 2014 pistache, mesquite, desert willow, and palo verde were not detrimentally affected by lack of irrigation during the growing season. During the simulated drought, the average overall quality of Arizona cypress, Afghan pine, Texas ebony and Rio Grande ash was at or below acceptable quality. Summer rains starting in July caused a flush of new foliage in several trees and some rain in fall helped many trees recover. However, overall quality of pine, cypress, ash, and some Texas ebony remained unacceptable. At the conclusion of the study in January 2015 the following species had 100% survival: mesquite, desert willow, pistache, and Southern live oak. Survival of the other species was between 78% and 94%. Results from this study lead to irrigation recommendations of 40/20% of reference ETo in summer and winter, respectively for palo verde, mesquite, pistache, desert willow, and Texas ebony. Recommended rates for live oak are 60/30 and for Arizona cypress, Afghan pine, and Rio Grande ash 60-80% ETo year-round with ash cutting this rate in half during the dormant period. Using this approach can sustain healthy and functional green canopies in urban landscapes of the Southwest.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2016 Citation: Schuch, U.K., T. Mahato, and E. Martin. 2016. Response of desert-adapted landscape trees to deficit irrigation. Acta Horticulturae 1112:193-199.

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:The audience for this project is professionals working in landscape irrigation management and water policy, and anyone irrigating landscape trees in the low desert Southwest. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?An undergraduate student studying Plant Sciences was employed to collect data on the tree ring analysis. A field day at the site of the study was held on October 21, 2014 with 94 green industry personnel and some Master Gardeners attending. Three hours of ISA CEU's were granted for participants. The field day included presentations and an exercise in the field to rate tree quality. How have the results been disseminated to communities of interest?Results from the study were presented to about 220 green industry professionals and some Master Gardeners through talks at the following venues: Desert Horticulture Conference in May 2015 in Tucson and the SHADE Conference in August 2015 in Phoenix. An article about the study was published in the trade journal Southwest Trees and Turf that is distributed to landscape professionals in the Southwest. What do you plan to do during the next reporting period to accomplish the goals?Publish results in refereed journals and on our commercial horticulture website.

Impacts
What was accomplished under these goals? The impact of the project to date is that welearned thatfive of the nine tree species tested can be grown under a range of irrigation treatments from wet to dry without differences in plant size or quality. Desert willow, mesquite, pistachio 'Red Push', blue palo verde hybrid, and Texas ebony can be grown with less than half the amount of water provided in the wet treatment compared to the dry treatment and result in the same size plant with a functional, aesthetically acceptable canopy. Water savings per tree when using the dry compared to the wet treatment are 580 gallons per year for one treeplanted 8 years ago from a #15 container.We also learned that Eldarica pine, Arizona cypress, Arizona ash, and live oak are not tolerant of the dry treatment followed by 9 months of permanent drought and willdevelop unacceptable canopy quality unless they receivethe medium or wet treatment. This requires 740 gallons for the medium or 1,040 gallons for the wet treatmentof irrigation water per year and tree for aesthetically acceptable and functional trees. This study is a long-term research and demonstration project and has been maintained with the following irrigation treatments from May 2010 until March 2014. Irrigation treatments were based on applying 80% (wet), 60% (medium), and 40% (dry) of reference evapotranspiration (ETo) from May to October and half of that (40%, 30%, and 20% of ETo) from November to April. In March 2014 the irrigation was turned off and trees received only moisture from precipitation at the site until January 2015. This was done to determine how trees are affected by permanent drought, similar to when irrigation is either malfunctioning or is turned off on purpose. Monthly evaluations of canopy density and observations of tree health were recorded in November 2014. An overall quality rating was given to each plant to determine whether it still fulfilled the criteria of a healthy, functional landscape tree. In January 2015 trees were cut closely above the soil and trunk samples were collected. Before trees were cut, plant height, stem circumference, canopy volume, and growth index were determined. Trunk samples were dried at room temperature, cut and sanded for analysis. Tree ring widths of the last 7 years were measured on each sample. All data were analyzed statistically with the program SAS. When analysis of variance indicated significant differences, means were compared by Student-Newman-Keuls Test. No differences between irrigation treatments for each species were found in January 2015 in plant height, stem area, canopy volume, and growth index with the exception of canopy volume in Afghan pine and growth index in southern live oak. The live oak result was consistent with previous year's results where the wet treatment had a larger canopy area than the other two treatments. Overall these results suggest that a similar area of shade from tree canopies of the same species can be grown with half the amount of water as in the wet treatment for desert willow, palo verde, mesquite, Texas ebony, and pistachio. Although some of the other species had similar size canopies their overall quality and health status was not satisfactory to grow them under the reduced irrigation regime of the dry treatment. Canopy density of 'Rio Grande' ash, pine, Arizona cypress, and Texas ebony was lowest among the tree species, and not acceptable for some treatments. Canopy density decreased for several species as the drought progressed. By the end of the year as temperatures were cooling and aided by the fall rains some plants recovered and grew new foliage. However, overall quality of pine, cypress, ash, and some ebony remained unacceptable. Texas ebony, a native species, was intolerant of sudden drought. Annual tree ring growth for all species showed a peak in 2008, one season after transplanting. Species differed significantly with palo verde, mesquite, and pistachio growing fastest. All species grew less as the experiment progressed, especially in the final season when no more irrigation was provided. Annual year ring growth was not consistently different between species. Afghan pine had greater annual growth in the last three years for the wet compared to the medium and or the dry treatments. Southern live oak showed the most consistent trend of dry irrigation treatment resulting in less growth than the medium and the wet one having the greatest growth. Ash trees grew more in 2011, 2012, and 2013 under the wet than dry treatment. Annual tree ring growth of live oak was consistently greater under the wet than dry treatment from 2010 to 2014.

Publications

• Type: Other Status: Published Year Published: 2015 Citation: Schuch, U.K. 2015. Irrigation Needs of Landscape Trees. Southwest Trees and Turf 21(1):5
• Type: Conference Papers and Presentations Status: Awaiting Publication Year Published: 2016 Citation: Schuch, U.K., T.R. Mahato, J. Subramani and E.C. Martin. 2016. Response of desert-adapted landscape trees to deficit irrigation. Acta Horticulturae.

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: The audience for this project is professionals working in landscape irrigation management and water policy, and anyone irrigating landscape trees in the low desert Southwest. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? An oral paper was presented at the International Horticulture Conference in Brisbane, Australia in August 2014. A field day at the site of the study was held on October 21, 2014 with 94 green industry personnel and some Master Gardeners attending. Three hours of ISA CEU's were granted for participants. The field day included presentations and an exercise in the field to rate tree quality. How have the results been disseminated to communities of interest? Results from the study were presented to about 150 green industry professionals and Master Gardeners through talks at the following venues: Sonoran Desert Master Gardener Conference, Tucson, AZ September 12, 2014 and Arizona Community Tree Council Annual Conference, Prescott, AZ, September 19, 2014; A summary of the study was prepared and published through the Arizona State Forestry newsletter in December 2014. What do you plan to do during the next reporting period to accomplish the goals? The experiment will be terminated in January 2015 when trees of five species will be cut down and cross sections of the stem will be collected to study tree ring growth. Cross sections of the trunk will be harvested, dried, and prepared to measure year ring growth during the experimental period and compare whether the tree irrigation treatments affected annual stem growth.

Impacts
What was accomplished under these goals? The impact of the project to date is that we learned that five of the nine tree species tested can be grown under a range of irrigation treatments from wet to dry without differences in plant size or quality. Desert willow, mesquite, pistachio 'Red Push', blue palo verde hybrid, and Texas ebony can be grown with less than half the amount of water provided in the wet treatment compared to the dry treatment and result in the same size plant with a functional, aesthetically acceptable canopy. Water savings per tree when using the dry compared to the wet treatment are 580 gallons per year for one tree planted 8 years ago from a #15 container. We also learned that Eldarica pine, Arizona cypress, Arizona ash, and live oak are not tolerant of the dry treatment followed by permanent drought since March 2014 and will develop unacceptable canopy quality unless they receive the medium or wet treatment. This requires 740 gallons for the medium or 1,040 gallons for the wet treatment of irrigation water per year and tree for aesthetically acceptable and functional trees. This study is a long-term research and demonstration project and has been maintained with the current treatments since May 2010. Irrigation treatments are based on applying 80% (wet), 60% (medium), and 40% (dry) of reference evapotranspiration (ETo) from May to October and half of that (40%, 30%, and 20% of ETo) from January through April and November to December. Irrigation treatments were applied as planned during the experimental period until the beginning of March when the irrigation was turned off and trees received only moisture from precipitation at the site. This was done to determine how trees are affected by permanent drought, similar to when irrigation is either malfunctioning or is turned off on purpose. Plant height, canopy width, and caliper of the stem were measured in March and September 2014. Data was analyzed by analysis of variance to determine whether the irrigation treatments resulted in different growth. Monthly evaluations of canopy density, phenological observations (flowering, fruits), and observations of tree health were recorded. An overall quality rating was given to each plant to determine whether it still fulfilled the criteria of a healthy, functional landscape tree. The three irrigation treatments resulted in different irrigation frequencies. Plants in the wet, medium, and dry treatment received 22, 16, and 10 irrigations over a 12 month period leading up to the end of irrigation in March 2014.Total ETo was 75.7 inches and precipitation was 10.4 inches during the 12 months at the study site. The fast growing species in descending order were palo verde hybrid, mesquite, desert willow, and pistache based on their growth index. Palo verde hybrid trees were the tallest followed by pistache, desert willow, Elderica pine, and mesquite. Trunk area was largest for palo verde hybrid trees, followed by pistache, mesquite, desert willow, and Elderica pine. Smallest trees based on growth index and trunk area were live oak and Arizona ash. All species maintained or increased in height, growth index, and trunk surface area, but no significant differences in growth of the same species receiving the different irrigation treatments were recorded with a few exceptions. Live oak under the wet treatment had a larger canopy volume than those under the medium or dry treatments and in Afghan pine the medium treatment resulted in larger canopy volume than the other two treatments. Tree quality was higher in Afghan pine and live oak under the wet treatment. Canopy density rating was greater in Arizona cypress under the wet treatment. All other species were not affected in density canopy, plant health, and overall quality by the different irrigation treatments. Symptoms of drought were starting to develop in spring and progress through the summer as foliage dieback, terminal branch dieback, or loss of interior foliage on conifers. Overall quality of Arizona cypress, Elderica pine, Arizona ash, and live oak is declining due to reduced foliage cover of trees in the dry treatment. Two ash, one Arizona cypress and one Texas ebony died in 2014.

Publications

• Type: Other Status: Published Year Published: 2014 Citation: Schuch, U. 2014 Determining Irrigation Needs of Landscape Trees. Urban Tree Talk Newsletter, Arizona State Forestry 4th quarter.

Progress 01/01/13 to 09/30/13

Outputs
Target Audience: The audience for this project is professionals working in landscape irrigation management and water policy, Master Gardeners and anyone irrigating landscape trees in the low desert Southwest. Changes/Problems: The study will be continued as described until February 2014when the irrigation waterwill be turnedoff to determine how the nine species of landscape trees in this study will survive under permanent drought. We will evaluate tree growth and quality for another 12 months andplant growth measurements and quality evaluationdata will be collected as described in the original study plan. Another field day for landscape professionals and Master Gardenerswill be held in October 2014. The study will be terminated in February 2015 because the canopies of the fast growing tree species are encroaching on neighboring trees. What opportunities for training and professional development has the project provided? An oral paper was presented at the annual conference of the American Society for Horticultural Sciences. How have the results been disseminated to communities of interest? A field day was organized and advertised to landscape professionals, water agencies, and Master Gardenersin August and September 2013. The field daywas held in October 2013. What do you plan to do during the next reporting period to accomplish the goals? The experiment willcontinue as described in the original study plan until February 2014 when the irrigation waterwill be turnedoff to determine how trees in this study will survive under permanent drought. We will evaluate tree growth and quality for another 12 months andplant growth measurements and quality evaluationdata will be collected as described in the original study plan. Another field day for landscape professionals and Master Gardenerswill be held in October 2014.

Impacts
What was accomplished under these goals? The impact of the project to date is that welearned thatfive of the nine tree species tested can be grown under a range of irrigation treatments from wet to dry without differences in plant size or quality. Desert willow, mesquite, pistachio 'Red Push', blue palo verde hybrid, and Texas ebony can be grown with less than half the amount of water provided in the wet treatment compared to the dry treatment and result in the same size plant with a functional, aesthetically acceptable canopy. Water savings per tree when using the dry compared to the wet treatment are 580 gallons per year for one treeplanted 7 years ago from a #15 container.We also learned that Elderica pine, Arizona cypress, Arizona ash, and live oak are not tolerant of the dry treatment and willdevelop unacceptable canopy quality unless they receivethe medium or wet treatment. This requires 735 gallons for the medium or 1,029 gallons for the wet treatmentof irrigation water per year and tree for aesthetically acceptable and functional trees. This study is a long-term research and demonstration project and has been maintained with the current treatments since May 2010. Irrigation treatments are based on applying 80% (wet), 60% (medium), and 40% (dry) of reference evapotranspiration (ETo) from May to October and half of that (40%, 30%, and 20% of ETo) from January through April and November to December. Irrigation treatments were applied as planned during the experimental period.Plant height, canopy width, and caliper of the stem were measured in March and September. Data was analyzed by analysis of variance to determine whether the irrigation treatments resulted in different growth. Monthly evaluations of canopy density, phenological observations (flowering, fruits), and observations of tree health were recorded. An overall quality rating was given to each plant to determine whether it still fulfilled the criteria of a healthy, functional landscape tree. Soil moisture data was collected from three species (palo verde hybrid, Arizona cypress, and Arizona ash) that were irrigated according to the medium treatment. Time domain reflectometry (TDR) data was collected one day after an irrigation event and immediately before the following irrigation event. Results of the study were presented at the annual conference of the American Society for Horticultural Science in July through an oral presentation andan abstract of the presentation was published in the conference proceedings. The three irrigation treatments resulted in different irrigation frequencies. Plants in the wet medium and dry treatment received 21, 15, and 9 irrigations over a 12 month period compared to plants in the dry treatment. In summer, irrigation was applied every 6, 8, and 13 days for the wet, medium and dry treatments, respectively. In winter the longest interval between irrigation was 109, 156, and 189 days for the wet, medium, and dry treatment, respectively. Total ETo was 73.8 cm and precipitation was 7.7 cm during 2013 at the study site. The fast growing species in descending order were palo verde hybrid, mesquite, desert willow, and pistache based on their growth index. Palo verde hybrid trees were the tallest followed by pistache, desert willow, Elderica pine, and mesquite. Trunk area was largest for palo verde hybrid trees, followed by pistache, mesquite, desert willow, and Elderica pine. Smallest trees based on growth index and trunk area were live oak and Arizona ash. All species maintained or increased in height, growth index, and trunk surface area, but no significant differences in growth of the same species receiving the different irrigation treatments were recorded during 2013. Deficit irrigation symptomsstarted to develop in spring and progress through the summer as foliage dieback, terminal branch dieback, or loss of interior foliage on conifers. Overall quality of Arizona cypress, Elderica pine, Arizona ash, and live oak is declining due to reduced foliage cover of trees in the dry treatment.

Publications

• Type: Other Status: Published Year Published: 2013 Citation: Schuch, U.K., E. Martin, T. Mahato, and J. Subramani. 2013. Performance of Landscape Trees in the Semi-Arid Southwest under Three Irrigation Regimes. http://ashs.org/abstracts/2013/abstracts13/abstract_id_15759.html

Progress 01/01/12 to 12/31/12

Outputs
OUTPUTS: This project investigates the response of nine commonly planted landscape plants to different irrigation treatments. The study is considered a long-term research and demonstration project and has been maintained with the current treatments since May 2010. Irrigation treatments were based on applying 80% (wet), 60% (medium), and 40% (dry) of reference evapotranspiration (ETo) from May to October and half of that (40%, 30%, and 20% of ETo) from January through April and November to December. Plant height, canopy width, and caliper of the stem were measured in March and September. Data was analyzed by analysis of variance to determine whether the irrigation treatments resulted in different growth. Monthly evaluations of canopy density, phenological observations (presence of flowers and fruit), and observations of tree health were recorded. An overall quality rating was given to each plant to determine whether it still fulfilled the criteria of a healthy, functional landscape tree. Soil moisture data was collected from three species (palo verde hybrid, Arizona cypress, and Arizona ash) that were irrigated according to the medium treatment. Time domain reflectometry (TDR) data was collected one day after an irrigation event and immediately before the following irrigation event. Results of the study were presented at the annual Desert Horticulture Conference to green industry personnel and water policy personnel through a presentation. A synopsis of previous irrigation treatments that varied in frequency but received the same amount of water was published in the Southwest trade journal The Arizona Landscape Contractors Association (ALCA) Influence. PARTICIPANTS: The study is done in cooperation with faculty from the School of Plant Sciences and the Department of Agricultural and Biosystems Engineering at the University of Arizona. TARGET AUDIENCES: The audience for this project is professionals working in landscape irrigation management and water policy. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The three irrigation treatments resulted in different irrigation frequencies. Plants in the wet treatment received about twice the number of irrigations compared to plants in the dry treatment and those in the medium treatment were in between for the number of irrigations. In summer, irrigation was applied every five, six and seven days for the wet, medium and dry treatments, respectively. In winter the longest interval between irrigation was 77, 94, and 136 days for the wet, medium, and dry treatment, respectively. The fast growing species in descending order were palo verde hybrid, mesquite, desert willow, and pistache based on their growth index. Palo verde hybrid trees were the tallest followed by pistache, desert willow, Elderica pine, and mesquite. Trunk area was largest for palo verde hybrid trees, followed by pistache, mesquite, desert willow, and Elderica pine. Smallest trees based on growth index and trunk area were live oak and Arizona ash. Although all species have increased in height, growth index, and trunk surface area, no significant differences in growth of the same species receiving the different irrigation treatments were recorded by October 2012 with one exception. Growth index for live oak was larger with the wet compared to the medium irrigation treatment and trees irrigated with the dry treatment did not differ from the other two. Two trees were lost in 2012 likely due to the irrigation treatment, one Arizona ash in the dry treatment and one Arizona cypress in the medium treatment. Deficit irrigation symptoms were starting to develop in spring and progress through the summer as foliage dieback, terminal branch dieback, or loss of interior foliage on conifers. Overall quality of some trees such as Arizona cypress, Elderica pine, and Arizona ash is starting to decline due to reduced foliage cover. The most important outcome to date is that the same size tree can be grown with half of the amount of water that is applied to the wet irrigation treatment without detrimental consequences for several species.

Publications

• Schuch, U.K. 2012. How often should landscape trees be irrigated The ALCA Influence, May/June p. 23.

Progress 01/01/11 to 12/31/11

Outputs
OUTPUTS: This project investigates the response of nine commonly planted landscape plants to different irrigation treatments. The study is considered a long-term research and demonstration project and has been maintained with the current treatments since May 2010. Irrigation treatments were based on applying 80% (wet), 60% (medium), and 40% (dry) of reference evapotranspiration (ETo) from May to October and half of that (40%, 30%, and 20% of ETo) from January through April and November to December. Plant height, canopy width, and caliper of the stem were measured in March and September. Data was analyzed by analysis of variance to determine whether the irrigation treatments resulted in different growth. Monthly evaluations of canopy density, phenological observations (presence of flowers and fruit), and observations of tree health were recorded. An overall quality rating was given to each plant to determine whether it still fulfilled the criteria of a healthy, functional landscape tree. Soil moisture data was collected from three species (palo verde hybrid, Arizona cypress, and Arizona ash) that were irrigated according to the medium treatment. Time domain reflectometry (TDR) data was collected one day after an irrigation event and immediately before the following irrigation event. Crop coefficients were calculated based on the measured soil moisture depletion between irrigation events. Results of the study were presented to irrigation managers, researchers, and water policy personnel through a presentation. Two field tours were given to landscape professionals. PARTICIPANTS: The study is done in cooperation with faculty from the Department of Agricultural and Biosystems Engineering at the University of Arizona. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The three irrigation treatments resulted in different irrigation frequencies. Plants in the wet treatment received about twice the number of irrigations compared to plants in the dry treatment and those in the medium treatment were in between regarding number of irrigations. In summer, irrigation was applied every five days for the wet treatment and every six days for the medium and dry treatments. In winter the longest time between irrigation was 77, 94, and 136 days for the wet, medium, and dry treatment, respectively. The fast growing species palo verde hybrid, mesquite, and pistache cultivar Red Push have the largest growth index and pistache trees have now exceeded the desert willow trees which until the previous year were the third largest species in the study. Although all species have increased in height, growth index, and trunk surface area, no significant differences in growth of the same species receiving the different irrigation treatments were recorded by September 2011. Calculated crop coefficients for palo verde were 0.2 and 0.4 for winter and summer months, respectively. Arizona cypress had crop coefficients between 0.3 and 0.6 and Arizona ash had the highest crop coefficients with 0.7 during the hottest part of the summer and 0.3 during the winter months. Models for crop coefficients of the species will be refined with further data. Water managers that have issued guidelines based on observations and experience for irrigation of tree species used in our study are starting to compare their recommendations and the performance of trees in our study that receive above or below their recommended quantities of water. The site visits were informative to tour participants as they were surprised to see the differential growth of the different species under the three irrigation treatments. The demonstration part of this project has served and will continue to raise awareness about using different quantities of water for tree irrigation in an arid climate. The most important outcome to date is that the same size tree can be grown with half of the amount of water that is applied to the wet irrigation treatment.

Publications

• No publications reported this period