By Larry C. Holmes – Holmes Landscape Company, San Diego, CA
Landscape and Irrigation Magazine, August 1994
Because of the extreme soil and water conditions the continued drought conditions and an increased need to conserve water in Southern California it became apparent that reduced watering was somehow contributing to the gradual decline in the overall appearance and quality of the landscape plants and ground cover we maintained.
We started noticing some of our landscape plants exhibiting tip bum, chlorosis, and lack of vigor. Annual seedlings that in previous years had germinated and grown were not reestablishing themselves. Many of the seeds that did germinate died shortly after germination. The annuals that did germinate and mature were very sparse and did not appear healthy. Trees and shrubs had declined in their overall appearance, displaying symptoms of nutrient deficiencies, interveinal chlorosis of the leaves, yellowing of the leaf margins, leaf tip bum and slow plant growth.
We were aware that we had mostly a saline-alkali soil with a very high pH averaging 8 to 8.4, and high salts, up to 2176 ppm. Our solution was to utilize deep irrigation thereby leaching the salt, keeping it moving in the direction of the water movement, either down, below and away from the root zone and off the top of the soil surface. By using this method we were able to keep the salts out of the immediate root zone and were able to keep our landscapes flourishing.
The inability to leach with our irrigation water had increased the salt at the plant root zone to a toxic level. When we did irrigate, we were irrigating with water at a pH of over 8. Basically we were watering an alkaline soil high in salts with an alkaline water also high in salt. Because of the drought conditions the watering was down to a minimum. This caused an increased salt build up on the soil surface and in the root zone of our plants. In order to survive the plants had shut down, not taking up any more nutrients and growth had basically stopped. The quality of our landscape was declining, and we started seeing an influx of plant pest and diseases unlike anything we had seen in previous years.
Initially believing that we needed to do a fertilization trial to determine if perhaps a different blend of fertilizer with minor nutrients was needed I set up a fertilizer test site and ran a series of fertilizer test using several different formulations of fertilizer with major and minor nutrients. To my surprise, no improvement was noticeable on any of the test -sites! It was then that I knew additional problems were being created due to the changes we had made with our water management.
Next I chose a specific site and did a series of complete leaf tissue analysis on the various ground covers and plants. Did an accumulative soil test, taking random samples throughout the test plot areas and received a water analysis from our water supplier for the irrigation water used on the area. Following are the results of the first series of tests we took.
Initial Test Results
- Plant Tissue Test:
- Nitrogen at 1.4%, and it should be over 3%. Plants need at least a minimum of 2%.
- Calcium at .5 %, and it should be over 2%.
- Sodium at .3 1 %, and it should not be over .25 % maximum.
- Soil Test:
- Soluble salts at 1216 ppm
- High Sodium
- Soil pH over 8.1
- E.C.e. of almost 2.0
- Irrigation Water Test:
- pH of over 8
- Sodium over 54 ppm
- Bicarbonates over 100 ppm
The results of the leaf analysis showed a lack of nitrogen and calcium in the leaf samples with sodium at a toxic level, yet soil test showed moderate levels of nitrogen and calcium in the soil. We had a major nutrient availability problem, the fertilizer, even though it was being applied to the soil was not available to the plants, and possibly contributing to the salt problem since it was not being taken up by the plants due to the chemistry of the soil and the high salts and carbonates in the soil. The high alkalinity did not allow nutrient minerals to be available for plant up take and use, confirming our original assumptions that the landscape plants were not taking up the fertilizer that was being applied, thereby not getting the necessary nutrients for proper growth. Some of our soil samples were recommending applications rates as high as 2.5 tons of gypsum per acre. We had existing ground covers, plants and trees on the slopes and had no way to properly amend the existing soil with a solid material such as gypsum and the time it would take for results to be achieved using this method were much longer than I wanted.
Through numerous discussions and field work with suppliers, soil laboratories, and eventually a chemist we kept returning to discussions about foliar and liquid applications to help eliminate our problems. This started us on a journey to find a way to chemically inject the fertilizer and chemicals needed for this specific test slope, directly into the landscape irrigation system mainline.
Knowing that farmers and golf courses had been chemically injecting for years I felt reasonably confident that we should be able to use this technique for our specific problems. But no one that I was able to contact knew of this process being done on landscaped slopes, or if it would work. It made sense to me that if we could use the existing irrigation system to apply the corrective chemicals we had been told about through injecting into the irrigation system mainline we would achieve two major goals. The first was being able to initiate the corrective measures needed to start correcting the problems and second the ability to do the first goal at a very reduced cost compared to the other options available to us such as manually spraying the slopes with a spray rig mounted on a truck. The labor cost for manually spraying would prohibit us from taking the necessary steps to start a corrective program.
By doing research with Greg Omori from Coast Garden Center on different pumps that were available we found a pump that was economical yet would do what we needed as easily as possible. Greg eventually loaned us our first model, a Chem-Tech Injector pump to try on our test site. We installed a manual ball valve into the mainline down stream from the backflow device for our point of injecting.
Eventually, after many days of field work we were able to determine the application rates for the injecting pump with the different materials we wanted to start injecting. With the recommendation of the soil laboratory we started a foliar feeding program of very diluted calcium nitrate. The liquid calcium nitrate was chosen to replenish the critically low levels existing in the leaf tissue of calcium and nitrogen shown on the leaf analysis tests. After several applications the plants started to responded with positive results from the foliar feeding. The leaves were much greener and healthier looking and the plants had started showing new growth.
After several applications of Calcium Nitrate we started working on injecting a water treatment additive, a urea-sulfuric acid combination, into the irrigation system. The additive was used to adjust the high water pH and high carbonates thereby eventually adjusting the soil pH and eliminating the toxic sodium level and high salts in the soil. Initially because we were unable to get rates for applying the chemicals from anyone, we spent hours doing field work to find the correct dilution rates needed to lower the water pH down to 6.5 – 6.8. Through the use of pH meters we took a pH reading of the water as it came out of the sprinkler heads on every valve in the test area. Through a series of adjustments to the concentrated material we injected into the irrigation water we were able to find the correct formula to keep our water pH at 6.5 to 6.8. every time we irrigated. Through the use of the water treatment additive we were able to constantly lower the water alkalinity, which normally runs around a pH of 8.1 to 8.4, to a pH of 6.5 to 6.8.
By lowering the water pH we strove to lower the soil pH, and solubilize the nutrients bound at the higher pH range in the soil. Once solubilized the nutrients would then be available for the plants to use and additionally, by injecting the water treatment into the water supply we were able to convert the bicarbonates and lime in the water to create calcium sulfate or a diluted solution of gypsum !! The dilute solution of calcium sulfate should react with the soil particle surface causing the release of unwanted salts especially sodium which we had a very toxic level.
After several weeks of injecting, we continued to monitor the water and plant material on the test slope. Much to our delight our second set of leaf and soil analysis supported what I was seeing in the landscape. The plants had visually started to appear much healthier and greener and the emergence of new growth led me to believe that the plants were finally able to absorb and take up additional nutrients. The plant tissue test showed that the calcium level had improved by 80%, nitrogen levels had improved by almost 30%. and the previous sodium level, which was well over the toxic point, had dropped to a safer level.
After months of repeated applications of injecting into the irrigation water, our soil test showed that our soil pH had dropped from 8.1 to 7.4. Our leaf analysis showed that the plants had started absorbing the available nutrients and the results were a rapid increase in the overall health and appearance of the plant material on the site. The crisp green had returned to the leaves of the plants and ground covers, the growth rate had increased and the overall appearance was noticeably improved. An additional benefit we found was the improved water penetration on the treated slope area compared to the untreated area. Our experience allows us to take these results and integrate them for successful landscape management.
At Holmes Landscape Company our goal is to offer our customers the latest in research and development to protect and enhance their landscape investment. After hundreds of hours of research, and development, seeing the dramatic improvement is extremely encouraging and rewarding and represents exciting opportunities for chemical injecting in future landscape projects.
Larry C. Holmes, President of Holmes Landscape Company teaches classes at Mira Costa Junior College and serves San Diego’s North County landscaping needs with the latest advances in landscape enhancement. He can be reached at 760.732.3379 for more information.