Maintaining water quality
An important factor to consider in any greenhouse is the quality of water being used to irrigate the crops. Many growers will face crop challenges that can be traced back to the quality of water they are using and its affect on pH and electrical conductivity (EC) in the root zone, says Brian Bourdon, senior manager of offsites and crop supply chain at Four Star Greenhouse Inc. “Knowing your water quality will allow you to be proactive rather than reactive in producing high-quality crops,” he says.
“Certain genera grow much better at a low pH (petunias), others at a high pH (geraniums), while some crops like New Guinea impatiens prefer low feed levels (low EC) and others, like petunias, prefer high EC.” Knowing these differences can be helpful, but also overwhelming, when trying to grow multiple crops in one greenhouse. “I often tell growers to worry less about the specifics and try to maintain a general pH in the root zone of 5.8 to 6.2 and EC of 0.6 to 1.0 when using the 1:2 method for testing,” says Bourdon. He adds that most crops will grow well in these ranges, but depending on your water source, these goals can be difficult to achieve.
WATER QUALITY BASICS
Getting a water test from a reputable lab to analyze your water quality is a great first step. These tests are affordable and can save you a lot of problems. “Even if you are on a municipal source like we are here at Four Star Greenhouse, it’s still a good idea to send samples out to be tested,” Bourdon says. Municipalities tend to have consistent results throughout the year, but Four Star still tests at least twice per year to be sure. Well water can vary more and should be tested more frequently.
Bailey Nurseries tests its water quality at different frequencies, depending on the location. Jean-Marc Versolato, Midwest plant health department manager at Bailey Nurseries in Minnesota, says the water is tested three times per week for pH, alkalinity and copper, since they use a copper ionizer to sanitize the irrigation water. At the Oregon location, greenhouse water is tested weekly during the growing season, and monthly outside of that time, for pH, EC, sodium hypochlorite, and alkalinity.
One important aspect of the water test results is the total alkalinity level, which has a big impact on pH in the root zone. The pH of your water test is good to know but does not impact the rise or fall of the pH in your root zone, according to Bourdon.
“Knowing your alkalinity is crucial to knowing which fertilizers to use on a regular basis,” he says. “With moderate alkalinity levels (50 ppm to 125 ppm), you can usually have good success with the right fertilizers alone but, as alkalinity levels rise, pH of the root zone becomes a greater challenge, and you may need to look at additional solutions.”
A common method is acid injection with the amount of acid needed depending on alkalinity level. Sulfuric acid is probably the most common, but nitric, citric and phosphoric acids can also be used, Bourdon says. Each has their own advantages and disadvantages, and it’s best to research the right fit for your operation.
High alkalinity is common in Michigan, but other areas can experience low alkalinity. “We recommend using calcium- or magnesium-based feeds to try to balance low alkalinity water, although you may need to look at amending your mixes to add some additional buffer to pH changes, if not,” Bourdon says.
“We inject sulfuric acid into the well water to bring the alkalinity down to 120 ppm and add ionic copper at 1.5 to 2.0 ppm to control algae and fungus on the farm,” Versolato says.
EC AND pH
Jeff Stoven, West Coast propagation production manager for Bailey Nurseries in Oregon, currently doesn’t do too much to alter the water. “The pH can fluctuate
seasonally, considering it’s all surface water and the alkalinity is consistently on the lower end, so we haven’t seen a great need for alterations regarding pH. Sodium hypochlorite is monitored and adjusted throughout the year,” he says.
EC is another factor to consider and dealing with it can be challenging.
“In areas that deal with a lot of soluble salts or sodium in their water, it is important to be conscious of this and leach with each watering,” Bourdon says. “It may be worth incorporating a slowrelease fertilizer and watering with clear water only. This will take some trial and error to find the right rates that work best for each crop and should be adjusted based on the time of year to adjust for environmental conditions. Other treatment options like installing a reverse osmosis system can be costly, depending on the size of your operation.”
WATER FILTRATION SYSTEMS
Well and surface water will often contain silt, causing irrigation nozzles to clog, while slow-moving water sources can contain algae and pathogens, bringing even more issues into the greenhouse. All water types come with problems, and using a water filtration system can be a great solution to improve water quality in your operation.
Bailey Nurseries in Minnesota uses a desanding filtration system after the water comes from the well to reduce particles and also has filters on all the traveling irrigators, Versolato says.
In Oregon, Bailey filters the water multiple times during its greenhouse irrigation process.
“We use pressurized sand filters for the water that is pumped from the reservoirs. The greenhouse/propagation water is filtered by two sets of sand filters before it’s used in the greenhouse area,” Stoven says. “These sand filters are inspected and filled on an annual basis or as needed. At each greenhouse there is an inline mesh/screen filter for anything coming out of the hose or pipe.”
At Mast Young Plants, water quality has been an ongoing issue since the facility opened in 1997.
“We drilled the well into an aquifer that met our size requirement and planned to adjust the water chemically as needed to suit our crops,” says Michael DeBerti, head grower. “The aquifer we chose had high alkalinity (close to 400 ppm bicarbonate) and a lot of iron, including iron-forming bacteria in the water, which created growing challenges completely different from our other facilities just a few miles away.
“We installed a reverse osmosis (RO) system after several years of struggling with water quality. RO is an expensive process that nearly purifies water by removing salt from it. Removing the salt also removes the bicarbonate, which makes adjusting the pH much easier,” DeBerti says. This greatly improved growing practices, allowing growers to easily adjust pH as needed.
The process of making RO water is slow and, with a facility that demands a high amount of water daily, it must be stored to have enough. “We choose to store 40,000 gallons of water and draw from that storage, allowing the RO system to run 24 hours a day to keep the tanks full. Growers draw down from the tanks during the day, and they’re replenished each night.
“After implementing this storage plan, we learned that we had to treat the storage water to prevent algae or biofilm from growing in our tanks, which led to the installation of a chlorine dioxide injection system. This new system is effective but requires regular testing to ensure smooth operation,” DeBerti says.
During the RO process, one of the hardest elements on the system filters is iron. “Since we had high levels of iron in our water, we also had to install a potassium permanganate filter to treat the water before it enters the RO filters,” DeBerti says. This system removes the iron from the water before it enters the RO, adding another piece to be monitored during the process.
Mast Young Plants’ RO system is effective for plant growth but must be managed regularly by DeBerti. These tasks include:
• Water testing from the well twice a year, in early spring and late fall.
• Alkalinity testing at least once a week, with maintenance at 80 to 120 ppm by blending back 10 to 20% raw water.
• Chlorine dioxide is applied to the water at a rate of 0.75 to 1.5 ppm, depending on the crop being grown.
Outside production with drip tape irrigation increases the rate to 1.5 to 2 ppm.
• Backflushing the potassium permanganate filters happens daily when water demand is at its lowest because it can take up to four hours.
OTHER FACTORS TO CONSIDER
Nutrient levels should not be ignored. Certain elements can be below recommended ranges and can be supplemented with fertilizer changes, while other elements like boron can be toxic at high levels.
“We have worked with some growers to get fertilizers manufactured without boron incorporated to help offset their water levels. It’s important to address any issues that are outside of normal range with experts to prevent costly challenges,” Bourdon says. “Unfortunately, some of these fixes can be expensive, but so can be not addressing them.”
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