Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversitySeptember, 1998
Initial Results from the OSU Nursery Irrigation Water Survey
Keywords: container production, irrigation, nursery, nutrition, new research, pH, water quality, water testing
T his year 80 Ohio nurseries are participating in a study to examine nursery irrigation water characteristics across the state. This article presents results from the first sampling date (mid April to early June), including the minimum, maximum and average levels for 19 water quality characteristics. Unless otherwise indicated, averages and other results are based on 120 water samples.
Presented with these averages are brief explanations of most of the characteristics and their importance to a nursery manager. This information should be helpful in interpreting any set of water test results. However, when looking over results from a water test there are a few things you should keep in mind.
Water tests should be reviewed in light of soil or soilless media test results to get a complete picture of potential problems. For example, some nurseries compensate for a water high in alkalinity by using a growing medium with a low pH. If a characteristic of your water is approaching a level that merits concern, don't panic; but keep a close watch on your production for problem signs such as slow growth, unusually pale or dark leaves, burning or increased susceptibility to disease and insects.
The good news is that most water samples we tested did not reveal serious problems. The most common problems found in these samples were high alkalinity and high pH.
pH
In a survey performed in fall, 1997, we found pH was the water quality characteristic most frequently tested by Ohio nursery growers. Many container growers still have the misconception that water pH has a dominant effect on growing medium pH. Instead the water's alkalinity (see below) has the greatest effect on medium pH. Nonetheless, water pH can be important because it affects stability and efficacy of some pesticides and solubility of fertilizers. Clogging of microirrigation systems is also more likely at high pH.
Depending largely on the alkalinity, pH can change rapidly, especially in a pond or other water source with much biological activity. Because it can change quickly, pH is best measured on site. However, litmus paper strips and hand-held meters used on site often are less accurate than testing equipment that would be used at a laboratory.
average: 7.9; maximum: 10.2; minimum: 6.9
# cases of concern (>6.9): 118
Alkalinity
Alkalinity is a measure of a water's ability to buffer or stabilize pH. While pH and alkalinity are related, they are not the same thing. High alkalinity water generally has a high pH; however, high pH water is not necessarily high in alkalinity. Alkalinity is important in container production, much less so in field production. Over time, using high alkalinity water on containers will cause an increase in media pH; the smaller the pot size, the greater the effect. High pH water will not do this unless it also has high alkalinity. As the container media pH rises, the availability of micronutrients decreases and plants may turn yellow. While some woody plants may tolerate 400 ppm CaCO3 alkalinity, azaleas, rhododendrons, and propagation will probably be affected at levels > 200 ppm. Greenhouse production may be affected at levels > 100 ppm.
average: 173.3; maximum: 433; minimum: 24
# cases moderate concern (100-200 ppm CaCO3): 49
# cases severe concern (>200 ppm CaCO3): 41
Soluble Salts
High soluble salt levels in the water can damage roots and decrease the ability of plants to take up water. Soluble salts can come from fertilizers or deicing salts, but a body of water also can become salty over time through evaporation. As water evaporates or is taken up by roots, the salts remain behind in soil or media and accumulate. Watch soluble salts levels in water recycling systems or any body of water receiving runoff.
Chloride, sodium and sulfate are ions that contribute to high soluble salts, but also may have specific toxic effects on plants. If you must use water with high levels of sodium or chloride, keep plants moist, and if possible, avoid getting water on the leaves since the ions may be absorbed through foliage. Leaching containers with another water source will help remove accumulated salts. Increasing the amount of available calcium can also help counteract high sodium levels. However, it may be necessary to dilute a high-salt water source with a low-salt source.
soluble salts
average: 0.53; maximum: 1.52; minimum: 0.1
# cases moderate concern (0.75 - 1.5 mS/cm): 18
# cases severe concern (>1.5 mS/cm): 1
chloride
average: 34.9ppm; maximum: 253 ppm; minimum: 2 ppm
# cases posing moderate concern (70 - 140 ppm): 12
# cases posing moderate concern ( >140 ppm): 5
sodium
average: 26.4 ppm; maximum: 188 ppm; minimum: 0.84 ppm
# cases posing moderate concern (50-100 ppm): 12
# cases posing moderate concern ( >100 ppm): 6
sulfate
average: 27.9 ppm; maximum: 190 ppm; minimum: 2 ppm
# cases posing concern (>200 ppm): 0
Primary Elements
The following four elements are all classified as primary nutrients for plant growth and usually occur at low concentrations in water. Since they are needed in rather large amounts by plants, there is only a remote chance of irrigation water levels of these nutrients being dangerously high for plant health. If runoff is recycled in the nursery, it will not be unusual to observe levels > 10 ppm. However, this concentration in a well source may indicate a leaky well or be a warning to other possible contamination ö many herbicides such as atrazine have been shown to follow the same contamination paths as nitrates when entering the environment. High concentrations of these primary nutrients ö especially phosphorus and nitrogen -- also encourage the growth of unwanted plants, such as aquatic weeds and algae in ponds and irrigation equipment.
nitrate nitrogen
average: 1.69 ppm; *maximum: 24 ppm; minimum: 0.2 ppm
ammonium nitrogen
116 samples were tested, only one was at a detectable range. Others were below one part per million.
maximum: 8 ppm; minimum: <1 ppm
phosphorus
19 of the 120 samples were at a detectable level (Others were below 0.10 ppm).
Average (of detectable amounts): 0.8 ppm; maximum: 8 ppm; minimum: <0.10 ppm
potassium
average: 3.39 ppm; *maximum: 26.2 ppm; minimum: 0.2 ppm
* NOTE: The highest levels of both potassium and nitrate were from recycled water sources.
Calcium and Magnesium
Calcium and magnesium are also important nutrients and rarely pose a risk to woody plants, although calcium-rich water may leave white deposits on leaves (see Hardness below). Many Ohio water sources contained levels of calcium and magnesium that were high enough to eliminate the need for nutritional supplements of these two nutrients in the media of container woody ornamentals.
calcium
average: 65.5 ppm; maximum: 196.8 ppm; minimum: 0.33 ppm
# cases where plants' calcium needs met through irrigation water (>40 ppm): 97
magnesium
average: 20.2 ppm; maximum: 74.9 ppm; minimum: 0.79 ppm
# cases where plants' magnesium needs met through irrigation water (>20 ppm): 42
Hardness. Hardness is based on the calcium and magnesium content of your water. Water that is excessively hard (over 180 ppm CaCO3), AND has high alkalinity and high pH values, can cause white carbonate precipitates on foliage and irrigation equipment. Whether or not precipitates form is a function of hardness, alkalinity, pH, total dissolved solids, pressure and temperature, so hardness alone can only give you a rough idea.
average: 246.8 ppm; maximum: 799.8 ppm; minimum: 4.1 ppm
# cases moderate concern for deposits: 76
# cases severe concern for deposits: 3
# cases concern for corrosion: 2
Calcium to Magnesium ratio. For container production, a certain balance of calcium and magnesium is desirable. If there is more than five times as much calcium as magnesium, magnesium uptake may be decreased for plants (some sources say 3 time as much is too much). Similarly, if there is more magnesium than calcium, calcium uptake could be affected. For field production, determine calcium and magnesium needs based on a soil test, not a water test.
average: 3.7; maximum: 7.2; minimum: 0.4
# cases posing concern for calcium uptake (<1): 1
# cases posing concern for magnesium uptake (>5): 18
Sodium Absorption Ratio (SAR). This ratio compares the amount of sodium to the amount of calcium and magnesium. It is rare to see problems in Ohio, but possible. When there is much more sodium than calcium and magnesium, the sodium can replace these more desirable elements in the soil, leading to poor soil structure, decreased infiltration and poor drainage. This characteristic is important for field as well as container production.
average: 0.83; maximum: 7.8; minimum: 0.07
# cases posing concern for soil structure or plants (>10 ppm): 0
The Micronutrients
Plants need micronutrients in very small amounts. High concentrations of some of these elements may be phytotoxic, although plants vary in their sensitivity. Micronutrients become more available for plant uptake as the pH decreases, thus toxicity is more likely at low pH. Iron and manganese precipitates also may cause problems with microirrigation systems at fairly low concentrations. Averages for these elements are based on the number of cases above a detectable level (in some cases, this is less than 10).
iron
# cases at or above detectable range (0.06 ppm): 24 out of 120
average for detectable cases: 0.31 ppm; maximum: 1.2 ppm; minimum: <0.06 ppm
# cases posing concern for trickle irrigation (>0.8 ppm): 3
# cases posing severe phytoxicity concern (>2 ppm): 0
manganese
# cases at or above detectable range (0.01 ppm): 33 out of 120
average for detectable cases: 0.14 ppm; maximum: 0.62 ppm; minimum: <0.01 ppm
# cases posing concern for trickle irrigation (>0.05 ppm): 17
# cases posing phytoxicity concern (>1.0 ppm): 0
zinc
# cases at or above detectable range (0.004 ppm): 28 out of 120
average for detectable cases: 0.10 ppm; maximum: 1.3 ppm; minimum: <0.004 ppm
# cases posing phytoxicity concern (>0.4 ppm): 1
boron
# cases at or above detectable range (0.03 ppm): 40 out of 120
average for detectable cases: 0.09 ppm; maximum: 0.48 ppm; minimum: <0.03 ppm
# cases posing moderate phytoxicity concern (0.3 - 2.0 ppm): 1
# cases posing severe phytoxicity concern (>2 ppm): 0
aluminum
# cases at or above detectable range (0.10 ppm): 7 out of 117
average for detectable cases: 0.79 ppm; maximum: 1.8 ppm; minimum: <0.10 ppm
# cases posing moderate phytoxicity concern (1.0 - 2.5 ppm): 3
# cases posing severe phytoxicity concern ( >2.5 ppm): 0
molybdenum
# cases at or above detectable range (0.06 ppm): 5 out of 117
average for detectable cases: 0.02 ppm; maximum: 0.06 ppm; minimum; <0.01 ppm
# cases posing severe phytoxicity concern ( >0.2 ppm): 0
Another round of water samples has recently been submitted from this same group of Ohio nurseries. It will be interesting to see how the measurements for nutrients, soluble salts and other characteristics have changed in this hot, dry summer weather most of us have been experiencing. These tests will be followed by one more round in September.
A sincere thank you to all the nurseries participating in the study!
--guest columnist: Cassandra Brown, OSU graduate student
