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UMass Extension Floriculture Water Quality Project: II. pH, Alkalinity, Calcium, Magnesium and Other Elements

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In 2004 the UMass Extension Floriculture Program began a project studying greenhouse irrigation water quality supported by the Massachusetts Flower Growers' Association, Ball Seed Co., and Scotts Testing Laboratory. In an earlier article (Cox, et al., 2006) Part I, we reported on the sodium, chloride, and EC levels found in the tests from our study. This article reports on the results of testing for pH, alkalinity, calcium (Ca), magnesium (Mg), and other elements. Water pH and alkalinity can have important effects on nutrition and crop quality of many annuals especially marigold, geranium, calibrachoa and petunia.

Over 50 growers in all regions of Massachusetts chose to participate in this project. Cooperating growers were asked to provide information about their water source, the crops they produce, their fertility program, and their testing history. Water was sampled and analyzed several times over two years. Analyses included pH, alkalinity, electrical conductivity (EC), and mineral composition. The tests were made by Scotts Testing Laboratory and Paul Lopes and Tina Smith helped the growers with test interpretation and gave advice based on the results.

In addition to providing useful information for growers, the water analysis data also gave us an opportunity to look at greenhouse irrigation water quality from different sources and in different regions of Massachusetts .

How the results are tabulated

Test results from a total of 183 water samples collected from about 50 growers in spring of 2004 and again in 2005 are reported in this article. It is important for the reader to know that the sample totals shown in the table includes results of as many as 2- 4 tests from some growers taken at different times during the sampling period.

The importance of pH and alkalinity in iron nutrition and iron/manganese toxicity is well known and in some cases the lack of Ca and Mg in water is a factor in occurrence of plant deficiencies of these elements. Table 1 shows accepted greenhouse irrigation water target and acceptable ranges for pH, alkalinity, Ca, and Mg. Compare these ranges to the water test results shown in Tables 2, 3, and 4. Water test results for other elements (nitrate, ammonia, phosphate, potassium, sulfate, iron, boron, copper, manganese, and zinc) are summarized at the end of the article.

Table 1. Greenhouse water analysis interpretation for pH, alkalinity, Ca, and Mg (Biernbaum,1994).
Factor Target range Acceptable range
pH 5.5-7.0 4-10
Alkalinity (ppm) 40-160 0-400
Ca (ppm) 25-75 Less than 150
Mg (ppm) 10-30 Less than 50

Table 2 shows the state- wide water test results from municipal, well, and surface water sources. "Municipal" refers to public drinking water originating from a surface body of water or from wells provided by a city, town, or other authority (like the MWRA). "Well" refers to a private well owned by the grower. " Surface" refers to water from a private pond or perhaps pumped by the grower from a river; generally the surface water sources in this project were for irrigation only and not for drinking.

Tables 3 and 4 show test results from municipal sources and wells, respectively, broken down for convenience into easily recognized regions by Massachusetts counties. Of course, counties are just political divisions drawn on a map, so they don' t have much to do with the water quality in a region. No samples were submitted from Suffolk county and only a handful were from the Cape and the Islands . There is not a table similar to Tables 3 and 4 for surface water because the number of samples collected for the whole state was very small (15).

Results - pH, alkalinity, Ca, and Mg

All water sources . Water test results from all municipal, well and surface sources are compared in Table 2. The average pH of all sources was well within the A acceptable range, but slightly above the A target range (Table 1) for greenhouse irrigation water. Most pH test results fell between 7.0 and 7.9. Minimum pH levels were within the acceptable and target ranges whereas pH levels at or near the maximum level were well above the target range. It is not surprising that many Massachusetts greenhouses have water pHs at least somewhat above target; it is generally not a concern unless the water also tests above target for alkalinity.

In fact, the average alkalinity of all water sources was close to the low end of the target range. Even the maximum recorded alkalinity levels fell within the target range for municipal and surface water, but a few well water samples had alkalinity levels above target. Overall, the alkalinity of 75% of all samples tested in the target range or lower.

Calcium and magnesium levels in most samples taken from all three water sources were within or somewhat below the target range for greenhouse irrigation water. Only in a few well water samples did Ca and Mg levels significantly exceed the target range. These samples also had high pH and alkalinity, factors of greater concern than high Ca and Mg from a crop growth and quality standpoint. More importantly were the many water samples that had low Ca and Mg levels reflected by the low average and minimum values for both elements in Table 2. Use of a water-soluble fertilizer supplying Ca and Mg to prevent deficiencies would be a desirable practice to adopt in many of these greenhouses.

Table 2. pH, alkalinity, Ca, and Mg levels in greenhouse water samples from three sources (all regions).
Water source Samples Average Minimum Maximum *75%
  pH
Municipal 82 7.6 6.3 8.8 7.9
Well 86 7.3 5.4 9.9 7.9
Surface 15 7.2 6.5 8.0 7.6
  Alkalinity ppm
Municipal 82 50 4 124 70
Well 86 67 8 262 90
Surface 15 48 12 158 72
  Calcium (Ca), ppm
Municipal 82 21 2 138 25
Well 86 38 1 701 33
Surface 15 20 6 43 25
  Magnesium (Mg), ppm
Municipal 82 4 0.1 31 6
Well 86 11 1 181 12
Surface 15 6 1 13 8

* 75% of the samples analyzed had levels lower than the value shown (25% had higher levels).

Municipal water. In Table 3 municipal water tests for pH, alkalinity, Ca, and Mg are compared by region. In all regions, the average pH was slightly higher than the "target range". Average alkalinity was within the target range in all regions except Worcester county where it was somewhat lower than target.

Ca and Mg levels were lower than or just short of the "target range" in all regions. High pH, at or near the maximum, was a potential problem in a few cases, however these high pH values were not coupled with high alkalinity above the target range. Potential problems might exist where Ca and/or Mg was low. Water tested from a few greenhouses had very low Ca, at or near the minimum, and 75% of all samples in all regions tested low for Mg.

Table 3. pH, alkalinity, Ca, and Mg levels in greenhouse municipal water samples.
Region (counties) Samples Average Minimum Maximum *75%
  pH
Berkshire 13 7.8 7.4 8.1 7.9
Franklin, Hampshire, Hampden 15 7.5 6.5 8.3 8.1
Worcester 11 7.2 6.5 7.8 7.4
Middlesex, Essex 20 7.5 6.7 8.3 7.8
Norfolk, Plymouth, Bristol, Barnstable 23 7.6 6.3 8.8 7.9
  Alkalinity, (ppm)
Berkshire 13 44 14 90 78
Franklin, Hampshire, Hampden 15 53 18 96 69
Worcester 11 27 14 81 33
Middlesex, Essex 20 63 16 116 96
Norfolk, Plymouth, Bristol, Barnstable 23 45 4 124 62
  Calcium (Ca), ppm
Berkshire 13 13 4 25 24
Franklin, Hampshire, Hampden 15 23 10 42 31
Worcester 11 24 3 138 20
Middlesex, Essex 20 22 2 58 36
Norfolk, Plymouth, Bristol, Barnstable 23 17 2 49 23
  Magnesium (Mg), ppm
Berkshire 13 4 1 8 7
Franklin, Hampshire, Hampden 15 4 1 11 3
Worcester 11 4 1 31 5
Middlesex, Essex 20 5 0.1 10 8
Norfolk, Plymouth, Bristol, Barnstable 23 4 1 10 6

* 75% of the samples analyzed had levels lower than the value shown (25% had higher levels).

Well water. Well water tests were similar to municipal tests in that pH was somewhat above the "target range" (Table 4). Berkshire county had the highest average pH of 7.8. In each region pH of well water from several greenhouses tested 8.0 or above raising concerns about the response of species sensitive to too high pH.

Significant differences between regions were found in the levels of alkalinity, Ca, and Mg in well water samples. Berkshire county and the Franklin, Hampshire, and Hampden region had the highest average and maximum alkalinity levels compared to the other regions. Average and maximum levels of Ca and Mg were highest in Berkshire county. High pH, alkalinity, Ca, and Mg is common in well water sampled in Western Massachusetts, especially in Berkshire county due to underlying limestone deposits. From a crop production standpoint the coupling of high pH and high alkalinity is of greatest concern.

Table 4. pH, alkalinity, Ca, and Mg levels in greenhouse well water samples.
Region (counties) Average Minimum Maximum * 75%
  pH
Berkshire 17 7.8 7.0 8.2 8.1
Franklin, Hampshire, Hampden 5 7.1 6.6 7.4 7.3
Worcester 19 7.3 5.4 8.2 8.1
Middlesex, Essex 11 7.4 6.0 8.1 7.7
Norfolk, Plymouth, Bristol, Barnstable 34 7.2 5.9 9.9 7.7
  Alkalinity, (ppm)
Berkshire 17 148 84 262 218
Franklin, Hampshire, Hampden 5 122 16 264 158
Worcester 19 44 16 81 56
Middlesex, Essex 11 67 14 160 92
Norfolk , Plymouth , Bristol , Barnstable 34 31 8 80 44
  Calcium (Ca), ppm
Berkshire 17 80 18 701 60
Franklin, Hampshire, Hampden 5 27 1 61 50
Worcester 19 21 9 56 28
Middlesex, Essex 11 30 7 82 32
Norfolk , Plymouth , Bristol , Barnstable 34 30 2 424 23
  Magnesium (Mg), ppm
Berkshire 17 25 9 106 27
Franklin, Hampshire, Hampden 5 7 1 16 13
Worcester 19 3 1 7 5
Middlesex, Essex 11 6 1 16 7
Norfolk , Plymouth , Bristol , Barnstable 34 11 2 181 7

* 75% of the samples analyzed had levels lower than the value shown (25% had higher levels).

Results - Other elements

In addition to pH, alkalinity, Ca, and Mg (and EC, Na, and Cl reported earlier [Cox, et al. 2006]), we also tested water for other elements: nitrate, ammonia, phosphate, potassium, sulfate, boron, copper, iron, manganese, and zinc (chemical symbols: NO 3 , NH 3 , PO 4 , K, SO 4 , B, Cu, Fe, Mn, and Zn). In general, regardless of water source or region, the average level of each of these elements fell in the "target range" and the broader "acceptable range" for greenhouse irrigation water (data not shown).

In a few cases, almost exclusively in well or surface water, some elements were found at quite high levels. For example, in three or four cases NO 3 exceeded the USEPA standard of 10 ppm for drinking water. While water with NO 3 exceeding this limit poses no threat to greenhouse crops, drinking this water would be unhealthful. Also, a well or a pond containing a high level of NO 3 might be an entry point for groundwater pollution. In another example, high levels of K and PO 4 were found. The levels were high enough to warrant a reduction of fertilizer K and PO4 levels to account for the extra applied to crops from the irrigation water alone.

Finally, some growers believe that the presence of Fe and Mn in their water might contribute to Fe/Mn toxicity affecting species like marigold and geranium. In almost every sample we collected Fe and Mn levels were well below the "target range" for greenhouse irrigation water. This finding suggests that fertilizers and growth media are the more likely sources of too much Fe and Mn rather than irrigation water.

Summary

Most growers in Massachusetts seem to be irrigating with water of normal or near normal pH and levels of alkalinity, Ca, Mg, and other elements. A few growers, especially in Western Massachusetts using private wells or ponds, face the challenge of crop production with high pH and high alkalinity water. The twin problem of high pH and high alkalinity can be solved by the use of acidic fertilizers or, in extreme cases, by irrigation water acidification. However, the use of acidic fertilizers or acidified water should be limited to calibrachoa, petunia, and other "acid-loving" plants. Our study revealed a more common, but more subtle, problem: the existence of low or borderline levels of Ca and very low Mg. Apart from water, limestone is the only other source of Ca or Mg for greenhouse crops unless a fertilizer containing Ca and Mg (i.e., EXCEL) is used or supplemental applications of calcium nitrate and/or magnesium sulfate are made. It' s been well-established that poinsettias need extra Ca to prevent bract necrosis and extra Mg, as well, to prevent leaf chlorosis. Many experts think that other crops could benefit from Ca and Mg even though the appearance of dramatic deficiency symptoms is not common. Solving the problem of low Ca and Mg is easy to do by careful fertilizer selection.

References

Dr. Douglas Cox, Paul Lopes, Tina Smith
University of Massachusetts, Amherst
Topics: 
Commercial Horticulture
Water
Commercial Horticulture topics: 
Greenhouse Management
Water topics: 
Watershed & Water Quality