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UMass Extension Floriculture Water Quality Project: I. Salinity, Sodium and Chloride

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In 2004 the UMass Extension Floriculture Program began a project studying greenhouse irrigation water quality supported by a grant from the Massachusetts Flower Growers' Association and watering testing services partially subsidized by Ball Seed Co. and Scotts Testing Laboratory. Water has become a major factor in successful production of greenhouse plants in Massachusetts through the effect of its pH, alkalinity, and mineral composition on the nutrition of many important species like marigold, geranium, calibrachoa and petunia. Some growers are also concerned about the presence of sodium (Na) and chloride (Cl) in their water and believe these elements might be adversely affecting the quality of their plants.

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 reviewed and interpreted and based on the results, knowledge of current fertilizer practices, and any suspected problems growers were advised on corrective measures. Paul Lopes and Tina Smith helped the growers collect the samples and provided interpretation and advice based on the results of the water tests made by Scotts Testing Laboratory.

The main objectives of this project were to provide growers with information about their water quality to make better future crop management decisions and to help growers better understand how water quality, media pH, and fertility relate to each other. However, the water analysis data provided an opportunity to look at greenhouse irrigation water quality from different sources and in different regions of Massachusetts . This article reports the results of EC (salinity), Na, and Cl tests; a second article in the September-October issue will report the results of pH, alkalinity, and mineral composition tests.

How the results are tabulated

Results from a total of 183 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 realize that the sample totals shown in the tables includes results of several tests (2-4) from several growers taken at different times during the sampling period. The Na and Cl results provided the biggest "surprises" our project. Na and Cl are naturally occurring elements in soils and water but their levels can become elevated due to road salt, water softeners, and some fertilizers. High levels of Na and Cl uptake can be can accumulate to toxic levels in plants and abundant amounts in water can raise the EC to levels undesirable for plants by inhibiting water uptake. Table 1 shows accepted greenhouse irrigation water target and acceptable ranges for EC, Na, and Cl. Compare these ranges to the water test results shown in Tables 2, 3, and 4.

Table 2 shows the state-wide results of EC, Na, and Cl tests 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 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 taken 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

All water sources. Water test results from all sources (municipal, well, and surface) sampled throughout Massachusetts are compared in Table 2. The average EC of most samples was well within the "target range" (Table 1) for greenhouse irrigation water. Many samples had very low EC as we would generally expect in most of Massachusetts . Overall 75% of all samples tested well within the target range regardless of water source. In a few greenhouses the EC greatly exceeded both the target and "acceptable" ranges for greenhouses. Adding water-soluble fertilizer to water with an already high EC would certainly increase the risk of soluble salts injury to greenhouse crops.

The average Na level in municipal and well waters exceeded the target range, but fell well within the acceptable range for greenhouse water; many samples contained very little Na. In surface water the average Na level exceeded both the target and acceptable ranges. This fact along with the very high (>100 ppm) Na levels in some samples from the other water sources could pose serious problems for some growers. Overall, 16% of all samples had Na levels between 25-49 ppm, 8% 50-99%, and 6% 100 ppm or more.

The average Cl level of all water sources exceeded the target level, but fell within the acceptable range. Overall, 18% of the samples had Cl levels between 25-49 ppm, 14% 50-99 ppm, and 15% 100 ppm or more. While many samples contained very little Cl, some had extremely high levels (>200 ppm) and these could result in toxicity to plants. In general, the highest EC, Na, and Cl levels occurred in the same samples. This combination of factors would make crop problems quite likely.

Municipal water. In Table 3 EC, Na, Cl test results for municipal water are shown by region. In all regions, average EC, Na, and Cl levels were within the acceptable range, but only in the 4 westernmost counties were Na and Cl in the lower, target range. Whether these results are broadly characteristic of water in the western counties or just a coincidence related to the water source in the communities where the greenhouses were located is not known. In all regions EC, Na, and Cl tested much lower than the average in many water samples, but some had much higher levels. It's puzzling that some municipal samples were so salty and had Na and Cl levels around the maximum level. A lot of effort has been made to protect public drinking water from road salt to reduce the Na content for people on a low Na diet. The USEPA recommends that Na in drinking water not exceed 20 ppm (Anonymous, 2003). A number of municipal samples in this project exceeded the Na limit to one degree or another if you look at the average and the maximum levels. In a few cases, around the maximum Na levels, water was undesirable for both greenhouse crops and human consumption.

Private well water. The average EC of private well water samples was within the target range for greenhouse crops (Table 4) in all regions. Many samples had very low ECs and a few were quite high, especially in the Berkshire and two eastern regions.

Na and Cl levels were within either the target or acceptable ranges in all but Franklin, Hampshire, and Hampden (Na, but only 5 samples total) and Berkshire (Cl) regions. Tests from a few greenhouses were quite high as suggested by the maximum levels shown in Table 4. Shallow wells and wells located near public roads and parking lots are most vulnerable to road salt contamination. In our experience road salt contamination is probably the main reason for high Na and Cl in well water used to water greenhouse crops.

Summary

The results of our greenhouse water testing project have shown that most Massachusetts growers are irrigating greenhouse crops with water containing safe levels of EC, Na, and Cl. However, a small, but significant number, of growers are using water containing elevated levels of Na and Cl and accompanying high EC with the result being lower quality and even crop loss. Most often this water is from a private well or pond, but sometimes public drinking water is the source.

The solutions to the problem of high Na and Cl include regular water testing during the growing season in borderline cases of excess Na and Cl and avoidance of over-fertilization to prevent high growth medium EC; installation of water treatment systems to remove Na and Cl; efforts to protect wells and ponds from salt contamination by runoff; or, in extreme cases, finding a new source of water.

References

  • Anonymous, 2003. Healthy drinking waters for Rhode Islanders. Sodium chloride in private water wells. Private wells series. R.I. Dept. of Health and U.R.I. Coop. Ext. Water Quality Program.
  • Biernbaum, J.A. 1994. Water quality. In Tayma, H.K., T.J. Roll, and M.L. Gaston. Eds. Tips on growing bedding plants, 3 rd ed., Ohio Flor. Assoc., Columbus , OH .
Table 1. Greenhouse water analysis interpretation for EC, Na, and Cl (Biernbaum, 1994).
Factor Target range Acceptable range
EC (mmho/cm) 0.2-0.8 0-1.5
Na (ppm) 0-20 Less than 50
Cl (ppm) 0-20 Less than 140
Table 2. EC, Na, and Cl levels in greenhouse water samples from three sources (all regions).
Water source Samples Average Min. Max. 75% z
  Electrical conductivity (EC), mmho/cm
Municipal 82 0.39 0.05 3.14 0.41
Well 86 0.52 1.07 7.15 0.53
Surface 15 0.61 0.95 3.93 0.64
  Sodium (Na ), ppm
Municipal 82 37 3.0 436 30
Well 86 37 1.0 544 32
Surface 15 79 4.0 685 79
  Chloride (Cl), ppm
Municipal 82 69 2.0 1020 66
Well 86 38 0.2 3510 49
Surface 15 105 2.0 748 120

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

Table 3. EC, Na, and Cl levels in greenhouse municipal water samples.
Region (counties) Samples Average Min. Max. 75% z
  Electrical conductivity (EC), mmho/cm
Berkshire 13 0.17 0.1 0.25 0.24
Franklin, Hampshire, Hampden 15 0.25 0.1 0.35 0.31
Worcester 11 0.52 0.1 3.14 0.31
Middlesex, Essex 20 0.52 0.2 2.90 0.56
Norfolk , Plymouth , Bristol , Barnstable 23 0.35 0.1 0.90 0.48
  Sodium (Na ), ppm
Berkshire 13 11 7 17 13
Franklin, Hampshire, Hampden 15 11 3 18 15
Worcester 11 53 11 382 49
Middlesex, Essex 20 49 10 436 39
Norfolk , Plymouth , Bristol , Barnstable 23 36 6 105 35
  Chloride (Cl), ppm
Berkshire 13 12 7 16 14
Franklin, Hampshire, Hampden 15 12 2 21 17
Worcester 11 129 10 1020 22
Middlesex, Essex 20 86 17 651 77
Norfolk , Plymouth , Bristol , Barnstable 23 64 8 193 79

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

Table 4. EC, Na, and Cl levels in greenhouse well water samples.
Region (counties) Samples Average Min. Max. 75% z
  Electrical conductivity (EC), mmho/cm
Berkshire 17 0.85 0.20 6.98 0.57
Franklin, Hampshire, Hampden 5 0.64 0.35 0.81 0.80
Worcester 19 0.24 0.10 0.54 0.34
Middlesex, Essex 11 0.53 0.10 2.30 0.52
Norfolk , Plymouth , Bristol , Dukes 34 0.50 0.10 7.20 0.32
  Sodium (Na ), ppm
Berkshire 17 37 1.0 401 33
Franklin, Hampshire, Hampden 5 85 11.0 193 163
Worcester 19 15 1.0 52 16
Middlesex, Essex 11 52 5.0 334 44
Norfolk , Plymouth , Bristol , Dukes 34 36 5.0 544 23
  Chloride (Cl), ppm
Berkshire 17 168 4.0 2310 82
Franklin, Hampshire, Hampden 5 8 4.0 19 10
Worcester 19 28 0.2 111 48
Middlesex, Essex 11 95 2.0 563 106
Norfolk , Plymouth , Bristol , Dukes 34 139 4.0 3510 34

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

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