Is Irrigation Water Quality Causing Yield Reductions?

A client purchased a small vegetable farm from a grower who had yet to be successful in raising high-yielding quality produce. The new owner of the farm thought that he was getting a real bargain on the property because it had a high-yielding well, a strong spring, a large stream, and an acre pond that was located adjacent to the main production area. On paper, this farm looked like a great investment, and any production troubles that had shadowed the previous owner were quickly forgotten by the new owner in his haste to initiate production the following spring.

In late February, the new grower initiated seedling production in the greenhouse utilizing the water from the adjacent pond. Days and weeks went by, and the grower noticed that his germination percentages were low. In some flats, he noticed tip burn on the seedlings and some white precipitate on the media surface. Perplexed by his newfound inability to produce seedlings/transplants, the grower contacted me to troubleshoot his emerging production issue.

When troubleshooting a greenhouse or vegetable operation, the first step is to evaluate the water source. The best practice is to submit an irrigation water sample to an accredited laboratory for analysis. Still, using simple, relatively low-cost equipment (meters, test strips, titrators) on the farm may help pinpoint water quality issues almost immediately.

The key piece of equipment that every vegetable grower should have is an EC/pH meter. EC or electrical conductivity meters are used to determine soluble salt levels in the soil, but they can also be used to determine the "salt" levels in irrigation water. Combo meters, which can measure electrical conductivity and pH, are often very popular on most farms because of their utility. If a grower does not own an EC/pH meter, submitting an irrigation water sample to a water testing laboratory may be the best option to expedite the analysis and diagnosis.

When I arrive on a farm, I first calibrate the EC/pH meter and ensure its accuracy when testing irrigation water or media. Once the meter has been calibrated, I begin my analysis by first evaluating the irrigation water quality. I turn on a hydrant connected to the irrigation system and allow it to run for about 10 minutes to flush the lines. After 10 minutes have elapsed, I take a clean collection container (beaker or measuring cup) and use it to collect my sample. Once the sample has been collected, the EC function is selected on the meter, and the probe is immersed in the water. Once the reading has stopped fluctuating, it is recorded. Next, I choose the pH function on the meter and submerge the probe into the irrigation water. Once the reading has stopped fluctuating, the value is read and recorded.

After testing the irrigation water for EC (electrical conductivity) and pH, I initially utilized alkalinity test strips to determine the total alkalinity of the irrigation water source. If the reading on the alkalinity test strip is exceptionally high, I will use an alkalinity titrator to pinpoint the total alkalinity of the sample accurately. Some alkalinity test strips have an effective testing range from 0 to 200 ppm. In some areas of Pennsylvania that are underlain with limestone, I have observed total alkalinity levels in excess of 400 ppm.

Once I have determined the electrical conductivity of the water source, its pH, and its total alkalinity level, I will be equipped with enough information to make an on-farm assessment of the irrigation water source. In the case of this farm, the EC (electrical conductivity) of the pond water source was extremely high at 2.37 mS. This high EC usually means sodium and chloride can be found at relatively high levels in the irrigation water source. When the EC of water is this high, the soluble salt levels in containerized crops in the greenhouse will quickly rise, resulting in plant injury or death. The pH of this irrigation water sample was 7.4, which means that the grower may also need to inject acid into his irrigation water source to maintain the appropriate media pH for the crop or crops being grown.

The total alkalinity of the irrigation water source on this farm was over 350 ppm calcium carbonate. This reading confirms that the utilization of this water source in the greenhouse will cause the pH of the media to rise dramatically over time. Acid injection will be required on this farm because of the elevated alkalinity levels of the water source.

After completing the evaluation of this initial water source, I informed the grower that he could not utilize the pond water to irrigate his greenhouse or field crops (because of the high EC level) unless he were able to dilute the water with a low EC (electrical conductivity) water source (rainwater) or invest in a reverse osmosis system that may be both impractical and expensive to implement on his farm.

Dismayed but not disheartened, the grower asked me to evaluate the other water sources on his farm. Next, I checked his well, and its water EC levels were extremely high, so I quickly ruled out its usage on his farm for irrigation purposes. I then checked the large spring, which was equally discounted because of its elevated soluble salt level. The last water source on the farm to evaluate was a large stream about a half-mile from his greenhouse. While the pH, alkalinity level, and EC (electrical conductivity) levels were lower in the stream, surface water can contain molds like Pythium spp. and Phytophthora spp. that can infect and kill various vegetable and greenhouse crops. The stream could be used to irrigate his field-grown vegetables, but its location would make it difficult to use in his greenhouse and high tunnels.

After carefully considering his various options, this grower realized he needed to be more cautious when considering this farm purchase. He should have evaluated each water source before signing the real estate contract. After considering his options like a cistern (for collecting rainwater for dilution purposes), reverse osmosis systems (that were grossly inadequate for the size of his operation), drilling a new well, or connecting to the public water supply, the grower decided that the best solution for him was to connect into the public water supply as soon as possible.

Water quality can be one of the leading causes of yield loss on Pennsylvania vegetable farms. Farm operations should evaluate their water sources annually since water quality can change dramatically from one year to the next. When assessing water quality on the farm, consider selecting the complete ($60) water testing package for greenhouses and nurseries. This testing package will give the grower enough information to formulate a plan to mitigate the water quality issues.