Many articles have been written over the past few years on water quality and the need for growers to adapt to their individual water supply. Most of these articles have been written by university or industry experts, and they have done a tremendous job explaining the scientific aspects of various water types and how the chemistry of these water types affect the pH of the soil, nutrient availability and overall plant quality. My favorite reference source on this subject is a book titled “Understanding pH Management,” by Bill Argo and Paul Fisher published by Greenhouse Grower.
Many frequently asked questions by our grower customers have focused on soil pH and plant nutrition. Countless callers have a question like this: “I grow in soil brand X, my salesman says the pH is 5.8 to 6.2 straight from the bag, I feed with 20-10-20, and my water pH is 6.0. So why are my petunias yellow?”
Get Water In Balance
A pyramid of growing elements exists, similar to the food pyramid for balanced eating. The three components of the growing pyramid are water, soil and fertilizer. A grower’s success is often based on how well he or she recognizes and addresses these three factors. Often, the challenges are not severe and a grower can produce consistently good plants solely by following general cultural and environmental guidelines. But the room for error can narrow with variances in overall water quality. In those cases, water supplies may need to be treated, specific fertilizers applied or soil mixes selected to address the chemistry of the water supply.
Testing a water supply is one of the cheapest investments any grower can make to ensure the success of a crop. There are many state, local and private labs that run detailed water tests at or well below $50 per sample. All that is usually required is a completed sample form, payment and 8 to 12 ounces of the incoming untreated water supply. (It’s usually recommended that growers send in untreated water for testing.)
Many factors need to be considered when evaluating any water sample. Key components to address are pH, electrical conductivity (EC) and total alkalinity. All nutrients, their individual levels and the ratio of these nutrients to each other must also be considered.
Analyzing Water Quality Problems
The most common problems found with irrigation water are high alkalinity, low alkalinity, low calcium, low magnesium, high boron and high sodium. These challenges can all be corrected with water-soluble fertilizers. But a clear understanding of the situation must be in place so that while addressing one issue, another is not created.
Water pH is listed on test results but has little if any effect on soil pH. The pH of the water source needs to be considered when using various chemicals. Read all labels closely for recommended solution pH levels. In some cases, pH adjustments may be needed to gain full response of the chemical being used.
EC levels of water supplies need to be within recommended levels, or plant growth and development can be greatly affected. The April and May 2011 Greenhouse Grower issues contain well-written articles addressing this subject and should be used as a reference.
More than any other factor, growers need to know and address total alkalinity of the water supply to maintain proper soil pH levels. Instead of looking at alkalinity as the parts per million (ppm) of calcium carbonate in the water and discussing the number of positive and negative hydrogen ions involved, let’s look at alkalinity as the amount of lime in a water supply. Simply said, the higher the alkalinity in a water source, the more “liming” effect will occur. More than likely, soil pHs will rise.
The desired alkalinity range in a water source is 60 to 120 ppm. At this level, the water is buffered enough to help protect the soil from sudden or rapid pH swings. Growers with water in this range should be successful managing soil pH by using most commercial soils designed for their crops and a fertilizer blend that is at or near neutral in pH response.
However, water supplies in nearly 18 percent of the United States have alkalinity levels lower than the recommended 60 to 120 ppm total alkalinity range. In this case, a fertilizer blend that is basic in nature should be used to help buffer the water supply and prevent unwanted soil pH drop. A soil mix with a higher lime charge may also be needed to further prevent soil pH drop.
High Alkalinity Levels
Roughly 40 percent of the United States has water alkalinity levels that are above the recommended ranges. Based on the severity of the alkalinity, growers will notice a gradual or sometimes more rapid rise in soil pH as routine irrigations are applied. Many times, the effect of iron uptake on low pH-loving plants such as petunias, and symptoms of high soil pH do not occur early in a crop, but laterâ€“toward the finish date. This can be confusing when the young crop looks good while being grown in poorer, late-winter conditions. But remember that the liming effect in the soil caused by high alkalinity is an accumulated effect. As plants grow and as weather improves, plant irrigations also increase.
So how should growers address a water supply high in total alkalinity? First, if levels are moderately high to high, consider acidification of the water. There is a great website with an alkalinity calculator, NHfloriculture.com, that can be used to calculate the amount of various acids available for reducing the alkalinity of a water supply. Generally, acids work well and are cost effective to use. Their downside is not only the added expense of a separate injector, but also the caustic nature of these materials. Use extreme care when handling these products.
In cases of high water alkalinity, it is much safer and easier to address the situation by selecting a soil mix with a lower lime charge. This soil will not only have a lower pH right out of the bag, but will also resist the natural rise in pH caused by the water supply for a longer time. Team a fertilizer blend with a strong acidic nature with the soil of a lower pH. These fertilizers will neutralize much of the alkalinity in the water and, with the soil mix, provide most crops with a desirable soil pH.
Remember that acidic fertilizers are high in ammoniacal nitrogen and take care to grow at proper temperatures. If crops are grown extremely cool, ammonium toxicity in the soil mix can occur and root damage may result. Or if crops are grown warmer than needed, excessive soft growth and leaf expansion may occur. But when used properly, acidic fertilizers can be great products for controlling soil pH.
Understanding EDDHA Iron
Another tool that can be used in the battle against high soil pH and iron deficiency is EDDHA iron. This iron form has been proven to supply iron to plants much better than other forms of iron, even when soil pHs climb to undesirable levels. It’s easiest and most economical to purchase fertilizer blends already containing the EDDHA iron but if needed, it can be purchased separately, applied as a drench or added to existing fertilizer mixes. EDDHA iron can quickly “green up” a crop but remember that it is a tool and not a cure-all. For long-term health and saleable appearance of crops, growers should focus on addressing proper soil pH ranges.
A grower’s job and success can be much easier and less stressful by testing the water source in advance and selecting the proper soil mix and fertilizer program, based on these tests. Tools like acid injection and EDDHA iron can be used to achieve the proper soil chemistry needed to overcome less than desirable water supply quality. I recommend growers regularly test the soil pH and EC levels of their crops to better manage and understand the status of these crops.