A sample from a floriculture crop growing in a high tunnel was submitted to the UMass Extension Plant Diagnostic Lab this week. The plants were stunted, leaves were turning yellow and brown, and flower stems were shriveled near the blossoms. No rot was observed in the crowns of the plants. Roots were dry and brittle. No pathogens were observed on microscopic examination. Roots were cultured on selective media, but no pathogenic organisms grew out. No Botrytis or other pathogens were observed in the flower stalks.
The soil accompanying the plant sample had a pH of 6.3 and electrical conductivity (EC) of 4.5 mS/cm (measured by 1:2 method). This EC value is very high and indicates that high soluble salts in the growing medium are most likely responsible for the symptoms observed.
Salts may accumulate through irrigation water that is high in salts, or by run-off from areas where road salt is used in winter. Soluble salts are also introduced to growing media whenever fertilizers are applied. Calcium, magnesium, sodium, chloride, sulfate, and bicarbonate salts are among the most common found in growing media.
It is important to note that soluble salts accumulate more rapidly in high tunnel and greenhouse media than in field soil, as exposure to rainfall dilutes salts and flushes them out of the root zone in the case of field soil. If salts are allowed to accumulate to levels beyond the optimum range for a crop, plant roots can be injured or impaired, plants may become stunted or wilted, and leaves may turn yellow or brown.
Suggestions for managing EC in high tunnel soil include:
- Regular monitoring of EC and pH. This can help growers understand the effects that management practices are having on the soil. Many greenhouse and high tunnel growers choose to purchase portable pH and EC meters for their businesses. For information on interpretation of EC values, please see https://ag.umass.edu/greenhouse-floriculture/fact-sheets/soluble-salts-electrical-conductivity-ec-for-greenhouse-crops
- Establishment of high tunnels in areas with good drainage. Raised beds can also improve drainage.
- When growing in structures where the covering may be removed, consider allowing a fallow period between crops during which covers are removed and the soil is exposed to rainfall.
- Reconsidering the fertilizer program. Avoid fertilizers with high soluble salts, such as animal manure. For more information on choosing organic fertilizers, see https://ag.umass.edu/greenhouse-floriculture/fact-sheets/organic-fertilizers-thoughts-on-using-liquid-organic-fertilizers
If the EC of the growing medium is too high, it should be flushed well with clear water to the extent reasonable. According to the Western Fertilizer Handbook (8th Edition) applying 6 inches of water will leach approximately 50% of the salts; 12 inches will leach about 80%.
High soluble salts may occur in conjunction with nutrient imbalances such as ammonium toxicity. After flushing with clear water, the medium should be re-tested for EC, pH, and nutrient status. For information on submitting a soil sample to the UMass Soil and Plant Tissue Testing Lab, see http://ag.umass.edu/services/soil-plant-nutrient-testing-laboratory
Angela Madeiras, Extension Educator & Diagnostician, UMass Extension Plant Diagnostic Lab