Nutrient deficiencies and toxicities can occur in greenhouse crops for numerous reasons other than simply a shortage or over application of nutrients. To prevent future issues and costly miscalculations, knowing how and when nutrient disorders can occur is highly beneficial. Unless you know why a nutrient disorder occurs, you will be unable to formulate a plan for preventing its reoccurrence in future crops. The
following are some of the common reasons for nutrient deficiencies and toxicities.
pH
One factor that can introduce nutrient problems in floriculture crops is the substrate pH. The general pH range for greenhouse crops in a soilless substrate is 5.8 to 6.2, but a wider pH range of 5.5 to 6.4 is sometimes used with more pH tolerant species. Low uptake of nutrients due to nutrient tie-up can occur if the substrate pH is too high. The most common situation is the induction of an iron (Fe) deficiency, and to a lesser extent boron (B) deficiency. Deficiencies of
copper (Cu), manganese (Mn) and zinc (Zn) resulting from an elevated substrate pH levels can also occur, but are rare.
Overwatering
Constant saturation of the substrate can lead to both macro- and micronutrient deficiencies. Overwatering reduces the oxygen levels available to the plant, and root growth can be negatively affected.
An inactive root system due to overly saturated conditions commonly results in limited Fe (upper leaf interveinal chlorosis, Fig. 1) and phosphorus (P) (lower leaf purpling) uptake by the plant.
Low temperature
Growing and substrate temperatures can also play a major role in the induction of nutrient deficiencies. One classic example is how low temperatures (less than 55F [13C]) results in a phosphorus deficiency in tomato, pansies and geraniums. Uptake of Fe is also hindered and can result in the appearance of interveinal chlorosis on the upper leaves. The lower temperatures result in a slower movement and a slower rate of uptake by the plants.
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