Author
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Frantz, Jonathan |
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Submitted to: Michigan State University Extension
Publication Type: Popular Publication Publication Acceptance Date: 12/10/2005 Publication Date: 12/10/2005 Citation: Frantz, J. 2005. Greenhouse nutrition. Michigan State University Extension Bulletin. Interpretive Summary: There are 18 essential elements that need to be present for the plant to grow well and withstand typical stresses. Of these 18, Nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S), the so called macronutrients, and iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), manganese (Mn), boron (B), and silicon (Si), the micronutrients, need to be added at some point during production. As a general rule of thumb, 100 to 200 ppm N on a continuous feed can supply sufficient N to a crop. Use a ratio of 2:1:2 or even 4:1:4 for N, P, and K for growth in most crops. Magnesium and S, along with Ca, can be supplied in the form of dolomitic lime and gypsum. There are many products designed to supply all or part of the required micronutrients and many can be supplied once, when the media is mixed, without deficiency symptoms. Fe is an exception to this, and Fe requirements can vary greatly from species to species. If Fe needs to be added, try a chelated form of Fe such as EDDHA or DTPA. Boron is often present in sufficient quantities in the water supply; if your water has anywhere from 0.1 to 0.8 ppm B, you may not need to add any more B. In some areas, the use of slow release or controlled release fertilizers (CRFs) is common. Due to increasing environmental restrictions, there is tremendous potential in its use because less fertilizer is lost through leaching. When used, half or two thirds of the total nutrients are supplied with CRFs and the rest is supplied as liquid feed. Regular monitoring of media, water, and plants, beyond just pH and EC readings are essential to achieve the highest quality and productivity in your production and can prevent a lot of problems while developing a fertilization program. Technical Abstract: There are 18 essential elements, including silicon, that need to be present for the plant to grow well and withstand typical stresses. Three of these, carbon (C), hydrogen (H), and oxygen (O) are acquired through the air (CO2 and O2) or water (H2O). Chlorine (Cl) and nickel (Ni) are usually present in sufficient quantities as contaminants in soilless media, water, or fertilizer to make their additions unnecessary. The remaining “essential” elements are Nitrogen (N), phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S), the so called macronutrients, and iron (Fe), zinc (Zn), copper (Cu), molybdenum (Mo), manganese (Mn), boron (B), and silicon (Si), the micronutrients. As a general rule of thumb, 100 to 200 ppm (100 to 200 mg liter-1, 7 to 14 mM N) on a continuous feed can supply sufficient N to a crop. A common N:P (as P2O5) ratio is 2:1, but most crops can probably do well with much lower P, for example 4:1 or even 10:1. A useful guideline is to supply K in a 1:1 ratio with N. Magnesium and S, along with Ca, can be supplied in the form of dolomitic lime and gypsum. There are many products designed to supply all or part of the required micronutrients and many can be supplied once, when the media is mixed, without deficiency symptoms. Fe is an exception to this, and Fe requirements can vary greatly from species to species. If Fe needs to be added, try a chelated form of Fe such as EDDHA or DTPA. Zinc and Cu can also be added as chelated forms. Boron is often present in sufficient quantities in the water supply; if your water has anywhere from 0.1 to 0.8 ppm B, you may not need to add any more B. Be careful of B in the fertilizer as a contaminant, and if composted material is used, B may be present in sufficient to toxic levels. Have your water and media tested for B regularly. Silicon allows for better use of Mn supply, and if you suspect Mn toxicity, supplying Si can protect against Mn toxicity. A supply of 100 ppm Si (3.4 mM) appears to be sufficient for most crops investigated to date. In some areas, the use of slow release or controlled release fertilizers (CRFs) is common. Due to increasing environmental restrictions, there is tremendous potential in its use because less fertilizer is lost through leaching. When used, half or two thirds of the total nutrients are supplied with CRFs and the rest is supplied as liquid feed. Regular monitoring of media, water, and plants, beyond just pH and EC readings are essential to achieve the highest quality and productivity in your production and can prevent a lot of problems while developing a fertilization program. |
