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    Thread: nutrients and plants

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      Default nutrients and plants

      By Erik Biksa

      Environmental factors such as temperature, humidity, carbon dioxide (CO2) and light must be supplied and managed at optimum levels to ensure bountiful harvests. This is what initiates the photosynthetic process leading to healthy plant growth. Water and nutrients are required by the plant to support the growth. Once the grower has achieved optimal environmental levels, it's time to pay a closer look at nutrient management to improve quality and yields. For the novice grower it's important to recognize that while nutrients play a role in the development of the crop, they do not always ensure bountiful yields if the growing environment is less than optimal (for example, excessive temperatures and poor air circulation.)
      There are many excellent articles and books detailing the role of specific elements in plant growth. Drawings, photos, and illustrations are also available for diagnosing nutrient deficiencies and toxicity levels. The following should provide a practical foundation for tailoring a nutrient diet specific to your production requirements.
      Nitrogen levels in fertilizers are represented as " % N" on fertilizer labels. The nitrogen found in hydro or hydro-organic fertilizers is available to the plant in either Nitrate (NO3) or Ammonium (NH4) forms, most often supplied in both forms. Ammonium levels should be in a significantly lower ratio than Nitrate levels. For example, a safe range would be to have 10 to 20 times more nitrogen available in the Nitrate form versus in the Ammonium form. For example, the label might read:
      4% N:
      0.25% Ammonical Nitrogen (NH4)
      3.75% Nitrate Nitrogen (NO3)
      Ammonium is too readily available to the plant and can quickly accumulate to toxic levels if it cannot be assimilated for plant growth. Once Ammonium forms of nitrogen are in the plant, they cannot be leached away. Over applications of fertilizers containing high levels of Ammonium nitrogen will lead to distorted and dark growth, usually appearing first at the growing tip of the plant. The imbalance may lead to symptoms appearing as other nutrient deficiencies; the nutrients are supplied, but a chemical imbalance has been created. Higher nitrogen levels are required for vegetative/green growth phases. After cuttings have rooted, gradually increase nitrogen levels from ¼ strength to full strength. This usually takes about 10 to 14 days. Over applications of nitrogen will delay flower and fruit development. Nitrogen levels should start near 100 ppm after cuttings have rooted and may increase to +250 ppm for aggressive growth under optimal conditions. Note that under higher light conditions, the ratio of Nitrogen to Potassium can be near 1 : 1, while under lower light conditions may be as high as 1 : 5.
      Phosphorous levels are represented as "% P" on fertilizer labels. Note that fertilizer labeling laws are very old, and not based
      on current knowledge of plant elements. The "P" on the fertilizer label is often represented as "P2O5", which is phosphoric anhydride; a form plants don't even use. So if a fertilizer label reads:
      4% P (as P2O5)
      What you actually get is:
      1.75% P

      To further confuse matters, phosphorous is most commonly absorbed by plants in the phosphate form, which is PO4. So if there was 1.75% actual P in the fertilizer, there would be 5.35% potential PO4 (phosphate).
      You need not overly concern yourself with this for practical purposes, just recognize that the "P" listed on the label is generally not telling you exactly how much "useable" phosphorous is in the solution.
      Phosphorous levels are required in relatively lower amounts for vegetative growth, and in higher concentrations for flowering/fruiting. The ratio of phosphorous to other elements may also increase slightly during the rooting phase of cuttings.

      During early growth, levels of phosphorous at 15 to 30 ppm are adequate for most crops. Over applications of phosphorous will trigger imbalances
      of iron (Fe) and calcium (Ca), and possibly zinc (Zn). Iron and zinc are very closely associated with keeping the plant "green". When increasing phosphorous levels, calcium, iron, and zinc levels should be increased proportionately. Calcium should be maintained in a 1.5 : 1 ratio with phosphorous. Commercial hydroponic liquid calcium supplement products often contain levels of iron and other trace elements, making them ideal to use when increasing phosphorous levels for blooms.
      Phosphorous levels
      may be increased to levels upwards of 250 ppm during the peak phase of bloom for heavy feeding crops, provided that it is done while maintaining important ratios such as calcium and micro-nutrients. Note that a strong "spike" of phosphorous levels in hydroponic crops during the first week of flowering may induce a slight stress/trigger; in some strains this helps control the height of the crop and flowering structure. This is an aggressive practice and is not recommended for the novice grower. You have to really know your plants before you consider subjecting them to short periods of stress for the long-term benefit of the crop. For example, increasing phosphorous levels to 200+ ppm during the first week of flowering and then gradually increasing phosphorous levels over the course of the crop after dropping to 100 ppm in the second week.

      Potassium, also sometimes referred to as "Potash", levels are represented as "%K" on fertilizer labels. Again, archaic labeling standards misrepresent the level of potentially useable potassium in the product. The "K" on the label generally represents potassium as K2O, which is "postash". Plants don't typically absorb potassium in this form.
      So, if a fertilizer label reads:
      4% K (as K2O)
      What you actually get is:
      3.3% K
      Potassium is required in relatively higher concentrations throughout the growing cycle. It plays a strong role in the internal "pressure" of the plant and acts as a carrier. In more basic terms, potassium assists in root development and in the ripening process of flowers, fruits, and seeds. For well-ripened fruits, flowers, and seeds, increasing potassium levels during the ripening of the flowering/fruiting phase ensures a heavy, colourful, and firm harvest. In some crops higher potassium levels help increase resistance to foliar diseases, such as powdery mildew. In outdoor crops it may increase hardiness to frost.
      For healthy vegetative growth under less intense lighting conditions, potassium may be in a 3:1 ratio versus nitrogen. Under brighter conditions maintaining ratios of closer to 1:1 may contribute to more vigorous green growth. Potassium levels may range from 100 to +400 ppm.

      Calcium levels are represented as "% Ca" on fertilizer labels. In most nutrient concentrate formulations, calcium is supplied separately from phosphates and sulphates. When in concentrated form, they may react and create a sludge that does not supply the crop with necessary and beneficial nutrients. However, when diluted they are relatively stable together. Note, that some newer nutrient manufacturing technologies allow for true "one part" liquid nutrient concentrates, where calcium, phosphorous, and sulphates are stable in concentrated form.
      So, if a fertilizer label reads:4% Ca (Calcium)
      You actually get 4% calcium. Note that this does not guarantee that all the calcium is available. However, if you are buying a modern hydroponic nutrient formulation, it is most likely that all the calcium is being supplied in a plant-available form.
      Calcium is found in the cell walls of plants and is very important in cell division (plant growth). It must be maintained in a ratio to phosphorous, or in simpler terms it should be supplied in 1.5X greater levels than phosphorous. The ratio of calcium to magnesium is important, too. Calcium should be maintained at 3:1 levels to magnesium. For example, 150 ppm is a good level of calcium in a nutrient solution, therefore magnesium levels should be maintained around 50 ppm.
      Magnesium levels are represented as "%Mg" on fertilizer labels. Plants absorb magnesium in this form.
      So if a fertilizer label reads:1.5% Mg (magnesium)

      In this instance there is actually 1.5% magnesium in the solution, but it does not guarantee that it is all in a plant-available form. The situation is similar to calcium. If using a modern hydroponic nutrient, it is very likely that all the magnesium in the solution is in available form. Less soluble sources of calcium and magnesium include Dolomite lime, Calcium Carbonate, and Magnesium Carbonate. Readily available sources are magnesium sulphate (Epsom salts) and magnesium nitrate.
      Many types of crops grown indoors will benefit from elevated levels of magnesium. Keep in mind that levels should be maintained near a 1:3 ratio to calcium. Many growers report harvesting firmer flowers and fruits with elevated levels of magnesium. Magnesium is closely associated with keeping the plant "green" and acts as a carrier molecule for certain plant processes. Additional magnesium is often contained in and supplied with calcium supplements intended for hydroponic usage. In aggressive feeding programs, magnesium levels should be maintained at a minimum of 50 ppm.
      So here we have had a very brief overview of the value of some of the macro-elements, the roles they play in plant growth and the levels needed to ensure healthy development. In the charts featured in this article we have an example of an 11 week feeding program.

      - Weeks one to three are vegetative growth after cuttings have rooted
      - Weeks four to five are transitional; shifting from veg. growth to flowering
      - Weeks five to ten are flowering
      - Week 11 is the ripening/flushing period

      These are actual levels achieved by combining concentrated one-part nutrients as a base, and then "dialing-in" other nutrient values by applying a variety of supplements at different times and at different strengths. The overall feeding levels of this program are very aggressive. If using these levels as a guideline, it would be recommended to start at half these strengths and gradually increase the concentration to determine the crop's threshold for nutrient levels before becoming counter-productive. For the simplicity and length of this article the charts do not indicate micro-nutrient values. When elevating levels of major nutrients such as Nitrogen, Phosphorous, Potassium, Calcium and Magnesium, micro and sub-micro nutrient levels must also be adjusted.Fortunately, most good quality nutrient supplements account for the required elevated levels.Don't pay so much attention to the actual numbers for the purpose of this example, and note that the individual charts have different ranges. Pay attention to the rhythm of the levels throughout the growing cycle, how they relate to each other and when they change - almost like sheet music for plants. These are not theoretically ideal numbers, but values that can be achieved with commercially available nutrients and supplements. Good luck, and remember that with feeding, sometimes less is more. It's much easier to increase the strength than it is to take it away once applied to the crop.
      Last edited by pistils; 6th February 2006 at 06:05 PM.
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