Environment plays a very important role in plant growth upto a point. Once optimal environmental levels have been achieved in the hydroponics grow room, however, it is the quality of nutrition that determines crop quality and output. The following background information will be useful in understanding of the role of nutrients in hydroponics cultivation.

Nitrogen
Plants absorb nitrogen from fertilizers in both Nitrate (NO3) and ammonium (NH4) forms. Both ammonium and nitrate forms are available in the standard fertilizer mix supplied. It should be noted however, that ammonium levels should be significantly lower than nitrate levels with a safe level being 10 to 20 times nitrogen available in the Nitrate form vis-à-vis the Ammonium form.
Ammonium is readily available to plants and can build up to toxic levels in plant tissue if it is not assimilated for growth. Besides, the Nitrogen from Ammonium is difficult to leach away once it is in plant tissue. It is therefore important too ensure that ammonium content in the nutrients is carefully regulated.
Over supply of fertilizers with high levels of Ammonium nitrogen manifests as distorted and dark growth starting at the plant's growing tip. The imbalance may also lead to symptoms of other nutrient deficiencies despite these nutrients being supplied in the correct amounts. This is because of the nutrient imbalance that is created. Higher nitrogen levels are required during vegetative/green growth phases. After proper rooting of cuttings, nitrogen levels can be increased from ¼ strength to full strength over 10 to 14 days. Over application of nitrogen causes delayed flower and fruit development. Nitrogen levels at the time of rooting of cuttings should be around 100 ppm and may be increased to +250 ppm for aggressive growth under optimal conditions. Light conditions can make a difference to the Nitrogen to Potassium ratio, which can be about 1:1 under higher light conditions, while under low light conditions it may be as high as 1:5.

Phosphorus
Plants require the phosphorus content of the nutrient mix to be high during the flowering/fruiting phase of their life cycle. At other times amounts between 15 to 30 ppm are quite adequate for most crops. Over supply of phosphorus will be harmful during these stages as it will lead to imbalances of iron and calcium and even zinc. Iron and zinc have an association with the greenness of plants, phosphorus levels should therefore be increased only with corresponding increases in levels of calcium, iron and zinc. Calcium levels should be maintained at 1.5:1 ratio with phosphorus. Most commercial calcium nutrient formulations include the right proportions of trace elements to cover flowering/fruiting requirements. Phosphorous levels may be increased to 250 ppm during the peak phase maintaining important ratios such as calcium and micro-nutrients.

Potassium
Potassium is required in root development and also for the ripening process of flowers, fruits, and seeds. Potassium levels can be increased during the flowering/fruiting phase to harvest a heavy, colorful and firm produce. High potassium levels in some crops help increase resistance foliar diseases such as powdery mildew.
Under low lighting growth conditions higher potassium to nitrogen ratios in the range of 3:1 helps healthy vegetative growth. Under brighter the same nutrient proportion may be closer to 1:1 to stimulate vigorous green growth. Most plants do well on potassium levels in the range of 100 to +400 ppm.

Calcium
Calcium is an important component of the cell walls of plants and is also plays an important role in the processes of cell division. It requires to be maintained in a ratio to phosphorus and is best applied in greater amounts 1.5X the level of potassium. The calcium magnesium ratio is also important and should be maintained at 3:1. For instance with 150 ppm calcium levels in a nutrient solution, magnesium levels should be maintained at around 50 ppm.

Magnesium
Magnesium is associated with keeping the plant "green" and is a carrier molecule for certain plant processes. Indoor crops will generally benefit from elevated magnesium levels. Reports on the use of elevated levels of Magnesium have been positive with growers harvesting firmer flowers and fruits. Hydroponics calcium formulations often contain additional amounts of magnesium. It should be noted however, that magnesium levels should be maintained around 1:3 ratio to calcium.

Other Nutrients
In addition to the above nutrients, that constitute the main macro-nutrients that plants need to obtain from the nutrient formulations, there are other macro and micro-nutrients that are vital to various plant processes. While plants use macro-nutrients in large or appreciable quantities, the micro-nutrients are required in trace amounts Plants absorb carbon, hydrogen and oxygen from the air and water. The following table lists various nutrients essential for plant nutrition and the different plant processes they serve.

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