heatherlonglee
Active member
Perfect pH
Thursday, April 25, 2013
A Word About pH and Nutrition
Ideal pH: The starting pH range for most PRO-MIX products is between 5.4-5.9. After watering and using fertilizer, the pH of the PRO-MIX is fluid and can change. Ideal pH for most crops is 5.5-6.2. If pH is higher, micronutrients become unavailable to the plant causing yellowing or distortion in new leaves. If the pH of the growing medium is lower, micronutrients are more available and if taken up in excessive quantities can cause leaf edge burn on the lower leaves.
Testing the pH of a crop: pH is best measured using the saturated media extract method (growing medium is removed from the root ball, distilled water is added to saturate the growing medium sample and the pH and salts are tested from the mud after 30 minutes). Some growers use a pour thru method, where a measured volume of distilled water is applied to the growing medium and the leachate (run-thru) is collected, but it is only as accurate as the amount leachate that comes out from the bottom of the container. If too much comes out, the pH and salts will be diluted and will not accurately reflect the levels in the growing medium. If too little comes out, the salts are concentrated and the pH is often unreliable, too. To avoid fluctuations, make sure the procedure is done the same way each time and measured accurately.
Maintaining the pH of PRO-MIX : There is a lot of misconception about the effects of ‘water pH’ on the pH of PRO-MIX. The truth is that the pH of the water has no bearing on the pH of the PRO-MIX. In other words, if the pH of the water is 5.5, that does not mean the pH of the PRO-MIX will be 5.5 overtime. So what influences the pH of the PRO-MIX?
Bicarbonates: Think of the bicarbonates in the water as dissolved limestone. If it is low (<50 ppm HCO3), then the pH of the PRO-MIX will not change much because there is little limestone supplied at very watering. If the bicarbonates are high >180 ppm HCO3, the media is being limed at every. This causes the pH of the PRO-MIX to rise to unacceptable levels (above 6.5), even if the pH of the water is 5.5. Ultimately the goal is to match up the fertilizer with the bicarbonates within the water.
Many companies recommend using water that has passed through a reverse osmosis unit. Often this is an unnecessary step, but it will filter out most of the bicarbonates from the water as well as beneficial calcium and magnesium. If the unit works properly, it will reduce the bicarbonates in the water to undesirable low levels. If you use a R.O. unit, it is best to blend the water R.O. water with some (505) of the source water to achieve a desirable bicarbonate level.
Fertilizer: Fertilizer elements that are absorbed by plant roots have an electrical charge. The plant root zone has to maintain its neutral electrical charge. For plant roots to uptake electrically charged nutrients, the root system must give off and exchange elements of the same charge. Therefore, for the plant’s roots to absorb positively charged ammonium, potassium, calcium or magnesium, the roots must give off hydrogen. Hydrogen is acid and will reduce the pH of the growing medium. If the root systems absorbs nitrate, phosphate and/or sulfate, it will release off negatively charged alkaline hydroxides – which increases the pH of the growing medium.
Of these elements, nitrogen is the only one that can have an acidic (ammonium and urea) or alkaline (nitrate) reaction with the plant roots. The ratio of these nitrogen forms within the fertilizer dictates whether the fertilizer is potentially acidic or alkaline, depending on how it is absorbed and reacts with plant root systems. As a guide, many fertilizer manufacturers will list the fertilizer’s “potential acidity” or “potential basicity” which indicates how much acid or base is added to the growing medium by the plant roots. Most growers will have their water tested and then match the fertilizer to the water quality. This matching will minimize pH fluctuations within the growing medium.
Having said all this, if the water has been processed through a reverse osmosis unit it most likely will have a slight change effect on the pH of the growing medium. However, any fertilizer will have a significant influence on the pH of the PRO-MIX. The fertilizer used should supply all 13 elements (N, P, K, Ca, Mg, SO4, Fe, Mn, B, Cu, Zn, Mo) and the fertilizer’s should provide potential acidity or potential basicity. Without this information, it is difficult to determine where the pH of the growing medium will go long term.
Copy and pasted from
www.pthorticulture.com/en/training-center/perfect-ph/
Thursday, April 25, 2013
A Word About pH and Nutrition
Ideal pH: The starting pH range for most PRO-MIX products is between 5.4-5.9. After watering and using fertilizer, the pH of the PRO-MIX is fluid and can change. Ideal pH for most crops is 5.5-6.2. If pH is higher, micronutrients become unavailable to the plant causing yellowing or distortion in new leaves. If the pH of the growing medium is lower, micronutrients are more available and if taken up in excessive quantities can cause leaf edge burn on the lower leaves.
Testing the pH of a crop: pH is best measured using the saturated media extract method (growing medium is removed from the root ball, distilled water is added to saturate the growing medium sample and the pH and salts are tested from the mud after 30 minutes). Some growers use a pour thru method, where a measured volume of distilled water is applied to the growing medium and the leachate (run-thru) is collected, but it is only as accurate as the amount leachate that comes out from the bottom of the container. If too much comes out, the pH and salts will be diluted and will not accurately reflect the levels in the growing medium. If too little comes out, the salts are concentrated and the pH is often unreliable, too. To avoid fluctuations, make sure the procedure is done the same way each time and measured accurately.
Maintaining the pH of PRO-MIX : There is a lot of misconception about the effects of ‘water pH’ on the pH of PRO-MIX. The truth is that the pH of the water has no bearing on the pH of the PRO-MIX. In other words, if the pH of the water is 5.5, that does not mean the pH of the PRO-MIX will be 5.5 overtime. So what influences the pH of the PRO-MIX?
Bicarbonates: Think of the bicarbonates in the water as dissolved limestone. If it is low (<50 ppm HCO3), then the pH of the PRO-MIX will not change much because there is little limestone supplied at very watering. If the bicarbonates are high >180 ppm HCO3, the media is being limed at every. This causes the pH of the PRO-MIX to rise to unacceptable levels (above 6.5), even if the pH of the water is 5.5. Ultimately the goal is to match up the fertilizer with the bicarbonates within the water.
Many companies recommend using water that has passed through a reverse osmosis unit. Often this is an unnecessary step, but it will filter out most of the bicarbonates from the water as well as beneficial calcium and magnesium. If the unit works properly, it will reduce the bicarbonates in the water to undesirable low levels. If you use a R.O. unit, it is best to blend the water R.O. water with some (505) of the source water to achieve a desirable bicarbonate level.
Fertilizer: Fertilizer elements that are absorbed by plant roots have an electrical charge. The plant root zone has to maintain its neutral electrical charge. For plant roots to uptake electrically charged nutrients, the root system must give off and exchange elements of the same charge. Therefore, for the plant’s roots to absorb positively charged ammonium, potassium, calcium or magnesium, the roots must give off hydrogen. Hydrogen is acid and will reduce the pH of the growing medium. If the root systems absorbs nitrate, phosphate and/or sulfate, it will release off negatively charged alkaline hydroxides – which increases the pH of the growing medium.
Of these elements, nitrogen is the only one that can have an acidic (ammonium and urea) or alkaline (nitrate) reaction with the plant roots. The ratio of these nitrogen forms within the fertilizer dictates whether the fertilizer is potentially acidic or alkaline, depending on how it is absorbed and reacts with plant root systems. As a guide, many fertilizer manufacturers will list the fertilizer’s “potential acidity” or “potential basicity” which indicates how much acid or base is added to the growing medium by the plant roots. Most growers will have their water tested and then match the fertilizer to the water quality. This matching will minimize pH fluctuations within the growing medium.
Having said all this, if the water has been processed through a reverse osmosis unit it most likely will have a slight change effect on the pH of the growing medium. However, any fertilizer will have a significant influence on the pH of the PRO-MIX. The fertilizer used should supply all 13 elements (N, P, K, Ca, Mg, SO4, Fe, Mn, B, Cu, Zn, Mo) and the fertilizer’s should provide potential acidity or potential basicity. Without this information, it is difficult to determine where the pH of the growing medium will go long term.
Copy and pasted from
www.pthorticulture.com/en/training-center/perfect-ph/
