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If we talk about the PH variation in cannabis plant, we come to the conclusion that varying pH of summer lettuce nutrient solutions also affects the solubility of calcium (Ca) and phosphorus (P). Due to calcium phosphate precipitation (Ca3(PO4)2) the availability of Ca and P decreases at pH values above 6.0. All other nutrients stay in solution and do not precipitate over a wide pH range. Poor water quality could exacerbate any precipitation reactions that may occur. Generally in the pH range 4.0 to 6.0, all nutrients are available to plants. Precipitation reduces Fe, Ca and P availability at pH 6.0 and over.
Adjusting pH The addition of acids or alkalis to nutrient solutions is the most common and practical means to adjust pH, and can be easily automated. There are ways to minimize pH variations and they are worth some consideration. Nitrogen is the essential inorganic nutrient required in the largest quantity by plants. Most plants are able to absorb either nitrate (NO3-) or ammonium (NH4+) or both. NH4+ as the sole source of nitrogen or in excess is deleterious to the growth of many plant species. Some plants yield better when supplied with a mixture of NH4+ (ammonium) and NO3- (nitrate) compared to NO3- alone. A combination of NH4+ and NO3- can be used to buffer against changes in pH.
Cannabis plants grown in nutrient solution containing only NO3- as the sole nitrogen source tend to increase solution pH, hence the need to add acid. But when approximately 10%-20% of the total nitrogen is supplied as NH4+, the nutrient solution pH is stabilised at pH 5.5. NH4+ concentration needs to be monitored as it has been shown recently that micro-organisms growing on plant root surfaces can convert the NH4+ to NO3-. Since hand-held ion-selective electrodes for measuring both NH4+ and NO3- are now available, it should be possible to accurately monitor and maintain a predetermined NO3-/NH4+ ratio throughout the life of the crop. Phosphorus is required in large amounts by plants. Interestingly, there are two forms of fertilisers containing both K and P – KH2PO4 mono-potassium phosphate (MKP) and K2HPO4 di-potassium phosphate. Equal quantities of both can be used to maintain the pH at 7.0. Using a higher proportion of K2HPO4 increases pH. MKP can be used to lower the solution pH. Buffers are solutions which resist pH change and are used to calibrate PH electrodes.
Buffers can be added to nutrient solutions in an attempt to maintain pH stability. One such buffer is called 2-(N-morpholino) ethanesulfonic acid – abbreviated to MES. Many of the companies who claim better pH control with their ‘specially’ formulated nutrient solutions add MES to their mixes. It is important to remember when using MES, that after MES addition the pH is low and needs to be adjusted to your required level with an alkali such as potassium hydroxide (KOH). Another method of pH stabilization is to use ion- exchange and chelating resins. Generally, these resins are small beads which have nutrients absorbed or chelated onto them – the nutrient solution circulates through the beads or the beads can be suspended in the nutrient tank. As plants absorb nutrients, more nutrients are released by the resins. The aim is to achieve controlled release of nutrients into the solution in an attempt to mimic the way the soil releases nutrients.
Ideally, such release can adequately supply the growing plants’ nutritional requirements and maintain pH stability.
Buffers can be added to nutrient solutions in an attempt to maintain pH stability. One such buffer is called 2-(N-morpholino) ethanesulfonic acid – abbreviated to MES. Many of the companies who claim better pH control with their ‘specially’ formulated nutrient solutions add MES to their mixes. It is important to remember when using MES, that after MES addition the pH is low and needs to be adjusted to your required level with an alkali such as potassium hydroxide (KOH). Another method of pH stabilisation is to use ion- exchange and chelating resins. Generally, these resins are small beads which have nutrients absorbed or chelated onto them – the nutrient solution circulates through the beads or the beads can be suspended in the nutrient tank. As plants absorb nutrients, more nutrients are released by the resins. The aim is to achieve controlled release of nutrients into the solution in an attempt to mimic the way the soil releases nutrients. Ideally, such release can adequately supply the growing plants’ nutritional requirements and maintain pH stability. Visit Dutch seeds online store to buy quality cannabis seeds from the quality cannabis seeds suppliers all over the world.