Maximum Yield Australia/New Zealand September/October 2021 | Page 31

Positive identification is the first step to addressing any toxicity issues in your hydroponic system .”

One of the many benefits of growing in hydroponic systems is the grower controls all the inputs . This means the quality and volume of nutrients the grower wants will go into the system . The downside is there is no help from Mother Nature . It is then totally on the grower to make sure they don ’ t get too much of a good thing and the hydroponic system becomes a toxic soup of too many nutrients for your plants . Like so many well-meaning , young goldfish owners who overfeed their pet to death , it ’ s possible to feed your plants in a hydroponic system to death as well . There is a lot of available information about nutrient deficiencies in crop production , but not as much information is available about toxicities . To correct or prevent nutrient toxicity in plants , we must first know what it is and how to identify it .

Identifying Nutrient Toxicity
Not all plants present symptoms of toxicity and not all show it in the same ways . There are , however , many similarities and some assumptions can be made to at least indicate there is a toxicity issue . It is , though , incredibly important to be able to distinguish between deficiency and toxicity symptoms . When one or more nutrients are present in a hydroponic system in abundance , it can impede the proper absorption and utilisation of other elements even if they , too , are present in sufficient amounts . The nutrient or nutrients in excess will block the other nutrients . The cure for deficiencies will almost certainly cause further harm in plants experiencing toxicities , so positive identification is the first step to addressing any toxicity issues in your hydroponic system . Let ’ s check out some of the most common toxicities and what they look like in hydroponic crops .
Macronutrient Toxicity Symptoms :
Nitrogen ( N ) — This is often the nutrient most likely to be found in toxic amounts , especially for newer hydroponic growers . Nitrogen toxicity can present in several possible ways . Leaves may be lighter green in colour than normal , especially older , lower leaves . The plant stalks may be shorter than normal and slenderer than expected . Flower heads may not fully form or may not form at all , and root systems may be exceedingly dense . In extreme cases of N toxicity , stems may become stiff and brittle .
Phosphorus ( P ) — Plants with excessive amounts of phosphorus can be difficult to diagnose as there are not always specific symptoms to identify . Phosphorus toxicity is somewhat rare and generally will present as copper ( Cu ) or zinc ( Zn ) deficiencies as too much P will impede the absorption of copper and zinc . Some symptoms may include stunted and abnormally green plants and / or purple pigmentation on the undersides of leaves . Potassium ( K ) — Potassium toxicity will generally present as an overall weaker plant . Growth will be stunted and leaves will be smaller than normal . Chlorosis may be noted at the leaf tips and veins and / or edges of the leaves may be purple . These symptoms generally appear on lower , older leaves first . Like phosphorus toxicity , potassium toxicity is not usually seen . Too much K can interfere with the uptake of several secondary macro- and micronutrients . This then can appear as deficiencies in nutrients such as magnesium , manganese , iron , and zinc .

Positive identification is the first step to addressing any toxicity issues in your hydroponic system .”

Secondary Macronutrient Toxicity Symptoms :
Calcium ( Ca ) — Toxicity with calcium can be difficult to identify . Too much of it will block potassium and manganese absorption so it is easier to spot calcium toxicity as a deficiency in the other two nutrients . Plants with too much Ca will often be severely stunted . Leaves may be more crinkled or form a rosette . Older leaves may have interveinal white spots near their margins and may curl downwards . Chlorosis and then necrosis ( cellular or tissue death ) will appear at leaf margins too . The growth pattern of the whole plant will be more horizontal overall .
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