“ The uptake of ammonium by roots can result in a lowering of the pH in the nutrient solution .”
An excess of the ammonium form of nitrogen can restrict calcium uptake and cause tip burn in some crops .
Theoretically , ammonium-N should be the superior source of nitrogen because it could be used more efficiently in the plant than nitrate-N . If ammonium-N only were absorbed by root systems , the internal nitrate-to-ammonium conversion that occurs inside plant cells and requires a supply of energy would not be required . However , in reality , if nitrogen is supplied only in the ammonium form , the toxic reaction of the accumulation of uncomplexed ammonium overrides any potential for this greater efficiency of assimilation . Despite this , there can be some benefits to supplying a small percentage of total N as ammonium , but overdoing this can cause some serious problems .
Excessive use of ammonium-N can predispose fruiting crops to blossom end rot , a calcium-related disorder .
Why Use the Ammonium Form of Nitrogen ?
While nitrate may be the dominant and safer form of nitrogen to supply via hydroponic nutrient solution , there can be circumstances when a small percentage of the ammonium form has a benefit . Firstly , a safe level of ammonium is generally regarded to be no more than 10-15 percent of total nitrogen , however , this varies somewhat between crop species and growing conditions . Under conditions of high light and rapid growth , the addition of even small amounts of ammonium-N has the potential to cause growth reductions and physiological disorders . However , under low light and reduced growth rates , such as commonly occurs in greenhouses in winter , a certain percentage of ammonium-N has been shown to be beneficial for the growth of crops .
High levels of ammonium-N competes for potassium uptake and can induce deficiencies .
Ammonium-N , being a cation with a positive charge ( NH 4 +) also competes for the uptake of other cations such as potassium , magnesium , and calcium and an oversupply of the ammonium form of nitrogen can induce deficiencies in these elements . Tip burn in lettuce and many other leafy crops and blossom end rot of tomatoes and capsicum are common issues when the ratio of ammonium to nitrate in a nutrient solution is too high . Ammonium toxicity itself often presents as yellowing or chlorosis between the veins of young leaves , followed by scattered brown , necrotic spots ( depending on the species ), and leaf edges may curl upwards or downwards , root tips may die back , and overall root growth is reduced ; this type of root damage can also provide an entry point for root disease such as Pythium .
The correct level of nitrogen will give healthy , well-coloured foliage .
Providing some of the nitrogen as ammonium-N under slower growing conditions can accelerate the uptake and utilisation of nitrogen , thus boosting growth . But care needs to be taken not to overdo this as too much ammonium-N can restrict calcium , potassium , and magnesium uptake which in turn restricts growth .
38 Maximum Yield