difference of ammonium nitrogen and nitrate nitrogen

[sixto]

hi ron,

can you please tell me the difference of ammonium nitrogen and nitrate nitrogen as far as its relationship to plant growth ?

secondly, my lettuce ... i place them under 75% shade cloth, temperature is also hot ... around 110F at mid-day .... result is gap between nodes are really abnormal.

i am using heat resistant and bolt resistant cultivar for my lettuce, do you suppose the shade cloth is the main problem ?
regards,

sixto