When a man has an erection does he releases sperm

Not necessarily.

Explanation:

An erection is caused by blood flow to the penis. A man can get an erection just by seeing a woman or hearing language that turns him on or excites him. A young man who is not experienced in controlling an erection may release sperm in a spontaneous ejaculation but more experienced men would not likely ejaculate without more stimulation, such as masturbation.

step 1: nitrogen fixation- conversion of atmospheric no₂ into forms useful to plants by lightning, bacteria, and cyanobacteria.

step 2: nitrification-process of converting ammonia to nitrite or nitrate.

step 3: assimilation-plant roots absorb new form of nitrogen.

step 4: ammonification-conversion of organic nitrogen to ammonia by bacteria involved in decomposition.

step 5: denitrification-bacteria turns the decomposed matter back into n₂o, which is released into atmosphere; repeat cycle.