Nitrogen cycling in soil

Statement 1 is correct: Animal urea is excreted and eventually decomposed, adding nitrogen to soil through organic decomposition. Statement 2 is incorrect: Burning of coal may release nitrogen oxides into the atmosphere, but does not directly add nitrogen to soil in a beneficial form. Statement 3 is correct: Dead vegetation decomposes and returns nitrogen (as part of organic matter containing proteins and nucleic acids) to the soil, replenishing it through the nitrogen cycle. Statements 1 and 3 both represent natural nitrogen cycling processes. > Remember: Organic nitrogen sources (animal waste, dead organisms) add to soil; combustion releases atmospheric oxides. Answer: c.