Question

The near and cheapest source of nitrogen for plants is

Answer 1

plants grow in  the soil meaning the first place nitrogen is obtained is in the soil becoz the soil also contains nitrogen

Answer 2

Answer:

The nearest and cheapest source of nitrogen for plants is nitrate or ammonium salts present in soil.

Explanation:

Atmosphere contains a huge percentage of nitrogen, about 78% of whole atmosphere. But the most disappointing thing is, plants can’t absorb atmospheric nitrogen.

So, they need nitrogen fixing bacteria, and minerals from soil like nitrate or ammonium salts to absorb nitrogen and prepare proteins.  Thus, nearest and cheapest source of nitrogen for plants is ammonium salts and nitrate salts.