Question

How does soil make up its nitrogen deficit
where leguminous plants are not grown?​

Answer 1

Soil organisms use any nitrogen to break down carbon sources, making N unavailable to plants. This is known as "robbing" the soil of nitrogen. All vegetables apart from nitrogen fixing legumes are prone to this disorder.

Answer 2

Soil contains many microoraganism that are responsible for nitrogen circulation in the soil there are bacteria which balance the nitrogen in the soil dead animal and decayed when is decomposed by the bacteria or fungii all the nutrients are absorbed in soil that are mostly nitrogen. Nitrogen  cycle balances the amount of nitrogen in the soil as there are not much leguminous plants .