A farmer tested the soil in a field and found that there was a high nitrate salt concentration. The farmer then grew a crop in this field. After the crop was removed, the soil was tested again.
The nitrate salt concentration had decreased.
(a) Suggest reasons why the nitrate salt concentration had decreased
(b) Some species of plant grow well in soil that is always low in nitrate salt. Explain how
they can obtain a source of nitrogen compounds.