Answer:

Farmers do not apply fertilizers while cultivating pulses because they are LEGUMINOUS plants, i.e. their root nodules contain NITROGEN-fixing bacteria such as RHIZOBIUM and Clostridium. These nitrogen fixing bacteria transform atmospheric nitrogen into fixed nitrogen (nitrogen compounds usable by plants), and thus we don't need to apply nitrogenous fertilizers as nitrogen is naturally made in their roots by the bacteria.

Explanation:

This whole process that enables the bacteria to transform free atmospheric nitrogen into fixed nitrogen like nitrates and nitrites is known as nitrogen fixation. These nitrates and nitrites are taken up by plants, as they are incapable of DIRECTLY taking in elemental nitrogen, or free nitrogen from the air. Hence, nitrogen intake in plants is through its compounds.

When a plant has these special nitrogen-fixing bacteria PRESENT in its root nodules, the plant is called a leguminous plant. These plants usually don't suffer from nitrogen-deficiency as these compounds that are needed by the plant for nitrogen intake are already being made by these bacteria at the roots. Hence, they don't need nitrogenous (nitrogen-containing) fertilizers too. But, they might need non-nitrogenous fertilizers, depending upon the nutrient deficiencies in the soil they are sown in.