Final answer:
Azolla spp. are aquatic ferns that fix atmospheric nitrogen, thus reducing the need for nitrogenous fertilizers when used as intercrops in paddy fields, which can lead to increased rice yield and sustainable farming.
Step-by-step explanation:
Farmers need to apply less nitrogenous fertilizers to paddy fields if they incorporate Azolla spp. as an intercrop after transplanting. Azolla is an aquatic fern that has a symbiotic relationship with nitrogen-fixing cyanobacteria, which allows it to fix atmospheric nitrogen and enrich the soil.
This process helps in two significant ways: it increases the rice yield substantially and decreases the dependency and cost associated with chemical nitrogen fertilizers. Besides Azolla, other practices like crop rotation and intercropping with different plant species can improve soil fertility and reduce pesticide and herbicide use, thereby promoting sustainable agriculture practices.