Q.Nitrogen Fixing Plants in Pots
I am residing in Bangalore, India. I am growing creeper vegetable plants such as bottle gourd, ridge gourd, snake gourd, and double beans (Lima beans) in pots on the terrace. I have erected bamboo poles with ropes for the plant to spread. How should I make up the soil without any chemicals? What are the nitrogen fixing plants that can be planted? The size of the cement pots are 20 inches (length) by 20 inches (width) by 20 inches (height). I have used wood shavings in the bottom, and ground soil on top with vermi-compost. The pots have a good drainage system that I devised my self. The yield is not satisfactory.

Certified GKH Gardening Expert
For pots, what you should get is well rotted manure and that will help raise the nitrogen levels. With nitrogen fixing plants, you would need to leave them in the pots to decompose after they grew, and that would not be practical.

Avoid using green manures or nitrogen-rich fertilizers. Beans have a mutual exchange with soil microorganisms called nitrogen-fixing bacteria which produce the soil nitrogen beans require. If there is too much nitrogen, lima beans will produce green foliage but few beans.
Do you drink coffee? Just save your coffee grounds and sprinkle them around the top! It's a great way to give your plants a slow-release nitrogen boost! No need to work them into the soil...