Groundnut is a good option. I have seen good inter-cropping of cotton and groundnut near Hyderabad. Sesbania and in-situ weed live mulches are also another options. You can try stylo also. 

Cowpea

Cowpea

Dr.Blaise,we have to see the opportunities to go for a cover crop in winter .How long the soil moisture will be available? When the temperature starts raising ?Can the residual fertility  support the crop or you have to go for cultivation, fertilizer  application and then raising crop? Can the short duration legumes like green gram ,black gram and cow pea meet your requirement of cover crop ?If you go for long duration crop which produces sufficient dry matter ,can the crop survive with limited moisture and raising temperatures? .These are the points which came to my mind when I thought of cover crop in Nagpur after cotton.Best wishes.

Groundnut does not come up well in this region. We saw poor emergence of this crop. Cowpea is good. We also found Sunnhemp and Sesbania perform well during the rainy season. In winter, soil moisture levels are quite low in the surface. Therefore, we cannot think of green gram or black gram. But these crops we found to perform well during the rainy season. Temperatures are quite low in winter around 23/10 (max/min). Increase in temperature noticed from Feb. Winter legumes should be hardy and able to establish with a single rain that we often receive. Chickpea comes to our mind. Further, they also have to be tolerant to trampling as cotton gets picked during November and January.

In India, we only think about legume cover crops but in European countries researchers tested non-legume crops like oat, rapeseed and mixture of legumes and cereals as cover crops for slow down mineralization and long term availability of nitrogen in the soil.  I think In-situ weed mulch will only serve your purpose because of no- fear of trampling.

I agree to Subba Rao suggestions because we have to look into available soil moisture, soil texture, harvesting time of cotton and the space available in between cotton rows. We have to keep in mind that the major crop is not affected badly. Sesbania and cowpeas may prove better.   

Mungbean is intercropped with cotton very successfully in Pakistan. 

Yes, Mungbean is also good option if Mosaic free varieties are available. The crop completely fails due to Mosaic virus attack sometimes.

Mucuna bracteata , a legume cover crop more popular as cover crop in rubber plantations can be tried to work out the feasibility. It may be noted that it is not edible for human and will not be eaten by the cattle also.

Farmer is more interested in food or fodder crops. Of course if Mucuna proves technically feasible and can bring cash to the farmers, it may be acceptable.

What is the common name of Mucuna? It will have to be solely for soil fertility build up, if it is not edible for human or animal consumption. How does it fare compared to Dhaincha (Sesbania)?

Belel! Your points are very good but consider the temperature when cotton is growing in India. It is mostly between 40-50C. I dont think that peanuts can grow successfully at this temperature. 

Groundnut,soybean or moongbean are most suitable for intercrop with cotton

We have identified moong, cowpea, soybean, cluster bean as good legume intercropping. But, soybean and moonbean do not perform that well in the event of heavy rainfall years. Further, I was

ookong f new options to improve use efficiency

Then it is better to sow spanish bunch ground nut in between two rows of cotton

In temperature range (35-45C) where you grow cotton, many variety of legumes would do a good job as a cover crop or intercrop. Ground nut (preferably dwarf variety with short life span), soybean, Mungbeans (Vigna radiata), black gram (Vigna mungo) and cowpea (Vigna unguiculata). All these legume species will fix nitrogen, but especially ground nut and cowpea will fix higher nitrogen per unit area in comparison to other legumes cited. All are proven intercrops for cotton, but I can specially recommend: groundnut > cowpea > mung (in this order in terms of cash return/acre). This is a proven combination as I have seen the combo working for my grandfather and father for more than 50 years!

Good information given by Rabadia. Any legume can be selected.

Thanks to all those who responded and gave suggestions. I agree that at the moment, we found cowpea, mung and sunnhemp as good legume intercrops. The first two provide additional remuneration. Cluster bean, moth bean are other possible options. If sufficient moisture is available during the October month, we can take up some hardy winter legumes; chickpea does come up well over here. 

Soybean, Urdben and Mungbean are good legumes for inter-cropping with cotton. 

What about mucuna or jackbean?