We tested about 20 species of cover crops, but mostly used in a temperate climate. I'm not sure these could also be used in your country. But you can look at the list in the articles listed in the project.

The question of rotation and cover crops is very important. Ideally for a maize rotation the grain legume will precede the cereal maize crop reducing needs for Nitrogen fertilizer. If you have an environment when winter annual production is possible it good to use winter barley as a crop to precede soybean. In areas where this is possible the winter grain can be used to provide a perennial grass cover ley for fodder production for mixed crop and animal farming. This is how this works in a eastern North American temperate environment. Winter wheat interseeded with clover and grass rotation to maize winter barley rotated with soybean winter broad bean sorghum back to winter wheat. With this system the soil nitrogen becomes sufficient for cropping of cereals and soil organic matter improves to allow better performance in drought years. Ideally in mixed plant and animal systems manures are used for compost which are added back to the crop system. 

Hello,

As @Paul Reed Hepperly commented, the ideal is a graminear rotation - legumes. In Argentina, we use the rotating vicia or trebol (legumes) / corn. In case of soybeans, the ancestor may be wheat, rye, oats (grasses). In the case of leguminous-maize the nitrogen supply is greatly improved. In rye-soybean greatly improves the physical condition of the soil and weed control. In addition to the species, it is necessary to evaluate the cultivars since there are important differences in crop growth.

In the attached I send a book of cover crops of Argentina. The cover crops we use in Argentina do not know if they can be implemented in Zambia.

Greetings.

http://inta.gob.ar/sites/default/files/script-tmp-inta_cultivos_de_cobertura_.pdf

culturas: Milho, feijão e mapira

I think it depends on the climate (precipitation) and type of soil, they are usually short-cycle annual crops.

Dear Kafula, If you are looking to optimize maize production and employ legumes in the heart of the system. The use of the push pull desmodium intercropping is very encouragind as it can contribute to both stem borer and witch weed control while providing the Nitrogen needs for the crop system. You may want to consider that well tested system. To accomplish the system elephant grass is used as a border which is attracted to moths of borers but does not support the worms. The intercropped desmodium is a repellent and provides nitrogen which reduces fertilizer requirement. The desmodium also can control witchweed which is problematic in many areas. 

Dear Hepperly &Kafula, I suggest  Stylo in Black soils under rainfed condition, which improves soil fertility through N fixation and attract predators. 

maize, sorghum and beans

Thanks all for the useful comments and suggestions!