In dry areas dominated by dual purpose cattle systems, the production of milk decreases significantly in the dry season. An alternative to maintaining production in the dry season is through the use of annual crops (corn and sorghum) to silage. The objective of this literature review was to compile information on aspects associated with the technology of green legume fertilizers and how they could be integrated into different agricultural and livestock production systems in tropical zones. Whether for crop production, animal feed or for use as hay directly. The use of forage crops to be sustainable requires the application of N since it is one of the most limiting elements to produce forage biomass. The use of synthetic nitrogen fertilizers is limited by high costs, and they also have adverse effects, such as production and leaching of nitrates that contaminate groundwater with negative effects on human health and production of nitrous oxide, which is a potent greenhouse gas which has negative effects on global warming. An alternative to the use of chemical nitrogen is the use of N-fixing forage legumes as green fertilizers to supply the N required by forage crops, but the adoption of green manures in livestock systems is very low, possibly since the benefits obtained with their use are not reflected directly in milk production at critical times of the year, which is important for producers. It is necessary to select N-fixing legumes with high biomass production and drought tolerance and demonstrate that these legumes have positive effects directly in the dry season.
Keywords: nitrogen, feed legumes, soil organic matter, soil fertility.