Owing to its contribution to the maintenance of carbon stocks, soil nitrogen and nutrient cycling for subsequent crops, the integrated systems become increasingly important for agricultural conservation. Thus, the objective of this study was to evaluate the biomass production of and total nutrient in Brachiaria spp. and Panicum maximum forage grasses used as mulch and soybean yields in an integrated crop–livestock system and second-crop maize succession system. The treatments consisted of the following cropping systems: Xaraes palisadegrass intercropped with soybean, Congo grass intercropped with soybean, Mombaça guinea grass intercropped with soybean, Tamani guinea grass intercropped with soybean and a soybean/maize succession system. The forage grasses were established during the soybean R6–R7 stage. Compared with Congo grass, Xaraes palisadegrass, Mombaça guinea grass and Tamani guinea grass produced more biomass and equivalent amounts of fertilizer returned to the soil and resulted in greater nutrient cycling, indicating the benefits of these grasses for use as mulch in integrated production systems. Maize had a greater C/N ratio, but the forage grasses also exhibited high potential by protecting the soil until the end of the soybean development cycle. The use of an integrated crop–livestock system combined with a forage cropping system provided greater soil nutrient cycling than the maize cropping system did, which resulted in increased soybean yields, thus contributing to the sustainability of agricultural systems.