Soil fertility depletion is one of the main concerns of the farmers in the Costa Chica, Mexico. The current crop management exacerbates nutrient cycling unbalances and threatens the sustainability of the common maize production systems. It is necessary to supply the soil with organic sources. Field experiments were established in farmers’ fields to estimate the decomposition rate and N release of organic materials: aboveground and belowground plant residues, and vermicompost. Decomposition was monitored using the litterbag method, and decomposition patterns were fitted by means of a dynamic mono-component mineralization model. To calculate the effects of crop residues retention and vermicompost on OM balance, five scenarios were evaluated with farm DESIGN model. The decomposition rate was greater during the first 4 months. After that period the remaining dry matter proportion of aboveground residues varied between 45 and 67%. In case of root residues, the dry weight loss ranged between 20 and 47% after the first month. For both types of residues, N released within the first month was 37%, on average. At the end of the sampling period 9 months, the remaining dry matter proportion of aboveground and belowground residues ranged from 30 to 55%, whereas more than 80% of their total N was released. After 6.5 months only 35% of the vermicompost mass was decomposed, but about 65% of its N was mineralized. Besides, around 70% of the vermicompost N was released during the first 30 days. In fields with vermicompost maize was responsible for 70% of total N uptake, on average. The N balance was 93% higher than maize fields without vermicompost. In scenario with 30% of crop residue retention along with vermicompost, OM balance was 86% higher than under current management. Vermicompost can be regarded as an attractive amendment for both crop N supply and soil organic matter build-up.