SUMMARY
Introduction: The Comarca Lagunera, located in the states of Coahuila and Durango, Mexico, is the region with the highest milk production in the country. In this region, dairy farms with agricultural areas for the production of forage crops are common, where excessive rates of manure are applied to the soil and nitrate contamination of groundwater has been reported; therefore, it is important to generate information on the manure available nitrogen (MAN) in a system of two crops per year. Method: A study was conducted with increasing doses of nitrogen (N), depending on the crop N requirement (CNR), using urea, corral manure (CM) and manure from the solid separator (SSM) as sources of N, in silage corn in spring and triticale in winter. The yield of the crops and the availability of N in both types of manure were evaluated. Results: Silage corn dry matter yield was similar in all treatments, from 13.9 to 15.5 t·ha-1, except in the 133% CNR with SSM, which had the lowest yield. In triticale, the differences in yield were not significant. In corn, the dose of 428.6 kg·ha-1 of total N with CM and 449.6 kg·ha-1 of total N with SSM, had the same extraction of N (Nex) of 141.2 kg·ha-1, equivalent to 185 kg·ha-1 of N with urea fertilizer, which corresponds to 100% of the CNR. The above indicates an availability of N of 43.2% in CM and 41.1% in SSM. In the winter season, available N was 19.5% and 11.1% in CM and SSM, respectively. Conclusion: Available N from both types of manure provided enough of this nutrient for two forage crops. Values of available N were similar in both types of manure when estimated in the spring-summer season, but in autumn-winter the MAN was higher in the CM.