Seasonal availability of nitrogen (N) from composted cattle manure (CCM) and poultry manure (PM) was studied in incubations and in fields with a crop of iceberg lettuce and leeks at two sites in Sweden during two seasons. Release of N from CCM was delayed for about 8 weeks in incubated soil and in soil with a crop of leeks, and N availability remained at the mineral N content of CCM at application. After 8 weeks, available N in CCM increased. However, in soil with a crop of iceberg lettuce, available N increased earlier and available N from CCM, as well as from PM, peaked during rapid crop growth. Available N from PM, both in the field and in incubated soil, dropped to a minimum after about two weeks and then increased during the season. N availability decreased at the end of the cropping period for both crops and both manures. The traits of the course of seasonal N availability were similar in the field and in incubated soil for both manures. However, the rapid increase of available manure N during growth of iceberg lettuce differed markedly from incubated soil. Initial losses of N from PM, possibly by volatilization, were higher in incubated soil.