Liquid swine (Sus scrofa domesticus) manure is a large crop nutrient resource in Iowa, but one that should be managed appropriately to gain maximum effectiveness. A multi-year project was initiated on producers' fields to determine the impact of liquid swine manure-N on corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production. Liquid swine manure was injected or broadcast applied (two sites) in field-length strips. The intended rates for corn-soybean were 0, 84, and 168 kg total manure-N ha−1, and for corn-corn and soybean-corn were 0, 112, and 224 kg total-N ha−1. Manure samples were collected during application, and in conjunction with applicator calibration, used to calculate total-N rates. Four fertilizer-N rates (0, 45, 90, and 135 kg N ha−1 for corn-soybean and 0, 67, 135, and 202 kg N ha−1 for corn-corn) were applied to small split-plots within each manure strip to measure response to additional N. Corn N status indicators and grain yield showed frequent and large increase to the low manure-N rate. Smaller additional yield increase was found with the high liquid swine manure-N rates at the most responsive sites. Corn typically produced highest yield increase to additional fertilizer-N when manure was not applied, frequent increase with the low manure rate (magnitude depending upon the site N responsiveness), and no response with the high manure rate. While it was not possible to determine the specific first-year availability of the liquid swine manure-N, we found no reason to estimate it is much different than fully crop available. Liquid swine manure application increased soybean grain yield at several sites, and did not reduce yield. When manure total-N was applied to soybean at rates < 225 kg total-N ha−1, post-harvest profile nitrate was similar to the control. This study has shown that liquid swine manure is an excellent source of N for corn production and application can improve soybean yield. Producers should consider that liquid swine manure-N is highly crop available. For it's best management, practices should focus on matching crop N needs through use of manure sampling, laboratory analyses, and application calibration.