Transformations and losses of swine manure 15N as affected by application timing at two contrasting sites

Abstract

An improved understanding of the fate of manure N is necessary for developing efficient manure management plans that ensure adequate crop nutrition and minimum environmental problems. This study quantified the fate of 15N-labelled liquid swine manure applied at three different times (late-fall, spring pre-plant and side-dress) on two soil types (a well-drained fine sandy loam and an imperfectly drained silt loam). Manure N uptake by corn (Zea mays L.) was significantly lower with fall application than with two spring applications (14-18% vs. 30-38% of applied N) in both soil types. Manure application increased total N leaching (30-43 vs. 27 kg N ha-1 yr-1 in the control), especially with fall application. Manure N contributed 18-25% of the total N leached in the fine sandy loam and 8-10% of the total N leached in the silt loam. Application timing did not affect manure N leaching in the silt loam, which ranged between 3 and 5% of applied N. In the fine sandy loam, fall application resulted in significantly higher manure N leaching (15% of applied N) than with two spring applications (8-10% of applied N). Unaccounted losses, assumed to be in gaseous forms, over 6 mo following fall application were higher in the silt loam than in the fine sandy loam (29% vs. 16% of applied N). Estimated NH3 losses were low (<7% of applied N); hence, denitrification is suggested to be the main mechanism for gaseous N losses. The estimated ratio of denitrification to leaching manure N loss for fall application was about 7:1 in the silt loam and 2:1 in the sandy loam. To maximize manure N use by corn and minimize environmental N losses, spring or side-dress application of liquid swine manure is recommended, particularly in well-drained soils.Key words: Swine manure, application timing, soil type, 15N, N losses