Fertilizer equivalence of organic nitrogen applied in beef cattle manure

The fertilizer N equivalent (FNE) value of applied organic N (OrgN) is poorly predicted, often resulting in over-application of fertilizer N. Research was conducted for irrigated, continuous-corn (Zea mays L.) in eastern Nebraska with three rates of beef (Bos taurus) feedlot manure as main plot treatments and five pre-plant fertilizer N rates as sub-plot treatments. The objective was to determine the FNE for the first, second and third successive crops following feedlot manure application with different rates of OrgN and fertilizer N application. The in-season FNE, based on normalized difference crop reflectance for the crop canopy, was less with 74 compared with 37 Mg ha⁻¹ manure applied for crop one after application but the manure rate effect on the subsequent two crops was inconsistent. The mean cumulative full-season FNE, based on grain yield, for the three successive crops, was 0.72 kg N kg⁻¹ OrgN which was twice the in-season estimate of 0.36 kg kg⁻¹ at growth stage V12, indicating significant apparent recovery of OrgN after V12. The full-season FNE varied inconsistently with pre-plant fertilizer N rate and the three successive crops following application. The mean manure N recovery efficiency was 0.139 kg N kg⁻¹ OrgN year⁻¹ for the three crops following application with no significant treatment effects. Manure is a valuable source of N but the N supply is highly variable for the crops following application so prediction of supply for a given season is unreliable.