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Fertilizer equivalence of organic nitrogen applied in beef cattle manure

Montealegre, Juan Pablo Garcia, Wortmann, Charles, Ferguson, Richard, Shaver, Timothy, Little, Richard, Schepers, James
Nutrient cycling in agroecosystems 2019 v.114 no.3 pp. 225-235
Zea mays, beef, beef cattle, canopy, cattle manure, crops, developmental stages, fertilizer rates, grain yield, irrigation, manure spreading, nitrogen fertilizers, organic nitrogen, prediction, reflectance, Nebraska
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.