Effect Of Manure Source and Application Timing On Nitrogen Use Efficiency Of Corn (Zea mays L.) During a Drought Year.

There are numerous methods for estimating nitrogen use efficiency (NUE) in corn based cropping systems such as relative yield (RY), partial factor productivity (PFP), fertilizer N recovery efficiency (FNRE), agronomic N fertilizer efficiency (ANFE), internal N use efficiency (INUE), and physiological efficiency (PE). The objective of this study was to evaluate these six NUE estimations during a drought year in manure amended corn based cropping systems. This study was conducted on silt loam soils at three on-farm sites in south central Wisconsin.Four manure treatments (none, raw slurry, digested/separated liquid, and digested/separated liquid with a nitrification inhibitor) targeting 85 kL ha-1 were applied in strips replicated four times at three application timings (early fall, late fall, and early spring). In addition, six sub-plot fertilizer N rate treatmentswere applied within each manure strip ranging from 0 to 224 kg N ha-1 in 45 kg N ha-1 increments. Grain was harvested from the center two rows of each four row plot. Whole plant samples for total biomass measurements were sampled at physiological maturity from each manure strip where 0 kg N ha-1 was applied.Soil samples were collected in 30 cm increments down to 120 cm at both pre-plant and post-harvest to monitor NO3- and NH4+concentrations within the soil profile. Grain yields at locations 1 and 2 where soils were well drained were well under the yield potential for these two locations ranging from 2.5 to 8.29 Mg ha-1 and 4.1 to 10.4 Mg ha-1, respectively. However, grain yieldsat location 3 where soils were poorly drained ranged from 11.3 to 13.6 Mg ha-1. Post-harvest nitrate concentrations showed a similar trend to observed grain yields across locations. The 0 to 120 cm profile NO3- concentrations ranged from 30 to 167 kg ha-1 and 87 to 251 kg ha-1 at locations 1 and 2, respectively. Lower post-harvest NO3- concentrations were observed at the greater yielding location 3 ranging from 20 to 140 kg ha-1 in the 0 to 120 cm profile.