3.1.4. Net Returns

Soil, landscape, and weather factors also had significant impacts on mean NR differences (Table 4). Silt soil textures (Pr ≤ 0.01) had a negative impact on VRN NRs when compared to FP NRs. As noted above, the silt texture also had a negative association to VRN yields and VRN N rates. The N rates savings may not have been enough to increase NR for that soil type. The soil texture reference variable sand (Pr ≤ 0.05), however, had positive associations with VRN NRs compared to FP. Soils with higher organic matter (Pr ≤ 0.01) or deeper profiles (Pr ≤ 0.01) were positively associated with VRN NRs compared to FP. Higher elevation (Pr ≤ 0.10) fields had a negative association with VRN NRs compared to FP. Soils at higher elevations may be more exposed to erosion from wind and rain events. All else equal, warmer growing conditions as measured by GDDs were negatively associated with VRN yields compared to FP, positively with N rates, and, thus, negatively with NR. Warmer temperatures are correlated with dryer climates, particularly during the summer months in the United States [46], which may cause the need for higher N rates because of increased volatilization of N to the atmosphere. However, the higher N applied was not sufficient to increase yields such that VRN NRs were increased relative to the FP.
