Relationships Among Crop Yield, Protein, Soil Properties and Response to Nitrogen Fertilizer Application in an Undulating Landscape in South Central Saskatchewan.

Grain protein can reflect the balance of nitrogen relative to other yield limiting factors. A field season initiated in spring 2012, in south central Saskatchewan, Canada, was established to 1) assess relationships between crop yield, protein content, and soil properties including elevation, electrical conductivity, pH, and organic carbon in an undulating landscape, and 2) determine feasibility of using protein content along with yield and soil data in identifying variable rate N application zones. In 2012, wheat, canola and peas were seeded. Soil samples and harvest measurements were taken from two transects in each field area. Wheat, canola and pea yields ranged from 882-2554, 1143-2342, and 839-3122 kg ha-1 respectively, while protein content for wheat, canola and peas ranged from 10.5-14.4, 14.2-20.6 and 14.5-17.7 percent respectively. Protein in wheat was positively correlated with pH in the 30-60 cm depth and negatively correlated with electrical conductivity in the 30-60 cm depth. Protein in canola was positively correlated with organic carbon in the 0-30cm depth. Wheat yield was positively correlated with organic carbon in the 0-30cm depth. Pea yield was negatively correlated with electrical conductivity in the 0-30 and 30-60 cm depths, reflecting its sensitivity to soil salinity. In spring 2013, wheat was seeded on canola and pea stubble, and canola seeded on wheat stubble with varied N rates on one side of each transect with a constant N rate on the other side. Greater mean yields were observed from the varied N-rate vs the control in the canola-wheat (3163 vs 2256 kg ha-1) and wheat-pea (4716 vs 4155 kg ha-1) rotations. A negative yield from the varied N-rate was observed in the wheat-canola (2216 vs 3012 kg ha-1) rotation. However, these yield differences were not significant (p = 0.05). Similarly, wheat and canola protein content showed no significant differences between the varied N-rate and constant N-rates (p = 0.05).