Impacts of 4R Nitrogen Management on Crop Production and Nitrate-Nitrogen Loss in Tile Drainage

This three-year study near Sutherland, Iowa began in January 2015 to evaluate three nitrogen (N) management practices in corn at 135 lbs of N/A (150 kg N/ha) and a no N control. The three practices are: 1) fall anhydrous ammonia with a nitrification inhibitor (Nitrapyrin), 2) spring anhydrous ammonia (no inhibitor), and 3) split fertilizer application, with variable N at sidedress (40 lb of N/A (45 kg/ha) of urea 2x2 (5x5 cm) starter at planting plus in-season urease-inhibitor-treated (Agrotain®) urea). Each treatment is replicated four times within a corn-soybean rotation, with each phase of the rotation present each year. The objectives are to: 1) determine the effects of N fertilizer application timing on nitrate leaching losses through tile (subsurface drainage) flow in each crop phase; 2) determine the effects of fertilizer N application timing on crop yield; and 3) disseminate project findings. The agronomic operations were completed in a timely manner in 2016. The 2016 year was characterized by greater annual precipitation than the 30-year average, with 167% more precipitation in April and 214% more precipitation in September.

There was an increase of 57 bu/A (3,580 kg/ha) with the use of N in treatments 1 to 3 (average 198 bu/A, or 12,430 kg/ha) compared to treatment 4 where no N was applied. During both 2015 and 2016, there was no significant yield difference caused by N placement. Soybean yields in 2016 exceeded 70 bu/A (4,710 kg/ha) for all treatments. For 2016 in the corn phase, lower nitrate concentrations in the zero N added N treatment did not occur as in 2015 (no significant difference between with and without N application). In 2016 within the soybean phase, the treatment where no N was applied to the 2015 corn crop had lower nitrate concentrations in the drainage water compared to the fall N treatment or the spring N preplant treatment. For both years in the corn phase, and in 2016 in the soybean phase, the nitrate concentration was the same for the control and the split N application. Overall, there were no statistically significant differences in subsurface drainage total P or soluble reactive P concentrations between treatments.