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Ontario Grain Farmer Magazine

Updating and harmonizing corn nitrogen recommendations

Principal Investigator: Greg Stewart and Ian McDonald

Research Institution: Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)

Timeline: December 2012 – March 2015

Objectives:

  • Develop a harmonized N recommendation system that draws on both general recommendation factors and soil N test factors.
  • Identify any gaps in knowledge and future research needs associated with the prediction of N availability to corn by the soil N test, particularly as it relates to climatic variability and manure and cover crop N supply.
  • Provide a platform to launch more site/season specific N recommendation research that could include adjustments for factors such as weather or canopy reflectance.

Impacts:

  • Update Pre-Sidedress Nitrogen recommendations with more recent research data.
  • Update Pre-Sidedress Nitrogen recommendations to include a yield expectation component.

Scientific Summary:

For some time now there have been two distinct nitrogen recommendation systems for corn in Ontario: the General Recommendation tool and the soil nitrate adjustment (Pre-Sidedress Soil Nitrate Test; PSNT). These two systems did not work particularly well together and stakeholders that used both tools found that recommendations could be distinctly different. General recommendations were developed using trial data from 1962-2002 to calculate maximum economic rate of N (MERN) and the associated yield (MEY) was calculated at a N:Corn price ratio of 5. The PSNT for Ontario was introduced in 1992 and the calibration data set consisted of 52 trial sites conducted throughout Ontario from 1986-1990.  At each site economic fertilizer N rates were calculated and regressed on near planting date (May) soil nitrate-N concentrations in the surface 60cm. This PSNT made no adjustment for crop demand (yield) and assumes that variation in fertilizer N requirements is entirely due to differences in soil N supply. Corn yield expectation is currently a component of the General recommendation tool but is absent in the PSNT recommendation. Corn yield was reported to have little effect in corn N requirements. 

This project aimed to update corn nitrogen recommendations. A comparison of N recommendations provided by General, Old PSNT and Refitted PSNT recommendations with actual MERN from a long-term corn N response trial located at Elora for years 2009-14. PSNT recommendations were refitted based on the delta-yield approach, assuming fertilizer recommendation is difference between corn N requirement (demand) and soil N available to corn (supply) adjusted for N use efficiency of applied N fertilizer. Delta-yield is the difference between the plateau yield and 0-N yield (kg/ha). Proven yield is expected to reflect an N-Rich yield while 0-N yield is estimated based on agronomic efficiency of proven yield and credit to PSNT sample results. New Refitted PSNT recommendations provide a more accurate nitrogen recommendation than both old PSNT recommendations and general recommendations, and therefore represent an opportunity to improve nitrogen management practices by better identifying a correct application rate, reducing costs associated with under-applying (economic loss due to yield loss) or over-applying (economic and environmental cost through excess N application rates). The PSNT recommendations have changed, and have been approved by Ontario Soil Management Research and Services Committee (OSMRSC) as a result of the improvement in prediction accuracy of the Refitted PSNT method relative to the old PSNT measurement. Harmonization with General recommendations was not supported as Refitted PSNT had a higher predictive power than general recommendations, so it was recommended that Refitted PSNT override General recommendations where PSNT is conducted.

External Funding Partners: Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)

Project Related Scientific and Popular Publications:

Stewart, G. and K. Janovicek. 2015. A New and Improved Soil Nitrate Test for Corn! Crop Talk. 15(1). http://www.omafra.gov.on.ca/english/crops/field/news/croptalk/2015/ct-0315a1.htm