Wednesday, November 15, 2006 - 1:05 PM

How to Mitigate the Effects of Season on Corn Nitrogen Fertilizer Requirements.

Nicolas Tremblay and Carl Bélec. Agriculture and Agri-Food Canada, Research Center, 430 Gouin Boulevard, St-Jean-sur-Richelieu, QC J3B 3E6, Canada

The effect of season on N fertilizer requirements of corn in Quebec is no different from temperate humid climates areas. Both the requirements and the supply of N vary among soils and across the landscape within a field and they are expected to vary within and between seasons due to variable weather conditions. Better weather predictions as well as agronomical, economical and environmental models are needed to account for these facts. In the meantime, solutions are available to mitigate seasonal effects. Early spring N application results in nitrate release in advance of crop N uptake, and may also result in leaching losses. Late spring precipitation and temperature are critical controls of this release and loss. It is important to postpone fertilizer application as late as possible in order to take these processes into account. On-the-go in-crop assessment of N sufficiency based on chlorophyll saturation index can be helpful. This strategy can be summarized through the following steps: 1) apply a minimum of N at sowing and keep most of the N for a later application; 2) establish a reference plot; 3) perform an in-crop assessment of N sufficiency based on chlorophyll saturation index. The assessment of N sufficiency will provide a potential response of the crop to N. This potential response should then be adjusted based on the yield potential of the soil as well as the risk of N losses with the help of easy-to-map terrain features (soil electrical conductivity and topography). The above strategy will likely allow for a reduction in average fertilizer N use, and make the use of “insurance” rates less necessary. Lower rates would likely be recommended for normal and dry years, and higher N rates when wet late spring conditions cause a loss of mineralized soil nitrate.