Weather Effects On Corn Response to in-Season Nitrogen Rates.

The response of corn yield to in-season nitrogen (N) fertilizer application (side-dressing; SD) in temperate humid climate is conditioned to a great extent by the prevailing weather conditions which affect N use efficiency and raise the level of uncertainty for field management decisions. Overfertilization is therefore used as a sort of insurance, with consecutive losses of N to the environment and increased production costs. Better understanding the effects of corn heat units (CHU) accumulation and precipitations would allow for adjustments the N rate targeted for optimal supply at SD. An N response trials database covering the years 1997 to 2008 in the grain corn growing area of Quebec was submitted to meta-analyses procedures in conjunction with a corresponding weather database constituted of daily interpolations on a 10 x 10 km grid of an existing network of weather stations. The merit of meta-analysis over qualitative approaches lies in the formal and reproducible investigation of heterogeneity, small study effects, and other data trends. The response of corn to N at SD was positively related to overall CHU accumulation, particularly at intermediate levels. Low CHU accumulation after SD was conducive to high responses to N. High precipitation levels before SD tended to increase N responses, a likely consequence of leaching or denitrification. Also, responses to N were higher as precipitations tended to be evenly distributed over the whole period before SD, rather than when they were concentrated on a few days. The different fertilization treatments in the database will be used to determine the N rates that can be considered optimal depending on weather scenarios. This information will be used in conjunction with soil textural and crop N status information to reduce the level of uncertainty related to optimal in-season application of N, maintaining crop productivity and limiting environmental losses.