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NITROGEN MANAGEMENT

Critical Nitrogen Curve and Nitrogen Nutrition Index for Corn in Eastern Canada

^a Agriculture and Agri-Food Canada (AAFC), Soils and Crops Research and Development Centre, 2560 Hochelaga Blvd., Quebec, QC, Canada G1V 2J3
^b AAFC, 430 Gouin Blvd., St-Jean-sur-Richelieu, QC, Canada J3B 3E6
^c Dep. of Soil and Agri-Food Engineering, Laval Univ., Sainte-Foy, QC, Canada G1V 0A6

^* Corresponding author (ziadin{at}agr.gc.ca).

Plant-based diagnostic methods of N nutrition require the critical N concentration (N_c) to be defined, that is the minimum N concentration necessary to achieve maximum growth. A critical N curve (N_c = 34.0W^–0.37 with W being shoot biomass in Mg DM ha^–1), based on whole plant N concentration, was determined for corn (Zea mays L.) in France. Our objectives were to validate this critical N curve in eastern Canada and to assess its plausibility to estimate the level of N nutrition in corn. Shoot biomass and N concentration were determined weekly during the growing season at three sites for 2 yr (2004 and 2005); four to seven N treatments were used at each site. Data points were divided into two groups representing either nonlimiting or limiting N conditions according to significant differences in shoot biomass at each sampling date. All data points included in the limiting N group were under the critical N curve and most data points of the nonlimiting N group were on or above the critical N curve, hence confirming the validity of the critical N curve determined in France. The nitrogen nutrition index (NNI), calculated as the measured N concentration divided by the predicted N_c, ranged from 0.30 to 1.35. A significant relationship between relative grain yield (RY) and NNI (RY = –0.11 + 1.17 NNI if NNI < 0.93 and RY = 0.98 if NNI > 0.93; R² = 0.89) was determined. The critical N curve from France is valid in eastern Canada and the NNI calculated from that curve is a reliable indicator of the level of N stress during the growing season of corn.

Abbreviations: CHU, corn heat units • DM, dry matter • LSD, least significant difference • NNI, nitrogen nutrition index • SEM, standard error of the mean

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Received for publication February 9, 2007.