Do Genotypes, Weather, and Soil-Related Characteristics Affect the Critical N Dilution Curve of Spring Wheat?

Abstract Commonly used cultivar testing trials, with standard nitrogen (N) rates applied, located in various pedoclimatic conditions of a region or country, could be potentially used as an alternative to N-response trials for the development of a critical N dilution curve (CNDC). These curves are used for diagnosing plant N deficiency with the Nitrogen Nutrition Index (NNI). This research, using the cultivar testing trials, evaluated the effect of genotype-, weather-, and soil-related factors on the critical nitrogen (N C ) concentration, aboveground dry matter (DM) yield, and the a and b parameters of the CNDC of spring wheat. An existing variability of the aboveground DM and shoot N concentration (2166 pairs of these traits), observed in wheat trials with sixteen cultivars of the Post-Registration Cultivar Testing System in fourteen site-years of different soil susceptibility to drought, was used. Wheat crop was grown at two N management (M) levels, with a total range of N rates applied to all plots from 70 to 176 kg ha −1 . None of the genotype (morphology-related) factors showed a clear tendency for a significant effect on the a and b parameters. However, seasonal weather patterns had a significant effect on both of the parameters. For the majority of the genotypes, weather-related variables had a stronger influence on the CNDC than the soil properties. Our findings suggest that the cultivar testing trials with standard N rates applied, located in various pedoclimatic conditions, can be recommended for the development of generic, refined CNDCs. The reason is that such experiments provide a wide range of N availability to spring wheat, resulting in a large variation in Nc and DM content, which is necessary to develop CNDC. The creation of year- and genotype-specific CDNCs for spring wheat seems unrealistic. This is because seasonal weather patterns affect the a and b parameters of the CNDC, and the ranking of the weather- and soil-related variables that influenced the CNDC was very cultivar-specific.