Determining of a critical dilution curve for plant nitrogen concentration in winter barley

• A critical nitrogen (Nc) dilution curve (Nc = 4.76DM−0.39) was developed for winter barley.
• The Nc dilution curve was proposed for diagnosis of plant N status in winter barley.
• Nitrogen nutrition index (NNI) and accumulated N deficit (Nand) can discriminate situations varying by N fertilization.

Accurate forecasting of nitrogen (N) required for plant growth can serve as a guide to improving agricultural practices and regulations. The objectives of this study were to: (i) establish a critical N (Nc) dilution curve for winter barley based on the shoot dry matter (DM), (ii) compare this curve with other Nc dilution curves of different species, and (iii) assess the plausibility of using this curve to estimate the N status of winter barley. Four field experiments were conducted with different N application rates. Twenty plants from each plot were sampled from the Feekes 3 to Feekes 10.51 stage for growth analysis. The relationship between Nc and shoot DM could be described by a negative power equation, Nc = 4.76DM−0.39, when shoot DM values were in the range of 1.79– 13.69 t ha−1. For DM values <1.79 t ha−1, however, the constant value Nc = 3.77% was used. The N nutrition index (NNI) ranged from 0.39 to 1.39 from Feekes 3 to Feekes 10.51 under different N application rates from 2005 to 2007. The Nc dilution curve identified limiting and non-limiting N status of winter barley and could be used as a reliable indicator of in-season N stress of winter barley grown.