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tAccurate forecasting of nitrogen (N) required for plant growth can serve as a guide to improving agricul-tural practices and regulations. The objectives of this study were to: (i) establish a critical N (Nc) dilutioncurve for winter barley based on the shoot dry matter (DM), (ii) compare this curve with other Ncdilutioncurves of different species, and (iii) assess the plausibility of using this curve to estimate the N status ofwinter barley. Four field experiments were conducted with different N application rates. Twenty plantsfrom each plot were sampled from the Feekes 3 to Feekes 10.51 stage for growth analysis. The rela-tionship between Ncand 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, theconstant value Nc= 3.77% was used. The N nutrition index (NNI) ranged from 0.39 to 1.39 from Feekes 3to Feekes 10.51 under different N application rates from 2005 to 2007. The Ncdilution curve identifiedlimiting and non-limiting N status of winter barley and could be used as a reliable indicator of in-seasonN stress of winter barley grown.
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