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

Abstract 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 (N c ) dilution curve for winter barley based on the shoot dry matter (DM), (ii) compare this curve with other N c 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 N c and shoot DM could be described by a negative power equation, N c  = 4.76DM −0.39 , when shoot DM values were in the range of 1.79– 13.69 t ha −1 . For DM values −1 , however, the constant value N c  = 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 N c 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.