Relationship between Phosphorus and Nitrogen Concentrations of Flax

Tools quantifying phosphorus (P) status in plants help to achieve efficient management and to optimize crop yield. The objectives of this study were to establish the relationship between P and nitrogen (N) concentrations of flax (Linum usitatissimum L.) during the growth season to determine the critical P concentration for diagnosing P deficiency. Field experiments were arranged as split plots based on a randomized complete block design. Phosphorus levels (0, 40, 80, 120, and 160 kgP(2)O(5) ha(-1)) were assigned to the main plots, and cultivars (Dingya 22, Lunxuan 2, Longyaza 1, Zhangya 2, and Longya 14) were allocated to the subplots. Shoot biomass (SB) and P and N concentrations were determined at 47, 65, 74, 98, and 115 days after emergence. Shoot biomass increased, while P and N concentrations and the N:P ratio declined with time in each year. The P concentration in respect of N concentration was described using a liner relationship (P = 0.05, N + 1.68, R-2 = 0.76, p < 0.01) under non-limiting P conditions, in which the concentrations are expressed in g kg(-1) dry matter (DM). The N:P ratio was fitted to a second-order polynomial equation (N:P = 11.56 x SB-0.1, R-2 = 0.71, p = 0.03), based on the SB of flax. This research first developed a predictive model for critical P concentration in flax, as a function of N concentration in shoots of flax. The critical P concentration can be used as a promising alternative tool to quantify the degree of P deficiency of flax during the current growing season.