Determination of Critical Phosphorus Dilution Curve Based on Capsule Dry Matter for Flax in Northwest China

One of the cores flax (Linum usitatissimum L.) production is to precisely measure requirement phosphorus (P) fertilization for optimizing seed yield, grower profits, P-use efficiency, and reducing environmental risk. Therefore, critical P concentration (Pc) was proposed as a suitable analytical tool assess nutrition status. Four field experiments, with five applications (0, 40, 80, 120, 160 kg P2O5 ha−1) four cultivars (Longyaza 1, Longya 14, Lunxuan 2, Dingya 22) were conducted from 2017 2019 seasons. The capsule Pc dilution curve based on dry matter (CDM) described by = 2.84 × CDM−0.22 (R2 0.87, p < 0.01), CDM ranging 0.60 4.17 t ha−1. index (PNI) exhibited significant positive relationship application rate. In addition, relative yield closely related PNI. Those results validate that can be an alternative more rapid diagnose status support precise decisions during reproductive growth in northwest China.