Abstract:

In order to conduct an in−depth investigation of the nitrogen nutrition diagnosis method and nitrogen fertilizer management recommendation scheme for oilseed flax based on the SPAD−502 chlorophyll meter, the oilseed flax variety Longya 11 was used as the experimental material. The study examined the relationships between SPAD values in oilseed flax leaves and nitrogen nutrition diagnostic indices, as well as nitrogen application rates, under different nitrogen treatments (N0: 0kg·ha⁻¹, N1: 60kg·ha⁻¹, N2: 120kg·ha⁻¹, N3: 180kg·ha⁻¹) and different nitrogen splitting ratios (T1: all as basal fertilizer, T2: basal fertilizer: budding fertilizer=2:1, T3: basal fertilizer: branching fertilizer: budding fertilizer=1:1:1). Additionally, the impact of nitrogen application rates on oilseed flax grain yield was analyzed. The results showed that under different nitrogen application levels, at the same growth stage of oilseed flax, the leaf SPAD values consistently showed a gradual increasing trend with higher nitrogen application rates across all treatments, in the order of N3>N2>N1>N0. Under different split nitrogen application ratios, the leaf SPAD values at all growth stages followed the order T2>T3>T1. The SPAD values of oilseed flax leaves at each key growth stage in the N3T2 treatment were significantly higher than those in the other treatments under each integrated nitrogen management regime, indicating a higher chlorophyll content in the leaves under this treatment. The SPAD values in the branching, budding, anthesis and kernel stages showed a significant linear correlation with the nitrogen nutrient diagnostic index and nitrogen application rate. The relationship between grain yield and nitrogen application rate followed a quadratic function: y=−0.0288x²+8.1724x+1090.2083. The maximum seed yield of 1670kg·ha⁻¹ was achieved at a nitrogen application rate of 142kg·ha⁻¹. The optimal SPAD values across growth stages ranged from 53.4 to 73.7, while the critical SPAD thresholds fell within 41.0 to 57.6. Additionally, recommended fertilization equations were established for key growth stages of oilseed flax. 

Key words: Oilseed flax, SPAD value, Nitrogen application rate, Nutritional diagnosis, Nitrogen fertilizer recommendation and management program