Effects of potassium fertilizer and humic acid interactions on glycometabolic enzymes and quality of walnut fruits

【Objective】 This study aimed to employ a multi-level fuzzy comprehensive evaluation （MFCE） method to investigate the effects of potassium fertilizer and humic acid interactions on glycometabolic enzymes and quality of walnut fruits， providing theoretical references for fertilization practices for walnut orchards in Xinjiang. 【Method】 The Wen 185 walnut was used as the experimental material， and the experiment adopted a randomized block design. Four potassium fertilizer （K） levels were set， which were 0 kg/plant （K₀）， 0.3 kg/plant （K₁）， 0.6 kg/plant （K₂）， and 0.9 kg/plant （K₃）； four humic acid （H） levels were set， 0 kg/plant （H₀）， 0.05 kg/plant （H₁）， 0.075 kg/plant （H₂）， and 0.1 kg/plant （H₃）； a total of 16 treatments were set. Appearance and internal quality indicators， sugar component content， and activities of glucometabolic enzymes of walnut fruits were determined， and the MFCE method was used to establish a comprehensive evaluation model of walnut fruit quality， with comprehensive index （CI） calculated， to analyze effects of potassium ferti-lizer and humic acid interactions on walnut fruit quality. 【Result】 Range analysis showed that： longitudinal diameter and lateral diameter at K₀ level were the largest， single fruit weight at K₁ level was the highest； activities of glycometabolic enzymes， sugar components， and soluble sugar content at K₂ level were the highest； crude protein content at K₃ level was the highest and transverse diameter was the largest； sucrose content was the highest at the H₁ level； activities of glycometabolic enzymes and contents of fructose， glucose， starch， and soluble sugar at H₂ level were the highest； at H₃ level， contents of crude fat and crude protein were the highest， transverse and lateral diameters were the largest， and single fruit weight was the highest. Comprehensive evaluation results showed that the T8 treatment had the highest CI of 5.062， followed by the T₅ treatment with a CI of 4.733， while the T₁₆ treatment had the lowest CI of 0.472. Regression analysis results indicated a significant regression relationship between potassium fertilizer application rate and CI （P<0.05）， and the highest application rate was 0.631 kg/plant， corresponding to a CI of 2.971； an extremely significant regression relationship between humic acid application rate and CI （P<0.01）， and the highest application rate was 0.083 kg/plant， corres-ponding to a CI of 1.989； when the application rates of potassium fertilizer and humic acid were 0.600 and 0.070 kg/plant respectively， the CI reached its maximum of 4.706. 【Conclusion】 The combined application of potassium ferti-lizer and humic acid can improve activities of glycometabolic enzymes， sugar component content， and indicators related to quality. The comprehensive evaluation model based on the MFCE method shows that potassium fertilizer and humic acid have significant interaction effects on CI of walnut fruits. When the application rates of potassium fertilizer and humic acid are 0.600 and 0.070 kg/plant respectively， the CI reaches its maximum， therefore this fertilization regimen is appropriate for walnut planting in Xinjiang.