Comprehensive Decision-Making for the Leaf-to-Fruit Ratio and Estimation of Economic Output Value of Walnut Trees Based on Statistical Analyses

This study examined the Juglans regia ‘Xinxin2’ walnut variety using combined field control experiments with laboratory chemical analyses and analyzed the effects of the relationships among net photosynthetic rate (Pn), specific mass transfer rate (SMTR), nut dry mass (NDM), and nut yield per girdled fruit-bearing shoot (Yield) on the leaf-to-fruit ratio (LFR). We used comprehensive decision-making based on mathematical programming to determine the optimal LFR for this walnut variety in the peak fruiting stage. The optimal LFR was calculated as the comprehensive expected value of the linear combination among the equations for the effects of LFR on the Pn, SMTR, NDM, and Yield and was determined to be 2.02. Compared with walnut plants without LFR adjustment, the walnut plants with LFR adjustment using 2.02 as the minimum threshold had a 19.52% lower nut yield, a higher nut quality (Special Class, Class I, and Class II accounted for 100% of the nut yield per 670 m2), and a 36.22% higher economic output value per 670 m2. This study indicates that improving fruit quality to produce Grade I and II nuts will increase economic output, although the total yield will decrease when managing efficient LFR in nut production.