Abstract:

Objective: This study aims to elucidate the quantitative relationships among soil fertility, tree nutritional status, and yield of Juglans regia (walnut), and construct a multi-factor yield prediction model to guide fertilization management, and overcome the limitations of single nutritional diagnostic techniques, so as to provide a scientific basis for precision fertilization in walnut orchards. Method: Thirty-four walnut orchards in Baokang County, Hubei Province were selected as study objects. The orchards were classified into high-yield (≥1200 kg·hm^–2), medium-yield (450–1200 kg·hm^–2), and low-yield (<450 kg·hm^–2) groups based on yield per unit area. The Nemerow Comprehensive Index and Diagnosis and Recommendation Integrated System (DRIS) were comprehensively applied to systematically evaluate the nutrient status of soil, leaves, and terminal buds. Subsequently, correlation analysis and regression analysis were used to construct yield prediction models. Result: 1) Among the 34 walnut orchards, 25 had medium soil fertility and 9 had high soil fertility, and all of the latter were high-yield orchards. 2) The soil of high-yield orchards possessed significantly greater hydrolyzable N, available K, organic matter, available P, and soil fertility index than that of low-yield orchards, and hydrolyzable N deficiency was the primary factor restricting soil fertility. 3) The mean values of fresh and dry weights of terminal leaflets and rachises, as well as the length and diameter of terminal buds of walnut trees in high-yield orchards were significantly higher than those in low-yield ones (P<0.05), indicating that biomass accumulation and bud development of walnut trees in high-yield gardens were better. 4) The average contents of N, P, K, Ca, and S in the leaves of walnut trees in high-yield orchards were higher than those in low-yield orchards, and there were significant differences in the contents of N and Ca between high-yield orchards and low-yield orchards (P<0.05). The average contents of N, P, K, and S in the terminal buds of walnut trees in high-yield orchards were also higher than those in low yield gardens, whereas Ca content in the terminal buds and nutritional imbalance index of leaves and terminal buds were significantly lower than those in low-yield gardens (P<0.05). 5) Correlation analysis indicated that there were predominantly positive relationships between soil and leaf nutrients, and mixed positive/negative correlations between soil and bud nutrients. Soil pH affected leaf nutrient uptake, and bud Ca was negatively correlated with soil nutrients. The soil fertility index (FI) was positively correlated with yield (P<0.05), whereas the leaf (Lnila) and bud nutritional imbalance index (Bnila) were negatively correlated with yield (P<0.05 and P<0.01, respectively). 6) A segmented linear regression model for yield (Y, kg·hm^–2) was derived as follows: when FI≤0.9 or FI>2.7, Y = 72.782 ? 0.012 Bnila ? 0.017 Lnila + 46.441 FI; when 0.9<FI≤1.8, Y = 162.598 ? 0.011 Bnila ? 0.016 Lnila + 4.276 FI; when 1.8<FI≤2.7, Y = 126.558 ? 0.011 Bnila ? 0.016 Lnila + 4.276 FI. Conclusion: Soil fertility in Baokang walnut orchards is generally at a moderate level, and nitrogen deficiency is the primary factor limiting yield improvement. High-yield orchards are characterized by superior soil fertility and balanced nutritional status in leaves and terminal buds.

Key words: Juglans regia, Nemerow fertility index, diagnosis recommendation integrated system, soil fertility, nutrient imbalance index, yield model