| Mechanisms of water\|fertilizer coupling effects on leaf nutrient dynamics and comprehensive growth index in subsurface drip\|irrigated walnut |
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| DOI：10.7606/j.issn.1000-7601.2025.06.22 |
| Key Words: walnut water and fertilizer coupling leaf nutrient subsurface drip irrigation principal component analysis |
| Author Name | Affiliation | | XU Jingbo | College of Hydraulic and Civil Engineering, Xinjiang Agricultural University, Urumqi, Xinjiang 830052, China
Key Laboratory of Water Conservancy Engineering Safety and Water Disaster Prevention, Urumqi, Xinjiang 830052, China | | MIAO Zhuang | Survey and Design Institute Group Co., Ltd., Xinjiang Production and Construction Corps, Urumqi, Xinjiang 830002, China | | YANG Rong | Shihezi Hydrology and Water Resources Management Center, Shihezi, Xinjiang 832000, China | | ZHAO Jinghua | College of Hydraulic and Civil Engineering, Xinjiang Agricultural University, Urumqi, Xinjiang 830052, China
Key Laboratory of Water Conservancy Engineering Safety and Water Disaster Prevention, Urumqi, Xinjiang 830052, China |
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| Abstract: |
| Targeting the issues of crude water and fertilizer management, soil salinization, and yield decline in walnut orchards of the northwest arid region, this study aimed to reveal the mechanism of water\|fertilizer coupling effects on walnut leaf nutrient dynamics and the comprehensive growth index (CGI) under subsurface drip irrigation. The study also sought to identify key pathways for water\|fertilizer regulation during different growth stages and establish appropriate thresholds for leaf nutrient levels, providing theoretical support for precision management of walnut cultivation in arid areas. A 16-year\|old “Wen 185” walnut orchard in Aksu, Xinjiang, was selected as the experimental site. Four irrigation gradients were applied: 75% ETc (crop evapotranspiration, W1), 100% ETc (W2), 125% ETc (W3), and 150% ETc (W4). Three fertilizer gradients were implemented: N 270-P 240-K 300 kg·hm-2 (F1), N 360-P 320-K 400 kg·hm-2 (F2), and N 450-P 400-K 500 kg·hm-2 (F3). Principal component analysis and partial least squares structural equation modeling were integrated to construct stage\|specific CGI models, elucidating the dynamic impact pathways of water\|fertilizer coupling on leaf nutrients (leaf nitrogen content, LNC; leaf phosphorus content, LPC; leaf potassium content, LKC) and growth indices. The probabilistic grading method was applied to determine the optimal thresholds for LNC and LKC. The results showed that(1) the interaction between water and fertilizer significantly influenced leaf nutrient dynamics. LNC gradually decreased with advancing growth stages, and a positive correlation between irrigation volume and LNC was observed under F3 fertilization. LPC exhibited a declining\|then\|increasing trend throughout the growth cycle, with optimal irrigation regulation effects under F2 fertilization; excessive fertilization (F3) weakened the influence of irrigation on LPC. The trend of LKC was similar to LPC; under the same fertilizer level, LKC peaked at the W3 irrigation level. The W3F3 treatment consistently yielded the highest LKC content across all growth stages. (2) Irrigation volume significantly affected CGI throughout the entire growth cycle. Leaf nutrient levels mediated walnut growth traits through strong indirect effects (total effect β was 0.619~0.692). In the later growth phase, both irrigation and fertilization exhibited enhanced direct effects on photosynthetic traits (total effect β was -3.17~0.360). (3) LNC and LKC showed strong correlations with CGI, while no significant correlation was found between LPC and CGI. The optimal LNC ranges across the entire growth cycle were 21.76~28.47 g·kg-1, 19.56~26.86 g·kg-1, 15.99~23.18 g·kg-1, and 13.52~20.72 g·kg-1, respectively. The optimal LKC ranges across the entire growth cycle were 14.56~17.40 g·kg-1, 11.11~13.96 g·kg-1, 13.23~16.05 g·kg-1, and 12.26~15.08 g·kg-1, respectively. This study, through dynamic modeling, elucidated the mediating role of leaf nutrients in walnut growth under water\|fertilizer coupling conditions and identified stage\|differentiated pathways for precision water\|fertilizer management along with specific nutrient thresholds. |
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