What question did this study set out to answer?

The aim is to assess soil fertility variability in walnut orchards and its relationship with fruit quality.

May 27, 2026Agronomy0 citationsOpen Access

Spatial Variability of Soil Nutrients in Walnut Orchards in the Middle and Lower Reaches of the Yarlung Zangbo River Valley and Its Association with Fruit Quality

Key Points

The aim is to assess soil fertility variability in walnut orchards and its relationship with fruit quality.
Evaluated soil fertility at different depths and sites in walnut orchards across three counties.
Analyzed 321 paired soil and fruit samples using multivariate statistical techniques and fuzzy evaluation.
Classified soil fertility into five grades and identified limiting nutrients through cluster analysis.
Overall soil fertility index averaged 0.527, with spatial variation observed across counties.
Available phosphorus was found to be deficient, while magnesium and zinc levels were low.
Fruit quality correlated with soil nutrients, particularly nitrogen, phosphorus, and potassium.

Abstract

This study evaluated the multi-scale spatial heterogeneity of soil fertility in walnut orchards in the middle and lower reaches of the Yarlung Zangbo River valley. The investigation focused on Jiacha, Lang, and Milin counties, covering four river terrace levels and three soil depths within the 0–60 cm layer, and further examined the effects of such heterogeneity on walnut fruit quality. Using integrated multivariate statistical approaches and fuzzy comprehensive evaluation, 321 paired soil and fruit samples collected in September and October of 2023 were analyzed. Overall soil fertility was moderate (0.4 ≤ IFI < 0.6) with a mean integrated fertility index (IFI) of 0.527, but showed pronounced spatial variation. PCA-based composite scores indicated the highest fertility in Milin County, followed by Lang County, with Jiacha County ranking lowest. Soil fertility across 11 towns was classified into five grades. Cluster analysis based on ten standardized soil fertility indicators revealed clear regional aggregation patterns, where close towns exhibited similar fertility conditions. Third-level river terraces exhibited significantly higher fertility than other terrace levels. Available phosphorus was widely deficient, while exchangeable magnesium and available zinc were also low, representing key limiting nutrients with strong regional variability. Spatial differences in soil enzyme activities reflected variation in microbially mediated nutrient cycling, with phosphatase activity negatively correlated with available phosphorus, suggesting potential microbial responses to phosphorus-stressed environments. Soil fertility significantly influenced walnut fruit quality, with alkaline hydrolyzable nitrogen, phosphorus, potassium, and exchangeable calcium and magnesium identified as key drivers. These findings provide a theoretical basis for suggesting a zoned precision fertilization strategy, where prioritizing P, Zn, and Mg inputs in deficient areas could be considered alongside organic fertilisation. Such site-specific management strategies are suggested to support the sustainable development of the walnut industry along the Yarlung Zangbo River valley.

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