Estimation of critical nutrient levels for kiwifruit trees using Bayesian quantile regression models

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Abstract
Kiwi orchards can be established on acidic soils with low nutrient availability, requiring amendments and fertilizers to meet the plant’s nutritional requirements. However, nutritional information requirements of the crop are scarce, which can support fertilizer recommendations. This study aimed to establish critical levels (CL), soil fertility classes (FC), and leaf sufficiency ranges (SR) of nutrients for kiwi cultivation in Southern Brazil. Diagnostic standards from commercial orchards were established using a database (fruit yield, nutrient levels in soil, and leaves). To establish CL, FC, and SR, the fruit yield was related to nutrient levels, and models were established using the boundary line (BL) method and Bayesian quantile regression models. The FC for soil available P and K levels were 30–37 and 127–135 mg·dm-3, respectively, while exchangeable Ca and Mg were 10–14 cmolc·dm-3 and 3.5–5.0 cmolc·dm-3, and V was 82–88%. In leaf tissue, the SR for N, P, K, Ca, Mg, and S were 27–31, 1.6–2.2, 18–22, 22–25, 4.2–7.5, and 2.1–4.2 g·kg-1, respectively. For micronutrients, the SR were 57–65 mg·kg-1 for Cu, 247–255 mg·kg-1 for Fe, 95–102 mg·kg-1 for Mn, 20–25 mg·kg-1 for Zn, and 10–13 mg·kg-1 for B. The diagnostic standards for soil fertility and plant nutritional status obtained in this study can be used by kiwi growers to increase fruit yield.
Funding Information
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico (302023/2019-4)
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico (001)
  • Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (302023/2019-4)
  • Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (001)

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