Geostatistical spatial mapping of soil potassium fractions and targeted fertilization strategies for improving apple productivity and fruit quality in highland orchards
Abstract
Potassium (K) deficiency has emerged as a critical constraint for sustainable apple production in highland regions, yet spatial variability of soil K status and site-specific fertilization responses remain poorly characterized. A survey-based study was initiated where soil samples (0–15 and 15–30 cm) were collected from 60 representative apple orchards to analyze various K fractions. Additionally, Geostatistical analysis using semi-variogram modeling in GIS was also used to map the spatial distribution of K, and then a field trial was conducted in orchards with low, medium, and adequate initial K status to assess the impact of variable doses of K2SO4 on apple fruit quality and yield attributes. Spatial analysis of the experimental site revealed that surface soil contained higher plant-available K fractions, while substantial reserves of non-exchangeable K (1500–3800 mg kg⁻¹) remained locked in mineral forms. Spatial analysis also showed that orchards of the central Swat valley had 20% lower extractable K compared to peripheral areas. Based on extractable K status, orchards were classified into deficient, medium, and adequate categories for targeted fertilization trials. Application of 300 g K2SO4 plant− 1 enhanced fruit yield, firmness, total sugars, and vitamin C content up to 45, 39, 37.98, and 23.57%, respectively, under K-deficient conditions, compared to the unamended control group. Strong positive correlations (p < 0.05) were observed between K application rates and apple fruit quality attributes. Overall, these findings provide evidence-based K status of Swat orchards and also highlight the significance of precision K management in enhancing apple productivity and quality attributes in the temperate highland apple-grown areas of Pakistan.