Available medium and micronutrients in the soils of major citrus-producing areas in Southeast China.

Globally, medium and micronutrients deficiency is a key concern affecting soil fertility, plant productivity, and human health. However, few studies have been undertaken to investigate the spatial distribution of medium and micronutrients availability at large spatial scales in citrus soils and to explore the corresponding impact of influencing factors at global and regional dimensions. Here, this study investigated the status, geospatial variation, and influencing factors of bioavailable medium and micronutrients, including iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), calcium (Ca), magnesium (Mg), boron (B), and molybdenum (Mo) in 503 citrus orchards across major citrus-growing in Southeast China (Hubei, Hunan, Jiangxi, Fujian, Guangdong Provinces). The effects of soil medium and micronutrients availability on the medium and micronutrients content of citrus leaves and fruits were also explored. Results revealed uneven regional distributions and large variations of available medium and micronutrients in Southeast China. There were 193, 132, and 103 soil samples with excessive levels of Fe (>50 mg kg-1), Cu (>2.0 mg kg-1), and Mn (>50 mg kg-1), respectively, and the proportions of the total samples were 38.4 %, 26.8 %, and 20.7 %, respectively. Relatively, there were 229, 158, and 80 soil samples with deficient levels of Mg (≤80 mg kg-1), B (≤0.25 mg kg-1), and Ca (≤200 mg kg-1), respectively, and the proportions of the total samples were 48.6 %, 32.1 %, and 17.0 %, respectively. Soil parent materials, soil types, and citrus varieties were the significant drivers of available medium and micronutrient concentrations in citrus soils (p < 0.05). A random forest model identified key predictors of medium and micronutrients availability, including soil physicochemical properties, geographical factors, and plant traits. Linear fitting analysis indicated that soil available Mn and Ca contents were significantly and positively correlated with the corresponding nutrient content in citrus leaf and fruit compared to other elements (p < 0.05). This research provides insights into the distribution and environmental drivers of available medium and micronutrients in citrus orchard soils in Southeast China, offering theoretical guidance for improving agricultural practices and fertilizer management strategies.