Evaluation of soil characteristics and fertility in forest land of main Camellia oleifera producing areas in Hainan Island

Through the analysis of soil characteristics in main Camellia oil producing areas in Hainan Island, this paper aims to reveal the geographical distribution characteristics of nutrients in Camellia oil forest soil in Hainan Island, and comprehensively evaluates the soil characteristics and fertility in Camellia oil forest land in Hainan Island.

The study measured 15 sample plots from the main Camellia oil production areas in Hainan Island, evaluating key parameters including bulk density, total porosity, capillary porosity, non-capillary porosity, moisture content (weight/volume), maximum capillary water retention, field water retention, saturated moisture content, soil solid-liquid-gas ratio, pH, organic carbon, organic matter, total nitrogen, total phosphorus, total potassium, nitrate nitrogen, ammonium nitrogen, alkaline-hydrolyzed nitrogen, available phosphorus, fast-acting potassium, slow-release potassium, cation exchange capacity, microbial nitrogen biomass, and microbial carbon biomass. Significant differences were analyzed using Duncan's multiple comparisons, visualized through correlation heat maps, and principal component analysis (PCA) was conducted to extract principal components. Comprehensive scores were calculated for ranking purposes.

The soil samples showed significant variations in moisture content: HK-1 and CM-2 had the highest relative moisture levels (62.54%-67.15%). Among the three phases (solid, liquid, and gas), the HK series (HK-1 and HK-2) contained the lowest proportion of solid matter (39.21%-43.05%) but higher air content (26.48%-30.23%). HK-2 demonstrated the highest total porosity [(60.79±4.48)%], weight moisture content [(32.35±0.65)%], total phosphorus (TP) (1 222.66±113.41 mg·kg^-1), and available potassium (AK) (210.80±1.61 mg·kg^-1). QH-3 recorded the highest bulk density (1.69±0.13 g·cm^-3), while CM-2 showed the highest organic carbon (OC) (24.13±0.45 g·kg^-1), organic matter (OM) (41.60±0.76 g·kg^-1), cation exchange capacity (CEC) (8.89±0.35 cmol⁺·kg^-1), and maximum specific binding capacity (MBC) (544.35±2.60 mg·kg^-1). DA-2 had the highest pH value (6.88±0.05), BT-2 exhibited the highest total nitrogen (TN) (1.83±0.18 g·kg^-1) and maximum binding capacity (MBN) (54.40±3.31 mg·kg^-1), while QH-1 showed the highest nitrate nitrogen (NO₃-N) (53.34±1.12 mg·kg^-1). Significant differences in soil quality were observed across different sample plots, with comprehensive scoring and ranking effectively distinguishing quality grades, confirming HK-2 as the most fertile.

Significant discrepancies in soil physical properties and nutrient profiles were identified across the principal oil-tea camellia cultivation areas of Hainan Island. Among the sampled plots, HK-2 and HK-1 exhibited the most favorable integrated soil functionality, whereas CM-2, BT-2, and HK-2 demonstrated particularly superior performance in key nutrient indicators. In contrast, plots WZS-1, CM-1, and QH-3 were characterized by pronounced soil compaction, nutrient deficiency, or strong acidification. These findings provide a critical scientific foundation for the precision management, targeted amelioration, and sustainable utilization of soil resources in oil-tea camellia production systems..