Spatial variation characteristics and influence factors of soil pH and nutrient availability in citrus orchards of Hunan Province

Objectives We studied the spatial variation characteristics, influencing factors of soil pH and the availability of main nutrients in citrus orchards of Hunan Province, aiming to provide scientific basis for slowing down soil acidification and improve soil fertility in citrus orchards.

Methods In this study, 15722 soil samples were collected from the citrus orchards of 38 citrus production counties in Hunan Province. The spatial variation characteristics of citrus orchard soil pH values across Hunan Province were explored using geostatistics, correlation analysis, structural equation models and other methods. The influence factors were screened from the aspects of geography, climate and soil properties, and the effects of soil pH on the availability of soil nitrogen (N), phosphorus (P), and potassium (K) were studied.

Results The soil pH of citrus orchards in Hunan Province ranged from 3.00 to 8.50, and averaged 5.58 with a coefficient of variation of 18.06%, belonging to moderate spatial variation. The weakly acid soils that was most suitable for citrus growth accounted for 44.35% of the total citrus growing area, while the acidic, strongly acidic, neutral and alkaline soils accounted for 48.92%, 1.69%, 4.95% and 0.08%, respectively. Pearson correlation analysis showed that soil pH was positively correlated with precipitation (P<0.05) and readily available potassium content (P<0.01), but negatively correlated with temperature, alkali-hydrolyzable N and available P (P<0.01). The simulation results of structural equation model indicated that soil types and parent materials were the main factors causing the spatial variation of soil pH. Except for a few strongly alkaline soils with low levels of alkali-hydrolyzable N and available P, the alkali-hydrolyzable N, available P and readily available K contents in most soils were all in suitable levels.

Conclusions More than half (50.61%) of the citrus orchard soils in Hunan Province are in a state of overacidity (acidic and strongly acidic) due to the soil types and parent materials. The available nitrogen, phosphorus and potassium contents in the citrus orchard soils in Hunan Province are basically at a suitable level. Therefore, more attention should be paid for the remediation of soil acidity.