Objectives To reveal the temporal and spatial variability of soil pH in tobacco-planting areas in Xiangxi, and to provide scientific basis for soil pH regulation.
Methods The spatial and temporal variability of soil pH and its impact factors in top soil of Xiangxi tobacco-planting soils in 2000 and 2015 were analyzed by multivariate statistics and geostatistics.
Results The average pH of tobacco planting soils in Xiangxi decreased from 6.21 to 6.12 from 2000 to 2015. The low pH soil became more acid, while high pH soil kept improving, leading to increased coefficient of variation of the soil pH in the whole tested area. Geostatistical analysis showed that the spatial structure models of soil pH for tobacco planting area in 2000 and 2015 fit exponential model and spherical model, respectively. Moran’s I became smaller, fractal dimension became larger, and the nugget effect increased from 58.17% to 64.13%, indicating that spatial variability mainly depends on structural and random factors, and the different pH levels were interlaced in spatial distribution both in 2000 and 2015. The area of soil pH in “very low”, “low”, “high” and “very high” levels was increased by 2.61, 6.48, 4.39 and 0.17 percentage points, respectively, while the area of soil pH in “suitable” level decreased by 13.65 percentage points. Exchangeable calcium, exchangeable magnesium, available sulfur, organic matter, clays (< 0.002 mm), slits (< 0.02–0.002 mm) and alkali-hydrolyzable nitrogen were the main factors affecting the pH of tobacco-planting soils, and these seven factors explained 83.8% of soil pH variations. Of the seven factors, the exchangeable calcium was the main impact factor which could explain 60.6% of pH variation. Exchangeable calcium, exchangeable magnesium and organic matter were the main acid controlling factors, while available sulfur and alkali-hydrolyzable nitrogen were the main soil acidifying factors.
Conclusions The difference in long-term application of chemical and organic materials has caused more varied soil pH in the tobacco planting soils across Xiangxi area, with general decrease of pH suitable soil area. The soil acid controlling factors are exchangeable Ca, as well as exchangeable Mg and organic matter, while the soil acidifying factors are available S and N. So sulfur-containing chemicals should be carefully applied, and nitrogen fertilizer input rate should be studied for a sustainable tobacco production in Xiangxi area.
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