Spatio-temporal variation of soil pH of Sichuan Province during the past 30 years

Objectives pH is an important chemical indicator of soil, affecting soil fertility and health. Studying of the spatio-temporal variation of soil pH will provided references for nutrient management in agricultural production.

Methods The data come from “the Second National Soil Census” during 1980s and the “Soil Testing and Formulated Fertilization Project” during 2010s. Spatial distribution map of soil pH was made by Inverse Distance Weighted (IDW) interpolation method from “Spatial Analyst” module in ArcGIS 10.2. The spatial-temporal change of soil pH was obtained by raster calculator in ArcGIS 10.2, and then calculated the area changes of different soil pH classification.

Results The average soil pH value of Sichuan Province decreased from 7.0 to 6.54 from 1980s to 2010s. In 1980s, the proportions of soil areas in pH grade of ≤4.5, 4.5−5.5, 5.5−6.5, 6.5−7.5, 7.5−8.5, and 8.5−9.0 accounted for 0.09%, 14.58%, 53.17%, 12.57%, 19.58% and 0.01%, respectively, while in 2010s, the proportions became 0.06%, 4.45%, 30.41%, 48.65%, 16.40% and 0.04%, respectively. From 1980s to 2010s, 49.63% of total soil was elevated in pH, which mainly distributed in west of Sichuan, and 20.13% was declined in pH, which was mainly distributed in the central area. In Chengdu Plain, the soil areas in each pH grade changed relatively small, with slightly increase of weakly acidic soil and a little bit decrease of alkaline soil. In the hilly central Sichuan, the proportion of acidic soil area increased and the alkaline soil area decreased. In the mountainous areas at the edge of Sichuan Basin, neutral soil increased, and both the acidic and alkaline soil areas decreased. In the mountainous area of southwestern Sichuan, acidic soil areas slightly decreased, while neutral soil increased. In the mountainous areas of Northwest Sichuan plateau, more than 30% of acidic and weakly acidic soils had changed into neutral soils, and the alkaline soil slightly increased.

Conclusions Overall, from the 1980s to the 2010s, the area of acidic and weakly acidic soil in Sichuan Province decreased, the area of neutral soil increased. However there is a certain proportion of soil acidification in the hilly area of central Sichuan, which requires more attention.