Factors affecting variations of soil pH in different horizons in hilly regions.

Yun-Yi Zhang,Wei Wu,Hongbin Liu,João Canário

doi:10.1371/journal.pone.0218563

Abstract

Soil pH is a key factor that controls soil nutrient availability, soil microbial activities, and crop growth and development. However, studies on the soil pH variations of cultivated lands in different horizons at the regional scale remain limited. In this work, 348 soil samples were collected from three soil horizons (A, B, and C) at 120 sites over the hilly region of Chongqing, southwestern China. Six topographic indicators, four climate parameters, and parent material were considered. Classification and regression trees (CARTs) were applied to investigate the relationships between soil pH and the variables in the A, B, and C horizons. Model performances were evaluated by root mean square error (RMSE), relative root mean square error (RRMSE), and coefficient of determination (R2). Results showed that soil pH increased obviously from the A to C horizons. Soil pH was predicted well by the forcing factors with the CART models in all horizons. RMSE, RRMSE, and R2 varied between 0.37 and 0.435, between 5.93 and 7.23%, and between 0.71 and 0.80, respectively. The relative importance of the studied variables to soil pH differed with the horizons. Annual temperature range (ATR), terrain wetness index (TWI), and Melton ruggedness number were critical factors that controlled soil pH variability in the A horizon. Parent material, precipitation of warmest quarter (PWQ), ATR, and TWI were important variables in the B horizon. Parent material, PWQ, ATR, and precipitation were key factors in the C horizon. The results are expected to provide valuable information for designing appropriate measurements for agricultural practices and preventing soil acidification.

Highlights

Soil properties are closely associated with soil-forming/environmental forcing factors, such as topography, climate, and parent material [1]
The minimum and mean values of soil pH increased from the A to C horizons
The values of the coefficient of variation (CV) of pH indicate the low variability of soil pH at each horizon over the area (CV75%), and others had medium (CV% = 25%– 75%) variabilities over the site

Summary

Introduction

Soil properties are closely associated with soil-forming/environmental forcing factors, such as topography, climate, and parent material [1]. The relationship between soil properties and soil-forming factors is an issue that has been studied all over the world [2,3,4,5,6,7]. Soil pH is a measurement of soil acidity and alkalinity [8], thereby representing the H+ concentration in the soil solution. Studies have shown that soil pH can influence crop yields, soil nutrient release, and soil microbial activity to a large extent [10, 11]. If farmland soil is too acidic or too alkaline, land production will be limited [12]

Methods

Results

Discussion

Conclusion