Abstract
Soil acidification, caused by intensified fertilizer application and acid deposition, has threatened the sustainability of agricultural ecosystems and soil quality in parts of China since the 1980s. However, little is known about the spatio-temporal change of soil pH in cropland at a large basin scale. Poyang Lake Basin of China was selected as the study area to identify the spatio-temporal change of cropland pH and detect potential soil acidification factors. A total of 507 and 503 topsoil samples were collected in 2012 and 2018, respectively, and methods including one-way analysis of variance (ANOVA), Pearson’s correlation analyses, and Inverse Distance Weighted (IDW) were applied. Results showed that soil pH ranged from 3.96 to 7.95 in 2012 and from 3.34 to 8.19 in 2018, with most samples being acidic (pH < 7) in both sets of data. The two soil datasets showed a significant decline (p < 0.05) of 0.1 pH units over the past six years and several soil samples that exhibited obvious uptrends in the groups of pH < 4.5 and 4.5–5.0 from 2012 to 2018. Overall, the distribution patterns of pH at the two sampling dates were similar, whereas local details of the pH spatial distribution patterns differed. While we found a significant correlation (p < 0.05) between soil pH and aspect, elevation and slope showed no significant correlation with pH. ANOVA showed that pH values in the water density (river or lake network density) range of 6.27–19.94 were significantly higher (p < 0.05) than the other water densities. Large amounts of precipitation with low pH values were found to significantly influence soil pH, whereas N-fertilizer inputs exerted limited effects on soil pH over the entire study area. These findings provided new insights on soil acidification assessment and potential factor detection at the basin scale.
Highlights
As a measure of soil acidity or alkalinity, soil pH regulates soil biogeochemical processes [1], controls soil quality [2], affects the structure and functioning of terrestrial ecosystems [3], and has some impact on crop productivity [4]
Xie et al [21] identified the spatial distribution of pH change in the Yangtze River Delta of China between 1989 and 2015 and found that significant topsoil acidification occurred in major croplands of the study area
According to the classification standard proposed by Nielsen and Bouma [25], the variations in soil pH in 2012 and 2018 were moderate, with coefficients of variation (CV) of 10.47% and 11.29% and standard deviations (SD) of 0.53 and 0.56
Summary
As a measure of soil acidity or alkalinity, soil pH regulates soil biogeochemical processes [1], controls soil quality [2], affects the structure and functioning of terrestrial ecosystems [3], and has some impact on crop productivity [4]. Soil acidification is defined as a decrease in soil pH and is commonly a slow process under natural conditions [8,9]. This process can be dramatically increased by a series of factors, including acidic precipitation and the deposition of acidifying gases or particles, resulting in a variety of environmental impacts [10,11]. Xie et al [21] identified the spatial distribution of pH change in the Yangtze River Delta of China between 1989 and 2015 and found that significant topsoil acidification occurred in major croplands of the study area. Yang et al [22] reported that mean soil pH across northern China's grasslands was 8.17 in the 1980s but 7.50 in the 2000s, with a decline rate of about 0.034 pH units per year
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