Enhanced acidification in Chinese croplands as derived from element budgets in the period 1980–2010

Abstract

Significant soil pH decrease has been reported in Chinese croplands in response to enhanced chemical fertilizer application and crop yields. However, the temporal and spatial variation of soil acidification rates across Chinese croplands is still unclear. We therefore assessed trends in soil acidification rates across provincial China for the period 1980-2010 by calculating inputs-outputs of major cations and anions in cropland systems. Nitrogen (N) induced proton production increased from 4.7keqH/ha/yr in 1980 to a peak of 11.0keqH/ha/yr in 1996 and remained nearly constant after 2000 at a rate of approximately 8.6keqH/ha/yr. The proton production induced by crop removal increased from 1.2 to 2.3keqH/ha/yr. The total proton production thus increased from 5.9 to 10.9keqH/ha/yr in the 30years. As a result, the actual acidification rate, reflected by (base) cation losses, accelerated from 2.3 to 6.2keqH/ha/yr and the potential acidification rate, reflected by phosphorus accumulation accelerated from 0.2 to 1.3keqH/ha/yr. The national averaged total acidification rates were thus estimated to increase from 2.6 to 7.6keqH/ha/yr in the past 30years. The highest soil acidification rate occurred in the Jiangsu Province with a rate of 17.9keqH/ha/yr, which was due to both high N application rates and high base cation removals by crops and crop residues. The combination of elevated N inputs and decreased N use efficiency (NUE) in response to those N inputs, thus enhancing the nitrate discharge, were the main reasons for the accelerated acidification in Chinese croplands. Considering the expected growth of food demand in the future, and the linkage between grain production and fertilizer N consumption, a further acceleration of soil acidification can thus be expected, unless the N inputs is reduced and/or the NUE is increased substantially.

Heavy Metal Bioaccumulation in Rice from a High Geological Background Area in Guizhou Province, China

“…In August 2018, China re-released the Chinese Soil Environmental Quality Standard (GB 15618-2018), which classifies heavy metal values into four grades according to the pH of the soil. However, the pH of the soil in China has decreased by 0.13 to 0.80 pH units in recent years, which means that the acidity of the soil has increased by 1.35 to 6.31 times; this extent of acidification takes tens of thousands of years to occur in normal soil processes [ 65 , 66 ]. Our results indicate that the total amount of heavy metals does not necessarily correlate with food security.…”

Dramatic loss of inorganic carbon by nitrogen‐induced soil acidification in Chinese croplands

“…Some studies have highlighted the increasing threat of acidification induced by N fertilization over the past decade (Guo et al, 2010; Zhou et al, 2014; Zhu et al, 2020). Soil acidification rate has increased from 2.6 to 7.6 keq H + ha −1 year −1 in the past 30 years in China (Zhu et al, 2018). Major cropland soils were acidified (0.13–0.80 pH units) during the 1980s–2000s mainly due to high amounts of N fertilization (Guo et al, 2010).…”

Growth and Distribution of Maize Roots in Response to Nitrogen Accumulation in Soil Profiles after Long-Term Fertilization Management on a Calcareous Soil

“…Crop yields and quality depend upon substantial nitrogen (N) inputs [1]. Modern agriculture depends on high external inputs of chemical N fertilizers to achieve high crop productivity, whereby excessive N leads to low nutrient use efficiency and is now recognized to be a major cause of environmental problems, including N leaching and soil acidification [2,3]. In intensive cropping systems, the overuse of chemical fertilizers in excess of crop nutrient demand does not increase grain yield.…”