Cause Of Soil Acidification Research Articles

The contribution of natural and anthropogenic causes to soil acidification rates under different fertilization practices and site conditions in southern China

Excessive application of mineral fertilizers has accelerated soil acidification in China, affecting crop production when the pH drops below a critical value. However, the contributions of natural soil acidification, induced by leaching of bicarbonate, and anthropogenic causes of soil acidification, induced by nitrogen (N) transformations and removal of base cations over acid anions, are not well quantified. In this study, we quantified soil acidification rates, in equivalents (eq) of acidity, by assessing the inputs and outputs of all major cations and anions, including calcium, magnesium, potassium, sodium, ammonium, nitrate, bicarbonate, sulphate, phosphate and chloride, for 13 long-term experimental sites in southern China. The acidification rates strongly varied among fertilizer treatments and with the addition of animal manure. Bicarbonate leaching was the dominant acid production process in calcareous soils (23 keq ha−1 yr−1) and in non-calcareous paddy soils (9.6 keq ha−1 yr−1), accounting for 80 % and 68 % of the total acid production rate, respectively. The calcareous soils were strongly buffered, and acidification led no or a limited decline in pH. In contrast, N transformations were the most important driver for soil acidification at one site with upland crops on a non-calcareous soil, accounting for 72 % of total acid production rate of 8.4 keq ha−1 yr−1. In this soil, the soil pH considerably decreased being accompanied by a substantial decline in exchangeable base cation. Reducing the N surplus decreased the acidification rate with 10 to 54 eq per kg N surplus with the lowest value occurring in paddy soils and the highest in the upland soil. The use of manure, containing base cations, partly mitigated the acidifying impact of N fertilizer inputs and crop removal, but enhanced phosphorus (P) accumulation. Combining mineral fertilizer, manure and lime in integrative management strategies can mitigate soil acidification and minimize N and P losses.

Influence of Nitrogen Fertilizer Application on Soil Acidification Characteristics of Tea Plantations in Karst Areas of Southwest China

Nitrogen (N) fertilizer application is one of the causes of soil acidification at tea plantations. However, the effect of N fertilizer application on the soil acidification characteristics of tea plantations with different acidities remains unclear. In this study, field experiments were conducted to investigate the effects of different nitrogen fertilizer application rates on the pH, pH buffer capacity (pHBC), exchangeable total acidity (ETA), exchangeable base cations (EBCs), and cation exchange capacity (CEC) in the topsoil of non-acidified (NA), mildly acidified (MA), and heavily acidified (HA) tea plantations. The results showed that the exchangeable Al3+ (E-Al) and CEC were HA > MA > NA in all tea plantations, whereas the EBCs and base saturation percentage (BSP) were HA < MA < NA. In the tea plantations with pH > 4.0, the pH, EBCs, and BSP showed decreasing trends with increasing N fertilizer application, whereas E-Al showed an increasing trend. In the tea plantations with pH < 4.0, the soil pH showed a small increasing trend with the increase in N fertilizer application, whereas the soil exchangeable H+ (E-H), E-Al, and CEC showed decreasing trends. Meanwhile, in the pH range of 4–6, the soil acid–base buffer curve rose sharply, and an excessive application of N fertilizer (N900) significantly reduced the pHBC. In addition, a stepwise regression analysis showed that the BSP, EBCs, and exchangeable Mg2+ (E-Mg) had significant direct effects on the soil pH, whereas the CEC and N application had significant direct effects on the soil pHBC. In conclusion, a decrease in the BSP and an increase in E-Al were the main mechanisms of acidification at tea plantations, whereas a decrease in the BSP caused by the application of N fertilizer was the main cause of exacerbated soil acidification in non-acidified tea plantations.

Soil Acidity Formation and its Amelioration Methods in Ethiopia: A Review

Soil acidification is one of the problems of chemical soil degradation affecting soil productivity in the world. This paper attempts to explain the concept of soil acidification, the causes of soil acidification and the methods to remedy it. Farmers need simple and sustainable techniques to improve acidic soils and increase yields of their chosen crops. Recommendations for reclamation of acid soils need to be adapted to new developments, such as liming, use of acid-tolerant crop varieties, integrated soil fertility management, and application of organic fertilizers. This review addresses the causes and management mechanisms of soil acidification and the resulting effects on soil fertility and crop yield. It also provides important information on management options to address soil acidity and improve overall soil fertility, as well as other organic amendments that can be applied to bring soil acidity to the desired pH and improve soil quality and health. Integrated management of acidic soils increases yield stability and maximizes nutrient use efficiency.

Modelling long-term impacts of fertilization and liming on soil acidification at Rothamsted experimental station

Liming is widely used to reduce the impacts of soil acidification and optimize soil pH for agricultural production. Whether models can simulate the effect of liming on soil pH, and base saturation (BS), and thereby guide lime application, is still largely unknown. Long-term experimental data from a grassland (Park Grass, 1965–2012) and arable land (Sawyers Field, 1962–1972) at Rothamsted Research, UK, were thus used to assess the ability of the VSD+ model to simulate the effects of long-term fertilization and liming on soil acidification. The VSD+ model was capable of simulating observed soil pH and BS changes over time in the long-term liming experiments, except for a treatment in which sulphur (S) was added. Normalized Mean Absolute Errors (NMAE) and Normalized Root Mean Square Errors (NRMSE) of simulated and observed pH values, averaged over the observation periods varied between 0.02 and 0.08 (NMAE) and 0.01–0.05 (NRMSE). The acidity budget results for Park Grass suggest that nitrogen (N) transformations contributed most to acidity production, causing predominantly aluminium (Al) exchange in the topsoil (0–23 cm) followed by base cation (BC) release, but in the treatment with S addition, BC uptake had a nearly similar effect on acidity production. However, in Sawyers Field, the acidity budget suggested that BC uptake was the dominant cause of soil acidification, while the impacts of N transformations were limited. Liming was found to sufficiently replenish BC and decrease Al exchange in the topsoil layer. Overall, the VSD+ model can adequately reconstruct the impacts of fertilizer and liming applications on acid neutralizing processes and related soil pH and BC changes at the soil exchange complex.

Spatial and temporal changes of farmland soil acidification and their influencing factors in different regions of Guangdong Province, Chin

Based on the three datasets from 1980s, 2010 and 2015 in Guangdong Province, we analyzed the spatial and temporal variations of soil pH in farmlands in different regions of Guangdong Province and analyzed the driving factors for such variations. The results showed that the spatial distribution of soil pH in Guangdong Province changed significantly in different periods. During 1980s to 2010, soil pH showed an acidification trend with a decline of 0.3, and increased by 0.09 from 2010 to 2015, with more uneven trend and more obvious acid base differentiation. From the perspective of each region, there was generally a trend of acidification from the 1980s to 2010. From 2010 to 2015, the average pH value of farmland soil in the Pearl River Delta increased by 0.27, while that on the east wing and west wing decreased by 0.05 and 0.15 respectively, showing a unapparent change of soil pH in the mountainous area. Our results showed that soil acidification in diffe-rent areas of Guangdong Province was affected by natural factors such as soil itself and precipitation. In addition, anthropogenic factors such as acid rain, unreasonable fertilization and the planting structure of high-yielding crops were also the main causes of soil acidification. Industrialization, urbanization, mining development, and the spread of soil testing formula fertilization increased soil pH in local areas. Our results could provide theoretical guidance for controlling and alleviating soil acidification and improving the quality of cultivated land in different areas.

Quantification of the contribution of nitrogen fertilization and crop harvesting to soil acidification in a wheat-maize double cropping system

Over fertilization with nitrogen (N) is considered the main driver of agricultural soil acidification in China. However, the contribution of this driver compared to other causes of soil acidification on intensive croplands has seldom been quantified under field conditions. We measured the fate of major nutrients, and calculated the related H+ production, based on the difference between inputs and leaching losses of those nutrients for a wheat-maize rotation system on a moderate acid silty clay loam soil in a two-year field experiment. Topsoil pH decreased 0.3 units in the plots with conventional (current farmer practice) high N fertilization after two years, with a proton production of 13.1 keq H+ ha−1 yr.−1. No apparent changes in topsoil pH were observed in the plots without N application, in spite of a proton production of 4.7 keq H+ ha−1 yr.−1. Crop uptake was the primary driver of H+ production, followed by N transformation processes and HCO3− leaching in both plots. Nitrogen fertilization had a relative small direct impact on soil acidification due to a very limited nitrate leaching, induced by large N losses to air by denitrification in this specific moderately acid soil, whereas elevated base cation uptake by crops induced by N fertilization indirectly had a relative large impact.

Attribution of Soil Acidification in a Large‐Scale Region: Artificial Intelligence Approach Application

Core Ideas Many knowledge gaps in using process‐based calculation remain. Random forest method is effective to attribute soil acidification on large scales. The drivers and processes of acidification and their interactions are estimated. Nitrogen (N) fertilizer was the dominant driver of the acidification of farmland. Acid deposition contributed the most to the acidification of forest soil. Attribution of causes of soil acidification is paramount for predicting the responses of terrestrial ecosystems to global change, and for defining mitigation policies. The conventional calculation of the hydrogen ion (H+) budget considering all the biogeochemical processes is used to make attribution assessments across large‐scale regions. However, many gaps in using this process‐based calculation remain‐ particularly concerning indirect and interactive effects of the drivers and processes of acidification in a changing environment. In this study the random forest (RF) analysis‐based artificial intelligence approach was adopted to estimate the contributions of the drivers and identify the key processes of soil acidification of different land uses (forest and farmland) and parent materials (fluvial deposit, granite and sandstone). The Pearl River Delta, China was considered in a case study. The results indicate that nitrogen (N) fertilizer was the dominant driver of the acidification of farmland due to nitrification of NH4+, whereas acid deposition contributed the most to the acidification of forest soil, NO3––N deposition played a major role, and small differences in contribution were observed among the parent materials. The direct and indirect drivers and processes of acidification and their interactive effects were considered and identified in the RF analysis‐based artificial intelligence approach. This artificial intelligence approach provides a powerful method for untangling the complex causes of soil acidification across large‐scale regions over a long time period, and consequently helps to develop fact‐based mitigation and adaption strategies.

Soil Properties and Land Capability Evaluation in a Mountainous Ecosystem of North-West Cameroon

Up to date, tropical mountainous ecosystems still lack in depth information on soil and environmental characteristics which are major factors limiting optimum crop production. The objective of this work was to study soil characteristics and to evaluate the land capability level for the production of some common tropical crops in mountainous ecosystem soils of North West Cameroon. Soil sampling was done following a randomized complete block design (RCBD) with four replications for three topographic positions (upslope, midslope and footslope) and at two depths (0 - 20 cm and 20 - 100 cm). It was completed by standard laboratory analyses. The fertility capability classification (FCC) system enabled to identify soil limitations and to classify soils into FCC units. Land and climate were evaluated by simple limitation and parametric methods. Globally, the soils were dark-colored, sandy clayey to clayey, compact and very acidic (pHH2O = 4.3 - 5.8). The organic matter (3.7% - 5.1% dry matter), total nitrogen (0.08% - 0.56%) and available phosphorus (22.1 to 30.9 mg⋅kg−1) recorded for the 0 - 20 cm depth then reduced with depth but midslope values were also lower. The C/N ratio varied between 9 and 45. Low C/N values appeared mostly in 0 - 20 cm depth at the upslope and downslope soils and subsurface soils of midslope position. Exchangeable Ca was very low to low (1.43 - 3.6 cmol + kg−1), Mg was very low to low (0.39 - 1.5 cmol + kg−1), K was low to medium (0.2 - 0.54 cmol + kg−1) and Na was very low (−1). The sum of exchangeable bases was very low (3.02 - 5.19 cmol + kg−1), cation exchange capacity was low to moderate (8.60 - 25.6 cmol + kg−1) and base saturation was very low to low (19.27% - 36.97%). Leaching of bases under heavy rainfall is a major cause of soil acidification under humid topical ecosystems. The Ca/Mg/K ratio was unbalanced and Mg was the most relatively concentrated base in all the soils. There was a clear variation of most of the soil properties along the slope and with depth. The soils were classified in the FCC system as aek for the upslope soils, Caek for the midslope soils and Cagk for the footslope soils. The principal limitations to production of huckleberry, beans, maize and potatoes were heavy rainfall, wetness, steep slope, soil texture/structure and low soil fertility. These constraints might be overcome by farming at the end of the raining season, contour ploughing, terracing, fertilization and liming.

Influence of experimental snow removal on root and canopy physiology of sugar maple trees in a northern hardwood forest

Due to projected increases in winter air temperatures in the northeastern USA over the next 100 years, the snowpack is expected to decrease in depth and duration, thereby increasing soil exposure to freezing air temperatures. To evaluate the potential physiological responses of sugar maple (Acer saccharum Marsh.) to a reduced snowpack, we measured root injury, foliar cation and carbohydrate concentrations, woody shoot carbohydrate levels, and terminal woody shoot lengths of trees in a snow manipulation experiment in New Hampshire, USA. Snow was removed from treatment plots for the first 6 weeks of winter for two consecutive years, resulting in lower soil temperatures to a depth of 50 cm for both winters compared to reference plots with an undisturbed snowpack. Visibly uninjured roots from trees in the snow removal plots had significantly higher (but sub-lethal) levels of relative electrolyte leakage than trees in the reference plots. Foliar calcium: aluminum (Al) molar ratios were significantly lower, and Al concentrations were significantly higher, in trees from snow removal plots than trees from reference plots. Snow removal also reduced terminal shoot growth and increased foliar starch concentrations. Our results are consistent with previous research implicating soil freezing as a cause of soil acidification that leads to soil cation imbalances, but are the first to show that this translates into altered foliar cation pools, and changes in soluble and structural carbon pools in trees. Increased soil freezing due to a reduced snowpack could exacerbate soil cation imbalances already caused by acidic deposition, and have widespread implications for forest health in the northeastern USA.

Factors affecting soil acidification under legumes. III. Acid production by N2 -fixing legumes as influenced by nitrate supply.

Leaching of nitrate through soil profiles is a major cause of soil acidification. Legume species differ in their ability to take up nitrate (NO3 - ) and in the degree to which soil NO3 - impairs legume nodulation and N2 fixation. This pot experiment examined species variation in N2 fixation and acid production in grain legumes grown for 6 wk on a sandy soil with Ca(NO3 )2 added at 0-56.7 mg N kg-1 soil. The eight legumes studied were Lupinus angustifolius ('Gungurru'), Lupinus albus ('Kiev mutant'), Lupinus luteus ('Teo'), Cicer arietinum (Selection T1587), Pisum sativum ('Dundale' and 'Wirrega'), Vicia faba ('Fiord') and Lathyrus sativus (Selection 453). While number of nodules was not significantly affected by treatment with NO3 - , increasing supply of NO3 - decreased nodule mass, with P. sativum'Wirrega' being most sensitive and C. arientinum and V. faba least sensitive. The concentrations of nitrogen in plants generally decreased as the supply of NO3 - increased. Increasing supply of NO3 - decreased the percentage of N2 fixation, most significantly in L. sativus and least in L. albus. In the absence of added NO3 - , the amounts of H+ produced per unit biomass (specific acid production) differed by as much as 2.2-fold among the species, with C. arientinum generating most H+ , followed by L. angustifolius, L. luteus, L. albus, V. faba, L. sativus, P. sativum'Dundale' and P. sativum'Wirrega'. This species variation was even greater at higher NO3 - supply. In the presence of NO3 - at up to 14.2 mg N kg-1 , acid production by these legumes correlated well with uptake of excess cations but not with the concentration of nitrogen in plants. For all species, release of H+ declined with increasing supply of NO3 - , decreasing most in L. sativus and least in C. arientinum. The results suggest that there might be scope for selecting grain legume species in order to minimize soil acidification by decreasing leaching of NO3 - .

Comparison of some soil properties under Pinus radiata and improved pasture

Some properties of surface mineral soils under Pinus radiata were compared with those under adjacent pasture at ten farm‐forestry sites in the Manawatu, New Zealand. None of the sites had received lime in the last 10 years. Generally, the soil samples under P. radiata had lower pH and higher extractable aluminium concentrations than their counterparts under pasture. Exchangeable calcium values were lower under P. radiata, by 96–1275 kg/ha. Tree uptake and forest floor development can account for up to 550 kg/ha; at six sites the difference was less than 550 kg/ha, suggesting that calcium generally was conserved by the P. radiata ecosystem. Soil exchangeable sodium and magnesium values were usually greater under P. radiata than under pasture; this probably resulted from the interception of airborne sea‐salt by the P. radiata canopy and subsequent transfer to the soil. There were no general trends in the data for available phosphorus and exchangeable potassium. Total nitrogen was often lower in the samples under P. radiata, and the C/N ratio was generally greater under P. radiata. Loss of soil nitrogen may arise from elimination of legumes, accumulation by the trees, and possibly by leaching. Mineralisation of nitrogen, together with production of organic acids and uptake of excess cations over anions, may be possible causes of soil acidification.

Modelling recent and historic soil data from the Rothamsted Experimental Station, UK using SAFE

Historic soil data from 1883, 1906, 1964 and new data from 1991 from the Geesecroft Wilderness Experiment at Rothamsted Experimental Station, UK, was used as a test of the dynamic biogeochemical model SAFE in a situation where the available data can be used to confine the model completely. The test indicated that the model is capable of predicting the observed changes over time in soil chemistry, without calibration. This suggests that the model formulation and choice of significant processes are quantitatively correct. The model application at Rothamsted shows that deposition of acidity because of sulphur and nitrogen emissions during the last 110 years, is the major cause of soil acidification in Geesecroft Wilderness. Natural afforestation of the site has also contributed with a significant but smaller amount of acidity input to the soil. Acidification has caused a possibly irreversible decrease in the cation exchange capacity of the soil because of weathering of clay minerals.

Mechanisms for carbon and nutrient release and retention in beech forest gaps

Nutrient cycling and water balance in forest gaps has received little attention until now, although gap regeneration is important to natural dynamics of temperate forests. Gaps of 30 m diameter, cut in a mature beech forest, exhibited a distinct change in microclimatic conditions in comparison with the surrounding stand. Soil moisture in gaps remained very high throughout the observation period. Disruption of the N cycle in gaps led to substantial nitrate losses; seepage water nitrate concentrations were 10-18 mg NO 3 -N L −1 . Excess nitrification was a significant cause of soil acidification and aluminium release. The pH in subsoil seepage water decreased by 0.25. Liming in gaps promoted the establishment of a herbaceous vegetation, which functioned as an important nutrient sink, and thus is recommended for tree regeneration in highly acidified forest ecosystems as it increases the resilience of the ecosystem to nutrient losses

Anthropogenic and natural acidification in terrestrial ecosystems

The total proton load found in these ecosystems exceeds by far the known rates of buffering in soils by silicate weathering and release of basic cations (see above). Under the present proton load most forest soils will therefore acidify and besides losses of nutrients the occurrence of possible toxic ions in the soil unavoidable (Al-buffer range)20, 21. The proportion of the total proton load of the soil that is represented by the internal production emphasizes the importance of acid deposition as main cause of soil acidification and destabilization of forest ecosystems under Central European conditions.

Soil acidification during more than 100 years under permanent grassland and woodland at Rothamsted

Abstract Soil samples have been taken periodically from unlimed plots of the 130‐year‐old Park Grass Experiment and from the 100‐year‐old Geescroft Wilderness at Rothamsted. Changes in the pH of the samples show how acidification has progressed. The soils are now at, or are approaching, equilibrium pH values which depend on the acidifying inputs and on the buffering capacities of the soils. We have calculated the contributions to soil acidification of natural sources of acidity in the soil, atmospheric deposition, crop growth and nutrient removal, and, where applicable, additions of fertilizers. The relative importance of each source of acidification has changed as the soils have become more acid. Acid rain (wet deposited acidity) is a negligible source, but total atmospheric deposition may comprise up to 30% of acidifying inputs at near neutral soil pH values and more as soil pH decreases. Excepting fertilizers, the greatest causes of soil acidification at or near neutral pH values are the natural inputs of H+ from the dissolution of CO2 and subsequent dissociation of carbonic acid, and the mineralization of organic matter.Under grassland, single superphosphate and small amounts of sodium and magnesium sulphates have had no effect on soil pH, whilst potassium sulphate increased soil acidity slightly. All of these effects are greatly outweighed under grassland, however, by those of nitrogen fertilizers. Against a background of acidification from atmospheric, crop and natural inputs, nitrogen applied as ammonium sulphate decreased soil pH up to a maximum of 1.2 units at a rate in direct proportion to the amount added, and nitrogen applied as sodium nitrate increased soil pH by between 0.5 and 1 unit.