Significant Soil Acidification Research Articles

Hedgerow Olive Orchards versus Traditional Olive Orchards: Impact on Selected Soil Chemical Properties

Olive orchards cover over 10 million hectares worldwide, with production techniques undergoing significant changes in the past three decades. The traditional rainfed approach, involving minimal inputs, has given way to irrigated super-intensive systems with higher planting density, increased productivity, a greater use of fertilizers and phytopharmaceuticals, and total mechanization. Its impact on soil chemical properties remains a topic of great debate, and no definitive consensus has been reached. Our main objective was to examine the different effects of traditional olive orchards and super-intensive orchards on soil chemistry over a decade. We collected and analyzed 1500 soil samples from an irrigation perimeter in southern Portugal in 2003 and 2013. Our findings indicate that, compared to traditional olive orchards, super-intensive ones show, in a decade, a significant decrease in soil organic matter (less 22.8%—p < 0.001), namely due to the increase in mineralization caused by an increase in soil moisture content as a result of irrigation practice, and an increase in sodization (more 33.8% of Ext Na—p < 0.001) highlighting the importance of monitoring this factor for soil fertility. In comparison to other irrigated crops in the region, super-intensive olive orchards promote a significant soil acidification (from 7.12 to 6.58), whereas the pH values of the other crops increase significantly (3.3%, 13.5%, and 3.0% more in corn, tomato, and cereals, respectively). Mainly because of the decrease in organic matter levels with soil acidification and soil sodization, we can underline that hedgerow olive orchards can affect soil characteristics negatively when compared with traditional ones, and it is necessary to adopt urgent measures to counter this fact, namely sustainable agriculture practices.

Differential soil acidification caused by parent materials and land‐use changes in the Pearl River Delta region

AbstractSoil acidification occurs widely across the world, which has been partly attributed to land‐use change. However, measureable effect of land‐use change as well as parent materials on soil acidification remains poorly understood. Here, a typical area with intensive land‐use change in the Pearl River Delta of China was chosen for this study. Topsoil (0–20 cm) and subsoil (20–40 cm) samples (n = 169) under different land uses (paddy fields, vegetable lands and orchards) and parent materials (granite and alluvial sediment) were collected in 2020. Soil pH, exchangeable base cations, exchangeable acidity and pH buffering capacity were measured to evaluate the status of soil acidification. The change of soil pH over the last 15 years was evaluated via comparing with historical data (n = 329) in 2005. The results showed a higher exchangeable acidity and lower pH buffering capacity and exchangeable base cations of soils derived from granite compared with soils derived from alluvial sediment in 2020. In the last 15 years, significant soil acidification under different parent materials was observed under vegetable lands and orchards but not paddy fields. Faster pH decline was found under land‐use change from paddy fields compared with the unchanged vegetable lands or orchards. Furthermore, stronger acidification under the same land‐use change was observed for soils derived from granite compared with soils derived from alluvial sediment. These results indicate that land‐use change induced soil acidification is dependent on parent materials. This study implies that cropping management such as suitable rotation operation may slow soil acidification, and measures including straw returning may ameliorate acidified soils.

Soil Properties and Maize Yield Improvement with Biochar-Enriched Poultry Litter-Based Fertilizer.

Conversion of poultry litter into fertilizer presents an environmentally friendly way for its disposal. The amendment of stabilizing sorption materials (e.g., biochar) to broiler chicken rearing seems promising, as it protects produced litter from nutrient losses and improves fertilizing efficacy. Thus, a pot experiment was carried out with maize and organic fertilizers produced from biochar-amended chicken bedding. The properties of three types of poultry-matured litter, amended with biochar at 0%, 10% and 20% dose, were analyzed. These matured litters were added to soil and physicochemical, biological properties and dry aboveground crop biomass yield were determined. Both biochar doses improved matured litter dry matter (+29%, +68% compared to unamended litter) and organic carbon (+5%, +9%). All three fertilizers significantly increased dry plant aboveground biomass yield (+3% and +42% compared to control litter-treated variant) and N-acetyl-β-D-glucosaminidase activity (+51%, +57%) compared to unamended control soil. The 20% biochar poultry-matured litter derived the highest dry plant aboveground biomass, highest respiration induced by D-glucose (+53%) and D-mannose (+35%, compared to control litter-treated variant), and decreased pH (-6% compared to unamended control). Biochar-derived modification of poultry litter maturation process led to organic fertilizer which enhanced degradation of soil organic matter in the subsequently amended soil. Furthermore, this type of fertilizer, compared to conventional unamended litter-based type, increased microbial activity, nutrient availability, and biomass yield of maize in selected biochar doses, even under conditions of significant soil acidification.

Lead dissociation and redistribution properties of actual contaminated farmland soil after long-term EKAPR treatment.

Electrokinetic-assisted phytoremediation (EKAPR) is a potential technology much affected by the metal species and accessibility to plant roots. In this study, Pb-contaminated red soil was remediated with Sedum plumbizincicola to investigate the changes in soil pH, available nutrients, dissociation and redistribution of Pb under a long-term periodic reversal direct-current electric field. This approach could effectively activate soil P, K, organic matter (OM)and Pb, without significant soil acidification; the effect was positively correlated with applied voltage. Soil Pb can be continuously dissociated, migrated, and tended to accumulate in the middle region. The maximum Pb removal rate in the anodic section of the EKAPR system was 21.4%, and the aggregation rate in middle regions was 14.4%, higher than the available Pb content of the original soil. The Pb desorption in aqueous solution increased significantly with increasing voltage, irrespective of the solution pH. At a voltage of 20V, the Pb cumulative desorption content reached 91.1mgkg-1 (pH = 7), which was 2.7 times than that without electric field (33.2mgkg-1). Compared to original soil (2.80mgkg-1) and the control (14.54mgkg-1), the available Pb in the anode section of EKAPR system (20.66mgkg-1) increased by 637.9% and 42.1%, respectively. These results indicated that except for the indirect influence of soil pH changes, electrodynamics can directly promote the bioavailability and dissociation of Pb at the soil-water interface. This finding provides a new perspective for further studies on the mechanism of Pb speciation evolution and accumulation changes using EKAPR.

Soil acidification and loss of base cations in a subtropical agricultural watershed

Soil acidification along with base cations loss degrades soil quality and is a major environmental problem, especially in agroecosystems with extensive nitrogen (N) fertilization. So far, the rates of proton (H+) production and real soil acidification (loss of base cations) remain unclear in subtropical agricultural watersheds. To assess the current status and future risk of soil acidification in subtropical red soil region of China, a two-year monitoring was conducted in a typical agricultural watershed with upland, paddy fields, and orchards where high N fertilizers are applied (320 kg N ha−1 yr−1). H+ production, neutralization and base cations losses were quantified based on the inputs (rainwater, inflow of water, and fertilizer) and outputs (outflow of water, groundwater drainage, and plant uptake) of major elements (K+, Ca2+, Na+, Mg2+, Al3+, NH4+, NO3−, SO42−, Cl−, and H+). The result showed that total H+ production in the watershed was 5152 molc ha−1 yr−1. N transformation was the most important H+ source (68%), followed by excess plant uptake of cations (25%) and H+ deposition (7%). Base cations exchange and weathering of minerals (3842 molc ha−1 yr−1) dominated H+ neutralization, followed by SO42− adsorption (1081 molc ha−1 yr−1), while H+ and Al3+ leaching amounted to 431 molc ha−1 yr−1, only. These results state clearly that despite significant soil acidification, the acidification of surface waters is minor, implying that soils have buffered substantially the net H+ addition. As a result of soil buffering, there was abundant loss of base cations, whose rate is significantly higher than the previously reported weathering rate of minerals in red soils (3842 vs 230–1080 molc ha−1 yr−1). This suggests that the pool of exchangeable base cations is being depleted in the watershed, increasing the vulnerability of the watershed, and posing a serious threat to future recovery of soils from acidification.

Featured Front Cover

The cover image is based on the Research Article Significant soil acidification caused by grazing exclusion across China's grasslands by Jiangtao Hong et al., https://doi.org/10.1002/ldr.3722.

Advantages of grass-grain crop rotations due to prolonged use of clover-alfalfa-timothy mixture

It is known that significant saving of nitrogen fertilizers are due to perennial legume-cereal grasses use in crop rotations. From 2013 to 2018in the Mari El Republic six-field grass-grain fodder crop rotations were compared on sod-podzolic soils with a very high level of phosphorus and potassium. In the third rotation their productivity and bioenergetic efficiency, changes in several important soil fertility indicators, and crud protein content in the produced fodder were evaluated. The main difference between the crop rotations was based on the duration of the clover-alfalfa-timothy grass mixture (CAG) use: from one year to three years. In given experiment there was also studied the effect of mineral nitrogen (variants N0, N60) against Р60К60 background on the yield of crop rotations. During six years, there was no significant soil acidification in the variants. Each additional year of clover-alfalfa-timothy grass mixture use raised the energy efficiency ratio of crop rotations by 24-47 % (from 1.13-1.24 by one-year use to 2.08-2.25 by three years of use). Three-year CAG use as compared with one- and two-years has given to the crop rotation significant advantages in energy efficiency (up to two times) and productivity (approximately 40-80 %) of cultivated crops. After refusing to apply nitrogen fertilizations in such crop rotation, average crop productivity, soil humus and nitrogen content in the soil were better preserved. The average crude protein content in dry matter of the obtained fodder increased from 12.7 % to 14.6 % when prolonging theca use up to two years. The average energy value of the yield per rotation was recorded low (8.4-8.7 MJ/kg) and did not depend on the studied factors.

Significant soil acidification caused by grazing exclusion across China’s grassland areas

AbstractSoil pH is strongly associated with soil biogeochemical cycles and biodiversity in terrestrial ecosystems. Grazing exclusion (GE) has been widely adopted as an effective practice to restore degraded grasslands. However, the effect of GE on soil pH is still poorly understood and remains inconclusive. We synthesized data for 63 sites from the peer‐reviewed literature and 43 additional field sites and investigated the differences in soil pH following grazing exclusion across China’s grasslands. The mean pH across all samples decreased by 0.13 units with grazing exclusion (mean pH 8.15 and 8.02 for the grazed and grazing exclusion groups, respectively, p < 0.001). The pH of the surface soil (0–20 cm) showed the greatest rates of decrease in grazing exclusion grasslands, whereas the pH of the deep soil layers (20–100 cm) showed a limited response to grazing exclusion. In general, the largest rate of decrease in soil pH occurred after medium‐term periods (5–15 years) of grazing exclusion, whereas a smaller rate of change was found over short‐ (≤5 years) and long‐term periods (≥15 years) of grazing exclusion. Of the environmental factors examined, the climatic conditions, accumulation of biomass and the soil carbon and nitrogen dynamics were important factors influencing soil pH following grazing exclusion. Our results indicate that grazing exclusion causes significant soil acidification, especially in surface soils and humid areas. Our results provide an important reference for the future management of China’s grasslands.

Nitrogen addition has contrasting effects on particulate and mineral-associated soil organic carbon in a subtropical forest

Increasing atmospheric nitrogen (N) deposition has substantially affected carbon (C) and nutrient cycling in forest ecosystems. However, the responses of different soil organic carbon (SOC) fractions with different turnover rates to N addition are highly divergent, and the underlying mechanisms remain elusive. In this study, we explored the responses of surface soil (0–10 cm) characteristics and microbial communities to six years of experimental N addition (0, 50, 100 and 150 kg N ha−1 yr−1) in a subtropical evergreen broadleaf forest in southern China. Our results showed that N addition led to significant soil acidification (pH from 5.3 to 4.9). Microbial biomass carbon and total microbial, bacterial and fungal abundance (phospholipid fatty acid, PLFA) were reduced by N addition, but extracellular enzymes involved in C, N and phosphorus (P) cycling were not responsive to N addition. Soil extractable Ca2+ concentration was depleted by N addition, while other extractable cations (Fe3+, Al3+, Mg2+, K+, Na+) were not affected. Moreover, N addition did not significantly change the C and N concentration of bulk soil. We further separated the bulk soil into particulate organic matter (>53 μm, POM) and mineral-associated organic matter (<53 μm, MAOM) fractions by wet sieving. Interestingly, C in the POM fraction was significantly increased by N addition, while C in the MAOM fraction was depleted by N addition. Correlation analysis and structural equation modeling results suggested that N addition may suppress microbial decomposition of plant inputs and thus lead to accumulation of C in the POM fraction, while it may reduce the mineral sorption of microbial necromass and products and thus cause depletion of C in the MAOM fraction. Taken together, our results highlighted the vulnerability of soil C in the stable MAOM fraction to N addition, and emphasized the role of soil metals (particularly extractable Ca2+) and pH in controlling soil C storage under N addition.

Soil acidification induced by nitrogen addition and its responses to water addition in Inner Mongolia Temperate Steppe, China

Soil acidification due to exogenous nitrogen (N) deposition has been received sufficient attention in the past several decades. Whether the N-induced soil acidification is modulated by the altering precipitation regimes remains unclear. In this study, based on a five-year (2013-2017) manipulative field experiment with factorial N addition (10 and 40 g N·m-2·a-1 ) and water addition (a total amount of 80 mm·a-1 was added in terms of five intensities, i.e., 2 mm×40 times, 5 mm×16 times, 10 mm×8 times, 20 mm×4 times, and 40 mm×2 times) in a typical steppe in Inner Mongolia, I analyzed the effects of water addition on soil acidification induced by N addition. I found that soil acidification induced by 40 g N m-2·a-1 N addition occurred earlier, more significant, and with a greater year by year changed rate than that of 10 g N·m-2·a-1 N addition. After one year treatment, I observed significant soil acidification at soil profiles of 0-5, 5-10, and 10-20 cm in the treatment of 40 g N·m-2·a-1 N addition, while significant soil acidification in 10 g N·m-2·a-1 N addition was observed after 1, 4, and 5 year since N was added for the three layers, respectively. In general, the magnitude of soil acidification induced by N addition increased with the increasing period after N addition, and the slope of the regression line was steeper in the relatively higher dose of N addition (40 g N·m-2·a-1). Soil acidification induced by N addition could not be reversed by water addition, but water addition in terms of relatively lower intensities (i.e., all the treatments except 40 mm×2 times) could relieve the N-induced soil acidification to a certain extent in the treatment with lower dose of N addition (10 g N·m-2·a-1) in dry years. In wet years, however, water addition exacerbated soil acidification after N was added, especially in the topsoil. The leaching of soil inorganic N after higher intensity of water addition (10-40 mm) could explain the deteriorated N-induced soil acidification when water was added. There was no significance for the relief or deterioration to N-induced soil acidification by water addition. Our results had important implications for understanding grassland responses to N deposition and altered precipi-tation regime in the future.

Quantitative and compositional responses of ammonia-oxidizing archaea and bacteria to long-term field fertilization.

Archaeal (AOA) and bacterial (AOB) ammonia-oxidizer responses to long-term field fertilization in a Mollisol soil were assessed through pyrosequencing of amoA genes. Long-term fertilization treatments including chemical fertilizer (NPK), NPK plus manure (NPKM), and no fertilization over 23 years altered soil properties resulting in significant shifts in AOA and AOB community composition and abundance. NPK exhibited a strong influence on AOA and AOB composition while the addition of manure neutralized the community change induced by NPK. NPK also led to significant soil acidification and enrichment of Nitrosotalea. Nitrosospira cluster 9 and 3c were the most abundant AOB populations with opposing responses to fertilization treatments. NPKM had the largest abundance of ammonia-oxidizers and highest potential nitrification activity (PNA), suggesting high N loss potential due to a doubling of nutrient input compared to NPK. PNA was strongly correlated to AOA and AOB community composition indicating that both were important in ammonium oxidization in this Mollisol soil. Total N and organic C were the most important factors driving shifts in AOA and AOB community composition. The AOA community was strongly correlated to the activities of all sugar hydrolysis associated soil enzymes and was more responsive to C and N input than AOB.

The contribution of atmospheric deposition and forest harvesting to forest soil acidification in China since 1980

Soils below croplands and grasslands have acidified significantly in China since the 1980s in terms of pH decline in response to acid inputs caused by intensified fertilizer application and/or acid deposition. However, it is unclear what the rate is of pH decline of forest soils in China in response to enhanced acid deposition and wood production over the same period. We therefore gathered soil pH data from the Second National Soil Inventory of China and publications from the China National Knowledge Infrastructure (CNKI) database in 1981–1985 and 2006–2010, respectively, to evaluate the long-term change of pH values in forest soils. We found that soil pH decreased on average by 0.36 units in the period 1981–1985 to 2006–2010., with most serious pH decline occurring in southwest China (0.63 pH units). The soil type with the strongest pH decline was the semi-Luvisol (0.44 pH units). The decrease in pH was significantly correlated with the acid input induced by atmospheric deposition and forest harvesting. On average, the contribution of atmospheric deposition to the total acid input was estimated at 84% whereas element uptake (due to forest wood growth and harvest) contributed 16% only. Atmospheric deposition is thus the major driver for the significant forest soil acidification across China.

Urbanization in China drives soil acidification of Pinus massoniana forests.

Soil acidification instead of alkalization has become a new environmental issue caused by urbanization. However, it remains unclear the characters and main contributors of this acidification. We investigated the effects of an urbanization gradient on soil acidity of Pinus massoniana forests in Pearl River Delta, South China. The soil pH of pine forests at 20-cm depth had significantly positive linear correlations with the distance from the urban core of Guangzhou. Soil pH reduced by 0.44 unit at the 0–10 cm layer in urbanized areas compared to that in non-urbanized areas. Nitrogen deposition, mean annual temperature and mean annual precipitation were key factors influencing soil acidification based on a principal component analysis. Nitrogen deposition showed significant linear relationships with soil pH at the 0–10 cm (for ammonium N (-N), P < 0.05; for nitrate N (-N), P < 0.01) and 10–20 cm (for -N, P < 0.05) layers. However, there was no significant loss of exchangeable non-acidic cations along the urbanization gradient, instead their levels were higher in urban than in urban/suburban area at the 0–10 cm layer. Our results suggested N deposition particularly under the climate of high temperature and rainfall, greatly contributed to a significant soil acidification occurred in the urbanized environment.

Effect of agricultural lands afforestation and tree species composition on the soil reaction, total organic carbon and nitrogen content in the uppermost mineral soil profile

Forests occupy one third of the world&amp;rsquo;s land area and govern carbon (C) transfers and influence nitrogen (N) content in the biosphere. Afforestation leads to soil changes of specific dynamics, often accompanied by acidification. Especially at higher altitudes this effect is accelerated and increased with the stand age since forestation. The change in soil C and N content following afforestation is controlled by a number of factors, including: previous land use (grasslands, cropland, etc.), tree species, soil cultivation method, soil properties (clay content, pH), stand age, site management, topography, and climate. In the Czech Republic, large area changes in land use took place in the last centuries &amp;ndash; forests covering roughly 20% in the 18&lt;sup&gt;th&lt;/sup&gt; century currently occupy almost 34%, with still increasing tendencies. This paper compares basic soil properties (soil reaction, total soil organic carbon as well as total nitrogen contents) of the agricultural land and land afforested 40&amp;ndash;60 years ago. The results confirmed the key role of afforestation in the change of soil organic matter dynamics after establishing new forests on the former agricultural lands in the uppermost mineral soil part of the Orlick&amp;eacute; hory Mts. region in the Czech Republic. During that time, comparatively substantial changes in soil organic matter and nitrogen were registered. Afforestation considerably increased organic matter content in the studied A-horizons of different land use types. Soil development resulted in a high production of C and N pools under the forest stands, contrary to agricultural land. In general, afforestation caused significant soil acidification. The common tendency of higher acidity of forest soils compared to agricultural ones was documented in the studied case as well. The general tendencies of soil reaction and soil organic matter dynamics at the studied sites are comparable to those in other regions of the Czech Republic.

Soil acidification and nutrient sustainability of forest ecosystems in the northeastern German lowlands - Results of the national forest soil inventory

Between the first and second national forest soil inventory in the northeastern German lowlands a significant soil acidification took place with regionally varying intensity. It manifests itself in a reduced base saturation in the whole rooting zone. This applies to the base cations magnesium and calcium. For potassium, however, no significant changes were detected. The acidification dynamic is the strongest in the southern part of Brandenburg. The specific immission situation in this region during the past four decades explains this. Particularly in southern Brandenburg high dust depositions (fly ashes from brown coal-fired power stations) buffered the acid components and enriched the soil with base cati ons in the 1970s and 1980s. Since the reduction of these atmospheric depositions, the bases were obviously totally incorporated in the biomass or leached out with seepage water. Currently, the majority of the forest sites in Mecklenburg-Vorpommern and Brandenburg are poor in basic nutrient elements (Ca, Mg, K). Especially the element magnesium is assumed to be lacking. This paper presents an assessment of the long-term availability of the nutrients Ca, Mg und K on the basis of calculated nutrient balances for various forest management scenarios (e.g. full-tree harvest). The results show that the sustainable supply is critical especially for intensive forest use on numerous sites.

Significant soil acidification across northern China's grasslands during 1980s–2000s

AbstractAnthropogenic acid deposition may lead to soil acidification, with soil buffering capacity regulating the magnitude of any soil pH change. However, little evidence is available from large‐scale observations. Here, we evaluated changes in soil pH across northern China's grasslands over the last two decades using soil profiles obtained from China's Second National Soil Inventory during the 1980s and a more recent regional soil survey during 2001–2005. A transect from the central‐southern Tibetan Plateau to the eastern Inner Mongolian Plateau, where Kriging interpolation provided robust predictions of the spatial distribution of soil pH, was then selected to examine pH changes during the survey period. Our results showed that soil pH in the surface layer had declined significantly over the last two decades, with an overall decrease of 0.63 units (95% confidence interval = 0.54–0.73 units). The decline of soil pH was observed in both alpine grasslands on the Tibetan Plateau and temperate grasslands on the Inner Mongolian Plateau. Soil pH decreased more intensively in low soil carbonate regions, while changes of soil pH showed no significant associations with soil cation exchange capacity. These results suggest that grassland soils across northern China have experienced significant acidification from the 1980s to 2000s, with soil carbonates buffering the increase in soil acidity. The buffering process may induce a large loss of carbon from soil carbonates and thus alter the carbon balance in these globally important ecosystems.

Tree species traits cause divergence in soil acidification during four decades of postagricultural forest development

AbstractA change in land use from agriculture to forest generally increases soil acidity. However, it remains unclear to what extent plant traits can enhance or mitigate soil acidification caused by atmospheric deposition. Soil acidification is detrimental for the survival of many species. An in‐depth understanding of tree species‐specific effects on soil acidification is therefore crucial, particularly in view of the predicted global increases in acidifying nitrogen (N) deposition. Here, we report soil acidification rates in a chronosequence of broadleaved deciduous forests planted on former arable land in Belgium. This region receives one of the highest loads of potentially acidifying atmospheric deposition in Europe, which allowed us to study a ‘worst case scenario’. We show that less than four decades of forest development caused significant soil acidification. Atmospheric deposition undoubtedly and unequivocally drives postagricultural forests towards more acidic conditions, but the rate of soil acidification is also determined by the tree species‐specific leaf litter quality and litter decomposition rates. We propose that the intrinsic differences in leaf litter quality among tree species create fundamentally different nutrient cycles within the ecosystem, both directly through the chemical composition of the litter and indirectly through its effects on the size and composition of earthworm communities. Poor leaf litter quality contributes to the absence of a burrowing earthworm community, which retards leaf litter decomposition and, consequently, results in forest‐floor build‐up and soil acidification. Also nutrient uptake andN2fixation are causing soil acidification, but were found to be less important. Our results highlight the fact that tree species‐specific traits significantly influence the magnitude of human pollution‐induced soil acidification.

Soil carbon and related soil properties along a soil type and land‐use intensity gradient, New South Wales, Australia

AbstractThe aim of this study was to systematically quantify differences in soil carbon and key related soil properties along a replicated land‐use intensity gradient on three soil landscapes in northwest New South Wales, Australia. Our results demonstrate consistent land‐use effects across all soil types where C, N and C:N ratio were in the order woodland &gt; unimproved pasture = improved pasture &gt; cultivation while bulk density broadly showed the reverse pattern. These land‐use effects were largely restricted to the near surface soil layers. Improved pasture was associated with a significant soil acidification, indicating that strategies to increase soil carbon through pasture improvement in these environments might also have associated soil degradation issues. Total soil carbon stocks were significantly larger in woodland soils, across all soil types, compared with the other land‐uses studied. Non‐wooded systems, however, had statistically similar carbon stocks and this pattern persisted whether or not carbon quantity was corrected for equivalent mass. Our results suggest that conversion from cultivation to pasture in this environment would yield between 0.06 and 0.15 t C/ha/yr which is at the lower end of predicted ranges in Australia and well below values measured in other cooler, wetter environments. We estimate that a 10% conversion rate (cultivation to pasture) across NSW would yield around 0.36 Mt CO2‐e/yr which would contribute little to emission reductions in NSW. We conclude that carbon accumulation in agricultural soils in this environment might be more modest than current predictions suggest and that systematically collected, regionally specific data are required for the vegetation communities and full range of land‐uses before accurate and reliable predictions of soil carbon change can be made across these extensive landscapes.

Long-term experiments for sustainable nutrient management in China. A review

China is facing one of the largest challenges of this century to continue to increase annual cereal production to about 600 Mt by 2030 to ensure food security with shrinking cropland and limited resources, while maintaining or improving soil fertility, and protecting the environment. Rich experiences in integrated and efficient utilization of different strategies of crop rotation, intercropping, and all possible nutrient resources accumulated by Chinese farmers in traditional farming systems have been gradually abandoned and nutrient management shifted to over-reliance on synthetic fertilizers. China is now the world's largest producer, consumer and importer of chemical fertilizers. Over- application of nitrogen (N) is common in intensive agricultural regions, and current N-uptake efficiency was reported to be only 28.3, 28.2 and 26.1% for rice, wheat and maize, respectively, and less than 20% in intensive agricultural regions and for fruit trees or vegetable crops. In addition to surface and groundwater pollution and greenhouse gas emissions, over-application of N fertilizers has caused significant soil acidification in major Chinese croplands, decreasing soil pH by 0.13 to 2.20. High yield as a top priority, small-scale farming, lack of temporal synchronization of nutrient supply and crop demand, lack of effective extension systems, and hand application of fertilizers by farmers are possible reasons leading to the over-application problems. There is little doubt that current nutrient management practices are not sustainable and more efficient management systems need to be developed. A review of long-term experiments conducted around the world indicated that chemical fertilizer alone is not enough to improve or maintain soil fertility at high levels and the soil acidification problem caused by over- application of synthetic N fertilizers can be reduced if more fertilizer N is applied as NO − relative to ammonium- or urea-based N fertilizers. Organic fertilizers can improve soil fertility and quality, but long-term application at high rates can also lead to more nitrate leaching, and accumulation of P, if not managed well. Well-managed combination of chemical and organic fertilizers can overcome the disadvantages of applying single source of fertilizers and sustainably achieve higher crop yields, improve soil fertility, alleviate soil acidification problems, and increase nutrient-use efficiency compared with only using chemical fertilizers. Crop yield can be increased through temporal diversity using crop rotation strategies compared with continuous cropping and legume-based cropping systems can reduce carbon and nitrogen losses. Crop yield responses to N fertilization can vary significantly from year to year due to variation in weather conditions and indigenous N supply, thus the commonly adopted prescriptive approach to N management needs to be replaced by a responsive in-season management approach based on diagnosis of crop growth, N status and demand. A crop sensor-based in-season site-specific N management strategy was able to increase N- uptake efficiency by 368% over farmers' practices in the North China Plain. Combination of these well-tested nutrient management principles and practices with modern crop management technologies is needed to develop sustainable nutrient management systems in China that can precisely match field-to-field and year-to-year variability in nutrient supply and crop demand for both single crops and crop rotations to not only improve nutrient-use efficiency but also increase crop yield and protect the environment. In addition, innovative and effective extension and service-providing systems to assist farmers in adopting and applying new management systems and technologies are also crucially important for China to meet the grand challenge of food security, nutrient-use efficiency and sustainable development.

Dynamic modelling of the response of UK forest soils to changes in acid deposition using the SAFE model

Both observed and modelled data have been examined from the ten UN-ECE Level II forest intensive monitoring sites in the UK to determine the changes and potential impact on soil solution chemistry resulting from changes in acid deposition inputs. The sites represent a range of forest tree types, soil sensitivities and pollutant deposition inputs found in the UK. The dynamic biogeochemical SAFE model was used to explore temporal changes in soil and soil solution chemical parameters that have been used as indicators for potential forest ecosystem and tree damage in national and international assessments of critical loads. The observed data and model results show that there is significant inter-site variation. The model indicates that the historical pollutant inputs have resulted in significant soil acidification at most of the sites. Model predictions generally match current day observations. Recently declining pollutant inputs have reduced and in some cases reversed the trend of increasing soil acidification. A discussion of the results in terms of critical loads, recovery, their wider implications and uncertainty is presented.