Human activities have dramatically increased nitrogen (N) and sulfur (S) deposition, altering forest ecosystem function and structure. Anticipating how changes in deposition and climate impact forests can inform decisions regarding these environmental stressors. Here, we used a dynamic soil-vegetation model (ForSAFE-Veg) to simulate responses to future scenarios of atmospheric deposition and climate change across 23 Northeastern hardwood stands. Specifically, we simulated soil percent base saturation, acid neutralizing capacity (ANC), nitrate (NO₃⁻) leaching, and understory composition under 13 interacting deposition and climate change scenarios to the year 2100, including anticipated deposition reductions under the Clean Air Act (CAA) and Intergovernmental Panel on Climate Change–projected climate futures. Overall, deposition affected soil responses more than climate did. Soils recovered to historic conditions only when future deposition returned to pre-industrial levels, although anticipated CAA deposition reductions led to a partial recovery of percent base saturation (60 to 72%) and ANC (65 to 71%) compared to historic values. CAA reductions also limited NO₃⁻ leaching to 30 to 66% above historic levels, while current levels of deposition resulted in NO₃⁻ leaching 150 to 207% above historic values. In contrast to soils, understory vegetation was affected strongly by both deposition and climate. Vegetation shifted away from historic and current assemblages with increasing deposition and climate change. Anticipated CAA reductions could maintain current assemblages under current climate conditions or slow community shifts under increased future changes in temperature and precipitation. Overall, our results can inform decision-makers on how these dual stressors interact to affect forest health, and the efficacy of deposition reductions under a changing climate.

The transformation of poultry litter waste through the pyrolysis process produces a product called biochar which, applied to the soil, improves its characteristics. The objective of this work was to evaluate the effect of biochar produced from poultry litter wastes, submitted to pyrolysis at 350 °C on soil chemical and physical characteristics. For this, an experiment was carried out involving soil incubation treatments during 100 days with six doses of biochar equivalent to 0.0, 2.02, 4.05, 6.07, 8.10, and 10.12 t ha⁻¹, calculated by the base saturation method, with correction levels from 61 to 87%. After the incubation, soil samples were physically and chemically analyzed. Biochar doses promoted significant increase in pH, electrical conductivity, potassium, sodium, carbon, phosphorus, and base saturation, and decrease in potential acidity and in the soil cation exchange capacity contributing to the increase of soil fertility. The application of the biochar to the soil decreased the bulk density and increased porosity, field capacity, wilting point, and available water for plants. In general, the use of the biochar demonstrates great potential of it as a soil amendment.

This study evaluated the effect of applying biofertilizer in the soil on the cultivation of corn. Different doses of biofertilizer associated with chemical fertilizer were applied in the soil to meet the plants’ nutritional demand. Four months after sowing, plant samples were collected and evaluated, by measuring the height and productivity of biomass, dry matter, neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP), and nitrogen (N). Soil samples were also collected to measure the concentrations of macronutrients, base saturation, and exchangeable acidity. The biofertilizer application did not alter the levels of dry matter, NDF, ADF, CP, and N in the plants, or the concentrations of nitrogen, phosphorus, magnesium, and copper in the soil. Besides this, the largest average values of the plant heights and levels of potassium in the soil were found in the treatment with the highest biofertilizer dose. Notably, there was a significant increase in the quantity of fresh and dry matter in the treatments that received biofertilizer in comparison with the controls. The results obtained indicated the potential of substituting conventional fertilization with fertirrigation using biofertilizer, an alternative procedure that can help reduce the environmental impacts caused by dairy farming, regarding the release of wastewater into watercourses.

The present study was conducted in tropical Sal forest ecosystem of the Doon valley in the Indian Himalayas to assess the critical load of sulfur and nitrogen and their exceedances. The observed pattern of throughfall ionic composition in the study are Ca2+>K+>Mg2+>Cl−> HCO3−> Na+>NO3 −> SO3 2−≥ NH4 +>F−. The sum of cation studied is 412.29 μeq l−1 and that of anions is 196.98 μeq l−1, showing cation excess of 215.31 μeq l−1. The cations, namely Ca2+, Mg2+, K+, Na+, and NH4 +, made a contribution of about 67% of the total ion strength, where as anion comprising of SO4 2−, Cl−, NO3 −, and HCO3 − contributed 33%. The chief acidic components were Cl– (12%) and HCO3 − (8%), while the presence of SO4 2− (5%) and NO3 − (6%), respectively. Percentage contribution of bole to total aboveground biomass was ∼72.38% in comparison to 2.24–2.93% of leaf biomass, 10.34–10.96% of branch biomass and 13.21–17.07% of bark biomass. There was high and significant variation (P < 0.001) in the total aboveground biomass produced at different sites. The aboveground net primary productivity (ANPP) in these sites ranged between 2.09 and 9.22 t ha−1 year−1. The base cations and nitrogen immobilization was found to be maximum in bole. The net annual uptake of the base cations varied from 306.85 to 1,311.46 eq ha−1 year−1 and of nitrogen from 68.27 to 263.51 eq ha−1 year−1. The critical appraisal of soil showed that cation exchange capacity lied between 18.37 and 10.30 Cmol (p+) kg−1. The base saturation percentage of soil was as high as 82.43% in Senkot, whereas in Kalusidh it was just 44.28%. The local temperature corrected base cation weathering rates based on soil mineralogy, parent material class, and texture class varied from 484.15 to 627.25 eq ha−1 year−1, showing a weak potentiality of the system to buffer any incoming acidity and thus providing restricted acid neutralizing capacity to keep the ecosystem stable under increased future deposition scenarios in near future. The appreciable BS of the soil indicates the presence of intense nutrient phytorecycling forces within this climate and atmospheric deposition in replenishing base cations in the soil, which includes intrinsic soil-forming processes, i.e., weathering. The highest value of critical load for acidity was 2,896.50 eq ha−1 year−1 and the lowest was 2,792.45 eq ha−1 year−1. The calculated value of the minimum critical loads for nitrogen varied from 69.77 to 265.01 eq ha−1 year−1, whereas the maximum nitrogen critical load ranged between 2,992.63 and 4,394.45 eq ha−1 year−1. The minimum and the maximum critical loads of sulfur ranged between 2,130.49 and 3,261.64 eq ha−1 year−1 and 2,250.58 and 3,381.73 eq ha−1 year−1, respectively. The values of exceedance of sulfur and nitrogen were negative, implying that in the current scenario Sal forests of the Doon valley are well protected from acidification.

Combustion of fossil fuels has contributed to many environmental problems including acid deposition. The Clean Air Act (CAA) was created to reduce ecological problems by cutting emissions of sulfur and nitrogen. Reduced emissions and rainfall concentrations of acidic ions have been observed since the enactment of the CAA, but soils continue to receive some acid inputs. Many soils sensitive to acid deposition are found to have low pH, a loss of base cations, and a shift in the mineral phase controlling the activity of Al³⁺ and/or SO₄²⁻. If inputs continue, soil may be depleted of base cations and saturated with Al and could cause low forest productivity. Soil samples and soil solutions from pan lysimeters were taken on ridge-tops in the Daniel Boone National Forest to evaluate potential impacts of acid deposition recently and in the future. Sample results were compared to historical data from identical locations. Physicochemical characteristics of the soils revealed that sites were very low in base saturation and pH and high in exchangeable acidity, illustrating change since previously sampled. Soil solution data indicated that sites periodically received high acid inputs leading to saturation of Al in soils and the formation of Al-hydroxy-sulfate minerals. Given these conditions, long-term changes in soil chemistry from acid deposition are acknowledged.

This study applied the Model of Acidification of Groundwater in Catchments (MAGIC) to estimate the sensitivity of 66 watersheds in the Southern Blue Ridge Province of the Southern Appalachian Mountains, United States, to changes in atmospheric sulfur (S) deposition. MAGIC predicted that stream acid neutralizing capacity (ANC) values were above 20 μeq/L in all modeled watersheds in 1860. Hindcast simulations suggested that the median historical acidification of the modeled streams was a loss of about 25 μeq/L of ANC between 1860 and 2005. Although the model projected substantial changes in soil and stream chemistry since pre-industrial times, simulated future changes in response to emission controls were small. Results suggested that modeled watersheds would not change to a large degree with respect to stream ANC or soil % base saturation over the next century in response to a rather large decrease in atmospheric S deposition. Nevertheless, the magnitude of the relatively small simulated future changes in stream and soil chemistry depended on the extent to which S emissions are reduced. This projection of minimal recovery in response to large future S emissions reductions is important for designing appropriate management strategies for acid-impacted water and soil resources. Exploratory analyses were conducted to put some of the major modeling uncertainties into perspective.

The acidity of Ultisols (pH <5) is detrimental to crop production. Technologies should be explored to promote base saturation and liming effect for amelioration of Ultisol pH. Column leaching experiments were conducted to investigate the amelioration effects of canola straw (CS) and peanut straw (PS) in single treatment and in combination whether with alkaline slag (AS) or with lime on Ultisol profile acidity. The treatment without liming materials was set as control, and the AS and lime in single treatment are set for comparison. Results indicated that all the liming materials increase soil profile pH and soil exchangeable base cations at the 0–40-cm depth, except that the lime had amelioration effect just on 0 to 15-cm profile. The amelioration effect of the liming materials on surface soil acidity was mainly dependent on the ash alkalinity in organic materials or acid neutralization capacity of inorganic materials. Specific adsorption of sulfate (SO₄ ²⁻) or organic anions, decarboxylation of organic acids/anions, and the association of H⁺ with organic anions induced a “liming effect” of crop residues and AS on subsoil acidity. Moreover, SO₄ ²⁻ and chloride (Cl⁻) in PS, CS, and AS primarily induced base cations to move downward to subsoil and exchange with exchangeable aluminum (Al³⁺) and protons (H⁺). These anions also promoted the exchangeable Al to leach out of the soil profile. The CS was more effective than PS in decreasing soil acidity in the subsoil, which mainly resulted from higher sulfur (S) and Cl content in CS compared to PS. The CS combined with AS was the better amendment choice in practical agricultural systems.

The rapid increase in agricultural pollution demands judicious use of inputs and outputs for sustainable crop production. Crop straws were pyrolyzed under oxygen-limited conditions at 400 °C for 2 h to prepare peanut straw biochar (PB), canola straw biochar (CB), and wheat straw biochar (WB). Then, 300-g soils were incubated each with urea nitrogen (UN) and UN + biochars with or without dicyandiamide (DCD) for 60 days. During the incubations, soil acidification induced by urea was somewhat inhibited by biochars, but nitrification of hydrolyzed NH₄ ⁺ produced much more acidity than the neutralization potential of the biochars. In single UN (200 mg/kg) treatment, soil pH decreased drastically and the final pH after incubation was lower than the control. Antagonistic to UN, all three biochars neutralized the soil acidity, which was consistent to their inherent alkalinity. DCD inhibited nitrification which was obvious throughout the incubations, as 30 mg/kg DCD + 200 mg/kg UN combined with 1 % PB, CB, and WB retained 0.94, 0.79, and 1.19 units higher pH, respectively, and significantly reduced exchangeable acidity over the treatments without DCD (P < 0.05). The treatments of UN + biochars with and without DCD had highly significant effects on soil pH, exchangeable Al³⁺, NH₄ ⁺-N, (NO₃ ⁻+NO₂ ⁻)-N, and available P (P < 0.05). Amplified NH₄ ⁺-N retentions at higher rates of PB referred increased negatively charged sites for nutrient adsorptions. Applied UN transformations varied among different treatments, and the maximum amounts of total mineral N recovered were 218.3, 218.5, and 223.8 mg/kg in the presence of DCD by PB, CB, and WB, compared to 198.2, 201.6, and 205.2 mg/kg, respectively, in no DCD treatments. Urea induced severe soil acidification and even lowered the ameliorative effects of applied biochars. Thus, ammonium-based fertilizers must include nitrification inhibitor (DCD) and, if used in combination with biochars will offer a suitable choice to reduce the acidity, improve base saturation and fertility of soil for sustainable agriculture.