Nitrogen Retention Capacity Research Articles

Phosphate buffer‐driven precursor polycondensation to promote fermentative humification

AbstractBACKGROUNDAerobic fermentation always suffers from nitrogen loss and low humification degree. The objective of this study was to investigate the promotion of phosphate buffer on organic matter degradation and precursor polymerization into humus (HS) in aerobic fermentation, and to analyze the key roles played by different precursors. In order to achieve this, sludge aerobic fermentation tests were conducted on control (CK), phosphate buffer addition treatment (KP) and potassium chloride addition treatment (K).RESULTSThe HS content of KP treatment exhibited a notable increase compared to the CK and K treatments, with a maximum increase of 38.29%. In addition, phosphate addition improved the nitrogen retention capacity and the complexity of the HS structure. Phosphate buffer enhanced both the polyphenol and Maillard humification pathways by promoting the condensation of precursors (polysaccharides, reducing sugars, polyphenols, amino acids and proteins). Among these precursors, reducing sugars, amino acids and proteins were identified as the key driving precursors of phosphate.CONCLUSIONSPhosphate, as an exogenous additive to the fermentation system, reduces nitrogen loss while promoting precursor polymerization to form HS, which benefits the improvement of soil fertility and crop growth upon organic fertilizer application. © 2024 Society of Chemical Industry (SCI).

Effects of Nitrogen Reduction Combined with Organic Fertilizer on Crops

By summarizing the methods of nitrogen fertilizer reduction combined with organic fertilizer, this paper discussed and analyzed the effects of nitrogen fertilizer reduction combined with organic fertilizer on soil carbon and nitrogen content and biological activity of crops, mastered the soil carbon and nitrogen retention capacity of orchards, clarified the relationship between fruit trees and soil environment, and established the optimal effect equation between fertilizer application and yield. It is of great scientific significance to provide theoretical basis and technical support for optimizing fertilizer application in orchards and realizing "zero growth" and "double reduction" of nitrogen fertilizer.

Biochar effects on soil nitrogen retention, leaching and yield of perennial citron daylily under three irrigation regimes

Biochar can serve as a soil amendment to immobilize soil nitrogen (N) and reduce N leaching from cropland without negative effect on crop yield. However, the interaction effect of biochar application and irrigation regimes on soil N status (N retention and N loss) and crop yield is rarely reported in the open perennial vegetable field. A two-years field trial (transplanting in first year and consecutive growth in second year) was conducted in citron daylily vegetable cropping system on a sandy brown alluvial soil. Two biochar application rates (0 and 30 t ha−1) and three irrigation regimes (CDI, conventional drip irrigation; WSDI, water-saving drip irrigation with 80% of full irrigation quota; APRDI, alternate partial root-zone drip irrigation with 80% of full irrigation quota) were included. The response of crop yield and soil N status to both biochar application and irrigation regimes varied across planting years for perennial citron daylily. After the first planting year's harvest, APRDI enhanced flower bud yield by 18–28% compared to CDI and WSDI, likely due to improved nitrate use efficiency evidenced by lower soil nitrate retention in the surface soil (0–20 cm) post-harvest. However, biochar application resulted in a reduction of yield by 27% under APRDI. Additionally, WSDI with reduced yields, decreased soil TN in the sub-surface layer (20–50 cm) with 9–19% by comparison with other two irrigation regimes, resulting in higher TN concentration in the soil solution (14–28%) in and thus an increased risk for N leaching. However, after the second harvest year, there were no variations in crop yield induced by biochar application and irrigation regimes. Irrigation regimes exhibited limited influence on soil N status, while biochar application mitigated soil nitrogen decline in the 0–50 cm layer by enhancing organic nitrogen retention capacity for nearly 16–85%. Furthermore, the lowest TN concentration in the soil solution in the sub-surface layer (20–50 cm) with biochar application under APRDI suggested a reduced risk for N leaching. We conclude that combining biochar application with the APRDI regime could help retain soil N, decrease the risk of N leaching, and enhance crop yield in total for two consecutive planting years. Therefore, this approach is recommended for sustainable N management in long-term planting of perennial crops.

Recovery of lakes from eutrophication: changes in nitrogen retention capacity and the role of nitrogen legacy in 10 Danish lakes studied over 30 years

AbstractUsing data on 23 Danish lakes, we conducted mass balances to develop total nitrogen (TN) models for predicting annual mean TN in lakes based on external TN loading and found high predictability when including lake hydraulic retention time and mean depth in the model. We further used a unique 30-year mass balance data series from 10 Danish lakes with contrasting mean depths and hydraulic retention times to elucidate the effect of external TN loading reduction and N legacy on lake TN. We found that the TN retention percentage during the 30 years was generally not sensitive to an often major reduction in the external TN loading; it overall followed the pattern of the above model predictions, suggesting a low TN legacy effect. Moreover, the TN retention percentage was not affected by changes in TP. Our results, therefore, show a fast response to TN loading reduction, indicating that we can expect an immediate effect on lake water quality in shallow lakes suffering from internal phosphorus loading during re-oligotrophication provided that inorganic N is low enough to become a growth-limiting nutrient.

Aerobic composting effect of crop straw with biogas residue

This study aims to improve the aerobic composting efficiency and quality of biogas residue. The residue of biogas production from pig manure was mixed with coconut leaves, sugarcane leaves, and sawdust, respectively, for the aerobic composting experiments. The pile temperature, pH, organic matter content, seed germination index, total nitrogen, total phosphorus, and total potassium were measured to evaluate the composting performance of different treatments. The results showed that the aerobic composting treatment of biogas residue mixed with sugarcane leaves had a seed germination index of 107.71%, the highest maturity, and the highest total phosphorus and total potassium. The aerobic composting treatment of biogas residue mixed with coconut leaves maintained high temperatures above 55 °C for the longest time (23 days) and demonstrated the most thorough harmless treatment, with the total nitrogen increase being the highest (75.63%), which indicated the strongest nitrogen retention capacity. Overall, the supplementation of coconut leaves and sugarcane leaves can improve the maturity and nutrient content, thus improving the aerobic composting quality of biogas residue. The findings provide a scientific basis for the harmless treatment and reuse of manure biogas residue and crop straw.

Nitrogen retention capacity of paddy soil improved under long-term garlic-rice rotation

ABSTRACT Although significant differences in soil nitrogen levels exist under different paddy-upland rotations, the main reason for this is unclear. The nitrogen retention capacity and loss of ammonia volatilisation, leaching, etc. of paddy soil with large differences in nitrogen levels from two long-term rotations, garlic-rice and wheat-rice, were measured using the soil column simulation method. The results showed that the loss rate of leaching was only 5.4%, whereas that of ammonia volatilisation was up to 22.8%, which was the main nitrogen loss way of paddy soil under the two rotations. The average ammonia volatilisation rates under wheat-rice rotation with high and low nitrogen application rates were 12.1% and 40.2% higher than that under garlic-rice rotation, leading to a decrease in the total nitrogen loss amount and rate through ammonia volatilisation by 29.8% and 8.8%, respectively. As a result, nitrogen retention in the soil under garlic-rice rotation increased by 12.7%. In conclusion, the long-term garlic-rice rotation could significantly inhibit ammonia volatilisation, thus improving the soil nitrogen retention capacity. The straw return may increase soil organic matter content, reduce ammonia volatilisation loss, and enhance soil nitrogen retention capacity and productivity.

DOM hydrophilic components of organic fertilizers increased the soil nitrogen retention capacity and succession of the microbial community.

Application of organic fertilizers affects soil properties and microbial communities, which in turn alters soil N transformation processes. Unfortunately, it is not clear how the difference in the character of the organic fertilizer DOM affects the soil nitrogen retention capacity and its microbial processes. According to the principle of equal nutrients, the treatments of chemical fertilizer alone (treatment CF), chemical fertilizer with organic fertilizer DOM hydrophilic components (treatment H), and chemical fertilizer with organic fertilizer DOM hydrophobic components (treatment P) were set up, where the characteristics of soil nitrogen transformation and changes in microbial community structure were studied with soil culture conditions for 24 days. It was discovered that the addition of organic fertilizer DOM components (H and P) slowed nitrification rate and increased protease activity resulting in a higher NH4+-N content compared to the CF treatment. The DOM addition (H and P) increased the microbial biomass nitrogen (MBN) levels in the soil and increased the soil nitrogen pool capacity. Moreover, the carbon use efficiency of the hydrophilic components is higher than that of the hydrophobic components, resulting in its further increase in nitrogen reservoir capacity and higher nitrogen retention capacity. Network analysis showed that the addition of organic fertilizer DOM hydrophilic components increased network complexity and synergy between microorganisms. In combination with random forest analysis, it was shown that Sphingomonas and Massilia were key species influencing soil nitrogen retention capacity and nitrogen availability characteristics.

Nitrogen retention capacity of paddy soil improved under long-term garlic-rice rotation

Nitrogen retention capacity of paddy soil improved under long-term garlic-rice rotation

Effects of the Ingredients on Maturity and Humification during Kitchen Waste Composting as Illustrated by Nuclear Magnetic Resonance

Kitchen waste (KW) production has risen considerably due to the increasing affluence of populations and a booming catering sector. If not properly disposed, KW can bring serious issues for the environment. Composting is widely used as an efficient method for the resource utilization of KW. In the present paper, the effects of different ratios of ingredients (corn straw: garden waste = 4:1, based on the dry mass) on maturity and humification during KW composting were investigated. The results showed that the nitrogen retention capacity of the treatments with a ratio of ingredients to KW of 1:2.5 and 1:5.0 was higher than that of other treatments. Additionally, it was found that the number of ingredients had an effect on the germination index (GI) during composting, and the final GI values of the four treatments were in the following order: 1:7.5 > 1:5.0 > 1:10.0 > 1:2.5. Nuclear magnetic resonance (NMR) showed that the organic matter (OM) content of each treatment increased after composting, and the maturity of the 1:2.5 and 1:5.0 treatments was higher than the other two treatments. Redundancy analysis (RDA) showed that the maturity and humification were correlated with moisture content, pH and NO3−-N during composting. This study concludes that the treatment with an ingredients to KW ratio of 1:5.0 was much more useful for KW composting, which is of importance to guide the disposal of KW.

Metabolic Profile of Growing Immune- and Surgically Castrated Iberian Pigs Fed Diets of Different Amino Acid Concentration.

The purpose of the current study was to further characterize the performance and nitrogen retention differences previously observed between immunocastrated (IC) and surgically castrated (SC) pure Iberian pigs. Fifty-four pigs were used (three sexes: IC males, IC females and SC males), fed three isoenergetic diets (160, 140 and 120 g CP/kg DM; six pigs/treatment combination) from 40 kg BW until slaughter (105 kg BW). Plasmatic post-absorptive metabolites and hormones, and backfat tissue composition were determined. The IC males showed a trend towards higher plasmatic creatinine (p = 0.06) and IGF-1 concentrations than SC males and IC females (p < 0.001). SC males showed a higher predisposition to carcass fatness and insulin resistance compared to IC males. Plasmatic isoleucine concentration was higher in IC and SC males compared to IC females (p < 0.01), and valine was greater in IC males compared to the rest of the pigs (p < 0.001). Total branched-chain amino acids (AA) were greater in IC males than in IC females (p < 0.01). Total plasmatic essential AA concentrations tended to be greater in IC males (p = 0.09). The present results support the increased performance and nitrogen retention capacity previously observed in IC male Iberian pigs compared to SC males and IC females, which can be attributed to increased anabolic capacity related with lean growth in Iberian IC males.

Enhancing Soil Nitrogen Retention Capacity by Biochar Incorporation in the Acidic Soil of Pomelo Orchards: The Crucial Role of pH

Biochar is commonly used to improve acidic soil and reduce nitrogen loss. However, the impact of biochar on soil nitrogen retention, especially at varying pH levels, is not fully understood. Soil samples were obtained from an acidic red soil citrus orchard. The soil pH was adjusted using CaO, with five levels (4.0, 5.1, 5.8, 6.6, and 7.2), and two biochar doses (0% and 1%) were applied. The study used 15N-Tracer and Ntrace to investigate biochar’s influence on soil nitrogen retention at different pH levels. The results showed that soil amendment with biochar improved gross mineralization rates (TM) and gross NH4+ immobilization rates (TI), except at pH 4.0 for TI. Biochar enhanced heterotrophic nitrification (ONrec) within pH 4.0–7.4, with a threshold for autotrophic nitrification (ONH4) at pH 6.4. The findings revealed biochar’s positive effect on soil nitrogen retention within pH 4.5–6.4. Biochar had a greater impact on TI than TM and inhibited ONH4, potentially enhancing nitrogen retention in this pH range. These results highlight the significance of considering biochar incorporation for improving nitrogen use efficiency and reducing NO3−-N loss in subtropical pomelo orchards.

Droughts can reduce the nitrogen retention capacity of catchments

Abstract. In 2018–2019, Central Europe experienced an unprecedented 2-year drought with severe impacts on society and ecosystems. In this study, we analyzed the impact of this drought on water quality by comparing long-term (1997–2017) nitrate export with 2018–2019 export in a heterogeneous mesoscale catchment. We combined data-driven analysis with process-based modeling to analyze nitrogen retention and the underlying mechanisms in the soils and during subsurface transport. We found a drought-induced shift in concentration–discharge relationships, reflecting exceptionally low riverine nitrate concentrations during dry periods and exceptionally high concentrations during subsequent wet periods. Nitrate loads were up to 73 % higher compared to the long-term load–discharge relationship. Model simulations confirmed that this increase was driven by decreased denitrification and plant uptake and subsequent flushing of accumulated nitrogen during rewetting. Fast transit times (&lt;2 months) during wet periods in the upstream sub-catchments enabled a fast water quality response to drought. In contrast, longer transit times downstream (&gt;20 years) inhibited a fast response but potentially contribute to a long-term drought legacy. Overall, our study reveals that severe droughts, which are predicted to become more frequent across Europe, can reduce the nitrogen retention capacity of catchments, thereby intensifying nitrate pollution and threatening water quality.

Biochar enhances the retention capacity of nitrogen fertilizer and affects the diversity of nitrifying functional microbial communities in karst soil of southwest China

Biochar is usually used as an agricultural soil amendment to improve soil nutrition availability and soil microbial environment. However, the effects of Moutai lees biochar on the migration and retention characteristics of nitrogen fertilizer and the changes of nitrifying microorganisms on yellow soil of southwest China are still not distinct. In this study, the migration distribution characteristics of nitrogen fertilizer, nitrogen retention capacity and microbial community structure were evaluated by a soil column leaching simulated experiment. Five application rates of biochar: 0%(BC0), 0.5%(BC0.5), 1.0%(BC1.0), 2.0%(BC2.0) and 4.0%(BC4.0) were respectively tried. The results showed that the application of Moutai lees biochar has significantly increased the total nitrogen (TN) and nitrate (NN) contents in yellow soil, but it has also significantly decreased the microbial biomass nitrogen (MBN) content. When compared with the BC0 treatment, it was found that the application of biochar increased nitrogen fertilizer retention rate (NF) to 49.84%–95.23%. Moreover, high biochar application rates (2.0% and 4.0%) were also able to improve the NF ratio, while low biochar application rates (0.5% and 1.0%) still had the risk of nitrogen leaching losses. Additionally, the application of biochar changed the bacterial community structure and the relative abundance of nitrogen-related microorganisms in yellow soil. Also, it was determined that Nitrite-oxidizing bacteria (NOB) played a major factor in affecting soil nitrogen, instead of ammonia-oxidizing archaea (AOA) and ammonium-oxidizing bacteria (AOB). Overall, research finally concluded that Moutai lees biochar decreased nitrite oxidation effect and changed ammoxidation to affect nitrogen nutrients availability in yellow soil and the biochar application rate of 4% has increased nitrogen fertilizer retention rate and decreased the risk of nitrogen leaching losses in yellow soil.

Management of nitrogen and phosphorus internal loading from polluted river sediment using Phoslock® and modified zeolite with intensive tubificid oligochaetes bioturbation

In situ sediment remediation using modified clay has become increasingly popular in aquatic ecosystem management. In this study, two modified clays, Phoslock® and modified zeolite, were used together to co-manage nitrogen and phosphorus loading from a polluted river sediment and intermittent aeration was used as an aid for this remediation. After 120 days of core incubation, results indicated that the two clays alone cannot effectively control all the total and soluble nitrogen and phosphorus concentrations in the overlying water all the time. However, the combined use of clays with intermittent aeration can effectively reduce the nutrient concentrations throughout the experiment. Sediment phosphate flux can be largely inhibited solely by clays or when combined with aeration. Meanwhile, the ammonium flux can only be inhibited effectively for 60 days and is not statically different from control after 120 days. Surprisingly, intensive bioturbation can create a vertical movement of the applied clays in sediment with time, which enhances the phosphorus and nitrogen retention capacity of the subsurface sediment. Phosphorus fractionation analysis indicated that around 50% of mobile phosphorus was reduced in a 4–6 cm sediment layer after 120 days. In contrast, the extractable ammonium and nitrate content in treated sediment increased 2–3 times in this layer. The short-term bioturbation experiment confirmed that bioturbation did not have a large effect on P control efficiency of the clay-treated sediment. Conversely, bioturbation can enhance ammonium release from sediment and the following gradual burial effect can have a negative effect on nitrogen removal from overlying water over time. These results indicate that intensive bioturbation should be considered in polluted river sediment remediation.

Potential of Wheat Straw, Spruce Sawdust, and Lignin as High Organic Carbon Soil Amendments to Improve Agricultural Nitrogen Retention Capacity: An Incubation Study.

Plants like winter wheat are known for their insufficient N uptake between sowing and the following growing season. Especially after N-rich crops like oilseed rape or field bean, nitrogen retention of the available soil N can be poor, and the risk of contamination of the hydrosphere with nitrate (NO3-) and the atmosphere with nitrous oxide (N2O) is high. Therefore, novel strategies are needed to preserve these unused N resources for subsequent agricultural production. High organic carbon soil amendments (HCA) like wheat straw promote microbial N immobilization by stimulating microbes to take up N from soil. In order to test the suitability of different HCA for immobilization of excess N, we conducted a laboratory incubation experiment with soil columns, each containing 8 kg of sandy loam of an agricultural Ap horizon. We created a scenario with high soil mineral N content by adding 150 kg NH4+-N ha-1 to soil that received either wheat straw, spruce sawdust or lignin at a rate of 4.5 t C ha-1, or no HCA as control. Wheat straw turned out to be suitable for fast immobilization of excess N in the form of microbial biomass N (up to 42 kg N ha-1), followed by sawdust. However, under the experimental conditions this effect weakened over a few weeks, finally ranging between 8 and 15 kg N ha-1 immobilized in microbial biomass in the spruce sawdust and wheat straw treatment, respectively. Pure lignin did not stimulate microbial N immobilization. We also revealed that N immobilization by the remaining straw and sawdust HCA material in the soil had a greater importance for storage of excess N (on average 24 kg N ha-1) than microbial N immobilization over the 4 months. N fertilization and HCA influenced the abundance of ammonia oxidizing bacteria and archaea as the key players for nitrification, as well as the abundance of denitrifiers. Soil with spruce sawdust emitted more N2O compared to soil with wheat straw, which in relation released more CO2, resulting in a comparable overall global warming potential. However, this was counterbalanced by advantages like N immobilization and mitigation of potential NO3- losses.

Rapid recovery of nitrogen retention capacity in a subtropical acidic soil following afforestation

Understanding soil nitrogen (N) dynamic and availability during afforestation (the conversion of cropland to forest plantations) is critical to maintain forest growth and long-term productivity, especially in rainfall-rich, subtropical region. However, only few studies have investigated the inherent N transformation processes involved in N availability in subtropical acidic soils. In a 15N tracing study, nine soils from croplands, 10-y and 50-y afforested woodlands were sampled to investigate the changes in soil gross N transformation rates in humid subtropical China. Gross N transformation rates were not significantly different in soils under 10- and 50-y after afforestation. Compared to cropland, however, afforestation stimulated the rates of mineralization, microbial NH4+ immobilization and adsorption of NH4+, leading to a faster turnover of NH4+ pool in afforested soils. Moreover, afforestation inhibited autotrophic nitrification and resulted in NO3− production dominated by heterotrophic nitrification. Furthermore, afforestation significantly enhanced NO3− consumption mainly through the increase in microbial NO3− immobilization rather than dissimilatory NO3− reduction to NH4+ in soil. These differences in gross N transformation rates resulted in low net NO3− production and strong NO3− retention capacity in afforested soils, similar to that found in undisturbed natural forest. Our results suggest a rapid recovery (several years) of soil N retention following afforestation. Soil NO3− retention capacity was correlated positively with TOC, TN, WHC, CEC, Al, free Al oxide and exchangeable Al3+, but negatively with pH, Ca and exchangeable Ca2+, indicating that the absence of agricultural management (e.g., N fertilizer and liming) and alteration in soil environment by tree establishment are responsible for the recovery of N retention capacity in subtropical acidic soils during afforestation.

Nitrogen leaching and ectomycorrhizal nitrogen retention capacity in a Norway spruce forest fertilized with nitrogen and phosphorus

To estimate the production of external ectomycorrhizal mycelia (EMM) in Norway spruce forests with varying nitrogen (N) and phosphorus (P) levels, and to relate this to the N retention capacity of ectomycorrhizal fungi (EMF) and N leaching. Seasonal changes in EMF production (in ingrowth mesh bags) and soil water N (in suction lysimeters) were analyzed after fertilization with N or N combined with P. The EMF N retention capacity was estimated by the addition of isotopically labeled N to the mesh bags. No relationship was found between the seasonal variation in EMF growth and N leakage from the soil. However, in the mesh bags, the total assimilation of 15N by EMF was almost halved by N fertilization, while twice as much 15N leached through. We found a high specific N assimilation capacity per unit weight of EMF mycelia. This was unaffected by N fertilization, but the total assimilation of N by EMF was drastically reduced due to reduced production of EMM. However, N-retaining processes other than N assimilation by EMF must be taken into account to explain the losses of N after fertilization.

Nitrogen-retention capacity in a fertilized forest after clear-cutting — the effect of forest-floor vegetation

Forest fertilization with nitrogen (N) has several benefits to society such as increased wood production and carbon sequestration. There are, however, concerns about N leakage, particularly following clear-cutting. The forest-floor vegetation may increase the N retention of forest ecosystems; however, very few studies have quantified the amount of vegetation required. We studied the relationship between vegetation cover and risk of N leakage, estimated by the amounts of ammonium-N and nitrate-N retained on ion-exchange capsules in the soil, during 4 years following the clear-cutting and harvesting of logging residues in a previously fertilized forest in southern Sweden. Previous fertilization increased the amount of nitrate-N captured on the capsules, whereas the amount of ammonium-N decreased. The vascular vegetation cover increased from almost zero to approximately 25% independent of fertilization. The amount of ammonium-N and nitrate-N retained on the capsules was already reduced by 50%–75% at 20% vegetation cover, and by 30%–40% cover, it approached zero, independent of the number of years since clear-cutting. The vegetation may impede tree-seedling establishment, implying a trade-off between seedling growth and N-retention capacity. However, our results indicate that maximum N retention may be achieved at a relatively low vegetation cover, which could be accomplished with less intrusive scarification methods than currently used.

Limitations of stream restoration for nitrogen retention in agricultural headwater streams

High nutrient loading and channelization reduce the nutrient retention capacity of agricultural streams and lead to increases in nutrient downstream transport. The aim of the current study was to study the effects of channel reconfiguration and riparian reforestation on the nitrogen retention capacity of eutrophic agricultural headwater streams. In addition, we investigated the role of stream sediments as a nitrogen sink or source for the stream ecosystem.We compared two restored reaches with two morphologically pristine and four channelized reaches in an agricultural catchment in the north-east of Austria regarding in-stream ammonium uptake, whole-reach retention of dissolved inorganic nitrogen, potential denitrification enzyme activity, and sedimentary ammonium release.Restored and pristine reaches exhibited significantly shorter ammonium uptake lengths (330m) and larger mass transfer coefficients (2.7×10−5ms−1) than channelized reaches (2500m and 1.1×10−5ms−1, respectively). Increased ammonium uptake was positively correlated with increased transient storage in restored and pristine reaches. Total DIN retention was slightly, though not significantly higher in restored sections (average rates 0.06g DINm−2h−1) and showed signs of temporal nitrogen saturation in all reaches. In general, sediments were characterized by small grain sizes (0.04–0.31mm), high ammonium (60–215μgg−1 DW), and low nitrate concentrations (0.4–5.7μgg−1 DW). Ammonium was released from sediments of all reaches below concentrations of 100μg NH4+-NL−1 in the overlying water column which shows the high potential of nutrient-rich sediments to act as an internal ammonium source for the stream ecosystem. Potential denitrification was lowest in sediments of restored reaches and significantly increased after nitrate amendment to 3–26mgNm−2h−1.The study reveals that stream sediments, which are loaded with nutrient-rich soil from the agricultural catchment, may limit the effects of stream restoration in agricultural streams. In order to improve the nutrient retention capacity of agricultural streams, reach-scale restoration measures have to be combined with measures in the catchment which reduce nutrient and soil inputs to streams.

Acidification trends in south Swedish forest soils 1986–2008 — Slow recovery and high sensitivity to sea-salt episodes

Soil water chemistry in forest soils over 20years was studied at nine sites in southern Sweden. The aim was to investigate the recovery from acidification and the influence of strong sea salt episodes that occur in the region. All sites but one showed signs of recovery from acidification along with the reduced sulphur deposition, but the recovery progress was slow and the soil water was in most cases still highly acidic at the end of the period. In several cases the recovery was delayed by episodes of sea salt deposition, leading to transient acidification. The less marked decrease of sulphur concentrations in soil water than of sulphur deposition, highlighted the importance of sulphur adsorption/desorption in the acidification and recovery process. Nitrogen retention capacity was exceeded on one site, leading to nitrate leaching and extremely low pH. Storm fellings on two sites in the end of the period led to effects similar to those of regeneration fellings. It was concluded that the soils in the region are in an early stage of recovery. The future progress of recovery strongly depends on future nitrogen retention of forest soils and the frequency of sea salt episodes.