Nitrogen Mineralization Rates Research Articles

Effects of organic composite fertilizer on soil nitrogen status and mineralization

A short-term soil incubation experiment was set up to obtain information to clarify the effect of our developed organic composite fertilizer on soil nitrogen mineralization. The composite was designed to have beneficial effects on the properties of chicken manure and to improve soil water management properties in addition to organic matter replenishment. In the incubation experiment, two different additives, bentonite, and super absorbent polymer, were used to enhance the properties of fermented chicken manure. Developed prototype products were tested in a four-week-long soil incubation experiment in two typical Hungarian soils: brown forest soil with a sandy texture and chernozem soil at two different water capacities (40 w/w % and 60 w/w %). Soil pH, and inorganic nitrogen forms, like nitrate and ammonium, were measured weekly. Furthermore, the potentially mineralized nitrogen and net mineralization rate were calculated. The applied composite was not affected the soil pH significantly in the examined period. The soil nitrate and ammonium ratio was changed during the incubation as the ammonium content in the soil decreased while nitrate content increased continuously throughout the experiment. This suggests that the incubation experiment successfully monitored the delicate balance of soil nitrogen forms. It was found that the chernozem soil type had a higher mineralization potential compared to brown forest soil due to its higher nutrient and organic matter contents. Moreover, our results pointed out that soil moisture content did not significantly affect the mineralization process. The amount of mineral nitrogen, generated per week can be described by a linear relationship for both soil types and water regimes. The composite product showed efficacy in promoting mineralization processes, particularly in soils with low nutrient status and mineralization potential.

Effects of Microplastics Addition on Soil Available Nitrogen in Farmland Soil

As microplastics (MPs) are an emerging pollution to farmland ecosystems, the research into the ecological and environmental effects of MPs need to be clarified urgently. Available nitrogen is the determining factor for productivity in most terrestrial ecosystems, especially for the farmland ecosystems with a high productivity. To explore the effects of MPs on soil available nitrogen in farmland soil, an incubation experiment was conducted by adding polyethylene MPs with different concentrations to farmland soil, which was collected from farmland in Fuqing, Fujian Province. The contents of three different nitrogen forms (nitrate, ammonium, and dissolved organic nitrogen) and soil dissolved organic carbon were measured, and the soil mineralization rate was calculated. Bacteria was quantified and bacterial community diversity indexes were measured. The results showed that the MPs addition (T1 and T2) had no significant effect on soil ammonium, nitrate and soil nitrogen mineralization rate compared to the control (p > 0.05). However, a significant increase was observed in soil dissolved organic carbon and dissolved organic nitrogen content (p < 0.05). It can be seen that the influence of PE MPs on the soil dissolved organic nitrogen is greater than that of inorganic nitrogen. The results of this study showed no major detrimental effects of MPs on the abundance of some bacterial families, whereas a significant change in soil bacterial evenness index was observed in T2 treatment compared to the treatment without MPs addition. In the background of current MPs pollution, the research results can provide a scientific basis for reducing nitrogen loss in soil and protecting farmland soil safety.

Greenhouse gas emissions from decomposition of biosolids as affected by stabilization method and soil moisture

AbstractComputational models are useful to estimate agricultural greenhouse gas emissions at regional scales. However, empirically based parameter values are required for the models to accurately represent carbon (C) and nitrogen (N) mineralization rates of different organic amendments in more and less humid regions or during wet and dry periods of the growing season. A controlled environment study was conducted to assess the rates of C and N mineralization in differently processed sewage sludge (biosolids) in wet and dry soil. Parameter values were estimated for use in modelling the degradation of three types of biosolids. A loam soil with either 49% water‐filled pore space (WFPS) or 29% WFPS was amended with mesophilic anaerobically digested (digested), alkaline‐stabilized, or composted biosolids. Headspace samples were collected and analysed for carbon dioxide (CO2) and nitrous oxide (N2O), and soil samples for nitrate () and ammonium (). Four different first‐order models were fitted to the cumulative CO2–C and N2O–N data (R2 > 0.98), and soil (R2 > 0.65) and (R2 > 0.93) concentrations. CO2–C data indicated that C mineralization was higher in soil with 49% WFPS than in soils with 29% WFPS. Seventy‐nine percent of the C compounds in digested biosolids degraded in soil with 49% WFPS, compared with 52% for alkaline‐stabilized biosolids and 8% for composted biosolids. The fitted coefficient values were similar for all of the four first‐order models used in this study and provide useful information for parameterizing more sophisticated mechanistic models of the degradation of biosolids in soil.

Effects of Spartina alterniflora invasion and subsequent mangrove restoration on soil nitrogen mineralization in Quangang, China

The Spartina alterniflora has severely invaded the coastal mangrove ecosystems in China. Here, we attempt to evaluate the invasion effect of S. alterniflora and the restoration effect of mangrove wetlands from the perspective of the nitrogen cycle characteristics. The inorganic nitrogen content, soil nitrogen mineralization, ammonification, and nitrification rate of uninvaded mudflats with those of invaded S. alterniflora site and native Kandelia obovata site at different restoration stages were compared. The results showed that the NH4+–N was the dominant form of soil inorganic nitrogen at all sites. Owing to its higher ammonification rates, the nitrogen mineralization rates at S. alterniflora site were highest in spring and summer among all sites except for mudflat. The young mangrove (1 year and 8 years) had significantly higher soil inorganic nitrogen content but lower nitrogen mineralization than the mature mangrove, indicated the short‐term response to restoration. The S. alterniflora invasion did not enhance soil nitrogen mineralization comparing with preinvaded mudflat, but it used more NH4+–N relative to K. obovata due to its higher soil nitrogen mineralization than mangrove communities in germination and growing seasons.

Effects of Freezing–Thawing Processes on Net Nitrogen Mineralization in Salinized Farmland Soil

Nitrogen is an indispensable and limiting element for plant and microbial growth. To investigate the combined effects of salinity and freezing–thawing (FT) processes on soil inorganic nitrogen (SIN) transformation in seasonally freezing salinized farmland, laboratory incubation experiments were conducted under five soil salt content (SSC) treatments (0.08%, 0.25%, 0.35%, 0.50%, and 0.70%), four FT temperature treatments (C (5 °C), FT (−5 + 5 °C), FT (−10 + 5 °C), and FT (−15 + 5 °C)), and two soil water content (SWC) treatments (40% and 80% of maximum water holding capacity (WHC)). Ammonium (NH4+-N) and nitrate (NO3−-N) nitrogen were monitored at the first, second, fifth, and eighth incubation days. The FT processes increased relative NH4+-N content by 13%, 39%, and 77% with the decreasing of freezing temperature from −5 °C to −15 °C compared with C (5 °C) treatments, respectively. FT (−5 + 5 °C) and FT (−15 + 5 °C) treatments decreased the relative NO3--N contents by 4% and 6% compared with C (5 °C) treatments, respectively. Under FT treatments, the increment of relative NH4+-N content was higher in low-SSC treatments and lower in high-SSC treatments. The relationship between relative NO3–-N content and SSC gradually changed from a decrease in C (5 °C) to an increase in FT (−15+5 °C) treatments. SWC decreased NH4+-N content in high-SSC and low-freezing temperature treatments (SSC × freezing temperature < −2.5%· °C), while NH4+-N increased in low-SSC and unfrozen treatments. The variations of SIN/Rmin (nitrogen mineralization rate) were mostly affected by NO3–-N/Rnit (net nitrification rate) and NH4+-N/Ra (net ammonification rate) in C (5 °C) and FT treatments, respectively. Overall, the results suggested that enhanced salinity inhibited the effects of freezing temperature on NH4+-N and NO3−-N formation, respectively. The increase in SWC weakened the NH4+-N formation induced by the decrease in freezing temperature, and this function increased with the increase in salinity.

Examining Decomposition and Nitrogen Mineralization in Five Common Urban Habitat Types across Southern California to Inform Sustainable Landscaping

Urban landscaping conversions can alter decomposition processes and soil respiration, making it difficult to forecast regional CO2 emissions. Here we explore rates of initial mass loss and net nitrogen (N) mineralization in natural and four common urban land covers (waterwise, waterwise with mulch, shrub, and lawn) from sites across seven colleges in southern California. We found that rates of decomposition and net N mineralization were faster for high-N leaf substrates, and natural habitats exhibited slower rates of decomposition and mineralization than managed urban landcovers, especially lawns and areas with added mulch. These results were consistent across college campuses, suggesting that our findings are robust and can predict decomposition rates across southern California. While mechanisms driving differences in decomposition rates among habitats in the cool-wet spring were difficult to identify, elevated decomposition in urban habitats highlights that conversion of natural areas to urban landscapes enhances greenhouse gas emissions. While perceived as sustainable, elevated decomposition rates in areas with added mulch mean that while these transformations may reduce water inputs, they increase soil carbon (C) flux. Mimicking natural landscapes by reducing water and nutrient (mulch) inputs and planting drought-tolerant native vegetation with recalcitrant litter can slow decomposition and reduce regional C emissions.

Effects of Tourism Trampling on Soil Nitrogen Mineralization in Quercus variabilis Blume Forests Varies with Altitudes in the Climate Transition Zone

Tourism trampling is one of the critical disturbance factors affecting forest structure and function apart from forest management activities. However, how tourism trampling affects soil nitrogen (N) mineralization rate at different altitudes in scenic forest spots is still unclear. To determine whether the responses of soil net N mineralization rate to tourism trampling varies with altitudes, we incubated soils using a field buried pipe method and analyzed soil ammonium N (NH4+-N) and nitrate N (NO3−-N) content at three altitudes (810 m, 1030 m, and 1240 m) at the Baotianman forest scenic spot in Henan Province. The results showed that tourism trampling significantly increased the soil bulk density and soil pH value but substantially reduced soil organic carbon (C) and total N content at all altitudes. Tourism trampling also resulted in a significant decrease in NO3−-N in the soil before and after incubation at all altitudes. The effects of tourism trampling on soil net N mineralization varied with latitudes, showing positive effects at 1030 m altitude (+51.4%), but negative effects at 1240 m altitude (−43.5%). For the soil net N nitrification rate, however, tourism trampling resulted in an increased rate (+141.1%) only at the 810 m altitude. Across all altitudes, soil microbial biomass C is primarily responsible for the variation in the soil net N mineralization rate. This study indicates that the effect of tourism trampling on soil net N mineralization rate varies with altitudes, which is related to the intensity of tourist disturbance and the synthetic effects of vegetation and soil microbes.

Conservation agriculture affects soil organic matter distribution, microbial metabolic capacity and nitrogen turnover under Danish field conditions

Conservation agriculture (CA) has been reported to affect nutrient cycling. This study aims to investigate how CA induced soil organic matter stratification affects carbon and nitrogen turnover. A case farm study was established on two Danish farms with conventional ploughed tillage (P) and CA practises. Here, we studied how organic matter stratification patterns to 50 cm soil depth differed between the two systems. Further we investigated differences in carbon and nitrogen mineralization patterns in lab incubation experiments. Average stratification ratio, the ratio between soil C and N content in the upper 5 cm and at 20–30 cm, the depth of the plough layer in the ploughed system, was 1.86 and 1.61 under CA and 1.04 and 1.06 under P. Carbon respiration from intact soil core incubation was affected by soil total carbon content, and showed stronger stratification in CA than in P. Nitrogen mineralization rates from intact soil core incubation was largest in CA top-layer compared to CA 13.5–16.5 cm layer and both P soil layers, with initial mineralization followed by immobilization during the second half of the a four-week incubation. Net change in mineral nitrogen after incubation was only apparent in the 13.5–16.5 cm layer in P, with an average N mineralization rate of 0.08 mg N kg−1 soil d−1. Sieving to 2 mm did not affect N mineralization dynamics. Field-based ammonium to nitrate ratio was higher in CA than in P soils, across varying soil depths and time-points over the entire year. Soil acidity was reduced by one pH unit in CA compared to P. Microbial metabolic capacity was significantly larger in the top 5 cm of CA from the deeper depths, and from the P soils. In conclusion, carbon and nitrogen mineralization, as well as microbial metabolic capacity were strongly affected by an increased stratification ratio of organic matter in CA.

Evaluation of nitrogen mineralization under various irrigation water qualities and nitrogen application rates for mulched drip irrigation in an arid region

AbstractUnderstanding the interactive effects of irrigation water quality and fertilization on nitrogen mineralization (Nmin) and accurately predicting Nmin are of great importance for the secure and efficient utilization of brackish water in arid regions. A pot experiment was conducted to determine the Nmin under different drip irrigation water salinities and nitrogen application rates and to modify the nitrogen mineralization potential (N0) and mineralization rate constants (k) of the first‐order kinetic equation of Nmin. An in situ field experiment was conducted to validate the modified equation. The results showed that the amounts of Nmin for water salinities of 1.27, 3.03, and 4.90 g L−1 were 58.9, 76.1, and 45.4 kg ha−1, respectively. Nmin was stimulated when the soil salinities were lower than 6.6, 6.1 and 3.9 g kg−1 for nitrogen application rates of 255, 315 and 375 kg ha−1, respectively. Nitrogen application significantly reduced Nmin. When the nitrogen application rate increased to 375 kg ha−1, the net Nmin rate remained lower, and the effects of salinity on Nmin were attenuated. The Nmin model with modified N0 and k values was developed considering the impacts of soil organic nitrogen, nitrogen application rate, and soil salinity. Model testing indicated that the modified model provided an acceptable estimation of Nmin under field conditions. It will be helpful for developing rational fertilization strategies of drip irrigation with brackish water in arid regions.

Rhizosphere Effects along an Altitudinal Gradient of the Changbai Mountain, China

Rhizosphere effects (REs) play important roles in regulating carbon (C) and nutrient cycling in terrestrial ecosystems. However, little is known about the REs of mature trees in the field, especially at the ecosystem scale. This study aimed to explore the variation and patterns of REs in natural ecosystems. Here, combining soil monoliths with an adhering soil (shaking fine roots) method was adopted to sample paired rhizosphere soil and bulk soil along an altitudinal gradient. Based on the relative REs and the percentage of rhizosphere soil mass, the REs on soil C and net nitrogen mineralization rates (Cmin and net Nmin) at the ecosystem scale were estimated. Our results showed that the REs on soil processes, soil microbial biomass C and extracellular enzyme activities (β-glucosidase and N-acetyl-glucosaminidase activities), and soil chemical properties (total C, total N, inorganic N, extractable P, K, Ca, Mg, Fe, and Mn) were significantly positive across altitudinal sites, while soil pH was significantly negative. Although the relative REs on investigated variables varied significantly among altitudes, the relative REs did not show a clear trend with the increased altitudes. Across altitudes, the mean magnitude of ecosystem-level REs on Cmin and net Nmin were 19% (ranging from 4% to 48%) and 16% (ranging from 3% to 34%), respectively. Furthermore, the magnitude of ecosystem-level rhizosphere effects increased linearly with the increased altitudes. The altitudinal patterns of ecosystem-level RE mainly depend on the percentage of rhizosphere soil mass. In conclusion, our results provided a set of new evidence for the REs, and highlighted the need to incorporate REs into land C and N models.

Early snowmelt by an extreme warming event affects understory more than overstory trees in Japanese temperate forests

AbstractThe occurrence of extreme warm events and early snowmelt is predicted to increase in high‐latitude ecosystems, even during periods of time when there is no coincident reduction in total precipitation. However, because extreme events like these occur unpredictably, little is known about how advancing snowmelt by a single extreme warm event, without a reduction in precipitation amount, influences overstory trees and understory vegetation simultaneously in an ecosystem. We conducted a warming experiment (four 20 × 20 m plots) in temperate forests of Japan to determine the effects of earlier snowmelt on both understory dwarf bamboo plants and overstory birch trees. Our experimental treatment advanced snowmelt by about 10 days and increased soil temperatures that were associated with increased rates of soil nitrogen (N) mineralization and nitrification. Furthermore, these changes led to lower C:N ratios of leaves together with the greater growth of understory bamboo vegetation, with no changes in leaf C:N or growth rates of overstory birch trees. Together, our results demonstrate that advancing snowmelt by an extreme warm event in temperate forests is likely to affect N cycling and will benefit understory vegetation without a commensurate change in overstory vegetation, likely due to the increase in available soil N. These results also demonstrate that with the projected increase in the frequency of extreme warm events and advanced snowmelt, understory vegetation is likely to benefit more than overstory trees in Japanese temperate forests with heavy snow.

Evaluation of the use of polyethylene mulches in the production of organic flue‐cured tobacco

AbstractWeed and insect pest management in organic flue‐cured tobacco (Nicotiana tabacum L.) is challenging due to lack of effective and affordable approved control options. Polyethylene plastic mulches are used in vegetable and berry production to manage in‐row weed populations, buffer soil temperatures, limit rain‐induced soil loss, and maintain soil moisture. Mulch color can affect plant growth, soil temperature, and insect pest populations in vegetable crops. Field trials were conducted in Kinston, NC, in 2019 and 2020 and Whiteville, NC, in 2020. Red, white, black, and silver polyethylene mulch (with drip irrigation) and bare ground with and without drip irrigation were compared to evaluate effects on tobacco yield, quality, and pests. Tobacco yields were elevated by at least 290% in mulch treatments compared with bare ground with irrigation in 2020 (p < .05), but did not differ in 2019 due to precipitation and temperature differences that conveyed an increased benefit in 2020. Opaque mulches successfully suppressed weed emergence. Fewer aphids were present in highly reflective silver mulch than all other treatments with irrigation in both years. Black and red mulch warmed soils while silver cooled them, affecting nitrogen mineralization rates. Higher levels of plant available nitrogen were maintained in mulch treatments, but tobacco nitrate levels and overall quality were not affected. These results are consistent with plasticulture research in other crops. The factors that make plasticulture well suited to intensively managed, high value crop production may benefit organic flue‐cured tobacco production especially when grown in rotation with other intensively managed crops.

Drivers of soil respiration and nitrogen mineralization change after litter management at a subtropical Chinese sweetgum tree plantation

AbstractLeaf litter decomposition transfers elements from litter to soils that are essential for regulating nutrient cycles in plantation ecosystems, especially carbon and nitrogen. However, soil carbon and nitrogen dynamics in response to tree litter management remains insufficiently researched. We conducted a one‐year field experiment at a fast‐growing sweetgum tree plantation to evaluate the effects of leaf litter management on soil available nutrients, respiration rate and nitrogen mineralization rate. Three leaf litter treatments were applied, which were: (1) natural input (control); (2) double input and (3) non‐input. It was found that the double input treatment increased soil inorganic nitrogen and microbial biomass nitrogen, but had little effect on microbial biomass carbon, dissolved organic carbon or dissolved organic nitrogen compared with natural input. The non‐input treatment caused dissolved organic carbon to decrease compared with natural input. The respiration rate increased in the double input treatment, with a positive priming effect observed. Soil net ammonification, nitrification and mineralization rates also increased in the double input treatment in specific seasons. Meanwhile, positive linear relationships between respiration rate and all nitrogen transformation rates were observed for all treatments. Soil temperature was found to be an important prediction factor for predicting the respiration rate and mineralization as seasonal variations, but not for litter‐induced fluctuations. Soil water content and mineral nitrogen were the primary drivers of litter‐induced change to the respiration rate, whereas mineral nitrogen and microbial biomass were primary drivers of mineralization change. These results suggest that changes in soil nitrogen mineralization rate are strongly associated with the soil respiratory process, resulting in a potentially strong plant–soil feedback mechanism.

Effects of eucalyptus on soil properties and litter decomposition processes

This study investigated the effect of plantation of exotic species Eucalyptus (Eucalyptus spp.) on the physico-chemical properties of soil by collecting field data and also on litter decomposition and nitrogen mineralization rates of the other selected species by following microcosm experimental design. Effects of Eucalyptus plantation on soil properties were studied by comparing soil properties of plots planted with Eucalyptus and other two species Acacia (Acacia auriculiformis A. Cunn. ex Benth.) and Lagerstroemia (Lagerstroemia speciosa (L.) Pers.) located at Madhupur, Tangail and Singra, Dinajpur, respectively. Effects of Eucalyptus litter on decomposition and nitrogen mineralization rates of litter of Axonopus (Axonopus compressus (Sw.) P. Beauv), Swietenia (Swietenia mahagoni (L.) Jacq.) and Teak (Tectona grandis L.f.) were studied by incubating leaf litter of these species with that of Eucalyptus at room temperature for 12 months. Results showed that soil moisture content was significantly lower in plot planted with Eucalyptus than that with Lagerstroemia. However, no significant difference appeared when soil moisture content was compared between Eucalyptus and Acacia indicating that plantation effects varied with the identity of species. Soil pH, total P (%) and organic C (%) contents were significantly lower in plots planted with Eucalyptus. Although mixing of leaf litter of Eucalyptus with that of A. compressus, S. mahagoni and T. grandis did not affect significantly, it affected mass loss rate of these three plant species significantly and such effect could be explained by the chemical composition of the litter used in the incubation study. Overall, the results of the present study indicated that plantation with Eucalyptus might have potential influence on altering soil properties and litter decomposition of other plant species, nevertheless, such effects varied with the species with whom the comparison was made. Dhaka Univ. J. Biol. Sci. 30(3 CSI): 443-452, 2022 (June)

Comparative soil restoration potential of exotic and native woody plantations on coal mine spoil in a dry tropical environment of India: A case‐study

AbstractOverburden excavated during opencast mining has poor soil properties due to non‐salvage and inversion of soil profiles. The soil properties of such overburden are often improved by biological reclamation techniques such as planting suitable plant species; however, the performance of species varies from site‐to‐site. Therefore, this article aims to evaluate the effects of woody plantations on coal mine spoil's physicochemical and biological properties. We synthesised the available data from previous studies conducted on 5‐year‐old plantations in the Singrauli Coalfields of India. These plantations have monocultures of eight species, in which four were exotic (Acacia auriculiformis, Casuarina equisetifolia, Cassia siamea and Grevillea pteridifolia) and four were native species (Albizia lebbeck, Albizia procera, Dendrocalamus strictus and Tectona grandis). We compared the soil properties under exotic and native species plantations to evaluate the effect of species and origin. The Wilcoxon's test showed that the clay content (p = 0.000), ammonium‐nitrogen (p = 0.002), phosphate‐phosphorus (p = 0.000) and microbial biomass nutrients (C, N and P; p = 0.000) were significantly higher under native plantations than the exotic plantations. Further, we observed a significant positive correlation (r = 0.86, p < 0.001) between soil organic carbon and microbial biomass carbon for native species. We also found that microbial biomass nutrients are negatively associated with nitrification rates and positively associated with nitrogen mineralisation rates. Overall, our study suggested that exotic species plantations are not as effective as native species in mine spoil rehabilitation. Thus, native species plantations should be promoted while restoring degraded coal mine habitats in a dry tropical environment.

Soil nutrient and moisture environments and shoot growth of Quercus crispula canopy trees in two areas that experienced contrasting effects of deer overabundance over an 11-year period

ABSTRACT To elucidate the effects of modification of the understory aboveground plant biomass and soil nutrient and moisture environments on canopy tree growth in deer overabundance sites, we compared the canopy shoot growth of oak trees (Quercus crispula), which are not a target for bark stripping or bark feeding by deer, understory aboveground plant biomass, and components of soil nutrient and moisture between inside (protected) and outside (exposed) a large fenced area. We found that canopy shoot growth in the exposed area was reduced compared with that in the protected area. Net nitrogen (N) mineralization rates did not differ between areas, although understory aboveground plant biomass, total carbon (C) and N, and total soil inorganic N content were significantly lower in the exposed area than in the protected area. Indices of canopy shoot growth correlated significantly with soil water content, but due to the limited scope of our study this result does not confirm an effect of soil moisture on canopy shoot growth. Further study is required to clarify the effects of deer overabundance on canopy tree growth.

Organic management enhances soil quality and drives microbial community diversity in cocoa production systems

Maintaining soil quality for agricultural production is a critical challenge, especially in the tropics. Due to the focus on environmental performance and the provision of soil ecosystem services, organic farming and agroforestry systems are proposed as alternative options to conventional monoculture farming. Soil processes underlying ecosystem services are strongly mediated by microbes; thus, increased understanding of the soil microbiome is crucial for the development of sustainable agricultural practices. Therefore, we measured and related soil quality indicators to bacterial and fungal community structures in five cocoa production systems, managed either organically or conventionally for 12 years, with varying crop diversity, from monoculture to agroforestry. In addition, a successional agroforestry system was included, which uses exclusively on-site pruning residues as soil inputs. Organic management increased soil organic carbon, nitrogen and labile carbon contents compared to conventional. Soil basal respiration and nitrogen mineralisation rates were highest in the successional agroforestry system. Across the field sites, fungal richness exceeded bacterial richness and fungal community composition was distinct between organic and conventional management, as well as between agroforestry and monoculture. Bacterial community composition differed mainly between organic and conventional management. Indicator species associated with organic management were taxonomically more diverse compared to taxa associated with conventionally managed systems. In conclusion, our results highlight the importance of organic management for maintaining soil quality in agroforestry systems for cocoa production.

Negative effects of brown bear digging on soil nitrogen availability and production in larch plantations in northern Japan: Their potential role as an agent of bioturbation

Digging mammals displace a large amount of soil, thereby strongly altering soil ecosystem processes such as nitrogen cycling through bioturbation. Although it is well known that bears displace a large amount of soil by digging for food and denning, there is negligible empirical evidence of the effects on soil properties. In the Shiretoko World Heritage site, we investigated the effects of brown bear digging for cicada nymphs on soil properties, such as soil water content, organic and inorganic nitrogen concentrations, and nitrogen mineralization rate that are important components of soil ecosystem function and are essential for plant growth. We compared the properties of soil recently dug by brown bears with undisturbed soil in larch plantations. We found that brown bear digging decreased soil water content, organic matter, inorganic nitrogen concentration, net mineralization rates. Our results suggest that soil digging by brown bear may reduce plant growth by decreasing soil nutrient availability, thereby diminishing the net primary production of the larch plantation at the study site.

Back to the Future: Restoring Northern Drained Forested Peatlands for Climate Change Mitigation

Draining peatlands for forestry in the northern hemisphere turns their soils from carbon sinks to substantial sources of greenhouse gases (GHGs). To reverse this trend, rewetting has been proposed as a climate change mitigation strategy. We performed a literature review to assess the empirical evidence supporting the hypothesis that rewetting drained forested peatlands can turn them back into carbon sinks. We also used causal loop diagrams (CLDs) to synthesize the current knowledge of how water table management affects GHG emissions in organic soils. We found an increasing number of studies from the last decade comparing GHG emissions from rewetted, previously forested peatlands, with forested or pristine peatlands. However, comparative field studies usually report relatively short time series following rewetting experiments (e.g., 3 years of measurements and around 10 years after rewetting). Empirical evidence shows that rewetting leads to lower GHG emissions from soils. However, reports of carbon sinks in rewetted systems are scarce in the reviewed literature. Moreover, CH4 emissions in rewetted peatlands are commonly reported to be higher than in pristine peatlands. Long-term water table changes associated with rewetting lead to a cascade of effects in different processes regulating GHG emissions. The water table level affects litterfall quantity and quality by altering the plant community; it also affects organic matter breakdown rates, carbon and nitrogen mineralization pathways and rates, as well as gas transport mechanisms. Finally, we conceptualized three phases of restoration following the rewetting of previously drained and forested peatlands, we described the time dependent responses of soil, vegetation and GHG emissions to rewetting, concluding that while short-term gains in the GHG balance can be minimal, the long-term potential of restoring drained peatlands through rewetting remains promising.

Assessment of the Carbon and Nitrogen Mineralisation of Digestates Elaborated from Distinct Feedstock Profiles

The carbon (C) and nitrogen (N) mineralisation rates of five digestates were studied and compared with pig slurry, compost, and a solid fraction of digestate in aerobic incubation experiments. The objective was to identify the most relevant drivers of C and N mineralisation based on the physicochemical properties of the products. Net organic nitrogen mineralisation of digestates (Nmin,net) was on average 30%, although the range was relatively wide, with digestate from pig manure (39%) reaching double the value of digestate from sewage sludge (21%). The total carbon to total nitrogen (TC:TN) (r = −0.83, p < 0.05) and ammonium nitrogen to total nitrogen (NH4+-N:TN) (r = 0.83, p < 0.05) ratios of the products were strongly correlated with Nmin,net, adequately mirroring the expected fertilising potential of the products. The digestates had C sequestration values between 50 and 81% of applied total organic carbon (TOC), showcasing their potential to contribute to C build-up in agricultural soils. The carbon use efficiency of the amended soils was negatively correlated with dissolved organic carbon (DOC) (r = −0.75, p < 0.05) suggesting that catabolic activities were promoted proportionately to the DOC present in these products. Ratios of DOC:TOC (r = −0.88, p < 0.01) and TC:TN (r = 0.92, p < 0.01) were reliable predictors of the fraction of C that would remain one year after its incorporation and thus could be used as simple quality parameters to denote the C sequestration potential of digestates prior to their use in the field.