Net Nitrogen Mineralization Research Articles

Effects of N and P additions on net nitrogen mineralization in temperate typical grasslands in Nei Mongol, China

Effects of N and P additions on net nitrogen mineralization in temperate typical grasslands in Nei Mongol, China

Asynchronous responses of soil carbon dioxide, nitrous oxide emissions and net nitrogen mineralization to enhanced fine root input

Global environmental changes can remarkably alter the amount of fine root litter inputs to the soil; these inputs affect soil CO2 and N2O emissions and net N mineralization processes by changing C and N supply to microorganisms. However, how these C and N processes respond to the amount of fine root litter input is yet not known. In this study, a year-long incubation experiment was conducted to investigate the impacts of changes in fine root litter biomass input on soil respiration, N2O emissions, and net N mineralization. Soil samples were obtained from forests of four biomes (boreal, temperate, subtropical, and tropical), and each sample was amended with fine roots from two species (either native tree species or maize roots) with four levels of root biomass input. The cumulative CO2 emissions increased linearly with root input levels, regardless of soil and root litter types. Soil respiration responded strongly to root inputs within the first 100 days and then leveled off. Root inputs retarded soil N2O emissions and net N mineralization, and the length of delay increased with root input levels, except for temperate and subtropical soils amended with tree roots, for which N2O emission dynamics were not altered by root input. Tree roots retarded net N mineralization more intensively than maize roots except for the tropical tree roots. Cumulative N2O emissions increased linearly with root input levels in only some soil type–root species–root input level combinations. Taken together, our results suggest that increased fine root biomass production might result in a linear increase of soil C loss via heterotrophic respiration, indicating that the first-order kinetic functions that have been widely used in the soil C models are still valid for predicting C mineralization rates in response to the changes in the amount of root litter inputs. Fine roots in their initial decomposition stage could be the predominant sources of soil N2O emissions in some but not all terrestrial ecosystems. However, increased fine root input might retard net N mineralization, which might disrupt the temporal pattern of ecosystem N cycling, and thus have important consequences on plant N supply and growth.

The effects of clear-cut on net nitrogen mineralization and nitrogen losses in a grey alder stand

Grey alder is a wide spread tree species in the Baltic region and a promising species for short rotation forestry. The symbiotic dinitrogen (N2) fixation ability makes this tree important for the regulation of nitrogen (N) cycle in forested areas.In a homogeneous 32-year-old natural grey alder stand (GAS) and an adjacent clear-cut (CC) in South-East Estonia (58°17′N; 27°17′E; set up in May 2011) we analyzed net nitrogen mineralization (NNM; with incubated bags), N leaching (with plate lysimeters), and nitrous oxide (N2O) fluxes (with static chambers).The total annual NNM did not intensify in the CC area: in the upper 0–20cm soil layer the NNM was 169.9 and 157.0kgha−1 in the (GAS) and in the CC, respectively. In both cases, the share of nitrification was 100% and NNM intensity was the highest in July. During the snow-melt in April, both in the GAS and in the CC site the leaching of total N was up to 25kgNmonth−1, whereas in the rest of study period it was negligible in both sites. Harvesting slightly decreased N2O emission, however, it was low at both study sites (−0.55 to 19.75 and −0.77 to 7.43kgN2Oha−1yr−1 in the GAS and the CC, respectively). Management of grey alder stands by traditional silvicultural methods (clear-cuts) did not to increased hazardous N losses through leaching.

Soil fertility controls soil–atmosphere carbon dioxide and methane fluxes in a tropical landscape converted from lowland forest to rubber and oil palm plantations

Abstract. Expansion of palm oil and rubber production, for which global demand is increasing, causes rapid deforestation in Sumatra, Indonesia, and is expected to continue in the next decades. Our study aimed to (1) quantify changes in soil CO2 and CH4 fluxes with land-use change and (2) determine their controlling factors. In Jambi Province, Sumatra, we selected two landscapes on heavily weathered soils that differ mainly in texture: loam and clay Acrisol soils. In each landscape, we investigated the reference land-use types (forest and secondary forest with regenerating rubber) and the converted land-use types (rubber, 7–17 years old, and oil palm plantations, 9–16 years old). We measured soil CO2 and CH4 fluxes monthly from December 2012 to December 2013. Annual soil CO2 fluxes from the reference land-use types were correlated with soil fertility: low extractable phosphorus (P) coincided with high annual CO2 fluxes from the loam Acrisol soil that had lower fertility than the clay Acrisol soil (P < 0.05). Soil CO2 fluxes from the oil palm (107.2 to 115.7 mg C m−2 h−1) decreased compared to the other land-use types (between 178.7 and 195.9 mg C m−2 h−1; P < 0.01). Across land-use types, annual CO2 fluxes were positively correlated with soil organic carbon (C) and negatively correlated with 15N signatures, extractable P and base saturation. This suggests that the reduced soil CO2 fluxes from oil palm were the result of strongly decomposed soil organic matter and reduced soil C stocks due to reduced litter input as well as being due to a possible reduction in C allocation to roots due to improved soil fertility from liming and P fertilization in these plantations. Soil CH4 uptake in the reference land-use types was negatively correlated with net nitrogen (N) mineralization and soil mineral N, suggesting N limitation of CH4 uptake, and positively correlated with exchangeable aluminum (Al), indicating a decrease in methanotrophic activity at high Al saturation. Reduction in soil CH4 uptake in the converted land-use types (ranging from −3.0 to −14.9 μg C m−2 h−1) compared to the reference land-use types (ranging from −20.8 to −40.3 μg C m−2 h−1; P < 0.01) was due to a decrease in soil N availability in the converted land-use types. Our study shows for the first time that differences in soil fertility control the soil–atmosphere exchange of CO2 and CH4 in a tropical landscape, a mechanism that we were able to detect by conducting this study on the landscape scale.

Effects of climate warming and elevated CO2 on autotrophic nitrification and nitrifiers in dryland ecosystems

Global climate change is predicted to enhance atmospheric temperature and CO2, with important consequences on biogeochemical nitrogen cycling in dryland ecosystems, which are highly vulnerable and characterized by extremely low nutrient availability. Belowground nitrification processes, predominantly mediated by ammonia-oxidizing archaea (AOA) and bacteria (AOB), are central to plant nitrogen availability and soil N2O emissions, but their responses to future climatic scenarios in drylands remain largely unknown. Here we investigated the impact of factorial combinations of elevated CO2 (+200 ppm) and elevated temperature (+3 °C) on dynamics of ammonia oxidizers and nitrification in three dryland soils planted with Eucalyptus tereticornis. Soil properties (including total carbon, H2O%, and nitrate) and potential nitrification rates were strongly impacted by elevated temperature after nine months, accompanied by significantly higher AOA abundance in two soils and a gradual decrease in AOB abundance under elevated temperature. DNA-stable isotope probing showed increased assimilation of 13CO2 by AOA, but not AOB, under warming, indicating that AOA were actively growing and utilizing the 13CO2 substrates, which was coupled with significantly higher net nitrogen mineralization and nitrification rates. High-throughput microarray analysis revealed temperature selections of particular AOA assemblages and a significant reduction in diversity and co-occurrence of the metabolically active AOA phylotypes. Although these responses were soil specific, structural equation modelling by compiling all the data together showed that warming had significant direct and indirect impacts on soil nitrification which were driven by changes in AOA community structure, but no obvious effects of elevated CO2 could be identified. Our findings suggest that warming has stronger effects than elevated CO2 on autotrophic nitrification, and AOA are more responsive to elevated temperature than AOB in the tested dryland ecosystems.

Disturbance Decouples Biogeochemical Cycles Across Forests of the Southeastern US

Biogeochemical cycles are inherently linked through the stoichiometric demands of the organisms that cycle the elements. Landscape disturbance can alter element availability and thus the rates of biogeochemical cycling. Nitrification is a fundamental biogeochemical process positively related to plant productivity and nitrogen loss from soils to aquatic systems, and the rate of nitrification is sensitive to both carbon and nitrogen availability. Yet how these controls influence nitrification rates at the landscape scale is not fully elucidated. We, therefore, sampled ten watersheds with different disturbance histories in the southern Appalachian Mountains to examine effects on potential net nitrification rates. Using linear mixed model selection (AIC), we narrowed a broad suite of putative explanatory variables into a set of models that best explained landscape patterns in potential net nitrification. Forest disturbance history determined whether nitrification and nitrogen mineralization were correlated, with the effect apparently mediated by microbially available carbon. Undisturbed forests had higher available carbon, which uncoupled potential net nitrification from potential net nitrogen mineralization. In contrast, disturbed watersheds had lower available carbon, and nitrification rates were strongly correlated to those of nitrogen mineralization. These data suggest that a history of disturbance at the landscape scale reduces soil carbon availability, which increases ammonium availability to nitrifiers at the micro-scale. Landscape-level soil carbon availability then appears to determine the coupling of autotrophic (nitrification) and heterotrophic (nitrogen mineralization) biogeochemical processes, and hence the relationship between carbon and nitrogen cycling in soils.

Assessing the potential benefits of organic and mineral fertiliser combinations on legume productivity under smallholder management in Zimbabwe

Productivity of grain legumes on sandy soils of southern Africa is critically limited by marginal fertilisation. Effects of co-applying phosphorus (P)-based mineral fertilisers and organic nutrient resources to cowpea (Vigna unguiculata (L.) Walp.) and soyabean (Glycine max L.) were investigated on smallholder farms in eastern Zimbabwe over two years. Over 70% of the surveyed farmers grew cowpea without fertilisation. Fertilisation of legumes with one or more nutrient resources increased shoot biomass productivity by between 20% and 300% relative to the non-fertilised control. Fertilised soyabean and cowpea yielded 2.2 t grain ha−1 and 2.5 t grain ha−1, respectively, translating to more than double the yields of unfertilised controls. In contrast, sole application of either mineral P-containing fertilisers or organic nutrient resources yielded less than 1 t ha−1 legume grain. The effects of combined organic and mineral fertilisation were also reflected in increased C〇2-carbon evolution from soils following growth of the legumes. Under the same soils, net nitrogen (N) mineralisation was highest where cattle manure was co-applied with an NP-containing fertiliser, with at least 85 mg N kg−1 soil released within six weeks. Co-application of organic and NP-containing fertilisers significantly enhance legume grain yields and residual soil N availability, but most smallholder farmers do not currently use this fertilisation strategy.

Net nitrogen mineralization enhanced with the addition of nitrogen-rich particulate organic matter

Particulate organic matter (POM) is a labile fraction of soil organic matter (SOM) that can contribute to nitrogen (N) mineralization. We added native and non-native POM to soils with contrasting properties and assessed net N mineralization during a 28days incubation study. Soils (0–15cm depth) for this study were a clay soil with a 3-year history of corn (Zea mays L.), a loam soil with a 2-year history of alfalfa (Medicago sativa L.) and sandy–loam and silty–clay–loam soils that were cropped in the previous 5years with a corn-soybean (Glycine max L.) — corn–forage–forage [45% alfalfa+55% timothy (Phleum pratense L.)] and corn–soybean–forage–forage–forage rotation, respectively. The POM was separated by size fractionation (>53μm) from coarsely sieved (>6mm) soil. The N concentration in POM followed the order loam>silty–clay–loam>clay>sandy–loam, whereas the acid unhydrolyzable fraction, a proxy for the lignin concentration, was the reverse. Compared to soil only, addition of N-rich POM from the loam soil increased net N mineralization in the clay soil and gave similar net N mineralization in the other soils, while addition of N-poor POM from the sandy–loam soil resulted in lower net N mineralization in the loam and silty–clay–loam soils. Multiple stepwise regression analysis showed that net N mineralized due to POM addition was related to the N concentration in the POM (partial R2=0.54) and the initial soil mineral N concentration (partial R2=0.33), suggesting that N mineralized from POM was related more to POM chemical composition than soil properties. We propose that information on POM chemistry in conjunction with soil mineral N concentration and texture could be useful for constructing N mineralization prediction models to improve N fertilizer management in agricultural soils.

Effects of Simulated Nitrogen Deposition on Soil Net Nitrogen Mineralization in the Meadow Steppe of Inner Mongolia, China.

Effects of simulated nitrogen (N) deposition on soil net nitrogen mineralization (NNM) were examined in situ during two growing seasons, using the resin-core technique in the semiarid meadow steppe in Inner Mongolia, China. The aim of this study is to clarify the effect of N levels (0, 10, and 20 kg N ha−1yr−1) and forms (NH4 + and NO3 -) on soil mineral N and NNM. Our results showed that N levels had no significant differences on soil mineral N and NNM. In the first year, three N treatments ((NH4)2SO4, NH4Cl and KNO3) increased soil NH4 + concentrations but had no significant effects on soil NO3 - concentrations. In the second year, (NH4)2SO4 treatment increased soil NO3 - concentrations, NH4Cl and KNO3 treatments decreased them. Three N treatments significantly decreased soil NH4 + concentrations in the later stages of the second year. As for the soil NNM, three N treatments had no significant effects on the rates of soil NNM (R m) and net nitrification (R n) in the first year, but significantly decreased them in the second year. The contribution of N addition to Rm was higher from (NH4)2SO4 than from NH4Cl and KNO3. However, Soil R m was mainly affected by soil water content (SWC), accumulated temperature (Ta), and soil total N (TN). These results suggest that the short-term atmospheric N deposition may inhibit soil NNM in the meadow steppe of Inner Mongolia.

Soil Nitrogen Availability Affects Belowground Carbon Allocation and Soil Respiration in Northern Hardwood Forests of New Hampshire

Plant nutrient acquisition in forests requires respiration by roots and mycorrhizae. Belowground carbon allocation and soil respiration should thus reflect plant effort allocated to nutrient uptake, for example in conditions of different nutrient availabilities controlled by site quality or stand history. Soil respiration, belowground C allocation, and fine root biomass were measured in three sites differing in nutrient availability in the northern hardwood forests of the White Mountains of New Hampshire. Annual soil respiration and belowground C allocation measured in two stands at each site were lowest at Jeffers Brook, the site with highest nutrient availability, and higher at Hubbard Brook and Bartlett Experimental Forests. Neither soil respiration nor belowground C allocation differed significantly between mid-aged (31–41 year old) and older stands (>80 year old) within the sites, despite higher fine root (<1 mm) biomass in old stands than mid-aged stands. During the growing season, soil respiration was low where net nitrogen mineralization and net nitrification were high across an extensive sample of thirteen stands and annual belowground C allocation decreased with increasing nitrification across the six intensively studied stands. Available P was not related to soil respiration. The relationships among N availability, belowground C allocation, and soil respiration support the claim that forests allocate more C belowground in ecosystems with low availability of a limiting nutrient.

Urbanization effects on soil nitrogen transformations and microbial biomass in the subtropics

As urbanization can involve multiple alterations to the soil environment, it is uncertain how urbanization effects soil nitrogen cycling. We established 22–0.04 ha plots in six different land cover types—rural slash pine (Pinus elliottii) plantations (n = 3), rural natural pine forests (n = 3), rural natural oak forests (n = 4), urban pine forests (n = 3), urban oak forests (n = 4) and urban lawns (n = 5) to investigate how net soil nitrogen mineralization rates and soil microbial biomass differed between urban forests and rural forests and between urban forests and urban lawns in the Florida panhandle. Urban forest sites have 2.5 times as much net total nitrogen mineralized than rural forest sites based on the mean daily rates averaged over the 2 years study (2010–2012). Urbanization may increase soil microbial biomass and activity (potential carbon mineralization rates) and this may be influencing the soil nitrogen mineralization rates in the forest sites. To include an urban lawn (turfgrass) component in the study, one time measurements of soils from the aforementioned forest sites and from urban lawn sites (no fertilization, no irrigation) were collected in 2012. Urban forest sites and urban lawns sites do not differ in their potential carbon mineralization rates, potential net total nitrogen mineralization rates or microbial biomass carbon and nitrogen contents. However, lawns have a higher potential net nitrification rate compared to urban forests.

Soil bacterial community structure remains stable over a 5-year chronosequence of insect-induced tree mortality.

Extensive tree mortality from insect epidemics has raised concern over possible effects on soil biogeochemical processes. Yet despite the importance of microbes in nutrient cycling, how soil bacterial communities respond to insect-induced tree mortality is largely unknown. We examined soil bacterial community structure (via 16S rRNA gene pyrosequencing) and community assembly processes (via null deviation analysis) along a 5-year chronosequence (substituting space for time) of bark beetle-induced tree mortality in the southern Rocky Mountains, USA. We also measured microbial biomass and soil chemistry, and used in situ experiments to assess inorganic nitrogen mineralization rates. We found that bacterial community structure and assembly—which was strongly influenced by stochastic processes—were largely unaffected by tree mortality despite increased soil ammonium () pools and reductions in soil nitrate () pools and net nitrogen mineralization rates after tree mortality. Linear models suggested that microbial biomass and bacterial phylogenetic diversity are significantly correlated with nitrogen mineralization rates of this forested ecosystem. However, given the overall resistance of the bacterial community to disturbance from tree mortality, soil nitrogen processes likely remained relatively stable following tree mortality when considered at larger spatial and longer temporal scales—a supposition supported by the majority of available studies regarding biogeochemical effects of bark beetle infestations in this region. Our results suggest that soil bacterial community resistance to disturbance helps to explain the relatively weak effects of insect-induced tree mortality on soil N and C pools reported across the Rocky Mountains, USA.

A meta-analysis of the effects of experimental warming on soil carbon and nitrogen dynamics on the Tibetan Plateau

Alpine ecosystems at high altitudes and latitudes are notably sensitive to climatic warming and the Tibetan Plateau is a widely distributed alpine ecosystem. The magnitude of climatic warming on the Tibetan Plateau is expected to be considerably greater than the global average. However, a synthesis of the experimental warming soil carbon and nitrogen data is still lacking and whether forest soils are more sensitive to warming than grassland soils remains unclear. In this study, we used a meta-analysis approach to synthesise 196 observations from 25 published studies on the Tibetan Plateau. Warming significantly increased microbial biomass carbon (MBC) by 14.3% (95% CI: 2.9–24.6%), microbial biomass nitrogen (MBN) by 20.1% (95% CI: 2.0–45.1%), net nitrogen mineralization by 49.2% (95% CI: 38.1–62.3%) and net nitrification by 56.0% (95% CI: 51.4–66.1%), but did not significantly affect soil carbon (95% CI: −13.9 to 2.7%) or nitrogen (95% CI: −12.4 to 2.6%). The mean annual air temperature was negatively correlated with the warming effects on MBC and MBN. Grasslands exhibited significant MBC and MBN responses to warming. Specifically, soil microbial biomass was more responsive to warming in colder environments. Moreover, forest soils are not always more sensitive to warming than grassland soils as previous studies have suggested. These findings indicate that clarifying the effect of warming on alpine soils need consider ecosystem types and their local climate.

Biochar and Manure Effects on Net Nitrogen Mineralization and Greenhouse Gas Emissions from Calcareous Soil under Corn

Few multiyear field studies have examined the impacts of a one‐time biochar application on net N mineralization and greenhouse gas emissions in an irrigated, calcareous soil; yet this use of biochar is hypothesized as a means of sequestering atmospheric CO2 and improving soil quality. We fall‐applied four treatments: stockpiled dairy manure (42 Mg ha−1 dry wt.), hardwood‐derived biochar (22.4 Mg ha−1), combined biochar and manure, and no amendments (control). Nitrogen fertilizer was applied in all plots and years based on treatment's preseason soil test N and crop requirements and accounting for estimated N mineralized from added manure. From 2009 to 2011, we measured greenhouse gas fluxes using vented chambers, net N mineralization using buried bags, corn (Zea mays L.) yield, and N uptake, and in a succeeding year, root and shoot biomass and biomass C and N concentrations. Both amendments produced persistent soil effects. Manure increased seasonal and 3‐yr cumulative net N mineralization, root biomass, and root/shoot ratio 1.6‐fold, CO2–C gas flux 1.2‐fold, and reduced the soil NH4/NO3 ratio 58% relative to no‐manure treatments. When compared with a class comprising all other treatments, biochar‐only produced 33% less cumulative net N mineralization, 20% less CO2–C, and 50% less N2O‐N gas emissions, and increased the soil NH4/NO3 ratio 1.8‐fold, indicating that biochar impaired nitrification and N immobilization processes. The multi‐year nature of biochar's influence implies that a long‐term driver is involved, possibly related to biochar's enduring porosity and surface chemistry characteristics. While the biochar‐only treatment demonstrated a potential to increase corn yields and minimize CO2–C and N2O‐N gas emissions in these calcareous soils, biochar also caused decreased corn yields under conditions in which NH4–N dominated the soil inorganic N pool. Combining biochar with manure more effectively utilized the two soil amendments, as it eliminated potential yield reductions caused by biochar and maximized manure net N mineralization potential.

Soil microbial community toxic response to atrazine and its residues under atrazine and lead contamination.

Intensive use of atrazine and extensive dispersal of lead (Pb) have occurred in farmland with chemical agriculture development. However, the toxicological effect of their presence on soil microorganism remains unknown. The objective of this study was to investigate the impacts of atrazine or Pb on the soil microbiota, soil net nitrogen mineralization, and atrazine residues over a 28-day microcosm incubation. The Shannon-Wiener diversity index, typical microbe species, and a Neighbor-joining tree of typical species from sequencing denaturing gradient gel electrophoresis (DGGE) bands were determined across periodical sampling times. The results showed that the existence of atrazine or Pb (especially high concentration) in soils reduced microbial diversity (the lowest H value is 2.23) compared to the control (H = 2.59) after a 28-day incubation. The species richness reduced little (from 17~19 species to 16~17 species) over the research time. But soil microbial community was significantly affected by the incubation time after the exposure to atrazine or Pb. The combination of atrazine and Pb had a significant inhibition effect on soil net nitrogen nitrification. Atrazine and Pb significantly stimulated soil cumulative net nitrogen mineralization and nitrification. Pb (300 and 600 mg kg(-1)) accelerated the level of atrazine dissipation. The exposure might stimulate the significant growth of the autochthonous soil degraders which may use atrazine as C source and accelerate the dissipation of atrazine in soils.

Effect of forest thinning on soil net nitrogen mineralization and nitrification in a Cryptomeria japonica plantation in Taiwan

We investigated the effect of forest thinning on soil nitrogen mineralization, nitrification and transformation in a Cryptomeria japonica plantation at high elevation to provide basic data for forest management. We chose four study plots for control, light, medium and heavy thinning treatment, and three sub-plots for buried bag studies at similar elevations in each treatment plot to measure the net N mineralization and nitrification rates in situ. The contents of soil inorganic N (ammonium and nitrate) were similar between treatments, but all varied with season, reaching maxima in September 2003 and 2004. The seasonal maximum net Nmin rates after four treatments were 0.182, 0.246, 0.303 and 0.560 mg·kg−1·d−1 in 2003, and 0.242, 0.258, 0.411 and 0.671 mg·kg−1·d−1in 2004, respectively. These estimates are approximate with the lower annual rates of N mineralization for this region. Forest thinning can enhance net N mineralization and microbial biomass carbon. The percentage of annual rates of Nmin for different levels of forest thinning compared with the control plot were 13.4%, 59.8% and 154.2% in 2003, and 0.1%, 58.8% and 157.7% in 2004 for light, medium, and heavy thinning, respectively. These differences were related to soil moisture, temperature, precipitation, and soil and vegetation types. Well-planned multi-site comparisons, both located within Taiwan and the East-Asia region, could greatly improve our knowledge of regional patterns in nitrogen cycling.

Stimulating Nitrate Removal Processes of Restored Wetlands

The environmental and health effects caused by nitrate contamination of aquatic systems are a serious problem throughout the world. A strategy proposed to address nitrate pollution is the restoration of wetlands. However, although natural wetlands often remove nitrate via high rates of denitrification, wetlands restored for water quality functions often fall below expectations. This may be in part because key drivers for denitrification, in particular soil carbon, are slow to develop in restored wetlands. We added organic soil amendments that range along a gradient of carbon lability to four newly restored wetlands in western New York to investigate the effect of carbon additions on denitrification and other processes of the nitrogen cycle. Soil carbon increased by 12.67-63.30% with the use of soil amendments (p ≤ 0.0001). Soil nitrate, the carbon to nitrogen ratio, and microbial biomass nitrogen were the most significant predictors of denitrification potential. Denitrification potential, potential net nitrogen nitrification and mineralization, and soil nitrate and ammonium, were highest in topsoil-amended plots, with increases in denitrification potential of 161.27% over control plots. While amendment with topsoil more than doubled several key nitrogen cycling processes, more research is required to determine what type and level of amendment application are most effective for stimulating removal of exogenous nitrate and meeting functional goals within an acceptable time frame.

Nitrogen Mineralization from Sugarcane Vinasse

Vinasse is a liquid residue applied as a fertilizer in sugarcane crops. However, in areas far away from sugarcane mills the cost of the distribution can be very high due, the large volume of water. So, one solution is to concentrate the vinasse by the evaporation process to reduce transport costs. Considering that the nitrogen mineralization kinetics is not known in concentrated vinasse, the objective of this study was to evaluate the net and potential nitrogen mineralization in soil that received vinasse concentrated and not concentrated. The treatments with concentrated vinasse provided the highest values of net mineralization and total nitrogen, which presented significant correlation each other, the same way as the potential mineralization values had a positive correlation with the doses and the amounts of total nitrogen. The total nitrogen values can be used as an index of nitrogen availability in soils that received concentrated vinasse.

C and N dynamics of a range of biogas slurries as a function of application rate and soil texture: a laboratory experiment

Digestates vary in composition and studies regarding their impact on C and N dynamics in soils are scarce. The objective was to analyse the C and N dynamics of digestates originating from various substrates applied to a sandy Cambisol and a silty Anthrosol. In three laboratory experiments (4–6 weeks), the effects of digestate properties, N rate and water content were tested. Averaged over both soils, 21% of the C supplied was emitted as CO2. Potential NH3 emissions during the first week ranged between 6% and 12% of NH4+ present in the digestates. The emission factors in the sandy Cambisol were on average 1.2 and 2 times higher for CO2 and potential NH3, respectively, compared to the silty Anthrosol. Similarly, net nitrogen mineralization in the sandy Cambisol was approximately twice the N mineralized in the silty Anthrosol. Net nitrification was not influenced by soil texture or different digestates, but increased with increasing application rates and had highest values at 75% of water holding capacity. Our results indicate that the type of substrate input for anaerobic digestion influences the properties of the digestate and therefore the dynamics of C and N. However, soil texture can affect these dynamics markedly.

Indicators and trade-offs of ecosystem services in agricultural soils along a landscape heterogeneity gradient

Soil functions can be classified as supporting (nutrient cycling) and provisioning (crop production) ecosystem services (ES). These services consist of multiple and dynamic functions and are typically assessed using indicators, e.g. microbial biomass as an indicator of supporting services. Agricultural intensification negatively affects indicators of soil functions and is therefore considered to deplete soil ES. It has been suggested that incorporating leys into crop rotations can enhance soil ES. We examined this by comparing indicators of supporting soil services – organic carbon, nitrogen, water holding capacity and available phosphorous (carbon storage and nutrient retention); net nitrogen mineralisation rate and microbial biomass (nutrient cycling and retention) – in barley fields, leys and permanent pastures along a landscape heterogeneity gradient (100, 500 and 1000m radii). In addition, barley yields (provisioning service) were analysed against these indicators to identify trade-offs among soil services. Levels of most indicators did not differ between barley and ley fields and were consistently lower than in permanent pastures. Leys supported greater microbial biomass than barley fields. Landscape heterogeneity had no effect on the indicators or microbial community composition. However, landscape heterogeneity correlated negatively with yield and soil pH, suggesting that soils in heterogeneous landscapes are less fertile and therefore have lower yields. No trade-offs were found between increasing barley yield and the soil indicators. The results suggest that soil ES are determined at the field level, with little influence from the surrounding landscape, and that greater crop yields do not necessarily come at the expense of supporting soil services.