Nitrogen Mineralization Rates Research Articles

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.

Hardwood mixtures facilitate leaf litter decomposition and soil nitrogen mineralization in conifer plantations

Productivity in conifer plantations can be increased by hardwood mixture. However, the underlying mechanisms that govern the relationship between hardwood mixture and productivity remain poorly understood, particularly with respect to nutrient cycling. We investigated how and to what extent hardwood mixtures alter nitrogen amounts in leaf litterfall, leaf litter decomposition rates, and soil nitrogen mineralization rates in an experiment that used different thinning intensities (i.e., a non-thinned “control” group with few hardwoods, a 33%-thinned “weak” group with a small amount of hardwoods, and a 67%-thinned “intensive” group with abundant hardwoods) in a conifer Cryptomeria japonica plantation (38-year old). Most of the hardwoods were 15-year old trees that have been regenerated after the first thinning. The annual leaf litterfall amount for the conifer was highest in the control group and lowest in the intensive group, whereas the reverse was true for hardwoods, although the hardwoods’ annual leaf litterfall amount was approximately half that of conifers, even in the intensive group. Consequently, the annual amount of leaf litterfall of hardwoods and conifers combined was lowest in the intensive group. However, the total amount of nitrogen in the annual leaf litterfall of hardwoods and conifers combined did not differ according to thinning intensity, because the mass-based nitrogen concentration in the leaf litterfall of hardwoods was twice that of conifers. The leaf litter decomposition rate in hardwoods was approximately three times faster than that in conifers irrespective of thinning intensity, mainly due to the lower carbon-to-nitrogen (C:N) ratio. Thus, the total amount of nitrogen in the decomposed leaves of hardwoods and conifers combined, calculated by multiplying the total amount of nitrogen in the annual leaf litterfall of hardwoods and conifers by the decomposition rate and summing the results, was highest in the intensive group. In soil from shallow depths (0–10 cm), the nitrogen mineralization rate increased in the order of control, weak, and intensive, attributable primarily to the C:N ratio, which decreased in the same order. The results indicated that increasing the hardwood content by intensive thinning significantly enhances the availability of soil inorganic nitrogen in conifer plantations, by facilitating leaf litter decomposition and soil nitrogen mineralization. These findings indicate that hardwood mixtures can increase forest productivity by enhancing nitrogen cycling.

Linking Phyllostachys edulis (moso bamboo) growth with soil nitrogen cycling and microbial community of plant-soil system: Effects of plant age and niche differentiation

Understanding the impacts of plant age on bamboo growth, soil nutrient and functional microorganism can assist in the development of management practices to maximize the benefits of nutrients and functional endophytic and soil microbes in moso bamboo plantations. In this study, moso bamboos of different ages (0.5, 2.5, 4.5 and 6.5 years) were selected. The above-ground biomass, soil properties and endophytic microbes of above-ground tissue and stump root of different age bamboos were quantified, and their interactive relationships were also examined. There were negligible differences in the heights and above-ground fresh biomass among the bamboo plants of different ages, but net nitrogen (N) mineralization and potential nitrification rates of soils were significantly affected by the bamboo ages. The soil nprA gene abundances decreased with the bamboo ages, and soil AOB amoA gene abundances of the 0.5-yr bamboo were significantly higher than those of the other older plants. Average soil urease activities of the 2.5-yr, 4.5-yr and 6.5-yr bamboos were 81.4%, 81.1% and 88.2% lower than those of the 0.5-yr bamboo, respectively. Bacterial diversity indices and richness estimators in the soils were significantly higher than those in the above-ground tissues. Endophytic microbial community structures were more sensitive to the bamboo ages than the soil counterparts, and endophytic microbial community diversities and structures in the above-ground tissues were significantly changed with the bamboo ages. Bacterial and fungal community structures in the above-ground tissues were significantly different from those in the soils. Bamboo ages significantly affected the N transformations in the soils and endophytic community structures, but niche differentiations among the above-ground tissue, stump root and soil outweighed the plant ages in shaping the whole microbial communities of plant-soil system.

Effect of Deficit Irrigation Practice on Nitrogen Mineralization and Nitrate Nitrogen Leaching under Semi-Arid Conditions

Agricultural sector acts as a major consumer of water which accounts for 70 percent of global freshwater use. Water scarcity acts as an imminent threat to agriculture, there is a need to use those irrigation and management practices that could overcome this overwhelming situation of water scarcity. Lab incubation study was designed to evaluate the effect of different moisture levels (50%, 60%, 70%, 80%, 90%, and 100% FC) on nitrogen mineralization rate. Net nitrogen mineralization was shown at 60% and 80% FC levels. Two optimized irrigation levels (I0.6 and I0.8) along with four levels of dairy manure (10, 15, 20, and 25 Mg ha-1) were used in a lysimetric trial. Nitrate-nitrogen was measured at four depths (D1: 30 cm, D2: 60 cm, D3: 90 cm, and D4: 120 cm). Results showed strong interaction of irrigation and dairy manure at all depths. Mean maximum nitrate-nitrogen concentration was shown under full irrigation at 120 cm soil depth with the application of DM ® 25 Mg ha-1. Under two levels of deficit irrigation, I0.8 has shown maximum nitrate-nitrogen concentration at 90 cm soil depth with the application of DM25, however, deficit irrigation level I0.6 restricted nitrate-nitrogen movement up to 60 cm soil depth, and high concentration was found at 30 cm soil depth. We concluded that deficit irrigation practice along with dairy manure resulted in more nitrate-nitrogen in the upper 60 cm layer of soil where it can be more available for the crops.

Residue decomposition dynamics in mixed ratios of two warm‐season cover crops

AbstractCover crop residue management has gained attention over the past few decades due to the potential of cover crop residues to provide soil cover and nutrient availability for subsequent crops. Nutrients released from cover crop residues depend on the nutrient composition of plant tissue and ensuing rates of mineralization. To evaluate the rate of carbon (C) and nitrogen (N) mineralization from cover crops, a field decomposition experiment was conducted in a humid subtropical agricultural field. Residues of two warm‐season cover crops, sunn hemp (Crotalaria juncea L.) and sorghum sudangrass (Sorghum bicolor L. × S. bicolor var. Sudanese), were placed in litterbags at various mixture ratios on the soil surface to quantify the amount of N and C released from the residues over 56 d. Residue biomass decomposition followed decay patterns that were similar despite treatment mixtures of cover crop ratios. The initial ratio of cover crop material in the litter mixture influenced early N release where ratios with increasing sunn hemp increased N decomposition. The majority of residue breakdown (50–75%), and C (50–75%) and N (65–75%) decomposition occurred during the first 7 d for all the treatments. A minor fraction of residue remained (10–14%) at Day 56, with 10–14% C and 7–25% N. The 25% N remained in the sole sorghum sudangrass treatment. These results indicate that N from legume cover crops may not be available to subsequent crops in humid subtropical soils lacking the capacity to retain nutrients leached out of cover crop residue, though small fractions of dry matter may remain.

Increased soil organic matter after 28 years of nitrogen fertilization only with plastic film mulching is controlled by maize root biomass

Nitrogen (N) fertilization and plastic film mulching (PFM) are two widely applied management practices for crop production. Both of them impact soil organic matter individually, but their interactive effects as well as the underlying mechanisms are unknown. Soils from a 28-year field experiment with maize monoculture under three levels of N fertilization (0, 135, and 270 kg N ha−1 yr−1) and with or without PFM were analyzed for soil organic C (SOC) content, total soil nitrogen (N), root biomass, enzyme activities, and SOC mineralization rates. After 28 years, N fertilization increased root biomass and consequently, SOC by 26% (averaged across the two fertilizer application rates) and total soil N by 25%. These increases, however, were only in soil with PFM, as PFM reduced N leaching and loss, as a result of a diurnal internal water cycle under the mulch. The SOC mineralization was slower with N fertilization, regardless of the PFM treatment. This trend was attributed to the 43% decrease of β-glucosidase activity (C cycle enzyme) and 51% drop of leucine aminopeptidase (N cycle) with N fertilization, as a result of a strong decrease in soil pH. In conclusion, root biomass acting as the main source of soil C, resulted in an increase of soil organic matter after 28 year of N fertilization only with PFM.

Impact of climate variability and extreme rainfall events on sugarcane yield gap in a tropical Island

• Sugarcane yield was simulated at the field scale over 20 years in Reunion Island. • Total sugarcane yield gap in Reunion was 96 Mg ha -1 of which 34% was explained throw crop management and hazards. • Yield gap increased with extreme daily rainfall. • Actual yield loss increased by 0.6 Mg ha -1 per daily events with extreme rainfall at regional scale. The increasing incidence and intensity of extreme climate events are a major threat to global crop production. Sugarcane represents the main source of sugar and ethanol in tropical and sub-tropical regions. Here, we assessed the impacts of climatic variability and extreme events on sugarcane yield gaps in Reunion Island which is characterised by extreme spatial contrasts in climate, and is regularly subjected to cyclones or drought. We combined a process-based crop model with spatial databases of soil, climate and management data, to predict the annual sugarcane yield in each field over the whole island from 1998 to 2018. Simulated yields were compared to actual sugarcane yields from sugar producers in five agro-climatic zones. Extreme climate indices were calculated for extreme daily rainfall, temperature and drought, and their influence on yield gap was assessed using a Principal Component Analysis (PCA). The average total yield gap (YG T , i.e. the difference between potential sugarcane yield and actual yield, Mg ha -1 ) over Reunion Island was 96 Mg ha -1 , explained by 34% throw crop management and hazards. YG due to crop management reached 65 Mg ha -1 with increasing rainfall and nitrogen mineralization rate and up to 88 Mg ha -1 with increasing temperature and radiation. Yield gap was correlated with the first axis of the PCA, highlighting how extreme rainfall induced increase in YG T . The actual yield loss was defined as the difference between the actual yield from sugarcane producers in a given year and the highest yield obtained during the whole studied period in the same zone. The annual actual yield loss increased by 0.6 Mg ha -1 per rainfall days higher than 29 mm d -1 along the annual crop cycle. Using this approximation, average actual yield loss due to heavy rain was estimated as 5.5 Mg ha -1 but it was higher than 10 Mg ha -1 for 25% of years in the East coast region. Our results highlight the need for improving sugarcane crop yield response to extreme rain in process-based crop models, in order to better assess climate change impacts in future.

Remotely detected aboveground plant function predicts belowground processes in two prairie diversity experiments.

Imaging spectroscopy provides the opportunity to incorporate leaf and canopy optical data into ecological studies, but the extent to which remote sensing of vegetation can enhance the study of belowground processes is not well understood. In terrestrial systems, aboveground and belowground vegetation quantity and quality are coupled, and both influence belowground microbial processes and nutrient cycling. We hypothesized that ecosystem productivity, and the chemical, structural and phylogenetic‐functional composition of plant communities would be detectable with remote sensing and could be used to predict belowground plant and soil processes in two grassland biodiversity experiments: the BioDIV experiment at Cedar Creek Ecosystem Science Reserve in Minnesota and the Wood River Nature Conservancy experiment in Nebraska. We tested whether aboveground vegetation chemistry and productivity, as detected from airborne sensors, predict soil properties, microbial processes and community composition. Imaging spectroscopy data were used to map aboveground biomass, green vegetation cover, functional traits and phylogenetic‐functional community composition of vegetation. We examined the relationships between the image‐derived variables and soil carbon and nitrogen concentration, microbial community composition, biomass and extracellular enzyme activity, and soil processes, including net nitrogen mineralization. In the BioDIV experiment—which has low overall diversity and productivity despite high variation in each—belowground processes were driven mainly by variation in the amount of organic matter inputs to soils. As a consequence, soil respiration, microbial biomass and enzyme activity, and fungal and bacterial composition and diversity were significantly predicted by remotely sensed vegetation cover and biomass. In contrast, at Wood River—where plant diversity and productivity were consistently higher—belowground processes were driven mainly by variation in the quality of aboveground inputs to soils. Consequently, remotely sensed functional, chemical and phylogenetic composition of vegetation predicted belowground extracellular enzyme activity, microbial biomass, and net nitrogen mineralization rates but aboveground biomass (or cover) did not. The contrasting associations between the quantity (productivity) and quality (composition) of aboveground inputs with belowground soil attributes provide a basis for using imaging spectroscopy to understand belowground processes across productivity gradients in grassland systems. However, a mechanistic understanding of how above and belowground components interact among different ecosystems remains critical to extending these results broadly.

Determination of the Effects of Copper (Cu) and Lead (Pb) Heavy Metals on Soil Carbon and Nitrogen Mineralization

Heavy metal (HM) pollution has become one of the most important environmental problems of the present day, as a result of the developing industrial activities. Accordingly, it is important to understand microorganism activities in soil ecosystems that have been exposed to HMs for a long time. The aim of this study was to show the potential effects of ores on soil carbon and nitrogen mineralizations which were taken from copper (Cu) and lead (Pb) mines in Balıkesir-Balya and Kastamonu-Küre districts in Turkey. The carbon (C) and nitrogen (N) mineralizations were determined by using the CO2 respiration method (30 days) and the Parnas Wagner method (42 days) under the controlled laboratory conditions (28 °C, 80% of field capacity), respectively. It was observed that carbon mineralization decreased depending on the dose increase. 250 mg kg-1 treatment with Pb was lower than the control and there was a significant difference between them (P < 0.001). In terms of nitrogen mineralization rate (%), there was no significant difference among all treatments. According to the results, Pb affected microorganisms more negatively; however, the presence of Cu slightly decreased its negative effect. It is possible to conclude that carbon mineralization can be indicator for HM pollution in the soil. However, nitrogen mineralization was not a determining factor at HM pollution in this study.

Nitrogen transport in a tundra landscape: the effects of early and late growing season lateral N inputs on arctic soil and plant N pools and N2O fluxes

Understanding N budgets of tundra ecosystems is crucial for projecting future changes in plant community composition, greenhouse gas balances and soil N stocks. Winter warming can lead to higher tundra winter nitrogen (N) mineralization rates, while summer warming may increase both growing season N mineralization and plant N demand. The undulating tundra landscape is inter-connected through water and solute movement on top of and within near-surface soil, but the importance of lateral N fluxes for tundra N budgets is not well known. We studied the size of lateral N fluxes and the fate of lateral N input in the snowmelt period with a shallow thaw layer, and in the late growing season with a deeper thaw layer. We used 15N to trace inorganic lateral N movement in a Low-arctic mesic tundra heath slope in West Greenland and to quantify the fate of N in the receiving area. We found that half of the early-season lateral N input was retained by the receiving ecosystem, whereas half was transported downslope. Plants appear as poor utilizers of early-season N, indicating that higher winter N mineralization may influence plant growth and carbon (C) sequestration less than expected. Still, evergreen plants were better at utilizing early-season N, highlighting how changes in N availability may impact plant community composition. In contrast, later growing season lateral N input was deeper and offered an advantage to deeper-rooted deciduous plants. The measurements suggest that N input driven by future warming at the study site will have no significant impact on the overall N2O emissions. Our work underlines how tundra ecosystem N allocation, C budgets and plant community composition vary in their response to lateral N inputs, which may help us understand future responses in a warmer Arctic.

Performance and mechanism of biochar-coupled BiVO4 photocatalyst on the degradation of sulfanilamide

The construction of a low-cost and efficient novel photocatalyst is extremely important for the treatment of refractory wastewater. In this work, biochar-coupled BiVO4 (CBi) photocatalysts are synthesized using a hydrothermal method. These photocatalysts are then characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transition electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), ultraviolet visible diffuse reflection spectroscopy (UV–Vis-DRS), and photoluminescence (PL). The photocatalytic performance was also evaluated using the degradation and mineralization of sulfaniamide (4-aminobenzene sulfonamide, SA) under visible light irradiation. The results indicated that the CBi photocatalysts showed larger surface areas, stronger absorption abilities, higher separation efficiencies of photogenerated electrons and holes, and powerful transfer abilities of photogenerated electrons than the photocatalyst without biochar (CBi-0%). The CBi photocatalyst with the 20 wt% biochar (CBi-20%) exhibited an optimal photodegradation ability for SA. The degradation rate of SA was approximately 97.0% after 7 h of visible light irradiation, and the removal rate of total organic carbon (TOC) was as high as 83.4%, indicating an excellent mineralization ability. In addition, the CBi-20% photocatalyst obtained the highest mineralization rate of organic nitrogen (92.7%) and organic sulfur compounds (75.8%). Furthermore, spectroscopic techniques revealed more information regarding the degradation of the benzene ring and fluorescent groups. The fluorescence intensity and UV254 of SA were reduced by 96.5%% and 90.0%, respectively, which provided specific evidence of the potential photodegradation mechanism.

Effects of precipitation change and nitrogen addition on soil net N mineralization in a saline-alkaline grassland of Northern Shanxi Province, China.

To explore the responses of soil net nitrogen (N) mineralization rate to precipitation varia-tion and nitrogen deposition in salinized grassland, we set precipitation manipulation and nitrogen addition experiments in the typical agro-pastoral ecotone saline-alkaline grassland of Northern Shanxi Province, China. The in situ soil net N mineralization rate was determined by top-cover buried PVC cylinder from May to September in 2019. The results showed that there were seasonal dynamics in soil net N mineralization rate. Soil net N mineralization rate was not affected by increase/decrease precipitation (±50%), nitrogen addition (10 g·m-2·a-1) or the combination of nitrogen addition and increase 50% precipitation treatments. The combination of nitrogen addition and 50% reduction of precipitation significantly improved soil net nitrification rate and net N mine-ralization rate by 10.8 and 8.6 times, respectively. Soil net nitrogen mineralization rate was positively related to soil water content, and negatively related to soil pH. The effects of nitrogen addition on soil nitrogen mineralization rate were dependent on precipitation conditions. Soil water content and pH were important factors regulating soil net nitrogen mineralization rate in the saline-alkaline grassland of Northern Shanxi Province. Therefore, to roundly assess the response model of soil N mine-ralization process to global change, it is necessary to consider the interaction of precipitation changes and nitrogen addition, and the soil physical and chemical properties of salinized grassland.

Effects of experimental warming on soil nitrogen transformation in alpine scrubland of eastern Qinghai-Tibet Plateau, China

We investigated the effects of warming on soil nitrogen cycling process in alpine scrub ecosystem, with an in-situ simulated warming experiment at Sibiraea angustata alpine scrubland on the eastern Qinghai-Tibet Plateau, China. We examined the responses of soil nitrogen transformation rate to warming in three critical periods (the early, late, and non-growing seasons). The results showed that warming increased soil temperature by 1.2 ℃, but decreased soil moisture by 2.5%. The soil net nitrogen mineralization rates (i.e., ammonification and nitrification) in the growing season were significantly higher than those in the non-growing season. The rates of soil net nitrogen fixation in the non-growing season were significantly higher than that in the growing season. Soil nitrification was the major process of soil nitrogen transformation in the early growing season, while soil ammonification was the major one in the late growing season and non-growing season. The effects of experimental warming on soil nitrogen transformation differed among those three periods. Experimental warming significantly increased soil net ammonification, nitrification, nitrogen mine-ralization and fixation in the early growing season, and enhanced soil net nitrification and nitrogen mineralization in the non-growing season. However, warming significantly decreased soil net nitrification, nitrogen mineralization and fixation in the late growing season and soil net ammonification in the non-growing season. Moreover, warming did not affect soil net nitrogen fixation rates in the non-growing season and soil net nitrification rates in the late growing season. Future climate warming would significantly change soil nitrogen transformation by accelerating soil nitrogen cycling in the alpine scrub ecosystem on the eastern Qinghai-Tibet Plateau.

Rhizosphere effects of woody plants on soil biogeochemical processes: A meta-analysis

Rhizosphere effects control soil biogeochemical cycling. However, quantitative assessment of rhizosphere effects on belowground processes such as carbon and nitrogen cycling remains rare, especially for woody species in field experiments. Here, we conducted a meta-analysis to synthesize the rhizosphere effects of woody plants (185 species from 128 sites) on belowground processes (20 variables), including soil carbon and nutrient pools, microbial biomass, enzyme activities, and carbon and net nitrogen mineralization rates. We also explored the effects of plant mycorrhizal types (arbuscular mycorrhizal, AM vs. ectomycorrhizal, ECM), leaf traits (evergreen vs. deciduous, broadleaf vs. coniferous), bulk soil properties and climatic factors on these rhizosphere effects. Our results indicated that the rhizosphere effects were positive on all variables except soil pH and phenol oxidase activity. Most rhizosphere effects did not vary significantly between mycorrhizal types, but the effect on soil nitrate-N was notably lower under ECM-associated species than under AM-associated species. Rhizosphere effects increased carbon and net nitrogen mineralization rates by 38% and 40% on average, and the variation was mainly affected by bulk soil properties (e.g., pH, soil organic carbon and available nitrogen concentrations) rather than plant functional types and climatic factors. Collectively, these results provide quantitative evidence that rhizosphere effects influence belowground carbon and nutrient cycling in forest ecosystems, which are helpful for the development of ecosystem models that explicitly consider plant-soil interactions in the rhizosphere.

Assessing the impact of soil aggregate size on mineralization of nitrogen in different soils, China

Soil aggregates play a critical role to support the development of soil nitrogen (N) pools, but the underlying mechanism by which soil aggregate size impacts N mineralization remains unclear. The objective of this study was to determine the effect of aggregate size in soil N mineralization through cultivation experiments of different type soils. The topsoil samples of ten typical profiles in different regions of China were collected, and a series of laboratory column incubation experiments were conducted to quantify the relationship between the distribution of soil aggregate size and the concentration and mass of mineral N (i.e., NH4-N and NO3-N) under N fertilizer addition. The results indicated that the weight of aggregate with different sizes was less affected by the intensity of fertilization, which was mainly influenced by the soil types. In most soils, the weight of soil aggregates of 1–0.5 mm accounted for the largest proportion of aggregates in the five categories (i.e., 5–2 mm, 2–1 mm, 1–0.5 mm, 0.5–0.25 mm, and < 0.25 mm). Moreover, the intermediate aggregates (1–0.5 mm and 0.5–0.25 mm) were detected to have the highest mineral N concentration and mass, and they were also demonstrated to be significantly (P < 0.05) correlated to the potential nitrogen mineralization (PNM) rates in most soils. Subsequently, the obtained PNM indices were classified into three levels: i.e., >65% (highly responsive), 45%–65% (moderately responsive), and < 45% (lowly responsive), and we proposed the preliminary strategies on fertilizer types, agricultural intensity, and crop selection for different soils. The outcome of this study provides new insights into the relationship between soil aggregate sizes and N mineralization abilities and will help in developing guidelines for fertilizer management.

Ant-mediated effects on soil nitrogen mineralization vary with species in a tropical forest

Ants as ecosystem engineers can modify soil heterogeneity and biochemical process, which regulates nitrogen mineralization dynamics. However, ant-mediated effects of different feeding-habits on nitrogen mineralization are not well documented, especially for underground-nesting ants in tropical forest soils. For this study, three dominant underground-nesting ant species with different feeding habits (i.e., honeydew-harvester Pheidole capellinii, predatory Odontoponera transversa, and saprophagous Pheidologeton affinis) were selected to identify their effects on nitrogen mineralization in a Xishuangbanna tropical forest. The results showed a higher average mineralization rate in nests of three ant species (0.88 mg kg−1d−1) compared with reference soils (0.36 mg kg−1d−1). The average nitrogen mineralization rates were 3.3 folds higher in P. capellinii nests than in reference soils, while those in nests of O. transversa and P. affinis were 2.3 and 1.8 folds, respectively. The change in nitrogen mineralization along soil profile varied with ant species. The greatest rates of nitrogen mineralization were observed in 10–15 cm layer of O. transversa and P. affinis nests, while those in P. capellinii nests were in 5–10 cm layer. The concentrations (87.4–269.6%) of carbon pools (i.e., microbial, readily oxidizable, and total organic carbon) and NH4+-N increased the greatest in nests of P. capellinii, whereas those (40.8–119.5%) of total, dissolved, and nitrate nitrogen were in nests of P. affinis. The shift in carbon pools was the most important factor that accelerated the nitrogen mineralization, followed by NH4+-N and total nitrogen. Our data indicated that nitrogen mineralization varied with ant species due to different modifications of feeding habits on soil variables in Xishuangbanna tropical forest.

How did the Addition of Indaziflam Affect on Carbon and Nitrogen Mineralizations in a Vineyard Soil?

Microbial activity can be affected by herbicides when they are introduced in soil. Indaziflam is a herbicide used for weed control in vineyards, apple, peach and orange orchards that inhibit cellulose biosynthesis in plants (500 g active ingredient/ l). Recommended field dose of herbicide (RD) containing Indaziflam (10 ml/ da) and its 2 (RD x2), 4 (RD x4), 8 (RD x8) and 16 (RD x16) times of RD were mixed with a loamy soil sampled from Cukurova University Faculty of Agriculture Vineyard (Adana, Turkey) in this study. These mixtures were humidified at 80% of soil field capacity and then incubated for 42 days at 28ºC for the determination of carbon and nitrogen mineralization. Effects of RD and RD x2 doses on soil carbon mineralization were similar to control and no significant difference was found between them. Higher doses of indaziflam (RD x4, RD x8 and RD x16) stimulated mineralization of soil carbon and there were found significant differences between control and these doses (P&amp;lt;0.05). All application doses of herbicide showed variability in ammonium (NH4-N) and nitrate (NO3-N) contents while there were generally found no significant differences between control and RD. In general, contents of soil NH4-N and NO3-N were increased in all applications as time passed and there were significant differences between days that were measured of these contents (P&amp;lt;0.05). Results of soil nitrogen mineralization rate were as following: 1) It was significantly decreased by only RD x2 on 11th day (P&amp;lt;0.05) 2) Higher doses of Indaziflam (RD x4, RD x8 and RD x16) significantly stimulated it on 26th day (P&amp;lt;0.05) 3) All doses of this herbicide significantly decreased it on 42nd day (P&amp;lt;0.05). In conclusion, the recommended field dose of Indaziflam had no negative effect on microorganisms that play an active role in soil carbon and nitrogen mineralization. It was suggested that higher recommended field doses of this herbicide can be used as an energy source by microorganisms in a loamy soil while these doses generally decreased production of ammonium and nitrate.

Effects of Climate Warming on the Key Process and Index of Black Soil Carbon and Nitrogen Cycle During Freezing Period

As an critical part of the global biogeochemical cycle, the winter soil carbon and nitrogen cycles are extremely sensitive to climate warming. Furthermore, the black soil in northeast China is fertile and rich in organic matter and is a vital production base of commodity grains in China. For as long as half a year, the black soil is in a freezing-thawing state. Climate warming will change the snow cover thickness and soil freezing degree on the surface of the black soil in the winter and affect the freezing-thawing cycle frequency and timing of the soil, thus exerting a profound influence on the fixation, transformation, and release of soil carbon and nitrogen during the freezing period and throughout the year. To better understand the effects of climate warming on the black soil carbon and nitrogen dynamics during the freezing period, an experiment was conducted with two warming levels (W1 and W2) using an infrared radiometer to simulate soil warming. The warming increased the surface soil temperature (0 cm soil temperature) by 1.54℃ (W1) and 4.10℃ (W2), respectively, and significantly increased the soil moisture content compared with the control (C) during the freezing period, most likely because of the melting snow. The snow cover thickness, soil freezing depth, soil organic carbon (SOC), and labile organic carbon (LC) content were reduced by both warming treatments. However, the effect of the temperature increase during the freezing period on the key processes and indicators of the nitrogen cycle in black soil was relatively more complicated. With the increase in temperature, the content of nitrate nitrogen (NO3--N) decreased significantly, and the content of total nitrogen (TN) and net nitrogen nitrification rate increased significantly, while the ammonium nitrogen (NH4+-N), total inorganic nitrogen (TIN) content, and the net nitrogen mineralization rate exhibited a significant increase first and then decreased. In summary, climate warming will bring a warmer and more humid environment to the black soil during the freezing period, and the resulting changes in the soil carbon and nitrogen content and transformation processes will have a profound impact on the structure, productivity of the plants and microbial communities, and carbon and nitrogen cycles in the subsequent growing season. The results provide a scientific basis for studying the carbon and nitrogen cycle mechanisms of the northeast black soil during the freezing period.

Responses of soil gross nitrogen transformations to three vegetation restoration strategies in a subtropical karst region

AbstractInvestigation of soil internal nitrogen cycles is useful for unravelling the mechanisms responsible for soil nitrogen availability change. Here, gross nitrogen transformations were investigated in a subtropical karst area after 16 years of vegetation restoration. The experiment included four treatments with one control and three restoration strategies, that is: (i) maize‐soybean rotation field (CR, control); (ii) restoration with Toona sinensis (TS); (iii) restoration with Guimu‐1 hybrid elephant grass (GG, Pennisetum americanum (L.) Leeke × Pennisetum purpureum Schumach); and (iv) restoration with Guimu‐1 hybrid elephant grass and Zenia insignis as a mixture (ZG). Soil NH4+ and NO3− responded differentially to three restoration strategies, resulting in no significant change of total inorganic N content following vegetation restoration. Gross nitrogen mineralization (GNM) rate increased by 124.0%, 96.8%, and 60.3% in TS, GG, and ZG, respectively, relative to CR (2.88 ± 0.05 mg N kg−1 d−1). The strongest explanatory variable was microbial biomass carbon for both GNM (R2 = 0.82) and gross nitrification (R2 = 0.66). Dissimilatory NO3− reduction to NH4+ (DNRA) rate in TS or ZG, which was significantly greater than that in CR, was significantly correlated with SOC: NO3− ratio (R2 = 0.61), implying that DNRA was limited by SOC availability. Gross NH4+ immobilization rate, which was highest in GG, and lowest in CR, was best predicted by carbon to nitrogen ratio (R2 = 0.65). However, gross NO3− immobilization rate could not be well predicted by the measured soil properties. Our results suggest that vegetation restoration especially TS significantly enhanced soil N availability as reflected by gross N mineralization rate.

Stakes High for Organic Farmers Assessing Nitrogen Mineralization Rates

CSA NewsVolume 66, Issue 2 p. 7-9 FEATURES Stakes High for Organic Farmers Assessing Nitrogen Mineralization Rates New Research Seeks to Help Predict Speed and Rate at Which Nitrogen Gets Released to Crops Megan Sever, Megan SeverSearch for more papers by this author Megan Sever, Megan SeverSearch for more papers by this author First published: 25 January 2021 https://doi.org/10.1002/csan.20384Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume66, Issue2February 2021Pages 7-9 RelatedInformation