Nitrogen Dynamics Research Articles

Dynamics of the Humus State of Southern Chernozem with Prolonged Use of Mineral Fertilizers in the Conditions of the Steppe Volga Region

The results of monitoring the dynamics of humus and total nitrogen of the southern chernozem in a long-term stationary experiment with the use of mineral fertilizers are presented. In the first 3 rotations of the grain-to-crop rotation, intensive mineralization of humus was noted in all variants of the experiment. In the conditions of grainsteam crop rotation, this process slowed down, and in the variant with the use of minimum doses of nitrogenphosphorus fertilizers in the 6th rotation, the accumulation of humic substances was revealed. The maximum decrease in humus content at the end of 8 rotations of crop rotation (more than 48 years) was observed in variants with the introduction of medium and high doses of nitrogenphosphorus fertilizers. The use of a minimum dose of fertilizers best compensated for the loss of humus of the southern chernozem during prolonged agricultural use. In comparison with the initial data, negative changes in the qualitative composition of humus were noted in the experiment, expressed in a decrease in the proportion of humic acids. At the end of the 8th rotation, the total nitrogen content in the soil decreased in all variants of the experiment.

Combining Urea with Chemical and Biological Amendments Differentially Influences Nitrogen Dynamics in Soil and Wheat Growth.

Nitrogen (N) losses from fertilized fields pose a major concern in modern agriculture due to environmental implications. Urease inhibitors, such as N-(n-butyl) thiophosphoric triamide (NBPT), nitrification inhibitors (NI), like dicyandiamide (DCD), and sulfur-oxidizing bacteria (SOB) could have potential in reducing N losses. For evaluating their effectiveness, investigations were undertaken through incubation and greenhouse experiments by mixing a urea fertilizer with sole NBPT, DCD, and SOB, as well as combined, on ammonia volatilization losses from silt loam soil. An incubation experiment was conducted in 1 L airtight plastic jars with adequate aeration and constant temperature at 25 °C for 10 days. Three replications of each treatment were conducted using a completely randomized designed. The ammonia emission rate gradually increased until the highest (17.21 mg NH3 m-2 h-1) value on the third day with sole urea and some other treatments except NBPT alone, which prolonged the hydrolysis peak until the fifth day with the lowest ammonia emission rate (12.1 mg NH3 m-2 h-1). Although the DCD and SOB treatments reduced ammonia emission, their difference with urea was nonsignificant. Additionally, mixing NBPT with urea exhibited the highest population of nitrifying bacteria in soil, indicating its potential role in promoting the nitrification process. In a greenhouse experiment, 10 treatments, i.e., T1 = control, T2 = N120 (urea fertilizer equivalent to 120 kg N ha-1), T3 = N90 (90 kg N ha-1), T4 = N90 + NBPT, T5 = N90 + DCD, T6 = N90 + SOB, T7 = N90 + NBPT + DCD, T8 = N90 + NBPT + SOB, T9 = N90 + DCD + SOB, and T10 = N90 + NBPT + DCD + SOB, were applied to investigate the wheat yield and N uptake efficiency. The highest N recovery efficiency (31.51%) was recorded in T5 where DCD was combined with urea at 90 kg ha-1.

Influence of Terrestrial Nitrogen Dynamics on Mesoscale Near‐Surface Meteorological Fields

AbstractThe influence of biogeochemical cycles, particularly the nitrogen cycle, on near‐surface meteorological fields is a critical yet understudied aspect of regional climate modeling. Neglecting such interactions may compromise the accurate representation of vegetation growth and hydrological processes in climate models, consequently affecting the simulated regional near‐surface climate conditions. In order to quantify such effects, we coupled the nitrogen‐augmented Noah‐MP land surface model with the Weather Research and Forecasting (WRF) model v4.1.2 (hereafter WRF‐CN) for regional climate modeling. Compared to the default WRF simulation without nitrogen dynamics, the WRF‐CN simulated net primary productivity, gross primary productivity (GPP), and leaf area index (LAI) were all higher in the study region. Because WRF underestimated the observed GPP and LAI due to the fixed nitrogen limitation of plant growth, these higher estimations improved WRF‐CN's performance in modeling GPP and LAI, which translated into improved simulations of near‐surface climate. Specifically, for the 2‐m air temperature, compared to WRF, WRF‐CN reduced the mean absolute error and root mean square error by 14.45% and 14.19%, respectively, while increased the Nash‐Sutcliffe efficiency coefficient by 7.23%, with the most pronounced improvements in the regions dominated by croplands. Our findings shed light on the crucial interactions between biogeochemical processes and near‐surface meteorological conditions, emphasizing the significance of incorporating terrestrial nitrogen dynamics in regional climate models. These insights contribute to advancing our understanding of climate system dynamics and improving the accuracy of climate predictions at the mesoscale.

Responses of Soil Carbon and Nitrogen Dynamics and GHG Fluxes in Forest Ecosystems to Climate Change and Human Activity

Forest soils are considered the largest carbon and nitrogen pools in soil organic matter among terrestrial ecosystems, and soil carbon and nitrogen dynamics and greenhouse gas (GHG) emissions are normally affected by climate change and human activity. The collection of recent research on this scientific theme would provide a basis for understanding the responses of soil carbon and nitrogen dynamics and GHG fluxes in forest ecosystems to climate change and human activity. A Special Issue was, thus, organized to discuss recent research achievements, including a total of nine research articles and one review. This Special Issue includes the effects of climate changes such as changes in throughfall, snow cover, and permafrost degradation; human activities such as nitrogen and/or phosphorus addition and the use of biochar; and soil–plant interactions on soil carbon and nitrogen dynamics and GHG fluxes in forest ecosystems. Although this collection of papers reflects only a small part of this scientific theme, it can, to some extent, provide a basis for understanding some important research aspects related to the future of forest soil carbon and nitrogen dynamics and GHG fluxes in a changing world, thereby enabling sustainable development and the mitigation of climate change.

Geographical factor dominates spatial patterns of potential nitrate reduction rates in coastal wetland sediments in Fujian Province, China

Nitrate (NO3−) reduction is a key process governing the nitrogen (N) dynamics of coastal wetland sediments. Although the effects of environmental factors on the NO3− reduction mechanism in coastal wetland sediments have been examined in various studies, the effects of spatial variation in potential NO3− reduction processes in coastal wetland sediments and the factors driving geographical variation in these processes have not been widely examined. Here, we conducted research on surface sediment samples from four different vegetation types at six coastal wetland sites across two regions. We characterized potential rates of NO3− reduction processes (including denitrification (DF), anammox (ANA), and dissimilatory nitrate reduction to ammonium (DNRA)) using a15N tracer method. Additionally, we assessed the abundances of functional genes, and microbial community structure using high-throughput sequencing, and metagenomic sequencing. In six wetland sites, the contribution ranges of DF, ANA, and DNRA to NO3− reduction were 38.43%–55.69%, 31.33%–45.65%, and 5.26%–17.11%, respectively, and potential NO3− reduction was mainly driven by N removal via gaseous N (DF+ANA). Significant spatial differences were observed in the structure of bacterial and fungal microbial communities, suggesting that geographical distance has a major effect on microbial community structure. Environmental factors and Functional gene abundances were significantly related to potential NO3− reduction processes, and physicochemical properties had a stronger effect on potential NO3− reduction processes than gene abundances. Factors showing significant differences across regions were the main drivers of variation in potential NO3− reduction processes. Overall, our study showed that sediment substrates and geographical environmental factors rather than the abundance of functional genes and vegetation types were the main indicators of potential NO3− reduction activities in coastal wetlands.

Effect of NPK fertilization and seed rate on barley (Hordeum vulgare) yield, yield component and nitrogen dynamics in semi-arid conditions

Objective: This study aimed to investigate the impact of varying of NPK fertilization doses and seed rates on barley (Hordeum vulgare) yield, yield components, and inorganic nitrogen (NH4-N and NO3-N) dynamics in semi-arid conditions without artificial irrigation. Material and Methods: The field experiment was conducted at the Gobustan Experimental Station from October 2018 to June 2019, utilizing the "Celilabad-19" barley variety. A randomized complete block design with four replications was employed, incorporating various seed rates and NPK fertilizer treatments. Plant and soil samples were collected at different phenological stages, and analyses included grain and straw yield, yield parameters, total N content of plant, and soil NH4-N and NO3-N levels. Results and Discussion: The results the treatment with a seed rate of 140 kg/ha and N60P45K45 fertilizer application consistently demonstrated the highest aboveground biomass, grain, and straw yields. This treatment exhibited optimal N content during the Full Maturity stage of plant. Conclusion: In conclusion, this study has provided insights into optimizing barley cultivation practices in semi-arid climates, such as seed rate and NPK fertilizer dose. With a seed rate of 140 kg/ha and N60P45K45 fertilizer application, the highest yield and performance indicators were achieved in the “Celilabad-19” barley variety.

Nitrogen and phosphorus mineralization dynamics in human excreta-derived fertilizers

Growing interest in human-excreta derived fertilizers requires more information on their agronomic relevance. In this study, we measured the nitrogen (N) and phosphorus (P) mineralization from fresh urine, stored urine, urine-enriched biochar prepared with either fresh or stored urine, and feces-derived compost application in a 90-day aerobic loam soil incubation. Soils were extracted for available N at days 0, 5, 10, 20, 30, 60, and 90, while soils were extracted for four biologically relevant P pools at days 0, 30, 60, and 90. We found that N in urine applied alone was immediately bioavailable, supplying nearly all the 200 kg-N ha-1 applied, while urine-enriched biochar supplied approximately half of the N applied. Feces-derived compost application led to a slow release of mineral N. Feces-derived compost application stimulated substantial native soil P mining, while urine-P was likely rapidly immobilized. These results are relevant to container-based sanitation and other source-separated sanitation endeavors, and researchers and producers interested in human excreta-derived fertilizers. Future research should explore, among other things, different urine-enriched biochar preparations and the co-application of urine-based fertilizers and feces-derived compost.

Contrasting nitrogen transport patterns in subtropical basins revealed by combined multiple isotopic analyzes and hydrological simulations

Although enhancing the knowledge of nitrogen (N) dynamics in aquatic systems is crucial for basin N management, there is still a lack of theories on the patterns of basin N sources and transport because of the intricate influence of human activities, climatic conditions, landscape patterns, and topography on the trajectory of basin N. To shed new light on the patterns of basin N sources and transport in the Chinese subtropical monsoon region, this study provides a comprehensive approach combining multiple isotopes and hydrological model based on monthly records of hydro-chemistry and isotopes (18O-NO3− /15N-NO-3 and 18O-H2O /2H-H2O) for river water, groundwater and rainfall in three basins over multiple years. Our observations of hydro-chemistry showed that fluvial N levels in highly urbanized basins (3.05 ± 1.42 mg·L−1) were the highest and were characterized by higher levels in the dry season. In the agricultural basin, fluvial N levels in February and March were approximately 1.9 times higher than those in the other months. The fluvial N load was higher in agricultural basins (0.624–0.728 T N km -2 y -1) than in urban basins (0.558 T N km -2 y -1), primarily because of variations in sewage treatment rates and fertilizer application. In highly urbanized basin, manure and sewage (46.9 %) were the dominant sources of fluvial N, which were discharged into rivers after treatment. In the plain agricultural basin, a substantial portion of diffused residential sewage leaches into aquifers and is stored. In the hilly agro-forest mixed basin, the high baseflow coefficient (75.8 %) and the key role of groundwater N, mainly from soil N (27.3 %), chemical fertilizers (20.2 %), manure and sewage (46.6 %), to fluvial N (26.5 %) indicated that a high proportion of the N sources leached into the aquifer and were then transported to rivers. For the first time, this study integrated multiple methods to substantiate the proposed typical patterns of N sources and transport within the basins. These findings have significant implications for tailored basin-specific N management strategies.

Spatiotemporal Dynamics of Carbon and Nitrogen in Subtropical Urban Streams (Santo André, SP, Brazil)

Urban sprawl poses a significant threat to urban stream water quality due to impermeabilization, reduced vegetation cover, and the release of diffuse pollutants. This study evaluates water quality in seven catchments in Santo André, SP, considering seasonality. Nutrient concentrations and in situ measurements were taken during both dry and rainy seasons. Comparisons were made using Kruskal–Wallis and Mann–Whitney tests. Streams showed significant differences in relation to water quality parameters. The Carapetuba, Jundiaí, and Apiaí streams were most adversely affected, underscoring the need for urgent water quality intervention (water conductivity above 500 μS/cm, dissolved oxygen below 2 mg/L, total dissolved carbon above 50 mg/L, and total dissolved nitrogen above 25 mg/L). Significant differences were observed across seasons. The dry season showed elevated temperatures (above 25 °C) and increased total dissolved carbon (above 50 mg/L) and nitrogen concentrations (above 30 mg/L), indicating reduced dilution effects from rainfall and heightened organic contamination. Conversely, the wet season demonstrated lower nutrient concentrations, emphasizing seasonal dynamics. Sustained, long-term monitoring of urban streams in Santo André and the implementation of sewage collection and treatment in irregular settlements are recommended. These measures are essential to mitigate the adverse impacts of urban expansion on water quality.

PBAT microplastics exacerbates N2O emissions from tropical latosols mainly via stimulating denitrification

Biodegradable plastic mulching films are regarded as promising substitutes for their non-degradable counterparts to ameliorate serious plastic pollution in agriculture. Inevitably, biodegradable microplastics (BMs) can be formed and profoundly affect the function of soil ecosystems. However, little is known about the effects of BMs loading on soil nitrogen (N) dynamics and loss in tropical agricultural soils. Hereby, a 120-day soil incubation trial was performed to evaluate the effects of polybutylene adipate co-terephthalate (PBAT) microplastics on nitrous oxide (N2O) emissions, N transformation, and bacterial community structure in latosols. The results showed that PBAT addition raised soil ammonium nitrogen (NH4+–N) and dissolved organic carbon (DOC) contents, but lowered nitrate nitrogen (NO3––N) contents, accompanied with a smaller potential nitrification rate and a greater potential denitrification rate. The microbial biomass nitrogen and nrfA gene abundance were increased by PBAT, suggesting the processes of microbial N immobilization and dissimilatory nitrate reduction to ammonia were largely promoted. Positive correlations existed between N2O emissions and denitrification-related enzymatic activities and functional gene abundances (narG, nirK/S and Fungal nirK). PBAT amendment stimulated N2O emissions by 54.8 − 317.3 %, accompanied with increased values of those denitrification-related parameters, suggesting that stimulated denitrification was responsible for the exacerbated N2O emissions. Moreover, PBAT addition changed bacterial alpha diversity and bacterial community composition, where the relative abundances of Proteobacteria increased while those of Nitrospirae and Acidobacteria decreased. These findings are beneficial to understanding the fate of N in microplastics-polluted soil, which will provide a new insight into the impact of BMs on soil functions and environmental risks.

Impact of nitrapyrin on urea‐based fertilizers in a Mediterranean calcareous soil: Nitrogen and microbial dynamics

AbstractNitrification inhibitors, such as nitrapyrin (NI), are increasingly co‐applied with nitrogen (N) fertilizers as part of sustainable agricultural practice. Several studies in temperate regions have documented the effectiveness of NI in retaining soil ammonium (NH4+), minimizing N loss and increasing crop yields. However, less is known about the effects of NI in Mediterranean regions, where agricultural production is challenging and requires intensive irrigation and fertilization. We investigated the short‐term impact of the nitrification inhibitor nitrapyrin (2‐chloro‐6‐(trichloromethyl)pyridine) in a two‐factor mesocosm experiment, using a typical Mediterranean soil, where NI was co‐applied with a selection of urea‐based fertilizers: urea (U), U with urease inhibitors (U + UI), methylene urea (MU) and zeolite‐coated urea (ZU). NI co‐applied with urea fertilizers resulted in higher availability of soil NH4+ and a concurrent increase in NH3 volatilization. Net cumulative soil NH4+ availability was 1.5–3.3 fold greater when NI was applied. Concurrently, net cumulative nitrate (NO3−) and nitrite (NO2−) availability was reduced by 10%–60%; this was found for all the tested fertilizer types except MU fertilizer, where the net cumulative soil NO3− and NO2− doubled. Nitrous oxide (N2O) emissions from urea fertilization were reduced by 40% with UI, 50% with NI and 66% with NI + UI. Interestingly, after 28 d, the composition of soil microbial communities was distinctly different, due to NI application. Specifically, NI application dramatically reduced the abundance of ammonia‐oxidizing and denitrifying bacterial functional groups. NI was effective in reducing N2O emissions in this calcareous soil; however, NH3 emissions were remarkably enhanced. These findings have important implications for the large‐scale adoption of inhibitor technologies in Mediterranean agroecosystems and for the reduction of greenhouse gas emissions.

Effect of Microbial Fuel Cell, fertilizer, and plant spacing on nitrogen dynamics in paddy soil

<p>Nitrogen is one of the primary nutrients required for growing rice. Still, the efficiency of urea fertilizer application is very low (20-40%) due to the nitrogen loss process, one of which is denitrification. This study aims to determine the effects of combining Microbial Fuel Cell (MFC), plant spacing, and fertilization on nitrogen dynamics in paddy fields. The combination of treatments are expected to reduce the nitrogen loss in paddy fields, and plants can absorb it efficiently. A total of six treatments included Microbial Fuel Cell (MFC) (2 levels: without MFC and with MFC), plant spacing (2 levels: conventional spacing 25 cm × 25 cm and <em>jajar legowo</em> spacing 25 cm × 12.5 cm × 50 cm), and fertilization (2 levels: without fertilizer and with 500 kg ha<sup>-1</sup> of NPK fertilizer), with three replications for each combination. The observed parameters included total soil nitrogen, nitrate, nitrogen uptake, chlorophyll, nitrogen-fixing and denitrifying bacteria, and N<sub>2</sub>O gas emissions. The results showed that combining MFC, conventional spacing, and NPK fertilizer in the paddy fields resulted in a high total soil nitrogen (0.44%). The results showed different effects on total soil nitrogen in the MFC and fertilization treatments, leading to increased nitrate levels, nutrient uptake, and chlorophyll. Increasing total soil nitrogen significantly contributes to leaf development and significantly aids photosynthesis. The integration of MFC and fertilization observed in this study resulted in a real impact on nitrogen dynamics in paddy fields. This combined treatment effectively reduces total nitrogen loss due to denitrification in paddy fields, thereby increasing the efficiency of uptake by plants.</p>

Water Hyacinth Biochar: A Sustainable Approach for Enhancing Soil Resistance to Acidification Stress and Nutrient Dynamics in an Acidic Nitisol of the Northwest Highlands of Ethiopia

Soil acidity impacted over 43% of Ethiopia’s arable land and debilitated agricultural productivity. Due to reacidification susceptibility, high costs, and inadequate availability of lime, biochar has emerged as an alternative soil acidity ameliorator. However, biochar application, particularly from invasive plants such as water hyacinth, as a soil acidity amendment and waste management strategy has not fully expanded in Ethiopia. Therefore, this study investigated the potential of water hyacinth biochar (WHB) to enhance soil resistance to acidification stresses and nutrient dynamics in an acidic Nitisol of the northwest highlands of Ethiopia. An incubation study was conducted using nine treatments viz. control (soil only), biochar produced using a furnace (WHBf), and a grounding method (WHBg) each at 1% and 2% application rates, lime (L), fertilizer (F), 2% WHBf combined with fertilizer (2WHBfF), and lime combined with fertilizer (LF). Soil samples, except the control, underwent simulated acidification with HNO3. The results showed that WHB decelerated nitrification, reduced H+ ions released into the soil, and enhanced available phosphorus and nitrogen dynamics. After incubation, 1% and 2% WHB applications increased soil pH in the range of 0.30–0.35 and 0.72–0.86 units, respectively, compared to the limed soil. Conversely, exchangeable acidity decreased by 26.5% to 28.8% and 58.4% to 63%, respectively. The 2WHBfF treatment led to soil pH increases of 0.71 and 0.90 units, with exchangeable acidity reductions of 49.8% and 64.7% compared to the LF and F treatments, respectively. Compared to lime, WHB treatments demonstrated more effective resistance against soil acidification from nitrification and simulated acidification with HNO3. Therefore, WHB can be used as a sustainable approach to increase soil resistance against various acidification stresses while aiding in soil nutrient management. The study’s findings can offer valuable insights to change environmental challenges into sustainable soil acidity management approaches.

Enhanced Removal of River‐Borne Nitrate in Bioturbated Hyporheic Zone

AbstractThe influence of bioturbation induced by bottom‐dwelling macrozoobenthos on nitrogen dynamics in lotic stream sediments remains unclear. In this work, we advance the understanding of faunal bioturbation in lotic environments by developing a fully‐coupled flow and multicomponent reactive transport model and investigate the influence of sediment reworking and burrow ventilation processes on nitrogenous transformations. The model results indicate that sediment reworking and burrow ventilation significantly increase nitrate (NO3−) influx, penetration depth, and reaction rates in the streambed. Denitrification rates were observed up to three times higher in beds with U‐shaped burrows compared to flatbeds. The ratio of mound height to stream water depth ratio (h/H0) is a dominant control on determining the relative importance of the sediment reworking and burrow ventilation processes in modulating nitrogenous reactions. A power‐law scaling framework is ultimately proposed to predict NO3− removal efficiency based on the Damköhler number in bioturbated lotic streambeds.

Enhancing Roselle Growth and Yield through Planting Density and Fertilization Strategies: A Study on BRIS Soil Area

Optimizing planting density and fertilization practices are crucial factors influencing the micro-environment of agricultural fields, thereby profoundly impacting the growth, development, and yield formation of Roselle plants. This study investigates the combined effects of planting density and Sesbania grandiflora integration on nitrogen dynamics within the BRIS soil area, aiming to enhance Roselle growth and yield. Employing a randomized complete block design (RCBD), three fertilizer treatments—control, green manure, and organic fertilizer—were implemented. Nitrogen content was analyzed using the Kjeldahl method, while phosphorus and potassium contents were determined via UV spectrometry and atomic absorption spectrophotometry, respectively. Within an agroforestry model employing a spacing of 20 cm between plants, results revealed that Roselle plants treated with organic fertilizer exhibited higher nitrogen (N: 3.54 %), phosphorus (P: 0.54 %), and potassium (K: 1.61 %) content in their leaves, and similarly in their roots (N: 1.93%, P: 0.45%, K: 2.11%). However, soil analysis indicated that green manure fertilizer treatment led to higher nitrogen (0.11 %), phosphorus (44.67 %), and potassium (0.17 %) content within the BRIS soil. In conclusion, the green manure fertilizer treatment demonstrated a propensity to enhance nitrogen dynamics within the poorly structured BRIS soil, thereby promoting growth and development. Conversely, the integration of Sesbania grandiflora along with suitable plant spacing appeared instrumental in sustaining Roselle yield productivity. This research sheds light on the interplay between planting density, fertilizer strategies, and soil dynamics, providing valuable insights for optimizing Roselle cultivation practices in similar agroecological contexts.

Key determinants of soil labile nitrogen changes under climate change in the Arctic: A meta-analysis of the responses of soil labile nitrogen pools to experimental warming and snow addition

The Arctic terrestrial ecosystems are undergoing rapid climate change, causing shifts in the dynamics of soil nitrogen (N), a pivotal but relatively underexplored component. To understand the impacts of climate change on soil labile N pools, we performed meta- and decision-tree analyses of 391 observations from 38 peer-reviewed publications across the Arctic, focusing on experimental warming and snow addition. Soil dissolved organic nitrogen (DON), ammonium (NH4+), and nitrate (NO3-) pools under experimental warming exhibited overall standard mean differences (SMDs) ranging from −0.08 to 0.02, with no significance (P > 0.05); however, specific conditions led to significant changes. The key determinants of soil labile N responses to warming were experimental duration and mean annual summer temperature for DON; annual precipitation, soil moisture, and sampling timing for NH4+; and soil layer for NO3-. Snow addition significantly increased all labile N pools (overall SMD = 0.23–0.36; P < 0.05), influenced by factors such as sampling timing and vegetation type for DON; experimental duration and soil moisture for NH4+; and soil pH for NO3-. By consolidating and reprocessing datasets, we not only showed the overall responses of soil labile N pools to climate manipulation experiments in Arctic tundra ecosystems but also identified key determinants for changes in soil N pools among environmental and experimental variables. Our findings demonstrate that warming and snow-cover changes significantly affect soil labile N pools, highlighting how the unique environmental characteristics of different sites influence terrestrial N cycling and underscoring the complexity of Arctic N dynamics under climate change.

Biochar-Poultry Manure Compost Alters Temperature and Nitrogen Dynamics during Composting and Improves Potato Growth Following Field Application

Composting is an aerobic process that transforms organic wastes into valuable agricultural product, but the composting process frequently results in losses of nitrogen (N) through NH3 volatilization. We evaluated the potential for high-temperature, wood-based biochar to reduce N loss when included as a compost feedstock. Biochar was composted with wood shavings and poultry manure (4:1 v/v) at rates of 0, 20 and 40% (v/v) in replicated, actively aerated 1.43 m3 in-vessel compost piles. Biochar addition caused more rapid temperature increase and truncated thermophilic phase. N loss from the entire compost mass was reduced with 40% and 20% biochar addition compared to the control (29.9, 32.3, and 35.6% N loss, respectively; P value = 0.027). However, assuming no N was lost from the added biochar, difference in N loss was less significant (P value = 0.100). With 40% biochar addition, finished compost had greater NO3 --N concentration, lower electrical conductivity, greater carbon to nitrogen ratio, and greater total carbon content. Compost products were amended to soil at rates of 7 or 15 Mg C ha−1 in potato production. Relative to an unamended control, the high application rates tended to decrease bulk density and increase total N in soil, but no differences were detected between the compost or composted biochar treatments. Tuber weights were increased 40% with application of composted biochar (biochar 40% v/v). Biochar is a promising bulking agent for composting which may reduce N loss and increase nitrification. Future studies should examine how specific biochar products affect the compost process, nutrient retention, and crop production.

Sustainable Soil Management for Climate Resilience: Long-Term Management Effects on Soil Carbon Sequestration and Nitrogen Dynamics in a Semi-Arid Tropical Inceptisol of India

Sustainable Soil Management for Climate Resilience: Long-Term Management Effects on Soil Carbon Sequestration and Nitrogen Dynamics in a Semi-Arid Tropical Inceptisol of India

Validated simulation of a long-term cropping experiment reveals a pathway for improved productivity

Long-term farming system experiments with comprehensive soil, plant and meteorological data combined with well-validated dynamic farming system models are a powerful combination to evaluate the production and environmental implications of novel innovations in agriculture. A current deficiency is the lack of adequate comprehensive validations for long term crop sequences that capture the dynamics of soil and crop responses without resetting soil conditions, especially for soil mineral nitrogen (Min-N). This reduces confidence in the outcome of scenario analyses for proposed improvements in productivity and sustainability given the central role played by nitrogen (N) dynamics in both processes. We used data from a 30-year long-term experiment (LTE) to validate the APSIM model and achieved excellent predictions for soil and crop responses including the dynamics of Min-N without resetting. A critical step was to ensure that the parameters required for the pools of soil organic matter matched those measured at the site over the full rooting depth (1.6 m) rather than limiting measured values to surface layers and relying on default parameters in deeper layers. In subsequent scenario analyses of agronomic innovations including fallow weed control, earlier sowing and improved N fertiliser strategies, the validated model predicted potential increases in average annual productivity of 1.2 t ha-1 (30%), WUE of 2.0 kg ha-1 mm-1 (30%) and NUE of 13 kg kg-1 (21%) and reductions in average annual N leaching of 8 kg N ha-1 (-33%) and soil organic matter loss of 3.1 t ha-1 (31%) (0–10 cm) could be achieved with specific combinations of synergistic innovations previously investigated separately in shorter-term experiments. Our study represents a rare case of model validation capturing the dynamics of soil water, Min-N, biomass and grain yield in a long-term diverse crop sequence to provide confidence in scenario analyses of production and environmental consequences of agronomic innovations. LTEs provide a valuable resource for such validation, while conclusions drawn from simulation studies that lack comprehensive validation must be considered with caution.

Isotope constraints on seasonal dynamics of nitrogen in Zhanjiang Bay, a typical mariculture bay in South China

Isotope constraints on seasonal dynamics of nitrogen in Zhanjiang Bay, a typical mariculture bay in South China