Optimising yield, quality, soil nitrogen dynamics and profitability in winter wheat: A multi-site assessment from Flanders

Cattle manure can be processed to produce bioenergy, resulting in by‐products with different physicochemical characteristics. To evaluate whether application of such bioenergy by‐products to soils would be beneficial compared with their unprocessed counterpart, we quantified differences in greenhouse gas emissions and carbon (C) and nitrogen (N) dynamics in soil. Three by‐products (15N‐labeled cattle manure, from which anaerobic digestate was obtained, which was subsequently pyrolysed) were applied to a loess and a sandy soil in a laboratory incubation study. The highest losses of soil C from biological activity (CO2 respiration) were observed in manure treatments (39% and 32% for loess and sandy soil), followed by digestate (31% and and 18%), and biochar (15% and and 7%). Emissions of nitrous oxide (N2O) ranged from 0.6% of applied N from biochar to 4.0% from manure. Isotope labeling indicated that manure N was most readily mineralized, contributing 50% to soil inorganic N. The anaerobic digestate was the only by‐product increasing the mineral N pool, while reducing emissions of N2O compared with manure. In biochar treatments, less than 18.3% of soil mineral N derived from the biochar, while it did not constrain mineralization of native soil N. By‐products of anaerobic digestion and pyrolysis revealed soil fertility in addition to environmental benefits. However, the reported advantages lessen when the declining yields of C and N over the bioenergy chain are considered.

Crop establishment methods play a vital role in the predominance of nutrient forms. Nitrogen dynamics in the soil can alter micronutrient availability and uptake. Four treatments each replicated thrice, comprising of three methods of rice establishment viz., puddled transplanted rice (PTR), unpuddled transplanted (UPTR), and direct seeded rice (DSR) in different combinations of rotation with conventionally tilled lentil (CTL) and zero till lentil (ZTL) were compared for their effect on inorganic nitrogen in the soil and its consequent effect on the micronutrient availability in soil and their uptake by rice grain. As per the results obtained from the study, the different establishment techniques with associated treatments after 7 years of continuous cultivation did not have any significant effect on general soil properties like pH, electrical conductivity (EC), organic carbon (OC), and cation exchange capacity (CEC). Treatments had a significant effect on soil nitrogen content and uptake and on soil micronutrient status and their uptake by rice as estimated after harvest of the rice crop. UPTR-ZTL crop rotation with crop residue management and biopriming with Azotobacter was found to be the most efficient management practice and performed better than the conventional crop establishment techniques like PTR and CTL systems. Nitrogen content in soil and plant N uptake showed positive correlations with micronutrient uptake by the rice grain. Significant positive correlations were obtained with the uptake of Fe, Mn, and Zn. Nitrogen dynamics (irrespective of crop establishment methods) in soil especially ammoniacal N, had a positive effect on the cationic micronutrient uptake by the crop, but results were not conclusive enough to suggest the role of N forms on uptake and translocation of micronutrient cations.

We used two independent methods to determine the dynamics of soil carbon and nitrogen following abandonment of agricultural fields on a Minnesota sand plain. First, we used a chronosequence of 19 fields abandoned from 1927 to 1982 to infer soil carbon and nitrogen dynamics. Second, we directly observed dynamics of carbon and nitrogen over a 12-yr period in 1900 permanent plots in these fields. These observed dynamics were used in a differential equation model to predict soil carbon and nitrogen dynamics. The two methods yielded similar results. Resampling the 1900 plots showed that the rates of accumulation of nitrogen and carbon over 12 yr depended on ambient carbon and nitrogen levels in the soil, with rates of accumulation declining at higher carbon and nitrogen levels. A dynamic model fitted to the observed rates of change predicted logistic dynamics for nitrogen and carbon accumulation. On average, agricultural practices resulted in a 75% loss of soil nitrogen and an 89% loss of soil carbon at the time of abandonment. Recovery to 95% of the preagricultural levels is predicted to require 180 yr for nitrogen and 230 yr for carbon. This model accurately predicted the soil carbon, nitrogen, and carbon:nitrogen ratio patterns observed in the chronosequence of old fields, suggesting that the chronosequence may be indicative of actual changes in soil carbon and nitrogen. Our results suggest that the rate of carbon accumulation was controlled by the rate of nitrogen accumulation, which in turn depended on atmospheric nitrogen deposition and symbiotic nitrogen fixation by legumes. Our data support the hypothesis that these abandoned fields initially retain essentially all nitrogen and have a closed nitrogen cycle. Multiple regression suggests that vegetation composition had a significant influence on the rates of accumulation of both nitrogen and carbon; legumes increased these rates, and C3 grasses and forbs decreased them. C4 grasses increased the C:N ratio of the soil organic matter and thereby increased the rate of carbon accumulation, but not nitrogen accumulation.

This study is focused on investigating the impacts of organic carbon on the denitrification process of nitrogen transformation and transport. A numerical model, Nitrogen-2D, is modified by considering the impact of organic carbon in the denitrification equation. The modified model is used to simulate the soil nitrogen (including nitrate and ammonium) dynamics under the primary and secondary sewage water irrigation with different organic carbon concentrations. The simulated results of accumulated drainage water amount, soil nitrogen concentration, and nitrogen concentration in the drainage water show that the simulations and measurements are consistent. The comparison of results from the original and improved models shows the necessity to consider the impact of organic carbon. The nitrogen mass balance is calculated to analyze the nitrogen transformation processes quantitatively under different input organic carbon sources. Furthermore, the effect of different input organic carbon sources on the soil nitrogen dynamics is investigated by using the modified Nitrogen-2D model with the calibrated parameters. The input organic carbon source helps to speed up the mineralization and denitrification, which contributes to the slight increase of ammonium concentration and the decrease of nitrate concentration in the shallow soil. Since a large number of soil water and nitrogen transformation and transport parameters are needed when setting up the model, a local sensitivity method is conducted to evaluate the input parameters by the sewage water irrigation case. The results show that the drainage water amount is very sensitive to the exponent n and the coefficient α of the soil water retention function and that the ammonium concentration is very sensitive to the first-order nitrification rate constant, the decomposition rate coefficient in humus pool, and the soil ammonium adsorption coefficient. The nitrate concentration is sensitive to more parameters, especially to the exponent n and the coefficient α in the soil water retention function and to the denitrification rate constant.

Rainfed wheat production systems are usually characterized by low-fertility soils and frequent droughts, creating an unfavorable environment for sustainable crop production. In this study, we used a processed-based biophysical numerical model to evaluate the water balance and nitrogen (N) dynamics in soils under rainfed wheat cultivation at low (219 mm, Pygery) and medium rainfall (392 mm, Yeelanna) sites in south Australia over the two seasons. Estimated evapotranspiration components and N partitioning data were used to calibrate and validate the model and to compute wheat’s water and N use efficiency. There was a large disparity in the estimated water balance components at the two sites. Plant water uptake accounted for 40–50% of rainfall, more at the low rainfall site. In contrast, leaching losses of up to 25% of seasonal rainfall at the medium rainfall site (Yeelanna) indicate a significant amount of water evading the root zone. The model-predicted N partitioning revealed that ammonia–nitrogen (NH4–N) contributed little to plant N nutrition, and its concentration in the soil remained below 2 ppm throughout the crop season except immediately after the NH4–N-based fertilizer application. Nitrate–nitrogen (NO3–N) contributed to most N uptake during both seasons at both locations. The N losses from the soil at the medium rainfall site (3.5–20.5 kg ha−1) were mainly attributed to NH4–N volatilization (Nv) and NO3–N leaching (NL) below the crop root zone. Water productivity (8–40 kg ha−1 mm−1) and N use efficiency (31–41 kg kg−1) showed immense variability induced by climate, water availability, and N dynamics in the soil. These results suggest that combining water balance and N modeling can help manage N applications to optimize wheat production and minimize N losses in rainfed agriculture.

A study was conducted to evaluate the effect of bio-methanated distillery spentwash, paper mill, soft drink factory and domestic sewage wastewaters on carbon and nitrogen dynamics in red, lateritic, and black soils of north Karnataka. Application of wastewaters from different sources influenced the carbon and nitrogen fractions across treated soils. Water-soluble carbon, labile carbon and organic carbon were significantly higher in bio-methanated distillery spentwash-treated soils. Wide variations in nitrogen fractions NH4 +–N, NO3 −–N were recorded under the influence of different wastewaters across the treated soils. Irrespective of the soil types, content of organic carbon and nitrogen fractions followed the order bio-methanated distillery spentwash > paper mill > domestic wastewater ≥ soft drink factory wastewater. Higher values of carbon and nitrogen fractions were observed in the surface layers (0–15 cm) in comparison with lower depths. Enumeration of the bacteria, fungi, actinomycetes, N2-fixers and P-solubilizers indicated higher microbial load in bio-methanated spentwash application followed by paper mill wastewater application. Microbial load was highly concentrated in the surface layer (0–15 cm) across the soils and wastewaters evaluated. The bacterial count in treated soils was double that of fresh water-treated soils. Among the soils used in the study, maximum bacteria, actinomycetes and P-solubilizers count were recorded in black soil under the influence of the bio-methanated spentwash.

The mineralization of urea fertilizer mostly regulates the nitrogen dynamics in the soil. A laboratory-scale study was conducted to compare the nitrogen dynamics in two tropical soil series incubated with either liquid urea (LU) or granular urea (GU) at 0, 300, 400 or 500 mg/kg of soil. The soils samples used in the experiment were the Bungor and Selangor soil series which have a sandy clay loam and clay texture, respectively. The NH4+-N, NO3−-N concentration in the soils were measured for four weeks to determine the urea-N mineralization while ten pore volumes of water were used for the NH4+-N and NO3−-N leaching loss. At the same application rate, higher NH4+-N and NO3−-N concentrations were recorded in the LU applied soils throughout the incubation period in case of N mineralization. Urea-N recovery was higher in GU than LU treated soils in the first two weeks while no urea-N was present in both GU and LU treated soils after the third week of incubation. The leaching of N (NH4+-N and NO3−-N) was higher in GU treated soils than that of LU and leaching was increased with increased application rate in both LU and GU in both soils. The NH4+-N and NO3−-N concentrations were higher in the Selangor soil whereas the total N leaching loss was higher in Bungor soil. The results suggest that the LU was a better N fertilizer source than GU for rapid mineralization, quicker N availability and lower N leaching loss.

Biochar modulates mineral nitrogen dynamics in soil and terrestrial ecosystems: A critical review

Field studies on nitrogen dynamics after cultivation of grain legumes Field trials were conducted in order to study the nitrogen dynamics in soil after cultivation of grain legumes and to investigate the possibility of reduction of nitrate leaching due to catch crops or suitable following crops. Accordingly, in 1989/90 soil samples were taken on 12 farms at depths of 0–80 cm in 4 week intervals and analysed for NO3‐N. Furthermore, Brassica napus and Sinapis alba were sown after grain legumes on two farms, and at the experimental station Roggenstein field trials were carried out with different catch crops (Sinapis alba, Raphanus sativus, Lolium multiflorum and Pisum sativum) after grain peas.Considerable amounts of nitrogen (100–150 kg N/ha) in the form of crop residues (straw and grains) were left on the fields cultivated with grain legumes. After harvesting, nitrate content in the soil layer 0–80 cm was on grain legume fields almost twice as high as on fields cultivated with winter wheat. During autumn, the soil nitrate contents increased remarkably. In the soil layer 0–80 cm the maximum values rose to 140 kg N/ha after peas, to 120 kg N/ha after faba beans and only to 65 kg N/ha after winter wheat. The more intensive N‐mineralization after peas compared to faba beans is due to a lower C/N‐ratio of crop residues and an earlier harvest time of 2‐3 weeks of peas.In winter extremely high N‐leaching was measured on fallow land after cultivation of grain legumes. Cultivation of catch crops makes it possible to retain up to 110 kg N/ha in plant material. Raphanus sativus and Sinapis alba are most suitable for this purpose due to their high N‐uptake even when they are sown late. Ploughing up catch crops in autumn results in a fast mineralization of their immobilized nitrogen. This implies the risk of N‐leaching into deeper soil layers during winter, depending on the amount of rainfall and water capacity of the soil. Particularly on soils with low water capacity, early N‐mineralization needs to be prevented by cultivating catch crops which freeze off or survive in winter. Cultivation of Brassica napus (winter form) after grain legumes leads to an extensive uptake of soil nitrate before the beginning of the seepage period, and therefore almost excludes enhanced N‐leaching.

Animal manure often contains antibiotic residues due to the prevalent use of these compounds in animal husbandry. After manure application, these residues could potentially affect soil microorganisms and plant growth, yet their impacts on soil nitrogen (N) dynamics in grasslands remain largely unexplored. We hypothesized that applying manure containing antibiotics would shift soil N dynamics by affecting plant morphology and certain N-cycling microbial guilds such as symbiotic N-fixing bacteria. To test this, we conducted a 64-day greenhouse experiment using field soil and including four plant treatments (no plants, ryegrass monoculture, clover monoculture, and a ryegrass-clover mixture) and three fertilizer treatments (antibiotic-free manure, manure containing oxytetracycline, and manure containing sulfadiazine). We measured nitrous oxide (N2O) emissions, N content in the shoot and root biomass, and antibiotic uptake in plant shoots, and used the δ15N technique to estimate symbiotic N fixation of clover. We also sampled soils at the end of the experiment to measure plant-available N pools (ammonia and nitrate) and the abundance of symbiotic N-fixing bacteria (by nifH gene). Our results showed that antibiotics in manure did not significantly alter soil N2O emissions, soil N pools, or plant aboveground N in any plant community. Both compounds were barely been taken up in plant shoots. However, both antibiotics significantly reduced root biomass in clover monocultures. Despite this root growth inhibition, N fixation (both aboveground and belowground) in clover monoculture was unaffected by both antibiotics. Interestingly, analysis of variance suggested that antibiotics in manure could lead to a higher abundance of nifH gene in soil than that of antibiotic-free manure in clover monoculture. In summary, although overall soil N dynamics were not impacted by antibiotics in manure, root growth inhibition in clover monoculture suggests varying grassland species susceptibilities to antibiotic stress. Our results also suggest that clover may adapt to antibiotic stress by modifying plant-microbe interactions. This study calls for further research on long-term environmental impacts of antibiotic residues in grasslands.

Conservation tillage (CsT) involves management that reduces soil erosion by maintaining crop residue cover on farm fields. Typically, both infiltration and soil organic matter increase over time with CsT practices. We compared the impact of a commonly used CsT practice, strip tillage (ST), to conventional tillage (CT) management on soil nitrogen (N) dynamics and leaching and examined associations to soil N availability and microbial biomass. A winter cover crop was used in both tillage treatments. The study was conducted over a five-year period during rotational cotton (Gossypium hirsutum L.) and peanut (Arachis hypogaea L.) production in the Atlantic Coastal Plain region in Georgia, United States. Fertilizer and poultry litter were applied ahead of the cotton crops. Sets of PVC cylinders were filled with soil from each of six plots, three in ST and three in CT, and maintained in situ in their respective plots for 16 intervals of about 90 days. After retrieval, the soil in each cylinder was analyzed for inorganic N (ammonium and nitrates [NH4+ and NO3−]), total N, total carbon (C), and microbial biomass. Leached NO3−-N was captured on anion exchange resin-filled bags attached to the bottom of each cylinder. After the five-year study period, the ST and CT soil C content increased by 22% and 23%, respectively. Total soil N content increased 27% with ST compared to 22% with CT. Temporal patterns in NO3−-N leaching were not different between CT and ST treatments, and a high amount of NO3−-N leaching was observed after the application of poultry litter. The cumulative amount of NO3−-N leached from soils throughout the five-year study was 141 and 122 kg N ha−1 (126 and 109 lb N ac−1) with CT and ST practices, respectively. Results suggest that leaching from the top 15 cm (6 in) of soil may be an important pathway of N loss from both CT and ST cropping systems in the region. Regardless of tillage, soil microbial biomass N was equal to or higher than the total inorganic N, but still represented a small percentage (up to 9%) of the total soil N. Overall, microbial biomass N was higher in ST compared to CT. Minimizing NO3−-N in the soil from reaching ground and surface waters while increasing crop productivity represents a major challenge. The use of ST in conjunction with winter cover crops may improve plant N availability by more than 27 kg ha−1 y−1 (24 lb ac−1 yr−1) in the sandy landscapes of the southeastern Coastal Plain region through microbial cycling of organic N while reducing subsurface NO3−-N losses.

Soil nitrogen (N) dynamics were studied in a dense, holm oak (Quercus ilex ssp. ilex) stand in the Montseny mountains to determine annual and seasonal patterns of N availability and uptake in an undisturbed Mediterranean forest on acidic soil. Soil mineral N content, net N mineralization (NNM), and net nitrification (NN) were determined by monthly sampling at two soil depths followed by in situ incubation in polyethylene bags. NNM per unit of soil mass was much higher at 0–5 cm than at 5–20 cm (annual means 24 and 2.5 mg N/kg, respectively) but on an area basis NNM was similar at both depths. A total of 80 kg N/ha/yr were mineralized from the first 20 cm of soil. NN amounted to only 9% of the annual NNM (7.5 kg N/ha/yr) and it occurred only in the upper 5 cm. NNM was maximum in June and July, while the NN peaked in May. Despite favourable soil temperature and moisture, NNM was negative in autumn because of microbial immobilization. Seasonal and depth variations of NNM appeared to be controlled more by substrate quality than by organic matter quantity, temperature or moisture. NN was not limited by ammonium availability. Calculated N uptake amounted to 91 kg/ha yr, peaking in June and July. The investigated stand showed a moderately high N availability, but ammonium was the major form of mineral N supply for holm oak.

Interest in biochar stems from its potential agronomic benefits and carbon sequestration ability. Biochar application alters soil nitrogen (N) dynamics. This review establishes emerging trends and gaps in biochar-N research. Biochar adsorption of NO3−, up to 0.6 mg g−1 biochar, occurs at pyrolysis temperatures >600 °C with amounts adsorbed dependent on feedstock and NO3− concentration. Biochar NH4+ adsorption depends on feedstock, but no pyrolysis temperature trend is apparent. Long-term practical effectiveness of inorganic-N adsorption, as a NO3− leaching mitigation option, requires further study. Biochar adsorption of ammonia (NH3) decreases NH3 and NO3− losses during composting and after manure applications, and offers a mechanism for developing slow release fertilisers. Reductions in NH3 loss vary with N source and biochar characteristics. Manure derived biochars have a role as N fertilizers. Increasing pyrolysis temperatures, during biochar manufacture from manures and biosolids, results in biochars with decreasing hydrolysable organic N and increasing aromatic and heterocyclic structures. The short- and long-term implications of biochar on N immobilisation and mineralization are specific to individual soil-biochar combinations and further systematic studies are required to predict agronomic and N cycling responses. Most nitrous oxide (N2O) studies measuring nitrous oxide (N2O) were short-term in nature and found emission reductions, but long-term studies are lacking, as is mechanistic understanding of reductions. Stable N isotopes have a role in elucidating biochar-N-soil dynamics. There remains a dearth of information regarding effects of biochar and soil biota on N cycling. Biochar has potential within agroecosystems to be an N input, and a mitigation agent for environmentally detrimental N losses. Future research needs to systematically understand biochar-N interactions over the long term.

The conversion of natural forests to plantations affects soil carbon (C) and nitrogen (N) dynamics. However, the underlying microbial mechanisms of C and N dynamics caused by forest conversion, particularly the functional role of ectomycorrhizal (ECM) fungi, remain largely unknown. Here, we investigated the soil and root-associated fungal communities, soil and ECM root enzyme activities, and C and N mineralization rates in natural forests and plantations in the western Sichuan subalpine coniferous forest. Soil fungal and root ECM fungal communities were determined by high-throughput and Sanger sequencing, respectively. ECM root surface enzymes were used to assess fungal function, while soil enzymes, C and N mineralization, were used to evaluate soil function.Our results showed that clearing natural forests and converting them to plantations led to lower soil organic carbon (SOC), total nitrogen (TN), and pH, which drove changes in ECM and saprophytic (SAP) fungal communities. After forest conversion, the main difference in the fungal community was an increase in the ratio of ECM to SAP fungi. The most apparent change in the soil ECM fungal community is the shift of the dominant genera from Russula to Cortinarius and Piloderma. Subsequently, the function of the ECM fungal community was altered. The results indicated that the conversion of the natural forest to the plantation reduced ECM community β-glucosidase (βG), β-glucuronidase (βLU), N-acetyl-β-D-glucosaminidase (NAG), and acid phosphatase (AP) activities, and soil βG, NAG, and leucine aminopeptidase (LAP) activities. Among them, the activities of βG, βLU, and NAG in the ECM fungal community were significantly correlated with the activities of βG, βLU, and NAG in soil, respectively. Finally, we show that converting natural forests to plantations significantly increased the ammonification rate while decreasing the nitrification and mineralization rates. The close relationship between the relative abundance and diversity of the ECM fungal community, ECM communities and soil NAG, and N processes indicated that the changes in soil N dynamic after forest conversion were directly related to the changes in the ECM fungal community. Our results provide insight into soil C and N dynamics mechanisms resulting from forest conversion.

We examined microclimatic conditions and soil nitrogen (N) dynamics of different alpine plant community types on the Bogong High Plains in Victoria, Australia. Three community types are predominant in the High Plains region, namely grassland, heathland and woodland and together they form so‐called inverted treelines, with grassland in valley floors below the treeline. Outdoor temperature loggers were deployed in the three vegetation types to establish differences among microclimatic conditions. We incubated soils to determine rates of N production and collected additional soil samples for analysis of soil properties and soluble N. Temperature data showed that only grassland communities experienced sub‐zero temperatures in winter. Temperature and soil moisture influenced indices of N mineralization and N nitrification in this alpine ecosystem. Rates of N mineralization were significantly faster than nitrification that only produced consequential amounts of nitrate in summer. This information, together with considerably lower pools of nitrate than ammonium and organic N in the soil, implies that ammonium is the dominant form of soluble N in the ecosystem whereas nitrate most likely only has minor importance for plant nutrition. The results of this study provide insight into ecological processes of this alpine ecosystem and demonstrate the vulnerability of the system to altered climatic and edaphic conditions in the course of climate change.