Mineralization Of Organic Nitrogen Research Articles

Application of stabilized sludge to extensive green roofs in Shanghai: Feasibility and nitrogen leaching control

Extensive green roofs, in which commercial compost is usually used as organic component, have great potential to mitigate some environmental problems caused by urbanization, but carry risks of nutrients leaching into downstream aquatic. Stabilized sludge (SS) from wastewater treatment plants could be potentially used as nutrient component for green roof, but the effects on effluent quality are uncertain. To investigate the problem, a pilot experiment was conducted under field conditions, the effluent quality of green roof using SS was compared with green roofs using peat soil and controlled release fertilizer. In the field experiment, the nutrient concentrations in effluent of the green roof using SS (TN, NO3−-N, NH4+-N and TP were 3.27 mg/L, 1.75 mg/L, 1.14 mg/L and 0.34 mg/L, respectively) were not significantly different from the green roofs using peat soil and controlled release fertilizer, and the chemical oxygen demand level (92 mg/L) was lower than the roofs using compost or commercial substrate. To reduce the environmental risks caused by the application of SS to green roofs, a laboratory test was carried out to analyze the effects of biochar and dual-substrate structure on nitrogen leaching. The results showed that both biochar and dual-substrate reduced nitrogen leaching, and nitrogen leaching from green roofs using SS was a combined effect of organic nitrogen mineralization during dry period and biological processes during wet period. A high temperature and low humidity environment which is common in green roofs reduced nitrate accumulation during dry period, and nitrate was transformed to other substances in gaseous form by denitrification, which tended to occur in long duration, low intensity rainfall events. The results suggest that the application of stabilized sludge to green roofs is feasible in area where average rain intensity is not high, preferably combined with amendment of biochar and a dual-substrate structure.

Suppression of amino acid and oligopeptide mineralization by organic manure addition in a semiarid environment

AbstractThe rapid mineralization of organic nitrogen (ON) in semiarid soils frequently results in large N losses, reduced crop yields, and environmental pollution. The addition of manures to soil has the potential to promote microbial growth, increase N immobilization, reverse the decline in soil organic matter, and enhance soil quality. In this study, three contrasting organic manures were used to determine their influences on amino acid and oligopeptide dynamics in soil (as key component of the soil ON‐cycle) as well their effects on the size of the microbial biomass and N immobilization. Laboratory incubation experiments were set up with soil obtained from experimental field trial sites for growing maize. Treatments included soil amended with either poultry manure (PM), farmyard manure, pressmud, or unamended (control). Radio‐ and stable‐isotope (14C–15N) techniques were used to assess ON mineralization, immobilization, and leaching using the amino acids alanine and valine as well as the oligopeptides trialanine and valine–proline–proline as model substrates. Quantitative polymerase chain reaction was used to determine soil bacterial biomass. The results showed that all manures increased microbial growth and total soil amino acids as well as protein content. Greater immobilization and subsequently lower mineralization and leaching were also observed in the manure‐amended soils, with this being most pronounced in the PM treatment. The application of PM also enhanced the half‐lives of the ON compounds in soil and increased the size of the bacterial biomass. Overall, our findings indicate that manure amendments, particularly PM, can help promote more efficient ON cycling in semi‐arid ecosystem by controlling N mineralization, reducing amino acid leaching, and elevating oligopeptide immobilization.

Ammonia and Ammonium Exposure of Basil (Ocimum basilicum L.) Growing in an Organically Fertilized Peat Substrate and Strategies to Mitigate Related Harmful Impacts on Plant Growth.

Organic pot-based production of basil (Ocimum basilicum L.) often has lower biomass yield than conventional cultivation. Previous investigations indicate that this growth impairment is related to high ammonium (NH4 +) concentrations in the growing media released by the mineralization of organic nitrogen (N) fertilizers. However, as a result of this ammonification process substrate pH may also increase. Under neutral to alkaline conditions NH4 + is converted to ammonia (NH3), which is known to be phytotoxic even at low concentrations. Therefore, we investigated the impact of both ammonical N species on basil grown in a peat substrate. In total, three fertilization pot experiments were conducted in a greenhouse in order to compare the effect of different organic base dressings [250 and 750 mg N (L substrate)-1 mainly supplied by a liquid amino acid fertilizer (AAF)] and two initial substrate pH levels (5.5 and 6.5). In two treatments, 5% (v/v) mature compost was mixed into the peat 1 day and 12–days before the substrate was used for sowing, respectively. The aim of this procedure was to stimulate nitrification in this way to reduce ammonical N concentration. Ammonia concentration in the aerial plant surrounding environment was measured by using NH3 detector tubes in combination with an open-top chamber method. The results showed that the growth of basil (number of plants, fresh matter yield, plant height) was significantly inhibited in the second and third week of cultivation by rising NH3 and NH4 + exposure, as well as by a substrate pH ≥ 7.0. These adverse effects were reduced by lowering the organic base dressing rate and adjusting the initial substrate pH to 5.5. Furthermore, the addition of mature compost to peat in combination with a 12-day storage was proven to be effective for promoting nitrification in the organically fertilized substrate. As a result, plant growth was improved by both lower NH3 and NH4 + exposure as well as a faster supply of nitrate (NO3 -) as an additional N source. Using this approach, it was possible to feed organically fertilized basil right from the seedling stage with a NO3 --N/NH4 +-N-balanced and later on providing a predominant NO3 --N supply.

Effect of conservation farming and biochar addition on soil organic carbonquality, nitrogenmineralization, and crop productivity in a light textured Acrisol in the sub-humid tropics.

Conservation farming (CF), involving basin tillage, residue retention and crop rotation, combined with biochar may help to mitigate negative impacts of conventional agriculture. In this study, the effects of CF on the amount and quality of soil organic matter (SOM) and potential nitrogen (N) mineralization were investigated in a maize-soya-maize rotation in an Acrisol in Zambia. A large field was run under CF for 7 years and in the subsequent three growing seasons (2015-2018), four management practices were introduced to study effects on soil characteristics and crop yield. We tested i) a continuation of regular CF (CF-NORM) ii) CF without residue retention (CF-NO-RES); iii) Conventional (CONV), with full tillage and removal of residues; and iv) CF with 4 ton ha-1 pigeon pea biochar inside basins and residue retention (CF-BC). The experiment involved the addition of fertilizer only to maize, while soya received none. Soya yield was significantly higher in CF systems than in CONV. Maize yields were not affected by the different management practices probably due to the ample fertilizer addition. CF-NORM had a higher stock of soil organic carbon (SOC), higher N mineralization rates, more hot-water extractable carbon (HWEC; labile SOC) and particulate organic matter (POM) inside basins compared to the surrounding soil (outside basins). Our results suggest that the input of roots inside basins are more effective increasing SOM and N mineralization, than the crop residues that are placed outside basins. CONV reduced both quality and quantity of SOM and N mineralization as compared to CF inside basins. CF-BC increased the amount of SOC as compared with CF-NORM, whereas N mineralization rate and HWEC remained unaffected. The results suggest benefits on yield of CF and none of biochar; larger impact of root biomass on the build-up of SOM than crop residues; and high stability of biochar in soil.

Distributions and origins of nitrate, nitrite, and ammonium in various aquifers in an urbanized coastal area, south China

High nitrogen loading in aquifers is an important issue because of its harmful effects on human health; its origins are often complicated, especially in urbanized areas. This study aims to investigate the distributions of nitrate, nitrite, and ammonium in various aquifers in the Pearl River Delta, and to identify their main sources using hydrochemical and socioeconomic data and principal component analysis. The results show that groundwater with high nitrate (>20 mg/L as N), high nitrite (>1 mg/L as N), and high ammonium (>0.5 mg/L as N) appeared in 7.0%, 4.3%, and 20.5% of granular aquifers, and in 8.3%, 0.8%, and 5.3% of fissured aquifers, respectively, but did not appear in karst aquifers. The proportions of high-nitrate and high-ammonium groundwater in urbanized areas were nearly or more than twice those in non-urbanized areas. High nitrate levels in both granular and fissured aquifers originated mainly from the wastewater leakage of township-village enterprises during the industrialization. Urbanization accompanied by leakage of domestic sewage was another main driving force for high nitrate levels in fissured aquifers. Housing construction aggravated groundwater nitrate contamination in newly urbanized areas. Nitrate contamination in granular aquifers was reduced via denitrification in urbanized areas developed in 1988–1998, whereas that in fissured aquifers was increased by nitrification in urbanized areas developed before 1998. High ammonium levels in granular aquifers in urbanized areas originated mainly from mineralization of organic nitrogen in overlying aquitards, whereas that in peri-urban areas and non-urbanized areas originated mainly from urbanization accompanied by leakage of domestic sewage and irrigation using ammonium-rich river water, respectively. By contrast, high ammonium levels in fissured aquifers are attributed mainly to mineralization of organic nitrogen in carbon-rich strata, which was enhanced by urbanization accompanied by a relatively anoxic environment. Our study implies that nitrate and ammonium contaminations in this area will worsen in the future owing to a lack of effective control and treatment in these rapidly urbanized areas. Naturally originating high-ammonium groundwater in this area can be used as a nitrogen resource, for example, as a nitrogen fertilizer in agricultural irrigation.

Effects of algal-detritus accumulation on the mineralization characteristics of lake sediment

蓝藻水华暴发形成的大量有机碎屑，沉降到沉积物表面，影响沉积物有机质矿化，进而影响碳氮磷循环.本实验选择于桥水库湖心区作为沉积物采样点，通过设置不同密度藻屑添加组（×1倍组和×20倍组）及空白对照组，研究藻屑堆积对沉积物矿化特征的影响及其环境效应，为蓝藻水华影响下的饮用水环境修复和科学管理提供一定的理论依据.结果表明：（1）藻屑添加降低了上覆水pH值，改变了沉积物生物酶活性.藻屑添加密度越大，上覆水pH值越低、波动越大，反映了培养过程异养微生物活性的变化.×1倍组的转化酶活性较高；×20倍组蛋白酶活性和碱性磷酸酶活性较高.（2）藻屑添加对沉积物的矿化途径和沉积物产物的释放速率产生了显著影响.藻屑添加密度越大，有机质矿化速率越大.其中，×1倍组主要增强好氧矿化，释放CO₂；×20倍组主要增强厌氧产甲烷矿化，释放CH₄.（3）不同密度的藻屑添加组，其氮磷扩散、释放通量存在明显差别.×1倍组以沉积物吸附为主，其上覆水NH₄⁺和PO₄^3-平均释放速率与对照组差异较小；×20倍组的NH₄⁺在第0~10天以沉积物吸附为主，之后和PO₄^3-均以向上覆水中释放为主，其NH₄⁺和PO₄^3-平均释放速率（分别为0.223）和0.075 mg/（L·d））明显大于其他实验组.因此，大量蓝藻堆积明显促进沉积物的碳氮磷矿化，释放大量CO₂、CH₄和氮磷营养盐至上覆水中，对湖泊水环境造成污染，为蓝藻的生长繁殖作贡献.;A large amount of organic algal-detritus after cyanobacterial bloom settled on the surface of the sediment, which has an effect on the mineralization characteristic of sedimentary organic matter, and then the biogeochemical cycle of carbon, nitrogen, and phosphorus. In this study, the central area of Yuqiao Reservoir was selected as the sediment sampling point. By the addition treatments of different densities of algal-detritus (×1 and×20 treatments) and blank controls, the effects of algal-detritus accumulation on the mineralization and their environmental effects were studied to provide some theoretical basis for drinking water environmental restoration and scientific management under the influence of cyanobacteria bloom. The results showed that the addition of algal-detritus lowered the pH value of overlying water and changed the activity of biological enzymes in the sediments. The higher the density of algal-detritus, the lower the pH value of the overlying water and the greater the fluctuation were. The×1 treatment had higher invertase activity, meanwhile the×20 treatment had higher protease activity and alkaline phosphatase activity. Secondly, the addition of algal-detritus had a significant effect on sedimentary mineralization pathways and release rates of mineralization products. The higher the density of algal-detritus, the greater the mineralization rate of sedimentary organic matter was. Moreover, the×1 treatment mainly enhanced aerobic mineralization with the increasing release of CO₂; the×20 treatment mainly enhanced anaerobic methanogens mineralization with the increasing release of CH₄. Thirdly, the diffusion and release fluxes of nitrogen and phosphorus were significantly different in algal-detritus addition treatments with different densities. Sediment adsorption was dominated in the×1 treatment, in which the average release rates of NH₄⁺ and PO₄^3- in overlying water differed slightly from the blank controls. In the×20 treatment, the flux of NH₄⁺ showed the tendency of sediment adsorption in the initial ten days and transferred to releasing potential in the remained time, while the releasing flux of PO₄^3- to overlying water was existed during the whole incubation period. The average release rates of NH₄⁺ and PO₄^3- in the×20 treatment (0.223 mg/(L·d) and 0.075 mg/(L·d), respectively) were significantly higher than those of the other treatments. In general, the accumulation of high density of algal-detritus promotes the mineralization of organic carbon, nitrogen, and phosphorus, releasing a large amount of CO₂, CH₄, and nutrients to the overlying water, which decreases water quality and contributes to the growth and reproduction of cyanobacteria.

NRT1.1s in plants: functions beyond nitrate transport.

Arabidopsis AtNRT1.1 (CHL1/AtNPF6.3) is the first nitrate transporter identified in plants and was initially found to play a role in nitrate uptake and transport. AtNRT1.1 also displays auxin transport activity and mediates nitrate-modulated root development, suggesting that it has transport capacity for multiple substrates. Subsequent work revealed that AtNRT1.1 can respond to environmental nitrate fluctuations by altering its nitrate transport activity, modulated by phosphorylation, leading to the critical finding that AtNRT1.1 acts as a transceptor for nitrate sensing. Recent studies have revealed how OsNRT1.1B, the functional homologue of AtNRT1.1 in rice, mediates nitrate signal transduction from the plasma membrane to the nucleus, and how OsNRT1.1B integrates the nitrate and phosphate signaling networks. OsNRT1.1B has also been shown to be involved in regulating the root microbiota to facilitate organic nitrogen mineralization in soil, thus mediating plant–microbe interactions. Furthermore, the divergent functions of OsNRT1.1A and OsNRT1.1B in regulating nitrogen use in rice suggest that the function of NRT1.1 is still far from fully understood. In this review, we focus on the most recent progress on the molecular mechanisms of NRT1.1s in plants, with the aim of providing an up-to-date view of the versatile functions of NRT1.1 in nitrogen utilization in plants.

Improving Nitrogen Availability on a Tropical Peat Soil Cultivated with Ananas comosus L. Merr. Using Pineapple Residue Ash

The objectives of this study were to use pineapple residue ash to (i) reduce ammonium and nitrate leaching and (ii) improve essential nutrient availability on a tropical peat soil under pineapple cultivation. Laboratory leaching experiments were carried out to determine the effectiveness of pineapple residue ash in controlling nitrogen loss from a tropical peat soil. Ion exchange resin method was used to determine nitrogen availability. Treatments evaluated were (i) different amounts of pineapple residue ash (25, 50, 70, and 100%) + NPK fertilizer, (ii) NPK fertilizer, and (iii) peat soil alone. Peat soils with pineapple residue ash reduced ammonium and nitrate losses because of adsorption of ammonium and nitrate by hydroxyl and C–O radicals of the pineapple residue ash. There was an improvement in ammonium and nitrate availability because the pineapple residue ash was able to increase the peat soil pH and this facilitated organic nitrogen mineralization and nitrification. The pineapple residue ash also improved nitrogen uptake, pineapple fresh fruit yield, and fruit quality. Ammonium and nitrate varied with soil depth because of high preferential flow of the peat soil water. Combined use of NPK fertilizers and 25% pineapple residue ash improved nitrogen availability whereas amending NPK with 50%, 70%, and 100% pineapple residue ash were more effective in improving nitrogen uptake, fresh fruit yield, and fruit quality of pineapple. Pineapple residue ash can also have significant liming effect.

고추 재배 밭에서 채취한 토양의 유기물 함량과 질소 무기화 량의 관계

고추 재배 밭에서 채취한 토양의 유기물 함량과 질소 무기화 량의 관계

Long-term modelling of soil N mineralization and N fate using STICS in a 34-year crop rotation experiment

Net soil N mineralization is a driver for N uptake and N losses at an annual scale, but is itself dependent on long-term N surplus and C-N storage in agricultural systems. The accurate modelling of N mineralization remains challenging. Thus, the STICS research version V1610 that includes modified soil organic nitrogen (SON) mineralization and root biomass turnover modules was assessed in this study regarding its predictions of net N mineralization and long-term N fate in a 34-year experiment comparing crop rotations with or without catch crops (CC) and bare soil. The in situ gross balance method was used as a reference to estimate net N mineralization based on measured N variables (i.e. N uptake, exported N and N leaching). The Index of Agreement (IA) of STICS predictions concerning crop biomass, crop yield, N uptake and exported N ranged between 0.61 and 0.76, 0.79–0.89, 0.49–0.64 and 0.47–0.58, respectively, depending on the crop rotations. STICS also enabled a good simulation of annual drainage and N leaching with IA ranges of 0.92–0.96 and 0.78–0.93, but high leaching values were not captured by the model. The STICS research version simulates the decay of deep roots (below a depth of 25 cm) but it neglects their decomposition. This simplification could cause an underestimation of N leaching. The observed N surplus ranged from 27 to 51 kg N ha−1 yr−1 in the cropped rotations depending on the crop rotations, and the N surplus was accurately simulated with an IA of 0.75–0.84. STICS produced a good prediction of changes in SON stocks under cropped rotations and bare soil, with both the rRMSE and rMBE being lower than 10%. Estimated mean annual N mineralization was 115 kg N ha−1 under cropped rotations and 42 kg N ha−1 under the bare soil treatment. STICS relatively well predicted net N mineralization regarding both differences between crop rotations and over time. Moreover, STICS correctly simulated the long-term effects of CC on drainage, N leaching, SON accumulation and net N mineralization. To conclude, STICS is a useful model to predict net N mineralization and N fate in long-term crop rotations. Moreover, this work raised new questions concerning the long-term fate of N stored in deep dead roots. Further improvements to describe the fate of these residues should enhance the prediction of N leaching by the STICS model and enable the optimization of N management in cropping systems.-

Nitrogen Mineralization in Mississippi River Deltaic Plain Freshwater Floating Marshes

ABSTRACTThe mineralization of soil organic nitrogen in two floating marshes types in Louisiana, USA with different vegetation and mat thickness (and biomass) was measured by incubating peat soil in situ in polyethylene bottles at depths of 10 and 25 cm. The size of the extractable inorganic N (NH4+ – N) pool was related to mat thickness and soil bulk density. The N mineralization rates were twice as great at the thick mat site (1.5 mg N/kg soil/day) compared to the thin mat floating marsh (0.71 mg N/kg soil/day). The amount mineralized on a volume basis to 30 cm depth were 22 mg N/m2/day for the thick mat marsh and 6 mg N/m2/day for the thin mat marsh. The nitrogen mineralization rates observed in this study reflect plant biomass differences between the thick mat and thin mat marshes, with the former exhibiting approximately 7-fold greater biomass. These low overall mineralization rates suggest that nitrogen entering these freshwater floating marshes from Mississippi River water percolating through the root zone, would result in increased plant productivity-increasing marsh stability and also providing a natural mechanism contributing to the processing and removal of dissolved inorganic nitrogen in river water entering these wetlands.

Electrochemical advanced oxidation processes using novel electrode materials for mineralization and biodegradability enhancement of nanofiltration concentrate of landfill leachates

The objective of this study was to implement electrochemical advanced oxidation processes (EAOPs) for mineralization and biodegradability enhancement of nanofiltration (NF) concentrate from landfill leachate initially pre-treated in a membrane bioreactor (MBR). Raw carbon felt (CF) or FeIIFeIII layered double hydroxides-modified CF were used for comparing the efficiency of homogeneous and heterogeneous electro-Fenton (EF), respectively. The highest mineralization rate was obtained by heterogeneous EF: 96% removal of dissolved organic carbon (DOC) was achieved after 8 h of electrolysis at circumneutral initial pH (pH0 = 7.9) and at 8.3 mA cm−2. However, the most efficient treatment strategy appeared to be heterogeneous EF at 4.2 mA cm−2 combined with anodic oxidation using Ti4O7 anode (energy consumption = 0.11 kWh g−1 of DOC removed). Respirometric analyses under similar conditions than in the real MBR emphasized the possibility to recirculate the NF retentate towards the MBR after partial mineralization by EAOPs in order to remove the residual biodegradable by-products and improve the global cost effectiveness of the process. Further analyses were also performed in order to better understand the fate of organic and inorganic species during the treatment, including acute toxicity tests (Microtox®), characterization of dissolved organic matter by three-dimensional fluorescence spectroscopy, evolution of inorganic ions (ClO3−, NH4+ and NO3−) and identification/quantification of degradation by-products such as carboxylic acids. The obtained results emphasized the interdependence between the MBR process and EAOPs in a combined treatment strategy. Improving the retention in the MBR of colloidal proteins would improve the effectiveness of EAOPs because such compounds were identified as the most refractory. Enhanced nitrification would be also required in the MBR because of the release of NH4+ from mineralization of refractory organic nitrogen during EAOPs.

Optimization of biomethane production from anaerobic Co-digestion of microalgae and septic tank sludge

The objective of this study was to analyze the effects of the total organic concertation and the proportion of microalgae to optimize biomethane production during anaerobic co-digestion of microalgae and septic tank sludge. To achieve this goal, a statistical tool, central composite design, was applied to design the co-digestion experiments. Using multiple variance analysis, the experimental data were analyzed, and the results were presented by the response surface methodology, which illustrated that peak methane production could be achieved when the total volatile solids concentration was in the range of 16–20 g/L and the proportion of microalgal biomass ranged from 26 to 47%. An inhibitory effect was observed from volatile fatty acids accumulation when the total volatile solids concentration was supplied as high as 35 g/L. Organic nitrogen mineralization took place in all groups, ranging from 23 to 62%. There was no direct evidence showing that produced ammonium ion nitrogen or the free ammonia nitrogen had inhibitive effects on methanogenic activity.

Priming effect of litter mineralization: the role of root exudate depends on its interactions with litter quality and soil condition

Root exudation can prime microbial synthesis of additional exoenzymes and consequently accelerate organic carbon (C) and nitrogen (N) mineralization. Such exudate induced priming effect (EPE) has been hypothesized to depend on exudate rate and stoichiometry. Little is known about how EPE would affect litter decomposition. We employed a microcosm experiment to evaluate the influence of root exudate on litter nutrient release and microbial enzyme functions. Leaf litters of Pinus massoniana, Quercus variabilis and Robinia pseudoacacia were incubated under two soil conditions (fertile versus barren). Solutions of chemicals often found in root exudates with contrasting C:N ratios were inoculated frequently into the microcosms to simulate exudation. By comparing with a water control, exudate effect was determined. In barren soils, exudates with C:N ratio of 10 significantly decelerated C loss of R. pseudoacacia, all N-containing exudates significantly enhanced the N-cycling related enzymes in decomposing Q. variabilis, while C-only exudate accelerated N loss of P. massoniana. In fertile soils, C-only exudate promoted the N-cycling related enzymes in decomposing R. pseudoacacia. A stoichiometric C:N constraint on microbial utilization of exudates arose in decomposing recalcitrant litters in barren soil. EPE and its stoichiometric constraint depend on interactions with litter quality and soil condition. The findings arouse the consequences of exudate rate and stoichiometry changes in determining soil nutrient balance.

Transformation of Nitrogen Compounds in Soils of Mountain Tundra Ecosystems in the Khibiny

The content of nitrogen compounds and processes of nitrogen mineralization and nitrification were studied in the soils of four tundra ecosystems in the Khibiny Mountains. The results obtained demonstrate the differences between soils of heath and meadow ecosystems in the concentrations of extracted inorganic and organic nitrogen and in the activity of nitrogen transformation. The relationships between the activity of organic nitrogen mineralization and the C/N ratio in organic matter, as well as between the activity of mineralization and the amount of microbial biomass in the soils, differ among the soils. At the high C/N ratios, microorganisms assimilate more available nitrogen, which leads to a decrease in the intensity of organic N mineralization. In soils of meadow communities, as compared to the heath ones, the activity of N mineralization responds more rapidly to changes in the microbial biomass, the C/N ratio and proportion of microbial nitrogen in the labile nitrogen pool. The microbial community in the studied soils of the mountain tundra ecosystems substitutes the nitrogen mineralization for nitrogen immobilization at the C/N ratio in organic matter of about 20.5 and the carbon content in the microbial biomass of about 1000 mg/kg.

The earthworm species Pheretima hawayana influences organic wastes decomposition, nitrogen mineralization and maize N recovery

We investigated the influence of the anecic earthworm Pheretima hawayana (Rosa, 1891) on decomposition, nitrogen (N) mineralization and maize apparent N recovery from farmyard manure (M), wheat straw + M (WSM), maize straw + M (MSM), compost (CO), and slurry (SL) applied to a sandy loam soil. Results revealed that inoculation of earthworm in organic waste treatments significantly increased CO2 emission (P = 0.02). The earthworms’ induced CO2 emission was the highest in MSM and the lowest in M treatment. Earthworms did not influence total dry matter yield or N uptake by maize (P > 0.05), however, organic wastes significantly affected these parameters (P < 0.01). Overall, earthworm enhanced apparent crop N recovery from M, CO and SL treatments by 543, 105, and 109%, respectively. Out of the total N applied, about 14, 8, 6, 2, and −11% was recovered in maize plants from M, SL, CO, MSM and WSM, respectively. The lower apparent N recovery in MSM and WSM could be attributed to the higher C:N ratio of these crop residues that may cause N immobilization. This was confirmed from the calculated N balance of WSM treatment, where net immobilization equal to 15% of the organic N was occurred. Despite of higher CO2 emission from WSM and MSM, earthworm could not increase maize N uptake or N recovery from crop straw treatments. Hence, in short interval-cropping systems like maize, earthworms may need an extra available N source to improve crop growth, where crop residues are part of fertilizer management strategy.

English

Biochar incorporation as a soil amendment has been shown to enhance soil quality. However, there has been conflicting reports on its short term effects on C and N mineralization and microbial biomass. An incubation experiment was conducted to determine the effects of three different levels (0.5, 1 and 2%) of biochar on carbon mineralization, soil organic carbon, nitrogen mineralization, microbial biomass and total nitrogen from mollisols of two different organic matter (high organic matter soil and low organic matter soil) levels. The experiment consisted of four treatments (Soil, Soil + 0.5% biochar, Soil + 1% biochar and Soil + 2% biochar) and each was replicated three times. Overall, soil respiration rate was reduced by biochar additions over a 100-day period. Two percent biochar application rate showed greatest CO2-C reduction. Soil respiration in high organic matter soil was higher than low organic matter soil. NO3--N level was reduced by biochar addition in both high and low organic matter soils. Control (Soil) of the high organic matter soil showed the highest NO3--N (33.79 mg kg-1) and NH4+-N (7.23 mg kg-1) values at 70 days. The total nitrogen was increased by biochar additions; 1 and 2% application rates showed the highest total nitrogen values. Biochar additions also increased soil microbial biomass carbon and soil microbial biomass nitrogen of both soils. Key words: Biochar, C mineralization, N mineralization, microbial biomass.

Research Progress on the Sources of Inorganic Nitrogen Pollution in Groundwater and Identification Methods

The identification of the main inorganic nitrogen (MIN, referring to NH4+-N, NO3--N, and NO2--N) pollution sources in groundwater is of great significance to its control and repair. A review of the MIN sources in groundwater and the main identification methods was conducted. The main sources of MIN pollution in groundwater (atmospheric nitrogen deposition, soil natural organic nitrogen mineralization, nitrogen from streams, and nitrogen emission from human activity), and its distribution in China were expounded. The common methods for tracing MIN sources include hydrochemical analysis, statistical estimation, regional nitrogen balance evaluation, stable isotopes tracer, and new types of tracers. Because of the variety of nitrogen sources and the complexity of the MIN pollution formation mechanism, the single identification methods shared limitations in application, whereas more comprehensive ones, especially the stable isotope tracer integrated with other methods, were mainstream. Furthermore, future research prospects, including the development of new types of tracing methods, the optimization of quantification methods, the integration of research on pollution source identification, transformation mechanism, groundwater recharge and discharge condition, and groundwater-surface water conversion, have been put forward.

Water quality modeling of a prairie river-lake system.

Eutrophication of an under-ice river-lake system in Canada has been modeled using the Water Quality Analysis Simulation Program (WASP7). The model was used to assess the potential effect on water quality of increasing inter-basin transfer of water from an upstream reservoir into the Qu'Appelle River system. Although water is currently transferred, the need for increased transfer is a possibility under future water management scenarios to meet water demands in the region. Output from the model indicated that flow augmentation could decrease total ammonia and orthophosphate concentrations especially at Buffalo Pound Lake throughout the year. This is because the water being transferred has lower concentrations of these nutrients than the Qu'Appelle River system, although there is complex interplay between the more dilute chemistry, and the potential to increase loads by increasing flows. A global sensitivity analysis indicated that the model output for the lake component was more sensitive to input parameters than was the model output of the river component. Sensitive parameters included dissolved organic nitrogen mineralization rate, phytoplankton nitrogen to carbon ratio, phosphorus-to-carbon ratio, maximum phytoplankton growth rate, and phytoplankton death rate. Parameter sensitivities on output variables for the lake component were similar for both summer (open water) and winter (ice-covered), whereas those for the river component were different. The complex interplay of water quality, ice behaviors, and hydrodynamics of the chained river-lake system was all coupled in WASP7. Mean absolute error varied from 0.03-0.08 NH4-N/L for ammonium to 0.5 to1.7mg/L for oxygen, and 0.04-0.13 NO3-N/L for nitrate.

Substrate Influences Temperature Sensitivity of Dissolved Organic Carbon (DOC) and Nitrogen (DON) Mineralization in Arid Agricultural Soils

The bioavailability of nitrogen (N) in soil relies on the progressive breakdown of necromass protein to peptide and amino acid components and conversion to inorganic N forms. We understand the fluxes and pathways of the N cycle downstream from amino acids, but our understanding of the factors controlling peptide and amino acid mineralization, particularly in arid soils, is lacking. We investigated the influence of temperature on the rate of dissolved organic carbon (DOC) and nitrogen (DON) cycling in three agricultural soils from Saudi Arabia. Although the physical and chemical properties of the soils differed markedly, phospholipid fatty acid (PLFA) analysis revealed they had similar topsoil and subsoil microbial communities. Soils behaved similarly in terms of the rate of substrate use, microbial C-use efficiency, and response to temperature. Substrate mineralization rate increased with temperature with more C being allocated to microbial catabolic rather than anabolic processes. Our results show that climate change is likely to lead to changes in soil organic matter turnover and shift C allocation patterns within the soil microbial community. This is expected to reduce soil quality and exacerbate nutrient losses. Management strategies are required to promote the retention of organic matter in these soils.