Water Extractable Organic Nitrogen Research Articles

Molecular transformation of organic nitrogen in Antarctic penguin guano-affected soil

Organic nitrogen (ON) is an important participant in the Earth’s N cycle. Previous studies have shown that penguin feces add an abundance of nutrients including N to the soil, significantly changing the eco-environment in ice-free areas in Antarctica. To explore the molecular transformation of ON in penguin guano-affected soil, we collected guano-free weathered soil, modern guano-affected soil from penguin colonies, ancient guano-affected soil from abandoned penguin colonies, and penguin feces from the Ross Sea region, Antarctica, and Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) was used to investigate the chemical composition of water-extractable ON. By comparing the molecular compositions of ON among different samples, we found that the number of ON compounds (>4,000) in weathered soil is minimal, while carboxylic-rich alicyclic-like molecules (CRAM-like) are dominant. Penguin feces adds ON into the soil with > 10,000 CHON, CHONS and CHN compounds, including CRAM-like, lipid-like, aliphatic/ peptide-like molecules and amines in the guano-affected soil. After the input of penguin feces, macromolecules continue to degrade, and other ON compounds tend to be oxidized into relatively stable CRAM-like molecules, this is an important transformation process of ON in guano-affected soils. We conclude the roles of various forms of ON in the N cycle are complex and diverse. Combined with previous studies, ON eventually turns into inorganic N and is lost from the soil. The lost N ultimately returns to the ocean and the food web, thus completing the N cycle. Our study preliminarily reveals the molecular transformation of ON in penguin guano-affected soil and is important for understanding the N cycle in Antarctica.

An exploration of manure derived N in soils using 15N after the application of biochar, straw and a mix of both

It is common practice to apply manure onto soil as an effective way to increase soil fertility. However, the impact of different carbon sources on the transformation and fate of manure derived nitrogen (N) remains poorly understood. This study investigated the mineralization and immobilization turnover (MIT) of various manure-N fractions using sequential extractions and 15N tracing techniques combined after soil amendment with biochar, straw and mixtures thereof. Soil N was fractionated into mineral nitrogen (NH4+ and NO3−), microbial biomass nitrogen (MBN), hot water extractable organic nitrogen (HWDON), hydrochloric acid extractable organic nitrogen (HCl–N), and residual nitrogen (RN). Results showed that biochar addition increased the 15NH4+ content by 45% during the early stage. However, the high pH and labile C absence of biochar inhibited the remineralization of microbial immobilization N during the mid–to–late stage. Straw addition enhanced 15NH4+ assimilation by 10% to form HCl–15N. After that, microbial cellular structures and secondary metabolites were remineralized to meet crop N requirements. Adding carbon source mixtures with the organic fertilizer manifested the relationship between biochar and straw. The labile C content of the carbon sources rather than the C/N ratio was the critical factor regulating the N-MIT process. Overall, these findings offer new insights into the N transformation approaches using the co-application technique of organic amendments.

Influence of selected maize cultivation technologies on changes in the labile fraction of soil organic matter sandy-loam cambisol soil structure

Disc cultivators are a commonly used method in soil processing when growing maize in Central Europe. However, the slope of the land leads to soil losses through water erosion. Therefore, conservation technologies for soil treatment—strip-till and no-till—are recommended. The aim of this research was to assess these technologies in terms of the labile fractions of soil organic matter and the structural state of the soil. Another goal of the work was to find the most sensitive indicators of change in the labile fractions of soil organic matter, which would indicate changes even over a relatively short-term experiment (three years). The experiment was conducted in Central Bohemia, Czech Republic on plots of sandy-loam cambisol. Changes in soil structure and carbon and nitrogen content in various soil fractions were monitored. The obtained results of two soil conservation technologies (strip-till, no-till) were compared with the results for a commonly used technology (disc cultivation). The strip-till technology led to the highest accumulation of a very labile fraction of organic soil matter and the most sensitive indicator of change was the content of water-extractable organic carbon. The no-till technology protected the soil organic matter from decomposition by physical protection in soil aggregates. Most of the soil organic matter remained un-decomposed. Sensitive indicators of change were the nitrogen content in particulate organic soil matter and the content of water-extractable organic nitrogen. It was found that changes in the labile fraction of soil organic matter can be monitored through suitable indicators during a short-term experiment. Furthermore, we found that no-till technology contributes to the protection of unstable soil organic matter against decomposition, especially through physical protection in soil aggregates. In terms of the content of labile fractions of soil organic matter and their possible effect on the potential soil fertility, it was shown in this short-term experiment that strip-till technology was optimal.

In-depth molecular characterization and biodegradability of water-extractable organic nitrogen in Erhai Lake sediment.

Dissolved organic nitrogen (DON) constitutes a significant fraction of the total dissolved nitrogen content of most aquatic systems and is thus a major nitrogen source for bacteria and phytoplankton. The present work applied Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to a compound-level analysis of the depth-dependent molecular composition of water-extractable organic nitrogen (WEON) in lake sediment. The study focused on Erhai Lake, China. It was found that a large portion (from 16.33 ± 7.87 to 39.54 ± 5.77%) of the WEON in the lake sediment was reactive under cultivation by algal or bacteria. The WEON in the mid-region of Erhai sediment particularly exhibited a lower bioavailability, having been less affected by the basin environment. The FT-ICR MS results revealed the presence of thousands of compounds in the Erhai Lake sediment samples collected at different depths, with the N-containing compounds accounting for 28.3-34.4% of all the compounds. The WEON molecular weight was also observed to increase with increasing sediment depth. A van Krevelen diagram showed that the lignin-type components were dominant (~ 56.2%) in the sediment WEON, contributing to its stabilization and reducing the risk of sediment nutrient release. The FT-ICR MS results further revealed 204 overlapping formulas of WEON for each core sediment sample, attributable to the presence of refractory components. It was observed that 78.4% of the formulas were within the lignin-like region, suggesting unique allochthonous DON sources. The aliphatic component proportion of all the unique formulas was also found to increase with increasing sediment depth. This indicates that, with the development and evolution of the Erhai Basin, the more labile WEON components were transformed into more stable lignin-like substrates, with a positive effect on the Lake Erhai ecosystem. Graphical abstract ᅟ.

Characteristics of Water Extractable Organic Nitrogen from Erhai Lake Sediment and Its Differences with Other Sources

The 47 samples from Erhai Lake surface sediments were collected in different seasons. The distribution and structure characteristics of sediment water extractable organic nitrogen(WEON) were investigated by using the combined techniques of UV-Vis absorption and three-dimensional excitation-emission matrix spectra(3DEEMs). The differences in DON of various sources(overlying water, pore water, inflow Rivers and wet deposition) were explored to analyze its effects on sediment. The results showed that:1the temporal distribution followed the pattern of summer > spring > autumn > winter, with the spatial WEON distribution of northern > southern > central. 2 The humic degree of Erhai sediment WEON was relatively high and mostly composed of fulvic acid, which mainly contained UV-like humic-like fluorescence peak A and high-excited tryptophan fluorescence peak B. This indicated that it was mainly affected by terrestrial input and microbial activity. 3 There were two fluorescent components(C1, C2) in the sediments and other sources of Erhai Lake. The component C1 was the endogenous visible ultraviolet peak formed by biodegradation, while the component C2 was the tryptophan peak. The bioavailability of wet deposition samples was comparatively high, greatly impacting Erhai Lake in heavy rainfall. The DON bioavailability in the inflow river was the lowest, which was prone to be accumulated in sediments. 4The DON component C1 and C2 in overlying water had significant negative correlation with Erhai sediment WEON contents(r=-0.79, P<0.01;r=-0.944, P<0.01). This suggested that the overlying water DON components could indirectly reflect the sediment WEON content of Erhai Lake, namely the higher the fluorescence components C1 and C2 in overlying water DON were, the lower the sediment WEON content was.

Molecular characterization of lake sediment WEON by Fourier transform ion cyclotron resonance mass spectrometry and its environmental implications

The compositional properties of water-extractable organic nitrogen (WEON) affect its behavior in lake ecosystems. This work is the first comprehensive study using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) for the characterization of the molecular composition of WEON in lake sediment. In sediments of Erhai Lake in China, this study found complex WEON species, with N-containing compounds in the northern, central, and southern regions contributing 34.47%, 42.44%, and 40.6%, respectively, of total compounds. Additionally, a van Krevelen diagram revealed that lignin components were dominant in sediment WEON structures (68% of the total), suggesting terrestrial sources. Furthermore, this study applied ESI-FT-ICR-MS to the examination of the environmental processes of lake sediment WEON on a molecular level. The results indicated that sediment depth impacted WEON composition and geochemical processes. Compared with other ecosystems, the double bond equivalent (DBE) value was apparently lower in Erhai sediment, indicating the presence of relatively fewer and smaller aromatic compounds. In addition, the presence of a large number of N-containing species and abundant oxidized nitrogen functional compounds that were likely to biodegrade may have further increased the potential releasing risk of WEON from Erhai sediment under certain environmental conditions.

Using multiple combined analytical techniques to characterize water extractable organic nitrogen from Lake Erhai sediment

In this study, UV–vis absorbance, fluorescence, and FT-IR spectroscopy were combined to characterize the components and structure of the water extractable organic nitrogen (WEON) in Lake Erhai sediment. Lake Erhai sediment WEON comprised predominantly high molecular weight WEON, with the fraction with a molecular weight>1kDa accounting for 87.7% of the total. It was mainly composed of humic acid-like substances, with fewer simple aromatic proteins. Large amounts of aliphatic and amide compounds were detected by IR in the sediments. There were more polymerizable aromatic rings and carbonyl, carboxyl, hydroxyl, and ester compounds in the high molecular weight WEON than in the low molecular weight WEON. Additionally, fluorescence regional integration results implied that the ratio PIII+V,n/PI+II+IV,n can be indirectly taken as an indicator for WEON content in Erhai sediments. Furthermore, the composition and structural characteristics of the WEON were found to be closely related with their properties in the sediment. The large amount of aliphatic compounds in the sediment as well as the relatively high humification and aromatic degree in high molecular weight WEON, stabilizes the WEON in Lake Erhai sediment. Compared with other lake sediments of different trophic statues (such as Lake Dianchi, Lake Poyang, Lake Taihu and Lake Donghu), Erhai sediment exhibited a higher degree of humification, which benefited for reducing sediment WEON releasing risk. And it can be regarded as the reason why the nutrient content in Erhai sediment is very high, but its water quality is still good.

Nitrogen Management in Organic Processing Tomato Production: Nitrogen Sufficiency Prediction Through Early-season Soil and Plant Monitoring

Organic processing tomato (Solanum lycopersicum L.) production is a significant industry in California, yet little nitrogen (N) fertility research is available to guide N management. A total of 37 certified organic processing tomato fields in the Sacramento Valley of California were monitored during the 2012 and 2013 production seasons, with two objectives: 1) to document current N management practices and 2) to investigate the utility of early-season soil and plant N monitoring techniques in predicting seasonal crop N sufficiency. Between ≈3 and 11 weeks after transplanting (WAT) soil mineral N (SMN), leaf N and petiole NO3-N were determined every other week. In 22 fields, whole plant N concentration at ≈11 WAT was determined as a measure of crop N sufficiency. Growers were surveyed regarding N management practices used and fruit yields achieved. Net N mineralization (Nmin) was measured for 20 fields soils by aerobic laboratory incubation. Carbon mineralization (Cmin) in 24 hours following rewetting of air-dried soil and water extractable organic nitrogen (WEON) and carbon (WEOC) were also determined and evaluated as predictors of Nmin. Nitrogen management was primarily based on the application of manure or manure compost in the fall. Organic fertilizers were applied mainly in spring (pre- and post-transplanting). SMN in the top 60 cm at 3 WAT ranged from 6 to 32 mg·kg−1. About 30% of fields were N deficient by 11 WAT. Sensitivity analysis showed that SMN (whether measured from 0 to 30 or 0 to 60 cm) and leaf N at 5 WAT correctly predicted late-season plant N status in &gt;60% of the fields. Nmin in 28 days ranged from 8 to 31 mg·kg−1, representing an average of 2% of total soil N. Correlation between Nmin and Cmin was weak (r = 0.44, P = 0.051) while stronger correlations were observed between Nmin and WEOC, WEON and total soil N (r = 0.63, 0.61 and 0.51, respectively, all P &lt; 0.03). A multiple linear regression model that used 3 WAT SMN (0–30 cm) and WEON as independent variables improved Nmin prediction (adj. R2 = 0.67). Significant fruit yield increase with sidedress N application of feather meal at 5–6 WAT was observed in 2 of 4 field trials, demonstrating the ability to remedy a soil N limitation identified by early-season N monitoring.

Effects of Crop Rotation and Management System on Water‐Extractable Organic Matter Concentration, Structure, and Bioavailability in a Chernozemic Agricultural Soil

Water-extractable organic matter (WEOM) in soil affects contaminant mobility and toxicity, heterotrophic production, and nutrient cycling in terrestrial and aquatic ecosystems. This study focuses on the influences of land use history and agricultural management practices on the water extractability of organic matter and nutrients from soils. Water-extractable organic matter was extracted from soils under different crop rotations (an annual rotation of wheat-pea/bean-wheat-flax or a perennial-based rotation of wheat-alfalfa-alfalfa-flax) and management systems (organic or conventional) and examined for its concentration, composition, and biodegradability. The results show that crop rotations including perennial legumes increased the concentration of water-extractable organic carbon (WEOC) and water-extractable organic nitrogen (WEON) and the biodegradability of WEOC in soil but depleted the quantity of water-extractable organic phosphorus (WEOP) and water-extractable reactive phosphorus. The 30-d incubation experiments showed that bioavailable WEOC varied from 12.5% in annual systems to 22% for perennial systems. The value of bioavailable WEOC was found to positively correlate with WEON concentrations and to negatively correlate with C:N ratio and the specific ultraviolet absorbance of WEOM. No significant treatment effect was present with the conventional and organic management practices, which suggested that WEOM, as the relatively labile pool in soil organic matter, is more responsive to the change in crop rotation than to mineral fertilizer application. Our results indicated that agricultural landscapes with contrasting crop rotations are likely to differentially affect rates of microbial cycling of organic matter leached to soil waters.

The dynamics of water extractable organic matter (WEOM) in common arable topsoils: I. Quantity, quality and function over a three year period

Compared to total soil organic matter (SOM) the concentrations of water extractable organic matter (WEOM) are very small. Nevertheless, it is linked to many important soil functions. Numerous factors affect WEOM dynamics, most of them interacting in the same or in different directions. Therefore, there are still marked gaps in knowledge about WEOM. The majority of field studies have been done in forest ecosystems, and results on arable soils are scarce, contradictory and often do not fit to laboratory studies. Our purpose was to elucidate WEOM parameters in arable soils. We followed the dynamics of WEOM in arable top soils located on three different research sites in Germany. We sampled nine soils differing in soil type, texture, and soil management. Samplings over three years were done in three depths (0–10, 10–20, 20–30 cm) three times a year (spring, summer, and fall). WEOM concentrations were quantified as WEOC after batch extraction. Quality was derived by optical methods (UV absorption, fluorescence spectroscopy). Additionally, WEON (water extractable organic nitrogen) and the biodegradable fraction (BWEOC) were quantified. Results are presented in three parts. For this first part we compared the differences in WEOM dynamics between three selected soils (Eutric Cambisol, Eutric Luvisol, and Haplic Chernozem) and the temporal variability of WEOM in each soil (seasonality). Concentrations averaged over three years and for 0–30 cm showed no significant differences. WEOC and WEON ranged between 34–42 mg WEOC kg − 1 d.m. and 1.9–2.9 mg WEON kg − 1 d.m. The lack of significant differences was explained by the marked seasonality on all sites. The Eutric Cambisol was characterized by a sharp decrease of WEOC/WEON concentrations with increasing depth (60.6 to 20.6 mg WEON kg − 1 d.m. (dry mass), 1.7 to 0.48 mg WEON kg − 1 d.m.) after more than 10 years under no-till management. SOM and total N also decreased from 12.9 g kg − 1 C (0–10 cm) to 2.8 g kg − 1 C (20–30 cm) and from 1.4 g kg − 1 N to 0.43 g kg − 1 . Highest SOM and total nitrogen contents of the Chernozem did not lead to highest WEOC and WEON concentrations. In contrast to quantity, the quality of WEOM differed temporally significantly between all soils, with the highest absorptivity in the Luvisol and highest humification in the Chernozem. Differences in BWEOC were small, ranging between 42 and 46%. All soils were characterized by a marked seasonality. Variability of concentrations was more pronounced than that in quality. ANOVA gave indications that the quality was mainly influenced by the factor “site and/or soil” and the concentrations by the factor “seasonality”. WEOM dynamics did not show uniform patterns when the same field crop was planted on different sites. A test for the suitability of spectral absorptivity measurements as predictor for biodegradability, as it is often mentioned in literature, gave weak results. While in the Cambisol ( r = − 0.61, r 2 = 37%) and Chernozem ( r = − 0.70, r 2 = 49%) negative correlations were found, no relation between BWEOC and absorptivity was detected in the Luvisol. Due to the marked dynamics of WEOM in arable soils general statements can hardly be concluded, even when results are based on iterated samplings.