Soil Organic Nitrogen Fractions Research Articles

Effects of Cover Measures on Soil Organic Nitrogen Fractions and Total Soluble Nitrogen Pools in Citrus Orchards of the Red Soil Hilly Region of Southern China

Effects of Cover Measures on Soil Organic Nitrogen Fractions and Total Soluble Nitrogen Pools in Citrus Orchards of the Red Soil Hilly Region of Southern China

Plateau pika bioturbation leads to lower soil organic nitrogen fractions of bare patches in alpine meadows

The small semi–fossorial herbivore bioturbation has been verified to affect available soil nitrogen in grasslands, but the effects of small semi–fossorial herbivore bioturbation on soil organic nitrogen (SON) fractions that are main compositions of soil total nitrogen and sources of soil available nitrogen remain poorly known. The plateau pika (Ochotona curzoniae) bioturbation creates numerous bare patches, which intersperse within vegetated surfaces in grasslands. In this study, plateau pika was considered as an example animal to examine the differences of SON fractions between bare patches and vegetated surfaces under the small semi–fossorial herbivore bioturbation across six sites. This study demonstrated that acid–hydrolysable nitrogen (AHN) was 27.58% lower in bare patches than in vegetated surfaces. Amino acid nitrogen (AAN), ammonium nitrogen (AN), amino sugar nitrogen (ASN) and unknown nitrogen (UN) in bare patches were 35.23%, 17.07%, 17.70% and 19.87% lower than those in vegetated surfaces, respectively. The contribution of AAN to AHN was 5.3% lower in bare patches than in vegetated surfaces, but the contributions of AN, ASN and UN to AHN were 2.42%, 1.11%, and 1.77% higher, respectively. The response of AAN to plateau pika bioturbation was more sensitive than AN, ASN and UN. These findings verify the plateau pika bioturbation leads to a lower potential capacity of soil nitrogen supply in bare patches than in vegetated surfaces, and present a possible pattern of SON fractions in relation to small semi–fossorial herbivore bioturbation in grasslands.

Response of bacterial communities, enzyme activities and dynamic changes of soil organic nitrogen fractions to six-year different application levels of biochar retention in Northeast China

Composition and availability of soil organic nitrogen play a key role in soil N retention and supply. The application of traditional chemical fertilizers can improve soil production and crop yields. However, it also leads to low N utilization efficiency and soil solidification. Previous studies have shown that fertilizers added with biochar can improve soil fertility and facilitate soil nutrient transformation by regulating soil biological indicators. However, whether biochar used with fertilizers can promote nutrient cycling in the long term, which remains to be tested. Therefore, this study aims to explore the long-term effects of biochar with different levels used with fertilizers on soil fertility, N supply potential of organic N, and microbial communities, thus, providing a theoretical reference for the rational management of biochar applications. In this study, a field experiment was carried out from 2013 to 2018 assess dynamic changes in organic N fractions and diversity and richness of microbial communities under the impacts of chemical fertilizers combined with different levels of biochar. Biochar with no amendment (CK), biochar with 15.75 t ha−1 (BC1), biochar with 31.5 t ha−1 (BC2), and biochar with 47.25 t ha−1 (BC3) are four biochar levels that were tested in this study. The results show that compared with CK, those other three biochar levels can increase soil organic matter, C/N, and pH values. Acid-hydrolysable N (AHN) makes a major contribution to organic N in soil. Biochar retention for six years has significantly affected AHN levels, as well as its four fractions, namely, amino acid N (AAN), acid-hydrolysable ammonium N (AN), amino sugar N (ASN), and hydrolysable unknown N (HUN). Some vital biological characteristics, with which each AHN fraction is primarily regulated, can be altered with the application of biochar. That is, AAN is mainly controlled by enriched Verrucomicrobia, Cyanobacteria, Glucosylbacteria, and Nitrospira, and reduced soil urease, while AN is mainly controlled by enriched Verrucomicrobia, Bacteroidetes, Gemmatimonadetes, Acidobacteria, and Proteobacteria. ASN is regulated by enriched Acidobacteria and depleted soil protease, while HUN is regulated by Gemmatimonadetes and enriched soil nitrate reductase. It has been found that microbial and soil enzyme activities are involved in N cycle processes, indicating that the formation of AHN fractions is closely associated with biochar-induced specific microbial and enzyme activities. This study has provided new insights into the influences of biochar with different levels on distribution of soil organic N fractions, and shifts in soil enzyme activities and microbial communities.

Long-term straw returning improved soil nitrogen sequestration by accelerating the accumulation of amino acid nitrogen

Straw incorporation has been widely recommended as an effective management practice to increase soil nitrogen stocks in agroecosystems worldwide. However, the overall trend and magnitude of changes in various soil organic nitrogen fractions in response to crop residue return and their contribution to soil nitrogen sequestration remain uncertain. Here, we show through a long-term experiment (12 years) that straw return increased soil total nitrogen and soil nitrogen sequestration rate by 20.01% and 120.95%, respectively. Ammonia nitrogen, amino acid nitrogen, and amino sugar nitrogen were affected by straw and its interaction with year, and increased by 43.08%, 27.70%, and 46.56%, respectively, with the highest growth rate in amino acid nitrogen (10.51 mg kg−1 yr−1). Furthermore, redundancy analyses showed that soil total organic carbon and C:N ratio were the major factors explaining the variations in soil organic nitrogen fractions, which increased by 46.22% and 21.75%, respectively. The structural equation model further revealed that amino acid nitrogen was a pivotal driver of soil nitrogen sequestration, because the soil C:N ratio indirectly influenced soil nitrogen sequestration via affecting the accumulation of amino acid nitrogen. Our results suggest that long-term straw return can improve nitrogen sequestration by accelerating the accumulation of amino acid nitrogen and that soil nitrogen storage and supply capacity may be improved by adopting straw incorporation and other appropriate management practices to regulate soil stoichiometry.

Effects of land‐use changes on soil organic nitrogen fractions in the black soil region of Northeast China

AbstractSoil organic nitrogen (SON) accounts for more than 90% of the total nitrogen (TN) in black soil and is one of the most important indicators of soil fertility. However, the effect of land‐use changes on SON fractions is still unclear in black soil. Hence, natural grassland (uncultivated), farmland (converted from natural grassland), and artificial forestland (grain plots converted into forests) in the black soil region of Northeast China were selected for research. TN, available nitrogen (AN) and SON fractions (ammonia nitrogen (AMN), amino acid nitrogen (AAN), hydrolysable unknown nitrogen (HUN), acid insoluble nitrogen (AIN)) in the topsoil (0–20 cm), and subsoil (20–40 cm) were analysed and compared with elucidate the effects of land‐use changes on SON fractions. The results showed that compared with natural grasslands, the contents of TN and AN in farmlands were 49.1%–67.4% and 48.0%–67.7% less, respectively, and the content of AAN decreased the most in SON fractions, by 52.2%–76.7%, followed by the content of AMN, which decreased by 46.9%–70.7%. The contents of TN and AN in the artificial forestland increased by 18.8% and 30.6%, respectively, compared with those in the farmland. Other than AAN, the content of the SON fractions in the artificial forestland soils was greater than that of the farmland, and the content of HUN increased the most in the SON fractions, by 29.6%, followed by the content of AIN, which increased by 25.8%. The proportions of AMN and AAN in the TN of the natural grassland were 1.2 and 1.7 times those of the artificial forestland, respectively. In conclusion, after natural grassland is converted to farmland, it will destroy the original soil structure, change the physical and chemical properties of the soil, significantly reduce the soil nitrogen supply potential, and significantly decrease nitrogen accumulation. The conversion of grain plots into forestland significantly improved the soil nitrogen storage capacity, but the potential nitrogen supply did not reach the levels of the uncultivated lands. Changes in land use types lead to changes in soil structure and vegetation cover, which in turn alter soil nitrogen cycling. These results provide a scientific basis for evaluating the nitrogen supply capacity of different land‐use types. The study suggests that the land use structure in the area should be properly matched to restore soil nitrogen reservoirs and maintain and improve soil fertility, taking into account local environmental conditions.

Interannual variation of soil organic nitrogen fractions and its response to straw returning.

Elucidating the interannual variation of soil organic nitrogen fractions and its response to straw returning is of great significance for rational regulation of soil organic nitrogen pool and sustainable soil utilization. We conducted a field microcosm experiment with typic hapludoll soil at the National Field Observation and Research Station of Shenyang Agroecosystems. Three treatments were set, including nitrogen fertilizer addition (200 kg N·hm-2, the same in other treatments), nitrogen fertilizer addition with 50% straw return, and nitrogen fertilizer addition with 100% straw return. We classified soil organic nitrogen fractions in the 1st, 3rd, 6th, and 9th years of the experiment by using the Bremner acid hydrolysis method. The results showed that the content of amino acid nitrogen increased with the tillage years, with an increase rate of 39.8% compared with 1st year. The content of hydrolyzable unknown nitrogen increased by 10.8% compared with 1st year, which reached the highest in the 3rd year. The content of total soil nitrogen and other organic nitrogen fractions showed limited variation with tillage years. The proportion of hydrolyzable total nitrogen that is relatively easy to mineralize in the total soil nitrogen gradually increased with the tillage years, and that of relatively stable acid insoluble nitrogen to total soil nitrogen gradually decreased, indicating that soil nitrogen availability increased with the tillage years, which would facilitate the soil nitrogen supply capacity. Compared with the treatment without straw returning, adding straw improved soil total nitrogen and each hydrolyzable nitrogen contents, with such positive effect be stronger under the treatment with heavier straw returning. The effect of straw returning on hydrolyzable nitrogen fractions mainly occurred in the 6th and 9th years. The components of soil total nitrogen that have been increased were mainly the amino acid nitrogen and hydrolyzed unknown nitrogen, resulting in increased proportion of hydrolyzable nitrogen. Straw returning could increase soil nitrogen pool and improve soil nitrogen conservation and supply capacity.

Climatic effects on soil organic nitrogen fractions and amino acid chirality in paddy soils

Soil organic nitrogen (N) accounts for more than 90% of the total N (TN) in paddy soils. An inadequate understanding of the different organic N fractions in paddy soils and their corresponding bioavailability under different climatic conditions has constrained the development of appropriate nutrient management strategies in rice production. Here we apply a modified Bremner method coupled with High Performance Liquid Chromatography (HPLC) to characterize how Soil Organic Nitrogen (SON) fractions and amino acid chirality vary under different climatic conditions by sampling five typical rice production sites along a latitudinal gradient. According to the results, climate had no obvious influence on TN, N form, and individual amino acid concentrations. However, the proportions of various N forms in TN had linear relationships with annual mean temperature, with high correlation coefficients. Amino acid components also exhibited similar trends (with correlation coefficients as high as 0.85). Most notably, consistent linear relationships were observed between the D/L ratios of several amino acids and annual mean temperature in paddy soils (correlation coefficients = 0.18–0.92). The findings of the present study could provide insights on SON and amino acid dynamics in paddy soil systems under intensive production along climate gradients.

Effects of harvest residue management on soil organic nitrogen fractions in young Cunninghamia lanceolata plantation

Different treatments of harvest residues will change the quantity and quality of soil organic matter, with direct or indirect effects on the composition and content of soil nutrient. Nitrogen is one of the most important soil nutrients. However, the response of soil organic nitrogen fractions to different harvest residue treatments is still unclear. In this study, harvest residue treatments, including harvest residue removed, residue retained and residue burnt, were set up after clear-cutting a 50-year-old mature Cunninghamia lanceolata forest in Sanming City, Fujian, China. The H2SO4 hydrolysis method was used to determine soil organic nitrogen fractions and their driving factors in the 0-10 cm and 10-20 cm soil layers after 5 years of harvest residue treatments. The results showed that residue retained treatment significantly enhanced the contents of soil organic nitrogen and its liable fractions. In the 0-10 cm soil layer, soil organic nitrogen content under residue retained treatment (3.36 g·kg-1) was 1.5 and 1.3 times as those of residue removed and residue burnt treatments, respectively. Residue retained treatment had the highest contents of labile nitrogen Ⅰ and Ⅱ fractions. In 10-20 cm soil layer, the contents of soil organic nitrogen and labile nitrogen Ⅱ fraction were also significantly higher in residue retained treatment (2.20, 0.73 g·kg-1) than that in residue removed and residue burnt treatments. The labile nitrogen index Ⅱ in residue retained treatment (33.9%) was significantly higher than in residue burnt treatment (26.1%). The contents of total carbon, dissolved organic carbon, dissolved organic nitrogen, microbial biomass under residue retained treatment were the highest in both soil layers. Compared with residue removed treatment, residue retained treatment significantly enhanced the abundance of soil bacteria (Gram-positive bacteria and Gram-negative bacteria) in 0-10 cm soil layer. In 10-20 cm soil layer, residue retained treatment had the highest content of fungi and the lowest content of actinomycetes. Pearson analysis showed that there were significant positive correlations of labile fractions of soil organic nitrogen with total carbon, dissolved organic carbon, dissolved organic nitrogen, microbial biomass carbon, microbial biomass nitrogen, bacteria (Gram-positive bacteria, Gram-negative bacteria), and fungi, and negative correlations with actinomycetes. It was concluded that the retention of harvest residue was beneficial to increase the content of soil organic nitrogen and labile fractions, improve soil biochemical properties and had a positive effect on soil microbial community composition. Retention of harvest residue was an effective management measure to maintain soil fertility and improve forest productivity.

Variations of soil organic nitrogen fractions during degradation succession in the Gahai Wetland, Northwest China.

This study amined to explore the variation of soil organic nitrogen components across the degradation succession of Gahai Wetland. By combining field sampling and laboratory analysis, the content and distribution characteristics of soil organic nitrogen components, i.e., hydrolytic total nitrogen (HTN), unidentified acidolytic nitrogen (HUN), ammonium nitrogen (AMN), amino acid nitrogen (AAN) and acid amino sugar nitrogen (ASN) were investigated in undegraded (UD), lightly degraded (LD), moderately degraded (MD), and heavy degraded (HD) Gahai Wetland. The results showed that, in the 0-10 cm layer, the contents of total nitrogen (TN), HUN, AMN, and AAN in LD decreased by 17.3%, 19.4%, 8.6%, and -5.6%, 28.0%, 19.4%, 17.1% and 0 in MD, and 35.8%, 28.8%, 28.6% and 55.6% in HD, respectively. In the 10-20 cm layer, the four components decreased by 4.0%, 10.3%, 2.9% and 9.1% in LD, 21.0%, 18.3%, -2.9% and -9.1% in MD, and 9.9%, 38.9%, 21.2% and 51.4% in HD, respectively. The corresponding contents in the 20-40 cm soil layer did not change. The proportion of soil acid-hydrolyzed nitrogen components to TN under four degradation stages was HUN (25.9%-32.5%) > AMN (6.7%-11.1%) > AAN (4.8%-11.1%) > ASN (1.2%-4.4%). Soil water content was the main driving factor for variations of soil organic nitrogen components as indicated by the results of redundancy analysis. Degradation of the Gahai Wetland significantly reduced the content of soil TN and the components of acid-hydrolyzed nitrogen in 0-10 cm soil layer, and weakened the nitrogen "sink" function of soils. The AAN and ASN were sensitive to wetland degradation.

Impact of amendments on soil organic nitrogen fractions irrigated with sodic water

Present study was carried out to evaluate the effects of FYM and gypsum on organic nitrogen fractions in soil of long-term field experiment irrigated with sodic water since 1994 at research farm of Department of Vegetable Science, CCS Haryana Agricultural University Hisar, India (2014-2015). Field was irrigated with high RSC (11.5 me/l) sodic water having three levels of gypsum G0 (control), G1 (50 % neutralization of RSC), G2 (100% neutralization of RSC), along with three levels of FYM; F0 (control), F1 (10 tonnes/ha), F2 (20 tonnes/ha). The Results obtained in April 2014 showed that all N fractions (Non hydrolysable-N, NH3-N, amino acid-N, amino sugar-N, hydrolysable unknown-N and total hydrolysable-N) were more dynamic in various treatments consisting FYM and gypsum levels. All nitrogen fractions increased with increasing levels of FYM and gypsum. Averages of amino acid nitrogen, amino sugar nitrogen, ammonia nitrogen and hydrolysable unknown nitrogen constituted about 28-30, 9-12, 27-29 and 29- 36% of total hydrolysable nitrogen, respectively. Adverse effect of residual alkalinity of irrigation water was quite prominent on chemical properties (pH, EC, organic carbon) of soil. The pH of soil was found to be very high under F0G0 and decreased with the use of FYM and gypsum as amendments. This result indicates that the combined use of FYM and gypsum improved soil health and maintained the sustainability of the different vegetable cropping system.

Effects of irrigation and nitrogen fertilization on greenhouse soil organic nitrogen fractions and soil-soluble nitrogen pools

Soil organic nitrogen fractions and soil-soluble nitrogen pools are important indicators of soil fertility and plant nutrition requirements. However, little is known about soil organic nitrogen fractions and their correlations with soil mineral nitrogen (SMN) and soluble organic nitrogen (SON). A five-year field experiment was conducted to determine the effects of lower irrigation limits (25, 35, and 45 kPa) and nitrogen fertilization (75, 300, and 525 kg ha−1) rates on greenhouse soil organic nitrogen fractions and soil-soluble nitrogen pools. The results indicated that the soil organic nitrogen fractions and soil-soluble nitrogen pools were significantly affected by the irrigation and nitrogen fertilization rates and their interactions at various greenhouse soil depths (P < 0.01). The soil organic nitrogen occurred mainly in the form of acid-hydrolyzable N (AHN). The soil organic nitrogen fractions other than the amino sugar N (ASN) and the soil-soluble nitrogen pools (SMN and SON) decreased with increasing soil depth. Our findings suggest that ammonium N (AN), amino acid N (AAN), and SMN may predict the soil nitrogen supply potential in greenhouse agroecosystems. Soil total nitrogen (Ntotal), soil organic carbon (SOC), and nitrate nitrogen (NO3−-N) appeared to be the major factors explaining the soil organic nitrogen fractions. Considering water saving, nitrogen reduction, and soil nitrogen supply optimization, it was concluded that the best schedules to use in the greenhouse were I2N1 and I2N2 treatments.

Effects of long-term fertilization on organic nitrogen fractions in aquic brown soil

The purpose of present research was to investigate how different fertilization regimes altered soil organic nitrogen fractions and their inter-annual dynamics based on a series of long-term experiment (initiated at 1990), including: CK (non-fertilization); M (recycled pig manure); NPK (chemical fertilizer NPK); NPK + M (recycled pig manure with chemical fertilizer NPK). The results showed that soil organic nitrogen components under the different fertilization treatments presented contrastive patterns from the establishment the experiments to 2015. Generally, acid hydrolysable organic nitrogen content increased year by year. The amino acid nitrogen content under CK and NPK treatments consistently declined, although amino acid nitrogen for M and NPK+M treatments showed a increasing trend. These phenomena were probably ascribed to the utilization of soil amino acids by microbes. From 1990 to 2015, NPK treatment substantially elevated the content of acid-released ammonium nitrogen by 31.1% compared with CK (mean value across the experiment), and for the treatments using organic manure (M and NPK+M), the contents of all fractions of soil organic nitrogen increased. Notably, the increase magnitudes for NPK+M were more dramatic than those of M. These results demonstrated that combined use of organic and inorganic fertilizers could more effectively elevate soil organic nitrogen, subsequently helping to improve the capacity of soil nitrogen supply and enhance the soil fertility.

Effects of elevated nitrogen and precipitation on soil organic nitrogen fractions and nitrogen-mineralizing enzymes in semi-arid steppe and abandoned cropland

Soil organic nitrogen (N) turnover is significantly influenced by elevated N deposition, precipitation and human-caused disturbances, but the underlying mechanism remains unclear. Identifying the relationships among the soil organic N fractions and N-mineralizing enzymes activities may advance our knowledge of the dynamics of soil organic N. A field experiment was conducted in a semi-arid steppe and an abandoned cropland in northern China to investigate the effects of elevated N deposition and precipitation on soil organic N fractions and their relationships with N-mineralizing enzymes, i.e., protease, amidase, urease and N-acetyl-β-D-glucosaminidase (NAG) activities. The concentrations of N in various fractions were consistently lower in the abandoned cropland compared with the steppe. Nitrogen addition consistently decreased amino acid N content and activities of urease, protease and amidase in both sites but increased amino sugar N content and NAG activity in the steppe. Water addition decreased hydrolysable ammonium N content but increased amino sugar N content and activities of protease and NAG in both sites. Furthermore, urease and NAG activities were significantly positively correlated with the proportions of amino acid N and amino sugar N and, explained significant proportions of the variations in soil organic N fractions in the steppe. However, soil organic carbon (C), rather than N-mineralizing enzymes, explained greatest proportion of the variations in soil organic N fractions in the abandoned cropland. The concurrent increase of N deposition and precipitation could promote the recovery of soil N (and C) losses in the abandoned cropland resulting from previous agriculture. Furthermore, in the steppe where NH4 + was available at relative high concentrations, enzymatic mineralization was the dominant route involved in potential soil organic N turnover. However, the direct route may be favored over the enzymatic mineralization route with decreasing availability of C relative to N in the abandoned cropland, which is driven by the need for C. These findings confirmed that the forms of N available, and the relative availability of C and N determine N uptake pathways both through enzymatic mineralization route and direct uptake route in the semi-arid grasslands.