Nitrogen In Agricultural Soils Research Articles

Development of near-infrared spectroscopy (NIRS) for estimating organic matter, total carbon, and total nitrogen in agricultural soil

The analysis of soil organic matter (OM), total carbon (TC), and total nitrogen (TN) using traditional methods is quite time-consuming and involves the use of hazardous chemical reagents. Absorbance spectroscopy, especially near-infrared (NIR), is becoming more popular for soil analysis. This method requires little sample preparation, no chemicals, and a single spectral analysis to evaluate soil properties. Thus, this research aimed to develop an NIR spectroscopy method for the analysis of OM, TC, and TN in agricultural soils. These findings can provide a good concept of using PLS regression with NIR techniques. The method is as follows:•Topsoil (0–20 cm) samples were collected from various agricultural fields. OM, TC, and TN were analyzed using traditional methods and NIR spectroscopy.•NIR spectra were obtained using an FT-NIR spectrometer, original spectral including with Savitzky–Golay smoothing, standard normal variate (SNV) and multiplicative scatter correction (MSC) preprocessing method were used to create a predicted model through Partial Least Squares (PLS) regression with 65 % calibration, and the rest 35 % for validation.•The results showed significant relationships between measured soil properties (SOM and TC) and NIR absorbance spectra in agricultural soil (R2 of calibration and validation higher than 0.80).

Portable gamma spectrometry for rapid assessment of soil texture, organic carbon and total nitrogen in agricultural soils

Portable gamma spectrometry for rapid assessment of soil texture, organic carbon and total nitrogen in agricultural soils

Assessing the Efficacy, Acute Toxicity, and Binding Modes of the Agricultural Nitrification Inhibitors 3,4-Dimethyl-1H-pyrazole (DMP) and Dicyandiamide (DCD) with Nitrosomonas europaea

Nitrification inhibitors have been coformulated with nitrogen fertilizers since the 1970s to modulate the microbiological conversion of nitrogen in agricultural soils. 3,4-Dimethyl-1H-pyrazole (DMP) and dicyandiamide (DCD) are currently the most used commercial nitrification inhibitors, but their mode of action is not well understood. This work seeks to fill this void by assessing for the first time in detail their mechanism of inhibition, efficacy, and acute toxicity with pure cell cultures of Nitrosomonas europaea. Bacterial assays based on the quantification of the nitrite (NO2–) production showed that both inhibitors reversibly target ammonia monooxygenase (AMO), which catalyzes the first step of the nitrification process. Michaelis–Menten kinetics suggest that both DMP and DCD act as uncompetitive inhibitors. Real-time measurements of the oxygen (O2) consumption confirmed the nonmechanistic mode of inhibition and showed that DMP reduced the O2 uptake rate by AMO much more at considerably lower concentrations than DCD, in line with the lower inhibitory efficiency of the latter. Acute toxicity tests revealed that DCD has a 10% higher toxicity than DMP when comparing treatments at the same inhibition efficacy (i.e., DMP at 10 ppm, DCD at 100 ppm), indicating that the inhibition of the nitrification process cannot simply be achieved by increasing the inhibitor concentration. The methods presented in this study could assist the development of more reliable nitrification inhibitors in the future.

Restoring wetlands on intensive agricultural lands modifies nitrogen cycling microbial communities and reduces N2O production potential

The concentration of nitrous oxide (N2O), an ozone-depleting greenhouse gas, is rapidly increasing in the atmosphere. Most atmospheric N2O originates in terrestrial ecosystems, of which the majority can be attributed to microbial cycling of nitrogen in agricultural soils. Here, we demonstrate how the abundance of nitrogen cycling genes vary across intensively managed agricultural fields and adjacent restored wetlands in the Sacramento-San Joaquin Delta in California, USA. We found that the abundances of nirS and nirK genes were highest at the intensively managed organic-rich cornfield and significantly outnumber any other gene abundances, suggesting very high N2O production potential. The quantity of nitrogen transforming genes, particularly those responsible for denitrification, nitrification and DNRA, were highest in the agricultural sites, whereas nitrogen fixation and ANAMMOX was strongly associated with the wetland sites. Although the abundance of nosZ genes was also high at the agricultural sites, the ratio of nosZ genes to nir genes was significantly higher in wetland sites indicating that these sites could act as a sink of N2O. These findings suggest that wetland restoration could be a promising natural climate solution not only for carbon sequestration but also for reduced N2O emissions.

Exchangeable cation effects on hot water extractable carbon and nitrogen in agricultural soils

Hot water is believed to extract bio-available soil organic matter (SOM), including organic compounds from the biomass of soil microbes. The role of soil physico-chemical factors in relation to extractability of SOM in hot water is not well understood. We evaluated the influence of exchangeable sodium (Na) on the quantity and quality of organic matter extracted in hot water from soils with a range of total and extractable C (total C 19–60 g kg–1; hot water extractable C (HWC) 659–3292 mg kg–1). The soils were pre-treated with different rates of Na (0–156 cmolc kg–1, as NaCl) to establish a range of exchangeable Na percentages (ESP), and then extracted with hot water (80°C) for 16 h. Hot water extractable C increased linearly as ESP increased, but the rate of increase differed between soils (the increase in HWC per unit increase in ESP ranged within 19–71 mg kg–1). At ESP 15, a threshold used to separate sodic and non-sodic soils, HWC was 30–60% greater than that measured without added Na. Ultraviolet absorbance (260 nm) data indicated that aromatic organic matter was preferentially released following Na pre-treatment. The proportion of HWC in phenolic form was generally little affected by Na treatment but there was a consistent increase in protein in response to Na (hot water extractable organic N in protein form increased from an average of 5.5 ± 2.2% without added Na to 11.0 ± 3.6% at the highest Na rate). The Na-induced increases in UV absorbance may be largely attributable to release of proteins containing aromatic amino acids (tryptophan and tyrosine). Our results suggest that organic matter desorbed from mineral surfaces may be an important contributor to hot water extractable C and N, and factors that affect the adsorption–desorption process may significantly influence organic matter extractability in hot water.

Seed provenance determines germination responses of Rumex crispus (L.) under water stress and nutrient availability

Abstract Aims Seeds of Rumex crispus from six provenances were studied in relation to their germination under drought and presence of nitrogen in the germination and emergence media. We also investigated whether adaptation to soil increases the ability of the species to colonize and establish in contrasting environments along a longitudinal gradient in western Spain by means of a reciprocal transplantation experiment. Methods We conducted a germination trial in the lab to test for the germination responses to water scarcity along a polyethylene glycol gradient and to varying concentrations of nitrogen compounds. Simultaneously reciprocal transplantations experiment was conducted, where seeds from six provenances were grown in the soils from the very same provenances. Seedling emergence, survivorship and fitness-related variables were measured in all plots. Important Findings We found that R. crispus has a cold-stratification requirement that enhances its germination. Significant differences between the six provenances were detected for time-to-germination, total seedling emergence, plant mortality and reproductive effort in all the experiments. The differences between provenances with respect to germination were confirmed by the significant statistical analyses of the variance, thus providing evidence that seeds from parent plants grown in different environmental conditions have an intrinsically different abilities to germinate and establish. Soil nitrogen content where seed germination and seedlings establish also play an important role in their performance in terms of survivorship and reproduction, being the higher levels of inorganic nitrogen and of microbial biomass those that increased biomass production, enhanced inflorescence formation and reduced plant mortality. We conclude that one of the main reasons for the spread and maintenance of R. crispus would be the increased levels of nitrogen in agricultural soils.

Effects of Various Combinations of Fertilizer, Soil Moisture, and Temperature on Nitrogen Mineralization and Soluble Organic Nitrogen in Agricultural Soil

An 84-day laboratory incubation experiment was conducted to investigate the effects of different fertilizers (urea; manure), moisture conditions (60%, 75% and 90% water holding capacity) and temperatures (15, 25 and 35℃) on nitrogen mineralization. The experiment included 3 treatments:①CK, unfertilized control; ② Ur, adding urea at N 120 mg·kg-1; 3 UM, adding urea and manure (equal to adding N 120 mg·kg-1). Total inorganic nitrogen and soluble organic nitrogen (SON) were determined at different times throughout the experiment. The results showed that soil temperature and fertilization type had significant impacts on the net mineralization rates, cumulative mineralization, and the potentially mineralizable nitrogen (N0) (P<0.01). In addition, the soil net N mineralization rates and cumulative mineralization significantly (P<0.05) increased by 1.46-8.17 and 2.00-8.15 times, respectively, when fertilizers were added into soils. The soil net N mineralization rates and cumulative mineralization increased with the increase of temperature. Compared with CK treatment, Ur and UM treatments could significantly increase the content of soil soluble organic nitrogen(SON). There was a significant negative correlation between the content of SON and cumulative mineralization. It indicated that SON was involved in soil nitrogen mineralization as a non-negligible component. Increasing the temperature could significantly increase the mineralization rate and mineralization intensity of SON in soil, but the water content had no significant influence on the SON of the soils. Moreover, the authors found that fertilization treatment worked significantly in decreasing the Q10 value for soil N mineralization compared with CK treatment. Further, the Q10 value was significantly lowest in UM treatment(Q10=1.01). The results showed that the application of organic manure significantly reduced the sensitivity of the rate of nitrogen mineralization to temperature changes, which was beneficial in slowing down the release rate of mineral nitrogen under high temperatures and improving the nitrogen utilization efficiency of crops.

Discovery of Fungal Denitrification Inhibitors by Targeting Copper Nitrite Reductase from Fusarium oxysporum

The efficient application of nitrogenous fertilizers is urgently required, as their excessive and inefficient use is causing substantial economic loss and environmental pollution. A significant amount of applied nitrogen in agricultural soils is lost as nitrous oxide (N2O) in the environment due to the microbial denitrification process. The widely distributed fungus Fusarium oxysporum is a major denitrifier in agricultural soils and its denitrification activity could be targeted to reduce nitrogen loss in the form of N2O from agricultural soils. Here, we report the discovery of first small molecule inhibitors of copper nitrite reductase (NirK) from F. oxysporum, which is a key enzyme in the fungal denitrification process. The inhibitors were discovered by a hierarchical in silico screening approach consisting of pharmacophore modeling and molecular docking. In vitro evaluation of F. oxysporum NirK activity revealed several pyrimidone and triazinone based compounds with potency in the low micromolar range. Some of these compounds suppressed the fungal denitrification in vivo as well. The compounds reported here could be used as starting points for the development of nitrogenous fertilizer supplements and coatings as a means to prevent nitrogen loss by targeting fungal denitrification.

Cattle manure and straw have contrasting effects on organic nitrogen mineralization pathways in a subtropical paddy soil

Organic materials are widely recommended for the maintenance and/or accumulation of organic carbon and total nitrogen in agricultural soils. However, the relative effectiveness of different organic materials on gross N transformation and inorganic-N supply is not known. Here, a 15N tracing incubation study was conducted to investigate the rates of gross N mineralization, nitrification, and microbial immobilization of and in a paddy soil managed using different organic materials. Soil samples were collected from a rice field that has been under long-term study (30 years) and is receiving four different fertilizer treatments: no fertilizer (CK), chemical fertilizer (NPK), chemical fertilizer plus cattle manure (NPKM), and chemical fertilizer plus straw (NPKS). The samples were incubated with 15NH4NO3 or NH415NO3, and the results were calculated based on a 15N tracing model. The analysis showed that mineralization of labile and recalcitrant organic-N pools was significantly stimulated by NPKM and NPKS treatments, respectively, but not by NPK alone. Heterotrophic nitrification was negligible in all treatments. Therefore, the enhanced inorganic-N supply rates (total mineralization + heterotrophic nitrification) due to NPKM and NPKS application could be attributed to the increasing mineralization of the labile organic-N pool and recalcitrant organic-N pool, respectively. The rate of autotrophic nitrification rate was significantly increased by NPK and NPKM application, but not by NPKS application. However, both consumption rates (immobilization of and dissimilatory reduction to ) were low and unaffected by fertilizer application. Our results suggest that NPKM stimulated the processes of mineralization of the labile organic-N pool and autotrophic nitrification to increase accumulation in soil. In contrast, application of NPKS increased the rate of mineralization of recalcitrant organic-N pool but did not affect the autotrophic nitrification rate.

Effect of Long Term Fertilization on Soil Carbon and Nitrogen Pools in Paddy Soil

Fertilizer management has the potential to promote the storage of carbon and nitrogen in agricultural soils and thus may contribute to crop sustainability and mitigation of global warming. In this study, the effects of fertilizer practices [no fertilizer (Control), chemical fertilizer (NPK), Compost, and chemical fertilizer plus compost] on soil total carbon (TC) and total nitrogen (TN) contents in inner soil profiles of paddy soil at 0-60 cm depth were examined by using long-term field experimental site at <TEX>$42^{nd}$</TEX> years after installation. TC and TN concentrations of the treatments which included N input (NPK, Compost, NPK+Compost) in plow layer (0-15 cm) ranged from 19.0 to 26.4 g <TEX>$kg^{-1}$</TEX> and 2.15 to 2.53 g <TEX>$kg^{-1}$</TEX>, respectively. Compared with control treatment, SOC (soil organic C) and TN concentrations were increased by 24.1 and 31.0%, 57.6 and 49.7%, and 72.2 and 54.5% for NPK, Compost, and NPK+Compost, respectively. However, long term fertilization significantly influenced TC concentration and pools to 30 cm depth. TC and TN pools for NPK, Compost, NPK+Compost in 0-30 cm depth ranged from 44.8 to 56.8 Mg <TEX>$ha^{-1}$</TEX> and 5.78 to 6.49 Mg <TEX>$ha^{-1}$</TEX>, respectively. TC and TN pools were greater by 10.5 and 21.4%, 30.3 and 29.6%, and 39.9 and 36.3% in N input treatments (NPK, Compost, NPK+Compost) than in control treatment. These resulted from the formation and stability of aggregate in paddy soil with continuous mono rice cultivation. Therefore, fertilization practice could contribute to the storage of C and N in paddy soil, especially, organic amendments with chemical fertilizers may be alternative practices to sequester carbon and nitrogen in agricultural soil.

Role of nitrifier denitrification in the production of nitrous oxide

Nitrifier denitrification is the pathway of nitrification in which ammonia (NH 3) is oxidized to nitrite (NO 2 −) followed by the reduction of NO 2 − to nitric oxide (NO), nitrous oxide (N 2O) and molecular nitrogen (N 2). The transformations are carried out by autotrophic nitrifiers. Thus, nitrifier denitrification differs from coupled nitrification–denitrification, where denitrifiers reduce NO 2 − or nitrate (NO 3 −) that was produced by nitrifiers. Nitrifier denitrification contributes to the development of the greenhouse gas N 2O and also causes losses of fertilizer nitrogen in agricultural soils. In this review article, present knowledge about nitrifier denitrification is summarized in order to give an exact definition, to spread awareness of its pathway and controlling factors and to identify areas of research needed to improve global N 2O budgets. Due to experimental difficulties and a lack of awareness of nitrifier denitrification, not much is known about this mechanism of N 2O production. The few measurements carried out so far attribute up to 30% of the total N 2O production to nitrifier denitrification. Low oxygen conditions coupled with low organic carbon contents of soils favour this pathway as might low pH. As nitrifier denitrification can lead to substantial N 2O emissions, there is a need to quantify this pathway in different soils under different conditions. New insights attained through quantification experiments should be used in the improvement of computer models to define sets of conditions that show where and when nitrifier denitrification is a significant source of N 2O. This may subsequently render the development of guidelines for low-emission farming practices necessary.

Soluble organic nitrogen in agricultural soils

The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation, leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N. DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients, chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but there are still many gaps in our understanding.

Polyacrylamide as an organic nitrogen source for soil microorganisms with potential effects on inorganic soil nitrogen in agricultural soil

Linear polyacrylamide (PAM) is gaining considerable acceptance as an effective anti-erosion additive in irrigation water. The potential effects of repeated PAM application on soil microbial ecology and the potential for biotransformation of this polymer in soils are not completely known. Untreated and PAM-treated soils (coarse-silty, mixed, mesic Durixerollic Calciorthids) were collected from agricultural fields near Kimberly, ID. Soils were analyzed to determine the effects of PAM treatment on bacterial counts and inorganic N concentrations and the potential for PAM biotransformation. Culturable heterotrophic bacterial numbers were significantly elevated in PAM-treated soil for the plot planted to potatoes; this effect was not observed in the plot planted to dry pink beans. Total bacterial numbers, determined by AODC, were not altered by PAM treatment in any of the soils sampled. Polyacrylamide-treated soil planted to potatoes contained significantly higher concentrations of NO 3 − and NH 3 (36.7±2.20 and 1.30±0.3 mg kg −1, respectively) than did untreated soil (10.7±2.30 and 0.50±0.02 mg kg −1, respectively). For bean field soil there was no difference between treated and untreated soil inorganic N concentrations. Enrichment cultures generated from PAM-treated and untreated soils utilized PAM as sole N source, but not as sole C source. While the monomeric constituents of PAM, acrylamide and acrylic acid, both supported bacterial growth as sole C source, the PAM polymer did not. Enrichment cultures that used PAM for N exhibited amidase activity specific for PAM as well as smaller aliphatic amides. Utilization of PAM for N, but not for C, indicates that ultimately PAM may be converted into long chain polyacrylate, which may be further degraded by physical and biological mechanisms or be incorporated into organic matter.

Determination of potentially mineralizable nitrogen in agricultural soil

Potentially mineralizable soil N was determined after incubation for 2, 4, 8, 12, 16, 22, and 30 weeks, according to the Stanford and Smith method. A first-order kinetics model was used, and a simulation study was performed using three different statistical methods to estimate potentially mineralizable N and the rate constant k. The first method was based on the maximum-likelihood approach. The second one relied on nonlinear least square data fitting. The third method was based on linear of logarithmically transformed data. The results of the simulation study suggested that the non-linear least square method was preferable to the others. This method was then applied to real data from 30 different Italian soils. The values obtained for potentially mineralizable N were, on average, 10% of total N (mean standard error=0.9). The estimated value of k was 0.050 (mean standard error=0.005). Finally, from the values obtained for k and the results of the simulation, the results indicated that significantly less reliable estimates of potentially mineralizable N were obtained by using data for up to only 22 weeks of incubation.