Soil Extractable Ammonium Research Articles

Effects of wheat straw addition on dynamics and fate of nitrogen applied to paddy soils

The effectiveness of plant residue addition to increase crop nitrogen (N) use efficiency while reducing N losses is dependent on whether residue management can improve the match between N immobilization-mineralization turnover and plant demand. To understand the effects of residue management on N cycle processes, we conducted a field study that included three treatments. These were a control without N fertilizer (CK), 15N-labelled urea (UR), and 15N-labelled urea + wheat straw (URS). Nitrogen immobilized in the top soil layer (0–20 cm) in the urea only treatment tended to decrease after the basal application and the second top dressing, but increased after the first top dressing, whereas the urea + straw treatment increased immobilization up to the second top dressing, before decreasing towards the end of the study. The addition of wheat straw led to a 24% reduction in ammonia loss after the basal application, corresponding well to lower soil extractable ammonium contents. The N uptake by the plant in the urea + straw treatment corresponded to 25% of applied N, which was higher than the 20% recorded in the urea only treatment. At harvest, 31% of the applied N was found in the 0–60 cm soil layer after the addition of wheat straw, whereas there was only 25% without straw addition. The results showed that 45% applied N was unaccounted for when wheat straw was added, compared to 55% unaccounted for without wheat straw. These indicate that the addition of wheat straw may increase plant N uptake by contributing to N immobilization early in the season, but then improving its subsequent mineralization later in the season.

Simultaneous Analysis of Inorganic Monovalent Anions/Cations Using Mixed-Bed Single-Column Ion Chromatography

The ion-exchange properties of a new mixed-bed ion-exchange column Scherzo SSC18 (Imtakt, USA) were investigated. This mixed-mode column is packed with two types of 3 µm spherical silica particles having either octadecyl- and strong cation-exchange functional groups or octadecyl- and strong anion-exchange functional groups. The regularities of the retention of alkali metal cations and inorganic anions were studied with diluted acids (sulfuric, perchloric to phosphoric, nitric, oxalic and citric acids) as eluents and direct conductivity for the detection. Eluent concentration, column temperature and organic solvent addition effects were investigated. The separations were achieved on the basis of ion-exchange interactions introduced by the strong anion and strong cation-exchange functionalities of the stationary phase; meanwhile, contribution of hydrophobic interactions was also evident for the hydrophobic iodide and thiocyanate. The simultaneous separation of 12 inorganic anions and cations in 20 min was obtained under isocratic conditions with 1 mM oxalic acid as eluent. The applicability of developed method to the determination of chloride, sodium, potassium as well as nitrite, nitrate and ammonium in soil extracts was demonstrated with good potential for nitrogen speciation studies.

Unexpected Effects of Chitin, Cellulose, and Lignin Addition on Soil Dynamics in a Wet Tropical Forest

Decades of studies on the role of decomposition in carbon (C) and nitrogen (N) cycling have focused on organic matter (OM) of plant origin. Despite potentially large inputs of belowground OM from fungal cell walls and invertebrate exoskeletons, studies of the decomposability of their major constituent, chitin, are scarce. To explore effects on soil C dynamics of chitin, in comparison with two plant-derived chemicals, cellulose and lignin, I conducted a field-based chemical-addition experiment. The design contained three chemical treatments plus a control, with four replicates in each of two species of tropical trees grown in plantations. The chemicals were added in reagent-grade form at a rate that doubled the natural detrital C inputs of 1000 g C m−2 y−1. Despite its purported recalcitrance, chitin was metabolized quickly, with soil respiration (R soil) increasing by 64% above the control within days, coupled with a 32% increase in soil extractable ammonium. Cellulose, which was expected to be labile, was not readily decomposed, whereas lignin was rapidly metabolized at least partially in one of the forest types. I examined effects of stoichiometry by adding to all treatments ammonium nitrate in a quantity that adjusted the C:N of cellulose (166) to that of chitin (10), using both field and in vitro experiments. For cellulose, CO2 release increased more than five- to eightfold after N addition in root-free soil incubated in vitro, but only 0–20% in situ where roots were intact. By the end of the 2-year-long field experiment, fine-root biomass tended to be higher in the chitin treatment, where R soil was significantly higher. Together these findings suggest that soil N availability limited cellulose decomposition, even in this Neotropical forest with high soil N stocks, and also that trees successfully competed for N that became available as chitin decomposed. These results indicate that the major constituent of cell walls of soil fungi, chitin, can decompose rapidly and release substantial N that is available for plant and microbial growth. As a consequence, soil fungi can stimulate soil OM decomposition and N cycling, and thereby play a disproportionate role in ecosystem C and N dynamics.

Short-Term Soil Responses for an Emulated Loblolly Pine Silvopasture

Pine (Pinus spp. L.) stands are often overstocked early in the tree rotation, prior to initial thinning. While pre- and/or post-thinning fertilizer applications are best-management practices to optimize growth of southern pines, there can be poor nitrogen (N) utilization and adverse environmental impacts associated with fertilization. Our objective was to determine short-term (3-year) soil responses of an emulated loblolly pine (P. taeda L.) silvopasture, which received a single application of commercial N–phosphorus (P)–potassium (K) fertilizer (CF) or pelletized poultry litter (PPL) applied at about midrotation (12 years postplanting). Compared to the control, CF decreased soil pH at depths of 0–10 and 10–30 cm, and PPL increased Mehlich 3 available P at 0–10 cm. Fertilizer responses were found for soil extractable ammonium (NH4 +)-N, and nitrate (NO3 −)-N concentrations, mineral N ha−1, pH, and available P but not for diel carbon dioxide–carbon (CO2-C) flux, total C, and total N. Total soil C, total soil N, pH, and available P decreased with depth, whereas mineral N ha−1 and 1 M potassium chloride (KCl)–extractable aluminum (Al) increased with depth. These results further our understanding of the nutrient dynamics during alley cropping of an upland soil and demonstrate the challenge in detecting short-term responses with fertilization.

Accumulation of Pollutant Nitrogen in Calcareous and Acidic Grasslands: Evidence from N Flux and 15N Tracer Studies

Semi-natural calcareous and acidic grasslands are known to be sensitive to increased atmospheric N deposition. However, the fate of pollutant N within these systems is unknown. This paper reports on the first studies to determine the fate of added N within a calcareous and an acidic grassland subject to long-term simulated enhanced N deposition. Intact soil/turf cores were removed from field plots treated for six years with enhanced N deposition (ambient +0,+35 and +140 kg N ha−1 year−1). Cores were inserted into lysimeters and output fluxes of N were monitored in detail. Complete N budgets - calculated from the N flux data - showed considerable accumulation of N within the treated grasslands, up to 76% and 38% of pollutantNin the calcareous and acidic grasslands respectively. In the second study, the short-term (21 day) fate of pollutant N was determined by tracing 15N labelled ammonium nitrate (+35 kg N ha−1 year−1) though the acidic and calcareous lysimeters into plant, soil and leachate pools. Up to 91% and 59% of 15N was recovered in soils and vegetation of the calcareous and acidic grasslands respectively, with negligible amounts recovered in soil extractable ammonium and nitrate (<0.3%) and in leachate (<0.02%). This rapid short-term immobilisation of pollutant N supports the long-term accumulation of the element calculated from the N flux study.

Within-season grass yield and nitrogen uptake, and soil nitrogen as affected by nitrogen applied at various rates and distributions in a high rainfall environment

A study was conducted to assess the effect of rates of nitrogen (N) fertilizer, and to compare the effectiveness of single and split applications of N on yield and quality of forage grass and on the potential for nitrate leaching. Three field trials were conducted at different sites in successive years, with plant and soil measurements made at each of four harvests. Extractable inorganic N was measured to 0.6 m in three depth increments prior to spring N application and after each cut in order to evaluate immediate and residual effects of the N fertilizer on plant growth, and the environmental implications of the applications. Response of yield and N uptake to N applications differed in the three trials. In all trials, the effect of N rate was greater than the effect of N distribution during the growing season. Although there were only small, whole-season yield increases associated with distributing the N over the season, the distribution of yield within the season was changed considerably. Soil data showed relatively little leaching of N during the growing season under contrasting weather conditions of the three growing seasons. Retention of N within the soil root zone contributed to residual effects on yield and plant uptake, and these effects frequently lasted to the end of the growing season. Crop response to N applications was apparently influenced by the N supplying capacity of the soil and the effect of weather on crop growth rate. Soil nitrate at harvest did not vary consistently with N application treatments in the three trials, other than having highest concentrations at the highest fertilizer rate. Soil nitrate was greatest after cut 1 and decreased sharply toward the end of the season following the single spring applications, whereas plots receiving equal distributions of N through the season had relatively high concentrations at all sampling times during the season. Soil extractable ammonium concentration was influenced by high rates of N application, but the effect was small and largely confined to the sampling after cut 1. The soil always contained about 10–15 mg kg−1 extractable ammonium in surface 0.3 m depth, with a tendency for slightly greater concentrations in early spring. Soil ammonium appears to be involved in soil and plant processes, but the exact magnitude and significance of its involvement could not be determined from the measurements made. The redistribution of grass yield by splitting the application of fertilizer N within the growing season would be beneficial for grazing systems. Unfortunately, soil inorganic N measurements will not greatly assist in determining the precise rate and distribution of fertilizer for varying field conditions. Key words: N response, N uptake, residual N effect, soil extractable N, N leaching

Nitrogen Retention and Release in Atlantic White Cedar Wetlands

AbstractThe fate of N inputs to freshwater wetlands from enriched runoff, ground water, or atmospheric deposition reflects a variety of processes that determine the net retention of N or its release to downstream ecosystems. The history of N enrichment may affect the relative importance of different pathways. We compared the ability of sediments from Atlantic cedar wetlands in suburban and undisturbed watersheds to remove added inorganic N in laboratory incubations. Three pulses of NH4NO3, at 50 mg N L−1 concentration, were added at consecutive 2‐wk intervals as an analog of pulsed stormwater inputs. After each incubation, soils were leached with CaCl2 and inorganic N concentrations in the leachate were analyzed. The peats retained added N during the first incubation, but after the second and third, all soils released more N than had been added. Nitrate concentrations were always lower than ammonium concentrations. Soils from hollows and most hummocks retained added nitrate throughout the study, but all soils released ammonium. Soil extractable ammonium increased four to 10 times after the 6‐wk incubation, while extractable dissolved organic N (DON) decreased. There also was a net decrease of soil total Kjeldahl N (TKN). The patterns of retention and release of nitrate and ammonium were correlated positively with the N mineralization and nitrification rates of the soils. Our results suggest that wetland peats in suburban drainages may have limited ability to retain frequent, pulsed N inputs from runoff and high intrinsic N mineralization in N‐saturated sediments can become a cause of water quality degradation.

Improving the Berthelot Reaction for Determining Ammonium in Soil Extracts and Water

AbstractColorimetric methods based on the Berthelot reaction are used widely for quantitative determination of NH4‐N in biological and environmental samples. Studies to evaluate phenol and salicylate, the most commonly used chromogenic substrates, revealed minor interferences by metallic cations, whereas up to a threefold shift in absorbance was observed with 38 diverse N‐containing organic compounds. Interferences differed markedly between phenol and salicylate. The possibility of a simple correction was precluded by the fact that interferences were both positive and negative, and depended on the temperature during color development and the concentration of NH4‐N. Fourteen compounds were evaluated as alternatives to phenol and salicylate, of which the Na salt of 2‐phenylphenol (PPS) proved to be the most promising. Using PPS, macro‐ and microscale batch methods and an automated flow‐injection method were developed. These methods are simple, convenient, and sensitive. Using the PPS microscale method, for which the limit of detection is 0.17 mg NH4‐N L−1, recovery of NH4‐N added to soil extracts ranged from 98 to 104%, with a coefficient of variation of 1.4 to 2.7%. As with phenol and salicylate, precipitation of metal hydroxides was observed. Precipitation was controlled by chelation with citrate rather than ethylenediaminetetraacetic acid (EDTA), which suppressed color development by preventing monochloramine formation. Compared with Berthelot methods that use phenol or salicylate, interference by amino acids was decreased by up to 10‐fold. Interference by other organic N compounds was virtually eliminated.

A rapid and sensitive flow injection technique for the analysis of ammonium in soil extracts

Abstract The steam distillation technique for the quantification of soil mineral nitrogen is not well adapted to estimate very low levels of NH4 + and NO3 −such as those found in tropical pastures. In this paper we describe a flow injection analysis (FIA) technique for the direct estimation of soil ammonium in potassium chloride extracts. The technique is based on the salicylate/hypochlorite colorimetric reaction with the resulting colouration read at 647 nm. The speed of the reaction was increased by immersing the reaction coils in a water bath maintained at 70°C. The technique was capable of accurately quantifying ammonium to concentrations as low as 0.05 mg NH4+‐N/L (equivalent to 0.25 mg NH4 +‐N/g dry soil) and sample thoughputs of at least 60 samples per hour could be achieved. It was found that amino acids would also give a positive colorimetric reaction but that in the ten tropical soils examined this was not a significant source of error.

Reducing interferences by amino acids in the determination of ammonium by an automated indophenol method

Abstract Positive interference by amino acids in the determination of ammonium in soil extracts by automated indophenol methods can be minimised by using the nitroprusside catalysed reaction. Hydrolysis of amino acids is virtually eliminated because this reaction enables the use of low sample volumes, reagent concentrations and reaction temperatures.

Improved method for automated determination of ammonium in soil extracts

Abstract An improved sodium salicylate‐hypochlorite, automated method for ammonium in soil extracting solutions using nitroprusslde as catalyst has been investigated. This method is 2 to 3 times more sensitive than previously published procedures and also is less subject to interferences, has less noise in the signal, and has two alternative ranges. The range with maximum sensitivity is linear to about 2.5 ppm; the second range is linear to 9 ppm. The procedures and instrumentation are simple for both ranges.

Determination of Nitrate and Exchangeable Ammonium in Soil Extracts by an Ammonia Electrode

AbstractA method for determination of NO3‐ in waters using an NH3 electrode was adapted for use with soils. Nitrate was determined in 1 N KCl soil extracts as the difference in NH3‐N concentration between aliquots treated with NaOH and Devarda's alloy to reduce NO3‐ and aliquots made alkaline without addition of Devarda's alloy. The rate of reduction of NO3‐ to NH3 was temperature dependent. The minimum recommended temperature for the procedure is 23°C. Rate of NH3 loss from solution and NH3 activity measured by the NH3 electrode increased with temperature.Nitrate‐N in extracts of nine Illinois soils determined with the NH3 electrode was highly correlated (r2 = 0.999***)3 with NO3‐‐N analyzed by the phenoldisulfonic acid method. Exchangeable NH4+‐N determined with the modified electrode filling solution was highly correlated (r2 = 0.99***) with exchangeable NH4+‐N determined by steam distillation. In addition to NO3‐, NO2‐ is reduced to NH3 by this procedure. Recovery of added NH4+, NO3‐, and NO2‐ was 97, 97, and 91%, respectively. Precision of NO3‐ and exchangeable NH4+ determinations were 0.2 and 0.1 mg/kg, respectively. The reagents used are relatively inexpensive and safe to handle, and reduction is carried out at room temperature. Only 20 ml of soil extract is required and soils containing 1 to 250 mg NO3‐‐N/Kg can be handled routinely. One worker can analyze 80 extracts/day.

Determination of ammonium in soil extracts and water samples by an ammonia electrode

Abstract Interference and recovery tests reported indicate that the Orion ammonia electrode can be used satisfactorily for determination of ammonium in soil extracts and water samples. The electrode method of analysis described is rapid, simple, and precise, and its results agree closely with those obtained by a distillation‐titration method of determining ammonium in soil extracts and water samples.

Determination of ammonium in soil extracts by an automated indophenol method

An automated method is described for the determination of ammonium in 2 N potassium chloride soil extracts. The determination is based on the indophenol blue method following a dialysing step. As little as 0·03 mg 1–1 of ammonium-nitrogen can be determined. The recoveries have been investigated for a number of different soil types and satisfactory results were obtained. Determinations can be carried out at the rate of thirty samples per hour.