Denitrification Losses Research Articles

Effect of an increasing carbon: nitrate-N ratio on the reliability of acetylene in blocking the N2O-reductase activity of denitrifying bacteria in soil

In model experiments with a silty loam soil the effect of different C : NOinf3sup--N ratios on the reliability of C2H2 (1% v/v) in blocking N2O-reductase activity was examined. The soil was carefully mixed with different amounts of powdered lime leaves (Tilia vulgaris) to obtain organic C contents of about 1.8, 2.3, and 2.8%, and of NOinf3sup-solution to give C : NOinf3sup--N ratios of 84, 107, 130, 156, 200, and 243. The soil samples were incubated in specially modified anaerobic jars (22 days, 25°C, 80% water-holding capacity, He atmosphere) and the atmosphere was analysed for N2, N2O, CO2, and C2H2 by gas chromatography at regular intervals. Destruction jars were used to analyse soil NOinf3sup-, NH4+and C. The results clearly showed that N2O-reductase activity was completely blocked by 1% (v/v) C2H2 only as long as NOinf3sup-was present. In the presence of C2H2, NOinf3sup-was apparently entirely converted into N2O. The C2H2 blockage of N2O-reductase activity ceased earlier in soils with a wide C : NOinf3sup--N ratio (156, 200, and 243) than in those with closer C : NOinf3sup--N ratios (84, 107, and 130). As soon as NOinf3sup-was exhausted, N2O was reduced to N2 in spite of C2H2. The wider the C : NOinf3sup--N ratio, the earlier the production of N2 and the less the reliability of the C2H2 blockage. In the untreated control complete inhibition of N2O-reductase activity by C2H2 lasted for 7–12 days. In the field, estimates of total denitrification losses by the C2H2 inhibition technique should be considered reliable only as long as NOinf3sup-is present. Consequently, NOinf3sup-monitoring in the field is essential, particularly in soils supplied with easily decomposable organic matter.

Denitrification measured directly using a single-inlet mass spectrometer and by acetylene inhibition

Most published efforts to measure total denitrification losses directly by mass spectrometry have employed dual-inlet mass spectrometers, which correct for instrumental drift between samples. Here we have employed a simpler and cheaper single-inlet instrument to measure fluxes from, and concentrations of denitrification gases, a clay loam under grass in southeast Scotland. The method involves periodic recalibration of the individual detectors using standard gas mixtures, and online sample pretreatment with an elemental analyser. Results exhibit the same patterns as more conventional measurements using field application of the acetylene inhibition technique, but consistently exceed them. This provides further evidence that the acetylene technique is not satisfactory for heavy-textured soils.

Seasonal fluctuations in the mineral nitrogen content of an undrained wetland peat soil following differing rates of fertiliser nitrogen application

Fluctuation in soil mineral nitrogen (N) caused by repeated applications of fertiliser N were investigated over 3 years in wetland hay meadows in Somerset. Swards were cut for hay after 1 July each year and the aftermath grazed continuously with beef cattle until October. Several N treatments between 0 (N-0) and 200 kg N ha −1 year −1 (N-200) were applied in two equal dressings each year. Denitrification rates were estimated over two consecutive autumn-winter periods, using a soil core incubation method. A high proportion of soil N was in nitrate form for most of the year and therefore at risk of loss from both leaching and denitrification. Estimated losses of total soil mineral N (ammonium plus nitrate) between October and March averaged 17.8 kg N ha −1 at N-0, 30.0 kg N ha −1 at N-100 and 88.2 kg N ha −1 at N-200for the 3 years 1987–1988, 1988–1989 and 1989–1990. Denitrification losses were significantly related to the amount of applied N in both 1988–1989 and 1989–1990, but only accounted for a small proportion of the N loss from N-200 soils. Mean leaching losses in autumn-winter were estimated at about 5 kg N ha −1 for N-0, 17 kg N ha −1 at N-100 and 67 kg N ha −1 at N-200. Further losses were suspected during the 1988 summer, when prolonged rain following N application resulted in flooding in early October. These estimates are based solely upon indirect measurements of N loss, but they do give a good indication of the scale of losses incurred. It is concluded that these soils are particularly susceptible to N leaching, as a result of a combination of high water-tables and apparently rapid conversion of ammonium N to nitrate (nitrification). Annual fertiliser rates should be kept below 100 kg N ha −1 to avoid leaching risk. Taking an earlier cut for hay or silage could increase N efficiency and reduce losses of mineral N into the environment, although early cutting might be unacceptable because of its adverse effect on the breeding success of wading birds.

Limits to denitrification in two pasture soils in a temperate maritime climate

Factors limiting denitrification in pasture soils under the climatic conditions typical of western Britain were investigated. Water and temperature were expected to be the most important factors in the control of denitrification but pasture management, season and spatial variability were also studied. Soil cores were incubated in bottles to examine the relative importance of water and temperature. Soils were incubated at field temperature with and without acetylene to block the reduction of nitrous oxide (N 2O) to nitrogen gas (N 2). Two pasture systems were studied: grass/fertiliser receiving 150 kg N ha −1 and grass/clover. The average rate of denitrification was 10 g N ha −1 day −1 under grass/ clover. Fertiliser increased the average rate to 60 g N ha −1 day −1 with a maximum of 500 g N ha −1 day −1. There was a larger potential for denitrification than could be realised, in part, by rainfall and solar warming because an average of 1600 g N ha −1 day −1 was measured from wet soils at room temperature. When these rates were corrected for the initial lag because of enzyme synthesis, the maximum rate was 5000 g N ha −1 day −1. Dung and urine from sheep caused spatial diversity. Under grass/clover in the autumn 70% of the denitrification loss came from only 14% of the area. Seasonal variations were confounded with variations caused by pasture management. Most denitrification losses occurred after the fertiliser applications on the grass/fertiliser pasture. Under grass/clover the fastest rates were measured in the autumn. Nitrous oxide formed 40–80% of the denitrification product from grass/clover. Its response to fertiliser varied widely. In March, fertiliser apparently caused the value to exceed 100% nitrous oxide; an artifact of the acetylene blocking method attributed to the release of nitrous oxide during nitrification. The value later fell to 20% nitrous oxide. A new model of denitrification was derived from published data, specifically to check the validity of the incubation data. In the model, denitrification depended on soil water content, temperature and nitrate supply. In these soils, the nitrogen supply limited field denitrification more than any other factor, followed in importance by soil moisture and temperature.

Measured and simulated denitrification activity in a cropped sandy and loamy soil

Denitrification activities were measured over a 3-year period in a coarse sandy soil and a sandy loam soil. In all years the crops were spring barley in combination with Italian ryegrass as a catch crop. The denitrification loss was measured using the acetylene inhibition technique on soil cores. Furthermore, a simple model was developed, based on daily values of soil moisture and soil temperature, to calculate the denitrification loss. Soil temperatures for the model were measured, whereas soil moisture was derived from a water-balance model. Measurements of denitrification gave an annual loss of 0.6 kg N ha-1, and the model calculated a loss of 1–2 kg N ha-1 in the coarse sandy soil. In the sandy loam soil annual losses were measured as 1.5, 3.0, and 13.0 kg N ha-1 in 1988, 1989, and 1990, respectively. The corresponding values from the model simulation were 14, 9 and 14 kg N ha-1.

Denitrification activity in the root zone of a sludge-amended desert soil

We evaluated potential NO inf3 sup- losses from organic and inorganic N sources applied to improve the growth of cotton (Gossypium hirsutum) on a Pima clay loam soil (Typic Torrifluvent). An initial set of soil cores (April 1989) was collected to a depth of 270 cm from sites in a cotton field previously amended with anaerobically digested sewage sludge or an inorganic N fertilizer. The denitrification potential was estimated in all soil samples by measuring N2O with gas chromatography. Soils amended with a low or high rate of sludge showed increased denitrification activity over soil samples amended with a low rate or inorganic N fertilizer. All amended samples showed greater denitrification activity than control soils. The denitrification decreased with soil depth in all treatments, and was only evident as deep as 90 cm in the soils treated with the high sludge rate. However, when soils collected from depths greater than 90 cm were amended with a C substrate, significant denitrification activity occurred. These date imply that organisms capable of denitrification were present in all soil samples, even those at depths far beneath the root zone. Hence, denitrification was C-substrate limited. A second series of soil cores taken later in the growing season (July 1989) confirmed these data. Denitrification losses (under laboratory conditions) to a soil depth of 270 cm represented 1–4% of total soil N depending on treatment, when the activity was C-substrate limited. With additional C substrate, the denitrification losses increased to 15–22% of the total soil N.

Factors controlling nitrification and denitrification: A laboratory study with gel-stabilized liquid cattle manure

Nitrification and denitrification were studied in a millimeterscale microenvironment using a two-phase system with a liquid manure-saturated layer. Samples consisted of liquid cattle manure and air-dried soil stabilized with silica gel, placed between two aerobic soil phases with a water content near field capacity. A high potential for NH4 (+) oxidation developed within 0-2 mm distance from the interface, and NH4 (+) diffused only 10-20 mm into the soil. Some NH4 (+) was probably immobilized by microorganisms in the soil between 0 and 4 days, after which nitrification was the only sink for NH4 (+). A potential for denitrification developed within the manure-saturated zone. Maximum rates of both potential and actual denitrification were recorded by Day 4, but denitrification continued for at least 2-3 weeks. The potential for nitrification peaked after 14 days. When the pH of the manure was adjusted to 5.5, nitrification was reduced close to the interface, and NH4 (+) penetrated further into the soil before it was oxidized. The pH adjustment had an inhibitory effect on denitrification: Both potential and actual rates of denitrification were almost eliminated for several days. The size of the manure-saturated layer strongly affected denitrification losses. With layers of 8 and 16 mm thickness, losses equivalent to 33 and 40% of the original NH4 (+) pool, respectively, were estimated. When manure corresponding to a 12 mm layer was homogeneously mixed with the soil, only 0.3% was lost.

Potential rates of denitrification in two field soils in southern England

SUMMARYPotential rates of denitrification from two field soils, differing in past history, were measured by anaerobic incubation of fresh samples in a glasshouse maintained at 15–25 °C at ARC Letcombe Laboratory, Wantage, Oxfordshire in 1981. Nitrate was not limiting. The topsoils (0–20 cm) from both sites denitrified more than the subsoils (20–60 cm). The production of nitrous oxide was positively correlated with the carbon content of the soils while potential rates of denitrification in the two soils were similar. The total accumulated loss of nitrogen was greater from the soil with the greater organic carbon content. The use of acetylene showed that the denitrification losses were underestimated by measuring only nitrous oxide. N2O was still being reduced to N2 even after 100 h continuous exposure to acetylene.

Denitrification and N 2O production in pasture soil: the influence of nitrogen supply and moisture

Denitrification was studied in packed soil columns and in soil cores in a controlled environment facility. The soils were kept warm (10–15°C) and moist (70–90% water-filled porosity). Urine, urea, ammonium or nitrate alone were added at rates typical of pasture systems. The denitrification from native nitrogen was low (less than 0.02 kg N ha −1 day −1) and addition of ammonium nitrate caused a rapid tenfold increase. All forms of nitrogen given at rates similar to urine deposits in the field gave much higher denitrification (up to 0.3–1.0 kg N ha −1 day −1); the highest rate came from 80 kg N ha −1 as nitrate (4.8 kg N ha −1 day −1). Nitrous oxide formed 8–76% of the product, but was always a smaller part of the product from ammonium nitrate (10–25%) than from urea (45–75%). Some of this extra nitrous oxide from urea probably came from nitrification not denitrification. This was calculated to be 50% in the controlled environment studies but was only 11% in a parallel field study. Field denitrification losses, based on these results, could range from 3 kg N ha −1 year −1, with neither added nitrogen nor grazing, to 20 kg N ha −1 year −1 or more from a grazed pasture with 200 kg N ha −1 year −1 fertiliser nitrogen.

Quantifying denitrification on a field scale in hummocky terrain

In this study a landscape classification and daily climatic data were used to extrapolate from a number of discrete denitrification rate measurements to an annual field average. Denitrification rates were calculated from modelled daily moisture contents and observed daily temperature using regression equations. Different regression equations were used for crop and fallowed fields, and for three distinct landscape groups; depositional, intermediate, and erosional. Good correlations were found between predicted and measured denitrification rates. Annual denitrification losses were greatest under fallow, ranging from 50.5 kg N ha−1 on the low level landscape element to 3.1 kg N ha−1 on the diverging blackslope. Losses from cropped soil ranged from 12.8 kg N ha−1 on the diverging footslope in 1988 to 0.7 kg N ha−1 on the diverging backslope in 1986. Field average denitrification losses were estimated to be 3 kg N ha−1 in 1986 (wheat), 16 kg N ha−1 in 1987 (the fallow year) and 4 kg N ha−1 in 1988 (canola). Key words: Denitrification, annual field averages, landscape elements, soil properties, simulation model

Decreased salinity effects in Lake Kinneret (Israel)

Kinneret is the only freshwater lake in Israel. It currently supplies about 30% of national water demands. Most pumped water is for drinking, and water quality is of major concern. During 1970–1987 temporal changes were observed in the lake ecosystem: decrease of salinity, decrease of total N (TN) and increase of total P (TP) mass contents, decline of TN/TP ratio, increase of phytoplankton biomass and increase of algal photosynthetic specific activity. It is suggested that because of decrease in salinity carbonic anhydrase activities in algal cells and nitrifying bacteria were enhanced. The increase of NO3 flux through nitrification consequently enhanced denitrification and nitrogen losses in lake waters. These increased N losses together with P increase, as reflected by the decline of TN/TP ratio might be a slight shift from the present both P and N deficiencies to a higher level of N limitation in the Kinneret ecosystem. This This may cause changes in phytoplankton community structure possibly without changing primary production levels but deteriorate water quality.

Denitrification‐ and Nitrate Leaching‐Losses in an Intensively Cropped Watershed

AbstractIn continuation of former measurements about gaseous denitrification losses, these losses together with those by nitrate leaching were measured by different methods in a field cropped during two years by wheat. Furthermore, N‐uptake by the plants of fertilizer‐ and soil‐N as well as N‐im‐mobilization in soils during and after the cropping periods was determined by application of highly enriched15N‐labeled fertilizer.Denitrification losses determined by the N2O release from C2H2–treated undisturbed soil cores agreed reasonably well with losses obtained by 15N‐balance measurements. They both amounted during the cropping periods 12–15 and 6–20 kg N ha−1, respectively. Gaseous N‐losses increased mainly during wet periods when the field was barren. Denitrifying enzyme activities and soil respiration (CO2‐release) was measured throughout one year.Leaching losses of NO3 from soil‐and fertilizer‐N occurred only during fall until spring. Leached NO3− originated mostly from mineralized soil‐N and very little from previously immobilized fertilizer‐N.

Simulation of field scale denitrification losses from soils under grass ley and barley

Denitrification losses from soils under barley and grass ley crops were simulated. The model, which includes the major processes determining inputs, transformations and outputs of nitrogen in arable soils, represents a scale compatible with information generally available in agricultural field research. The denitrification part of the model includes a field potential denitrification rate and functions for the effect of soil aeration status, soil temperature and soil nitrate content. Easily metabolizable organic matter is assumed not to limit denitrification. Simulated values were compared with denitrification measurements made during two growing seasons in the barley and grass ley treatments of a field experiment in central Sweden.

Reuse of Wastewater from Meat Processing Plants for Agricultural and Forestry Irrigation

Meat-processing wastewaters contain high concentrations of nitrogen, phosphorus and potassium (in this study 40-230 g m−3, 6-35 g m−3 and 20-130 g m−3 respectively), but only low concentrations of heavy metals and other toxic compounds. The nutrients can be recovered by agricultural or forestry irrigation schemes. Application of these wastes to land in excess of plant requirements results in elevated concentrations of organic nitrogen, nitrate, phosphorus, potassium and sodium in the plant material, with nitrate approaching levels toxic to ruminant animals. Excess phosphorus that is applied to the land is precipitated as metal phosphates, and excess nitrogen is partially denitrified, thereby reducing nitrate contamination of ground water. At an experimental pasture site, receiving nitrogen loadings of 1200 kg N ha−1 y−1, denitrification losses averaged about 4% of that applied. Denitrification losses at an experimental forestry site receiving 715 kg N ha−1 y−1 averaged about 27%. Similar losses were observed at a full-scale pasture and forestry irrigation site. Sodium concentrations in meat processing wastewaters could, on occasions, detrimentally affect soil structure and sodium concentrations should be closely monitored.

Denitrification potentials, controls and spatial patterns in a Norway spruce plantation

The effects of lime and urea applications on denitrification losses from a lowland Norway spruce forest were investigated. Amendments of soil cores in the laboratory, together with field experiments, showed moisture to be the main factor regulating denitrification at this site. Lime increased the ratio of N 2/N 2O gas products but not total rates of N losses; urea and lime caused a four-fold increase in denitrification; but urea alone had a comparatively small effect, suggesting N saturation of this stand. In the light of variability of nitrification and nutrient inputs, the need for a clearer understanding of the controls on spatial and temporal patterns of denitrification is stressed.

Crop Residue Type and Placement Effects on Denitrification and Mineralization

AbstractNutrient release from legume and cereal crop residue is important to N crycling and the success of conservation and sustainable farming systems. Residue type, placement, and degree of incorporation, and soil water regimes largely control availability and loss of soil N and were evaluated in the laboratory. Four residues, i.e., vetch (Vicia villosa Roth.), soybean (Glycine max [L.] Merr.), corn (Zea mays L.), and wheat (Triticum aestivum L.) having C/N ratios ranging from 8 to 82 were applied on the soil surface or incorporated in repacked cores of a Nicollet loam (fine‐loamy, mixed, mesic Aquic Hapludoll) and incubated for 17 or 35 d at 60 and 90% water‐filled pore space (WFPS) with enriched 15N‐NO3 (76.7%). Denitrification losses from all treatments were negligible at 60% WFPS. At 90% WFPS, total denitrification losses from residue‐incorporated soils represented 87 to 127% of the initial soil NO3 level (80.5 mg N kg−1); losses increased with decreasing residue C/N ratio. Denitrification was greatest during the first 8 d, as was CO2 evolution. Initial denitrification with surface‐placed residues was less than with incorporated residues, but cumulative losses over 35 d did not differ significantly. Substantial N immobilization occurred with incorporated or surface‐placed wheat, corn, and soybean residue with wide C/N ratios at 60% WFPS, whereas, with low‐C/N‐ratio vetch, significant mineralization occurred. After 35 d, 51 and 36% of N in incorporated and surface‐placed vetch residue, respectively, was mineralized. Residue C/N ratio was inversely related to initial rates of residue decomposition, and effects of residue type and placement and soil water on denitrification and mineralization were most important during early (8‐10 d) decomposition.

Cover crop management effects on soybean and corn growth and nitrogen dynamics in an on-farm study

AbstractCombining cover crops and conservation tillage may result in more sustainable agricultural production practices. Objectives of this on-farm study were to quantify effects of cover crops on growth and nitrogen accumulation by soybean [Glycine max (L.) Merr,] and corn (Zea mays L.) on a Nicollet loam (fine-loamy, mixed, mesic Aquic Hapludoll) near Boone, Iowa, Our farmer-cooperator planted soybean in 1988 using ridge tillage into an undisturbed strip with a hairy vetch (Vicia villosa L. Roth) cover crop and into a strip where previous crop residue and a negligible amount of cover crop had been incorporated by autumn and spring disking. In each strip, we established four plots for soil and plant measurements. Our cooperator planted corn on the same strips in 1989 into a cover crop that consisted of both hairy vetch and winter rye (Secale cereale L.). We determined the source of N accumulated by the corn by applying 67 kg N/ha of 15N depleted NH4NO3 fertilizer. In the absence of cover crops, early season soil NO3-N levels in the top 30 cm were higher, and corn growth and N accumulation were more rapid. At harvest, the corn grain, stover, and cob together accounted for 36 and 39 percent of the 15N fertilizer for the ridge tillage and disked treatments, respectively. We suggest that lower net mineralization of organic matter or greater denitrification losses before planting reduced the availability of soil N, This created an early season Nstress in corn grown with cover crops that was not overcome by broadcast fertilizer N applied three weeks after planting. Our on-farm research study has helped focus continuing efforts to determine if non-recovered fertilizer N is being immobilized in microbial biomass, lost by denitrification, or leached below the plant root zone.

Patterns of denitrification loss from grazed grassland: Effects of N fertilizer inputs at different sites

Factors influencing the seasonal and daily variation in denitrification rates in grazed swards were examined at 5 experimental sites in England with wide ranging environmental/geographic conditions. There was a wide range of fertilizer inputs at each site. Rates of denitrification were estimated by a coring and field incubation technique using acetylene to inhibit the reduction of N2O to N2. Major features of the detailed results from two of the sites were: (i) the large ranges in rates of loss, (ii) the relatively low contributions to total annual loss during autumn and winter, (iii) the apparent association of high rates of loss with fertilizer additions made when the soil was wet or immediately preceding a rainfall event, and (iv) significant losses from soil at 10–30 cm in the profile. Multiple quadratic regression analysis of the effects of soil NO3 --N, soil temperature and water was used to explain variability in rates of loss. When separate regressions were fitted within each site × year × season × fertilizer level subset, 51% of the variation in loss was explained on a poorly drained fine loam/silt but only 38% on a freely drained loam.

Legume residue and soil water effects on denitrification in soils of different textures

Legume cover crops commonly used to supply additional N and reduce potential for over-winter N leaching losses may also influence denitrification depending upon soil water status and soil type. Interrelationships between incorporated hairy vetch ( Vicia villosa) residue and soil water status on denitrification in coarse, medium and fine textured soils were investigated in the laboratory. Repacked soil cores were incubated, 10, 20 and 30 d with and without acetylene (C 2H 2). Denitrification losses were 20–200 μg N kg −1 from each soil when 60% of the soil pore space was filled with water and increased to from 14.0 to 18.6mg N kg −1 at 90% water-filled-pore space (WFPS). Incorporation of vetch residue (2.5 g kg −1) greatly stimulated denitrification (51.1–99.5 mg N kg −1), probably due to greater availability of organic C as indicated by higher CO 2 emissions. The major denitrification losses occurred during the first 10 days and more so in residue-amended soils. The supply of C from incorporated legume crop residue was a major factor influencing denitritication especially when soil wetness restricted aeration and adequate nitrate was present. At similar water contents, rates of denitrification differed greatly in soils of varying texture, but when varying water holding capacity and bulk density were accounted for using WFPS. all soils behaved very similarly. Use of WFPS as an index of aeration status enabled identification that differences in denitrification losses in vetch-amended soils of varying texture resulted in part from varying capacity to supply NO 3 − and metabolize organic matter. These results illustrate the utility of WFPS, compared with soil water content, and its reliability as an indicator of reduced aeration dependent denitrification for soils of varying texture.

Dinitrogen and Nitrous Oxide Flux from Urea Basally Applied to Puddled Rice Soils

AbstractNitrification‐denitrification is often regarded as an important N loss process in puddled rice soils, but few direct field measurements of denitrification loss have been reported. Field studies were conducted on a Typic Tropaquept in Thailand, an Aeric Tropaqualf in Indonesia, and an Andaqueptic Haplaquoll in the Philippines to measure (N2 + N2O)‐15N flux, (N2 + N2O)‐15N trapped in soil, and total gaseous 15N loss following basal application of 15N‐labeled urea (87 kg N ha−1) to irrigated rice (Oryza sativa L.) grown on puddled soils. Urea treatments included broadcast applications with and without incorporation to 0.07‐m soil depth. Directly measured (N2 + N2O)‐15N flux during the 10 d following urea application by each method was less than 0.1% of the applied N at the Thailand and Indonesia sites. The (N2 + N2O)‐15N collected from the soil after 10 d did not exceed 0.02% of the applied N. Total gaseous N loss determined from a 15N balance at 10 d after N application without incorporation was 34% of the applied N in Thailand and 31% in Indonesia. Incorporation reduced total N loss to 22% in Thailand and 10% in Indonesia. In the Philippines, the measured (N2 + N2O)‐15N flux during the 15 d immediately following urea application with incorporation was 2.2% of the applied N with chambers placed between rice plants and 3.0% with chambers over the plants. Total N loss at the Philippine site was 40% of the applied N. Ammonia volatilization appeared to be much more important than nitrification‐denitrification as a mechanism of urea‐N loss at the three irrigated lowland study sites.