Denitrification loss from a grassland soil in the field receiving different rates of nitrogen as ammonium nitrate

Denitrification loss from a loam under a cut ryegrass sward receiving 0, 250 and 500 kg N ha^?1 a^?1 in four equal amounts was measured during 14 months using the acetylene-inhibition technique. The rate of denitrification responded rapidly to changes in soil water content as affected by rain. Mean rates of denitrification exceeded 0.2 kg N ha^?1 day^?1 only when the soil water content was >20% (w/w) and nitrate was >5μ N g^?1 in the upper 20 cm of the profile and when soil temperature at 2 cm was >5–8°C. When the soil dried to a water content <20%, denitrification decreased to <0.05 kg N ha^?1 day^?1. Highest rates (up to 2.0 kg N ha^?1 day^?1) were observed following application of fertilizer to soil at a water content of about 30% (w/w) in early spring. Denitrification in the control plot during this period was generally about a hundredth of that in plots treated with ammonium nitrate. High rates of N₂O loss (up to 0.30 kg N ha^?1 day-1) were invariably associated with high rates of denitrification (> 0.2 kg N ha^?1 day^?1). However, within 2–3 weeks following application of fertilizer to the plot receiving 250 kg N ha^?1 a^?1 the soil acted as a sink for atmospheric N₂O when its water content was >20% and its temperature >5–8°C. Annual N losses arising from denitrification were 1.6, 11.1 and 29.1 kg N ha^?1 for the plots receiving 0, 250 and 500 kg N ha^?1 a^?1, respectively. More than 60% of the annual loss occurred during a period of 8 weeks when fertilizer was applied to soil with a water content >20%.     

N2O and CH4 fluxes from a volcanic grassland soil in Nasu,Japan: Comparison between manure plus fertilizer plot and fertilizer-only plot

Abstract

We examined the effects of manure + fertilizer application and fertilizer-only application on nitrous oxide (N₂O) and methane (CH₄) fluxes from a volcanic grassland soil in Nasu, Japan. In the manure + fertilizer applied plot (manure plot), the sum of N mineralized from the manure and N applied as ammonium sulfate was adjusted to 210 kg N ha^?1 year^?1. In the fertilizer-only applied plot (fertilizer plot), 210 kg N ha^?1 year^?1 was applied as ammonium sulfate. The manure was applied to the manure plot in November and the fertilizer was applied to both plots in March, May, July and September. From November 2004 to November 2006, we regularly measured N₂O and CH₄ fluxes using closed chambers. Annual N₂O emissions from the manure and fertilizer plots ranged from 7.0 to 11.0 and from 4.7 to 9.1 kg N ha^?1, respectively. Annual N₂O emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). This difference could be attributed to N₂O emissions following manure application. N₂O fluxes were correlated with soil temperature (R = 0.70, P < 0.001), NH⁺ ₄ concentration in the soil (R = 0.67, P < 0.001), soil pH (R = –0.46, P < 0.001) and NO^? ₃ concentration in the soil (R = 0.40, P < 0.001). When included in the multiple regression model (R = 0.72, P < 0.001), however, the following variables were significant: NH⁺ ₄ concentration in the soil (β = 0.52, P < 0.001), soil temperature (β = 0.36, P < 0.001) and soil moisture content (β = 0.26, P < 0.001). Annual CH₄ emissions from the manure and fertilizer plots ranged from –0.74 to –0.16 and from –0.84 to –0.52 kg C ha^?1, respectively. No significant difference was observed in annual CH₄ emissions between the plots. During the third grass-growing period from July to September, however, cumulative CH₄ emissions were greater from the manure plot than from the fertilizer plot (P < 0.05). CH₄ fluxes were correlated with NH⁺ ₄ concentration in the soil (R = 0.21, P < 0.05) and soil moisture content (R = 0.20, P < 0.05). When included in the multiple regression model (R = 0.29, P < 0.05), both NH⁺ ₄ concentration in the soil (β = 0.20, P < 0.05) and soil moisture content (β = 0.20, P < 0.05) were significant.     

Variables controlling denitrification from earthworm casts and soil in permanent pastures

Summary Denitrification (using the acetylene block method) was determined in earthworm casts and soils from permanent, drained or undrained pasture plots fertilized with 0 or 200 kg N ha^-1 year^-1 as ammonium nitrate. Rates of N₂O production from soil cores were about three times higher from the fertilized than from the unfertilized plots while drainage had a relatively small effect. Denitrification rates from casts were 3–5 times higher than those from soil irrespective of the drainage treatment. Casts generally had higher NO _inf3 ^sup- , NH _inf4 ^sup+ , and moisture contents, and higher microbial respiration rates than soil. Rates of N₂O production were determined primarily by NO _inf3 ^sup- supply, secondarily by moisture; available C did not appear to limit denitrification in these pastures. Estimates of the potential contribution of casts to denitrification ranges from 10.1% of 29.3 kg ha^-1 year^-1 from the unfertilized, drained plot to 22% of 82.5 kg ha^-1 year^-1 from the fertilized undrained plot.     

Nitrogen Balance in the Magruder Plots Following 109 Years in Continuous Winter Wheat

Abstract

The Magruder plots are the oldest continuous soil fertility wheat research plots in the Great Plains region, and are one of the oldest continuous soil fertility wheat plots in the world. They were initiated in 1892 by Alexander C. Magruder who was interested in the productivity of native prairie soils when sown continuously to winter wheat. This study reports on a simple estimate of nitrogen (N) balance in the Magruder plots, accounting for N applied, N removed in the grain, plant N loss, denitrification, non‐symbiotic N fixation, nitrate (NO₃ ^?) leaching, N applied in the rainfall, estimated total soil N (0–30 cm) at the beginning of the experiment and that measured in 2001. In the Manure plots, total soil N decreased from 6890 kg N ha^?1 in the surface 0–30 cm in 1892, to 3198 kg N ha^?1 in 2002. In the Check plots (no nutrients applied for 109 years) only 2411 kg N ha^?1 or 35% of the original total soil organic N remains. Nitrogen removed in the grain averaged 38.4 kg N ha^?1 yr^?1 and N additions (manure, N in rainfall, N via symbiotic N fixation) averaged 44.5 kg N ha^?1 yr^?1 in the Manure plots. Following 109 years, unaccounted N ranged from 229 to 1395 kg N ha^?1. On a by year basis, this would translate into 2–13 kg N ha^?1 yr^?1 that were unaccounted for, increasing with increased N application. For the Manure plots, the estimate of nitrogen use efficiency (NUE) (N removed in the grain, minus N removed in the grain of the Check plots, divided by the rate of N applied) was 32.8%, similar to the 33% NUE for world cereal production reported in 1999.     

Nitrogen leaching from grassland ecosystems managed with organic fertilizers at different stocking rates

This study shows the effect of organic fertilizers at different stocking rates, on nitrogen (N) leaching, measured using zero-tension lysimeters under undisturbed grassland soil. The experiment included two organic fertilizer types – cow dung with dung water (D) and slurry (S), both at a range of stocking rates: 0.9 LU (livestock unit) ha^?1, 1.4 LU ha^?1, 2.0 LU ha^?1 (corresponding to 54, 84 and 120 kg N ha^?1, respectively) and a control (C) treatment. In percolated water, the contents of ammonia nitrogen (NH₄⁺–N) and nitrate nitrogen (NO₃^?–N) were studied. The average concentration of NH₄⁺–N ranged from 0.91 to 1.44 mg l^?1 on fertilized plots compared to 0.55 mg l^?1 on the control plot. The average concentration of NO₃^?–N ranged from 5.2 to 9.5 mg l^?1 on fertilized plots compared to 3.2 mg l^?1 on the control plot. The results of this study showed that the use of organic fertilizers at chosen stocking rates influenced N leaching, but the concentration of N did not exceed the limits for drinking water permitted by Czech legislation. Stocking rates at 2.0 LU ha^?1 and below do not result in elevated N concentrations in percolated water that pose environmental threat.     

Influence of drip and furrow irrigation systems on nitrogen oxide emissions from a horticultural crop

Irrigation management has an important influence on emissions of nitrous oxide (N₂O) and nitric oxide (NO) from irrigated agricultural soils. In order to develop strategies to reduce the emission of these gases, a field experiment was carried out to compare the influence of different irrigation systems: furrow (FI) and drip-irrigation (DI), on N₂O and NO emissions from a soil during the melon crop season. Two fertilizer treatments were evaluated for each irrigation regime: ammonium sulphate (AS) as a mineral N fertilizer, at a rate of 175 kg N ha^?1; and a control without any N fertilizer (Control). On plots where the AS treatment was applied, drip irrigation reduced total N₂O and NO emissions (by 70% and 33% respectively) with respect to values for furrow irrigation. This was probably due to the lower amount of water applied and the different soil wetting pattern associated with DI. Dry areas of the drip-irrigated plots emitted a similar amount of N₂O to the wet areas (0.45 kg N₂O-N ha^?1) in the Control and greater quantities in the AS treatment (0.92 kg N₂O-N ha^?1 for dry and 0.70 kg N₂O-N ha^?1 for wet areas). We suggest that the N oxide pulses observed throughout the irrigation period on DI plots could have been the result of frequent increases in the soil wetting volume after the addition of water. Denitrification losses (from depths of 0–10 cm) were estimated at 11.44 kg N₂O- N ha^?1 for the AS treatment under FI and at 4.96 kg N₂O-N ha^?1 for DI. Under DI, nitrification was an important source of N₂O, whereas denitrification was the most important source under FI. The addition of NH₄⁺ and the use of DI enhanced the N₂O/N₂ ratio of gases produced through denitrification. The quantity of dissolved organic C (DOC) in the soil generally decreased with addition of NH₄⁺.This work showed that, in comparison with furrow irrigation, drip irrigation is a method that can be used to save water and mitigate emissions of the atmospheric pollutants NO and N₂O.     

The effects of biocidal treatments on metabolism in soil—V: A method for measuring soil biomass

A new method for the determination of biomass in soil is described. Soil is fumigated with CHCl₃ vapour, the CHCl₃ removed and the soil then incubated. The biomass is calculated from the difference between the amounts of CO₂ evolved during incubation by fumigated and unfumigated soil. The method was tested on a set of nine soils from long-term field experiments. The amounts of biomass C ha^?1 in the top 23 cm of soil from plots on the Broadbalk continuous wheat experiment were 530 kg (unmanured plot), 590 (plot receiving inorganic fertilizers) and 1160 (plot receiving farmyard manure). Soils that had been fallowed for 1 year contained less biomass than soils carrying a crop. A calcareous woodland soil contained 1960 kg biomass C ha^?1, and an unmanured soil under permanent grass 2020. The arable soils contained about 2% of their organic C in the biomass; uncultivated soils a little more—about 3%.     

Nitrous oxide emissions and nitrogen cycling in managed grassland in Southern Hokkaido,Japan

Abstract

Nitrous oxide (N₂O) emissions were measured and nitrogen (N) budgets were estimated for 2?years in the fertilizer, manure, control and bare plots established in a reed canary grass (Phalaris arundinacea L.) grassland in Southern Hokkaido, Japan. In the manure plot, beef cattle manure with bark was applied at a rate of 43–44?Mg fresh matter (236–310?kg?N)?ha^?1?year^?1, and a supplement of chemical fertilizer was also added to equalize the application rate of mineral N to that in the fertilizer plots (164–184?kg?N?ha^?1?year^?1). Grass was harvested twice per year. The total mineral N supply was estimated as the sum of the N deposition, chemical fertilizer application and gross mineralization of manure (GMm), soil (GMs), and root-litter (GMl). GMm, GMs and GMl were estimated by dividing the carbon dioxide production derived from the decomposition of soil organic matter, root-litter and manure by each C?:?N ratio (11.1 for soil, 15.5 for root-litter and 23.5 for manure). The N uptake in aboveground biomass for each growing season was equivalent to or greater than the external mineral N supply, which is composed of N deposition, chemical fertilizer application and GMm. However, there was a positive correlation between the N uptake in aboveground biomass and the total mineral N supply. It was assumed that 58% of the total mineral N supply was taken up by the grass. The N supply rates from soil and root-litter were estimated to be 331–384?kg?N?ha^?1?year^?1 and 94–165?kg?N?ha^?1?year^?1, respectively. These results indicated that the GMs and GMl also were significant inputs in the grassland N budget. The cumulative N₂O flux for each season showed a significant positive correlation with mineral N surplus, which was calculated as the difference between the total mineral N supply and N uptake in aboveground biomass. The emission factor of N₂O to mineral N surplus was estimated to be 1.2%. Furthermore, multiple regression analysis suggested that the N₂O emission factor increased with an increase in precipitation. Consequently, soil and root-litter as well as chemical fertilizer and manure were found to be major sources of mineral N supply in the grassland, and an optimum balance between mineral N supply and N uptake is required for reducing N₂O emission.     

Die Rolle der mikrobiellen Biomasse und des mineralisch fixierten Ammoniums bei den Stickstoff-Transformationen in niedersächsischen Löß-Ackerböden unter Winter-Weizen. I. Poolgrößenveränderungen

Significance of microbial biomass and non-exchangeable ammonium with respect to the nitrogen transformations in loess soils of Niedersachsen during the growing season of winter wheat. I. Change of pool sizes Nitrogen transformations in loess soils have been examined by laboratory and field experiments. After straw application (· 8 t · ha^?1), N in microbial biomass (N_mic) increased by about 20 mg · kg^?1 soil (· 90 kg N · ha^?1 · 30 cm^?1) after 9 days of incubation (20 °C). Another laboratory experiment yielded an increase of about 400 mg of NH₄+-N · kg^?1 fixed by minerals within 1 h after addition of 1 M NH₄+-acetate. Defixation of the recently fixed NH₄+ after addition of 1 M KCl amounted to only 60 mg · kg^?1 within 50 days. In a field experiment with winter wheat 1991, an increase in N_mic of about 80 kg N · ha^?1 · 30 cm^?1 was observed from March to June. After July, growth of the microbes was limited by decreased soluble carbon concentrations in the rhizosphere. Different levels of mineral N-fertilizer (0, 177 and 213 kg N · ha^?1) did not affect significantly the microbial biomass. The same field experiment yielded a decrease of non-exchangeable ammonium on the “zero”-fertilized plot in spring by 200 kg N · ha^?1 · 30 cm^?1. The pool of fixed ammonium increased significantly after harvest. After conventional mineral N-fertilizer application (213 kg N · ha^?1). NH₄+-defixation was only about 120 kg N · ha^?1 · 30 cm^?1 until July.     

Wood ash effects on chemical and microbiological properties of digestate- and manure-amended soils

A field study was carried out to evaluate the potential of wood ash as a fertilizer in grassland systems in combination with enriched N organic wastes. Six treatments including manure or digestate, each combined with wood ash at 0, 1, and 3 t?ha^?1 were spread onto the soil to an amount equivalent to 120 kg?N ha^?1. Three soil samplings and one cutting was carried out within one growing season (3 months). A higher pH value was found in manure-treated plots, the pH rise being proportional to the amount of wood ash added. Those plots amended with digestate were characterized by a larger content of total C, NH₄ ⁺, and total P (TP) regardless of the amount of ashes. Microbial activity, assessed by basal respiration and microbial biomass carbon of the differently treated soils, was not affected neither by the nature of the organic waste nor by the amount of wood ash added. However, amending soil with digestate resulted in a more efficient soil microbial community, as shown by the lower values of the metabolic quotient. Such effects were accompanied by a higher percentage of plant cover, particularly of leguminous plants in digestate-treated plots. The time of sampling (seasonal effects) was found to influence the soil pH and electrical conductivity (EC), as well as the nutrient content (total N, NH₄ ⁺, and NO₃ ^?). Overall, the combined use of wood ash and biogas digestate can constitute an efficient way for the disposal and recycling of both products and additionally, it may constitute an environmentally friendly alternative to mineral fertilizers for acid soils.     

Effects of application of lime nitrogen and dicyandiamide on nitrous oxide emissions from green tea fields

Abstract

The aim of this study was to assess the mitigating effects of lime nitrogen (calcium cyanamide) and dicyandiamide (DCD) application on nitrous oxide (N₂O) emissions from fields of green tea [Camellia sinensis (L.) Kuntze]. The study was conducted in experimental tea fields in which the fertilizer application rate was 544 kg nitrogen (N) ha^?1 yr^?1 for 2 years. The mean cumulative N₂O flux from the soil between the canopies of tea plants for 2 years was 7.1 ± 0.9 kg N ha^?1 yr^?1 in control plots. The cumulative N₂O flux in the plots supplemented with lime nitrogen was 3.5 ± 0.1 kgN ha^?1, approximately 51% lower than that in control plots. This reduction was due to the inhibition of nitrification by DCD, which was produced from the lime nitrogen. In addition, the increase in soil pH by lime in the lime nitrogen may also be another reason for the decreased N₂O emissions from soil in LN plots. Meanwhile, the cumulative N₂O flux in DCD plots was not significantly different from that in control plots. The seasonal variability in N₂O emissions in DCD plots differed from that in control plots and application of DCD sometimes increased N₂O emissions from tea field soil. The nitrification inhibition effect of lime nitrogen and DCD helped to delay nitrification of ammonium-nitrogen (NH₄⁺-N), leading to high NH₄⁺-N concentrations and a high ratio of NH₄⁺-N /nitrate-nitrogen (NO₃^–-N) in the soil. The inhibitors delayed the formation of NO₃^–-N in soil. N uptake by tea plants was almost the same among all three treatments.     

Effect of Raw and NH4+-enriched Zeolite on Nitrogen Uptake by Wheat and Nitrogen Leaching in Soils with Different Textures

Leaching of nutrients in soil can change the surface and groundwater quality. The present study aimed at investigating the effects of raw and ammonium (NH₄⁺)-enriched zeolite on nitrogen leaching and wheat yields in sandy loam and clay loam soils. The treatments were one level of nitrogen; Z₀: (100 kg (N) ha^?1) as urea, two levels of raw zeolite; Z₁:(0.5 g kg^?1 + 100 kg ha^?1) and Z_2: (1 g kg^?1 + 100 kg ha^?1), and two levels of NH₄⁺-enriched zeolite; Z₃: (0.5 g kg^?1 + 80 kg ha^?1) and Z₄: (1 g kg^?1 + 60 kg ha^?1). Wheat grains were sown in pots and, after each irrigation event, the leachates were collected and their nitrate (NO₃^?) and NH₄⁺ contents were determined. The grain yield and the total N in plants were measured after four months of wheat growth. The results indicated that the amounts of NH₄⁺ and NO₃^? leached from the sandy loam soil were more than those from the clay loam soil in all irrigation events. The maximum and minimum concentrations of nitrogen in the drainage water for both soils were observed at control and NH₄⁺-zeolite treatments, respectively. Total N in the plants grown in the sandy loam was higher compared to plants grown in clay loam soil. Also, nitrogen uptake by plants in control and NH₄⁺-zeolite was higher than that of raw-zeolite treatments. The decrease in the amount of N leaching in the presence of NH₄⁺-zeolite caused more N availability for plants and increased the efficiency of nitrogen fertilizers and the plants yield.     

长期施肥对土壤固定态铵含量及其有效性影响

棕壤连续13年定位试验表明,长期施用化肥或低量有机肥对土壤固定态接含量均无显著影响;而施用高量有机肥区固定态接含量比试验前平均增加30.2％。这部分增加的固定态按主要来自土壤有机氮矿化补充。施肥后固定态铵的净增加量超过作物施氮量是土壤激发效应的结果。土壤原有固定态铵含量在113～116mg／kg,对作物无效,而新固定态按时作物有效。生长季耕层土壤固定态铵总释放量（N）对照区为43kg／hm2,化肥区平均为110kg／hm2;有机肥与化肥配合区平均为165kg／hm2。施钾对固定态铵的释放有一定抑制作用。     

Does the potential ammonium fixation of soils have an impact on the optimum nitrogen fertilizer rate?

Field experiments were conducted to determine the effect of nitrogen (N) fertilizer forms and doses on wheat (Triticum aestivum L.) on three soils differing in their ammonium (NH₄) fixation capacity [high = 161 mg fixed NH₄-N kg^?1 soil, medium = 31.5 mg fixed NH₄-N kg^?1 soil and no = nearly no fixed NH₄-N kg^?1 soil]. On high NH₄⁺ fixing soil, 80 kg N ha^?1 Urea+ ammonium nitrate [NH₄NO₃] or 240 kg N ha^?1 ammonium sulfate [(NH₄)₂SO₄]+(NH₄)₂SO₄, was required to obtain the maximum yield. Urea + NH₄NO₃ generally showed the highest significance in respect to the agronomic efficiency of N fertilizers. In the non NH₄⁺ fixing soil, 80 kg N ha^?1 urea+NH₄NO₃ was enough to obtain high grain yield. The agronomic efficiency of N fertilizers was generally higher in the non NH₄⁺ fixing soil than in the others. Grain protein was highly affected by NH₄⁺ fixation capacities and N doses. Harvest index was affected by the NH₄⁺ fixation capacity at the 1% significance level.     

Nitrous oxide emission from simulated overland flow wastewater treatment systems

Nitrous oxide evolution was measured from overland flow models receiving daily applications of municipal wastewater with NH₄⁺-N concentration in the wastewater of 10 or 47 μgN ml^?1. The amount of N₂O evolved from the system ranged from 0.07 to 1.3 mg N day^?1, or 1.5–25.5 kg N ha^?1yr^?1, respectively. Liming the soil or increasing the NH₄⁺-N in the wastewater increased the emission of N₂O from the system. The N evolved as N₂O did not exceed 1.2% of the applied NH₄⁺-N, indicating N₂ to be the major denitrification end product in the overland flow wastewater-treatment system.     

Seasonal pattern of denitrification under an irrigated wheat-maize cropping system fertilized with urea and farmyard manure in different combinations

Under semiarid subtropical field conditions, denitrification was measured from the arable soil layer of an irrigated wheat–maize cropping system fertilized with urea at 50 or 100 kg N ha^–1 year^–1 (U₅₀ and U₁₀₀, respectively), each applied in combination with 8 or 16 t ha^–1 year^–1 of farmyard manure (FYM) (F₈ and F₁₆, respectively). Denitrification was measured by acetylene inhibition/soil core incubation method, also taking into account the N₂O entrapped in soil cores. Denitrification loss ranged from 3.7 to 5.7 kg N ha^–1 during the growing season of wheat (150 days) and from 14.0 to 30.3 kg N ha^–1 during the maize season (60 days). Most (up to 61%) of the loss occurred in a relatively short spell, after the presowing irrigation to maize, when the soil temperature was high and a considerable NO₃^–-N had accumulated during the preceding 4-month fallow; during this irrigation cycle, the lowest denitrification rate was observed in the treatment receiving highest N input (U₁₀₀+F₁₆), mainly because of the lowest soil respiration rate. Data on soil respiration and denitrification potential revealed that by increasing the mineral N application rate, the organic matter decomposition was accelerated during the wheat-growing season, leaving a lower amount of available C during the following maize season. Denitrification was affected by soil moisture and by soil temperature, the influence of which was either direct, or indirect by controlling the NO₃^– availability and aerobic soil respiration. Results indicated a substantial denitrification loss from the irrigated wheat–maize cropping system under semiarid subtropical conditions, signifying the need of appropriate fertilizer management practices to reduce this loss.     

Effect of long-term beef manure application on soil test phosphorus,organic carbon,and winter wheat yield

In this study, 24 years (1990–2013) of data from a long-term experiment, in Stillwater, Oklahoma (OK), were used to determine the effect of beef manure on soil test phosphorus (STP), soil organic carbon (SOC), and winter wheat (Triticum aestivum L.) yield. Beef manure was applied every 4 years at a rate of 269 kg nitrogen (N) ha^?1, while inorganic fertilizers were applied annually at 67 kg N ha^?1, 14.6 kg phosphorus (P) ha^?1, and 27.8 kg potassium (K) ha^?1 for N, P, and K, respectively. Averaged across years, application of beef manure, and inorganic P maintained STP above 38 mg kg^?1 of Mehlich-3 extractable P, a level that is far beyond crop requirements. A more rapid decline in SOC was observed in the check plot compared to the manure-treated plot. This study shows that the application of animal manure is a viable option to maintaining SOC levels, while also optimizing grain yield.     

Evaluation of denitrification losses by the acetylene inhibition technique in a permanent ryegrass field (Lolium perenne L.) fertilized with animal slurry or ammonium nitrate

In a field experiment, the effect of animal slurry, (with and without the nitrification inhibitor dicyandiamide on total denitrification losses estimated by the C₂H₂ inhibition technique was measured over 2 years (1989–1990). During this period, four different plots (each with four replicates) were fertilized six times with 150 kg N ha^-1 in the form of cattle-pig slurry or NH₄NO₃. Soil samples (0–20 cm) were analysed at regular intervals for NH _inf4 ^sup+ and NO _inf3 ^sup– concentrations. The soil water content was determined gravimetrically. During the first year (1989) total denitrification losses from unfertilized, mineral-fertilized, and animal slurry-amended plots (with or without dicyandiamide) were estimated as 0.2, 3.1, 0.7, and 0.6 kg N ha^-1, respectively. During the second year (1990) the denitrification losses were 0.4, 1.3, 0.7, and 0.7 kg N ha^-1, respectively. There was a clear relationship between the NO _inf3 ^sup– concentration or soil water content and the denitrification rate. The results are siteund experiment-specific and cannot be generalized so far.     

Re-Evaluation of Soil Nitrogen Sampling Strategy Effects on Statistical Power

Soil sampling may be used as a decision-making tool for late-vegetative stage nitrogen (N) fertilizer applications in corn (Zea mays L.). Recommended sampling strategies following banded fertilizer applications commonly suggest taking cores from both on the fertilizer band (B) and off the band (O-B), however we hypothesized that soil nitrate concentrations (NO₃^?ppm) in the O-B were not influenced by N application rate. Analyzing samples from six experiments, we found there was a strong relationship between NO₃^?ppm and applied N rate in the B, but not the O-B position. Power analysis revealed that finding significant differences in applied N rates was only likely when sampling on the B and the difference in N rate was greater than 110 kg N ha^?1. This demonstrates that soil N sampling is not sensitive to small differences in applied N, and that O-B soil cores may only dilute the ability to detect these differences.

Abbreviations: B, on N fertilizer band; O-B, halfway between the corn row and the N fertilizer band; NO₃^?ppm, log-transformed nitrate-N concentration (ppm); NH₄⁺ppm; ammonium-N concentration (ppm); D1, 0–30 cm depth; D2, 30–60 cm depth; C-220, contrast of N rates differing by 220 kg N ha^?1; C-110, contrast of N rates differing by 110 kg N ha^?1; C-55H, contrast of N rates differing by 55 kg N ha^?1 at high N rates; C-55L, contrast of N rates differing by 55 kg N ha^?1 at low N rates; A:N, ratio of non-transformed ammonium-N to nitrate-N concentrations; 0N, unfertilized treatment; CV, coefficient of variation; SE, standard error.     

What happens to in situ net soil nitrogen mineralization when nitrogen fertility changes?

Does net soil nitrogen (N) mineralization change if N‐fertility management is suddenly altered? This study, conducted in a long‐term no‐tillage maize (Zea mays L.) fertility experiment (established 1970), evaluated how changing previous fertilizer N (PN) management influenced in situ net soil N mineralization (NSNM). Net soil N mineralization was measured by incubating undisturbed soil cores with anion and cation exchange resins. In each of three PN fertilizer application plots (0, 84, and 336 kg N ha^?1), another three fertilizer application rates (0, 84, and 336 kg N ha^?1) were imposed and considered the current fertilizer N (CN) management. Generally, PN‐336 (336 kg N ha^?1) had significantly greater NSNM than PN‐0 (0 kg N ha^?1) or PN‐84 (84 kg N ha^?1), which reflected differences in soil organic‐C (SOC) and soil total‐N (STN). The three CN rates had no significant effect on NSNM when they were applied to PN‐0 or PN‐84, but CN‐336 (336 kg N ha^?1) had significantly higher NSNM than CN‐0 (0 kg N ha^?1) or CN‐84 (84 kg N ha^?1) in the PN‐336 plots. The CN or “added N interaction” used the indigenous soil organic matter (SOM) pool and the added sufficient fertilizer N. Environmental factors, including precipitation and mean air temperature, explained the most variability in average daily soil N mineralization rate during each incubation period. Soil water content at each sampling day could also explain NSNM loss via potential denitrification. We conclude that “added N interaction” in the field condition was the combined effect of SOM and sufficient fertilizer N input.