Nitrate leaching,nitrous oxide emission and N use efficiency of aerobic rice under different N application strategy

A field study was conducted in the sub-humid tropical region of India to examine the effect of different nitrogen (N) management strategies on nitrate leaching, nitrous oxide (N₂O) emission and N use efficiency in aerobic rice. Treatments were: control (no N), 120 kg N ha^?1 applied as prilled urea (PU) in conventional method, 120 kg N ha^?1 applied as neem coated urea (NCU) in conventional method, N applied as PU on the basis of leaf colour chart (LCC) reading, N applied as NCU on the basis of LCC reading, and 120 kg N ha^?1 applied as PU and farm yard manure (FYM) in 1:1 ratio. Results showed that 3.4–16.1 kg NO₃-N ha^?1 was leached below 45 cm depth and 0.61–1.12 kg N₂O-N ha^?1 was emitted from aerobic rice during the growing season. NCU when applied conventionally reduced nitrate-nitrogen (NO₃-N) leaching and N₂O emission by 18.6% and 21.4%, respectively However when applied on the basis of LCC reading NCU reduced NO₃-N leaching by 39.8% as compared to PU applied in conventional method. NCU when applied on the basis of LCC reading synchronized N supply with demand and reduced N loss, which resulted in higher yield and N use efficiency.     

Fluxes of N2O from farmed peat soils in Finland

Agricultural peat soils are important sources of nitrous oxide (N₂O). Emissions of N₂O were measured from field plots of grass, barley, potatoes and fallow on a peat field in northern Finland during 2000–2002 and in southern Finland in 1999–2002. In the north the mean annual fluxes of N₂O (with their standard errors) during 2 years were 4.0 (±1.2), 13 (±3.0) and 4.4 (±0.8) kg N ha^?1 from the plots of grass, barley and fallow, respectively. In the north there were no significant thaw periods in the middle of winter. As a result, the thawing in the spring did not induce especially large N₂O emissions. Emissions of N₂O were larger in the south than in the north. In the southern peat field the mean annual fluxes during 3 years were 7.3 (±1.2), 15 (±2.6), 10 (±1.9) and 25 (±6.9) kg N₂O‐N ha^?1 for grass, barley, potato and fallow plots, respectively. Here, the largest single episodes of emission occurred during the spring thaw each year, following winter thaw events. An emission factor of 10.4 kg N₂O‐N ha^?1 year^?1 for the N₂O emission from the decomposition of the peat results from these data if the effect of fertilization according to the IPCC default emission factor is omitted. The direct effect of adding N as fertilizer on N₂O emissions was of minor importance. On average, 52% of the annual N₂O flux entered the atmosphere outside the cropping season (October–April) in the north and 55% in the south. The larger N₂O fluxes from the peat soil in the south might be due to the more humified status of the peat, more rapid mineralization and weather with more cycles of freezing and thawing in the winter.     

Nitrous oxide emissions from a rainfed-cultivated black soil in Northeast China: effect of fertilization and maize crop

Nitrous oxide emission (N₂O) from applied fertilizer across the different agricultural landscapes especially those of rainfed area is extremely variable (both spatially and temporally), thus posing the greatest challenge to researchers, modelers, and policy makers to accurately predict N₂O emissions. Nitrous oxide emissions from a rainfed, maize-planted, black soil (Udic Mollisols) were monitored in the Harbin State Key Agroecological Experimental Station (Harbin, Heilongjiang Province, China). The four treatments were: a bare soil amended with no N (C0) or with 225?kg?N ha^?1 (CN), and maize (Zea mays L.)-planted soils fertilized with no N (P0) or with 225?kg?N ha^?1 (PN). Nitrous oxide emissions significantly (P?<?0.05) increased from 141?±?5?g N₂O-N?ha^?1 (C0) to 570?±?33?g N₂O-N?ha^?1 (CN) in unplanted soil, and from 209?±?29?g N₂O-N?ha^?1 (P0) to 884?±?45?g N₂O-N?ha^?1 (PN) in planted soil. Approximately 75?% of N₂O emissions were from fertilizer N applied and the emission factor (EF) of applied fertilizer N as N₂O in unplanted and planted soils was 0.19 and 0.30?%, respectively. The presence of maize crop significantly (P?<?0.05) increased the N₂O emission by 55?% in the N-fertilized soil but not in the N-unfertilized soil. There was a significant (P?<?0.05) interaction effect of fertilization?×?maize on N₂O emissions. Nitrous oxide fluxes were significantly affected by soil moisture and soil temperature (P?<?0.05), with the temperature sensitivity of 1.73–2.24, which together explained 62–76?% of seasonal variation in N₂O fluxes. Our results demonstrated that N₂O emissions from rainfed arable black soils in Northeast China primarily depended on the application of fertilizer N; however, the EF of fertilizer N as N₂O was low, probably due to low precipitation and soil moisture.     

Zeolite influences on nitrate leaching,nitrogen-use efficiency,yield and yield components of canola in sandy soil

With regard to the low cation-exchange capacity and large saturated hydraulic conductivity of sandy soils, a field experiment was carried out in 2006–2007 to determine the impact of zeolite on nitrogen leaching and canola production. Four nitrogen (N) rates (0, 90, 180, and 270 kg ha^–1) and three zeolite amounts (3, 6 and 9 t ha^?1) were included as treatments. The results demonstrated that the highest growth parameters and seed yield were attained with 270 kg N ha^?1 and 9 t zeolite ha^?1. However, the highest and the lowest seed protein percentage and oil content were obtained with 270 kg N ha^?1 accompanied by 9 t zeolite ha^?1, respectively. Nitrate concentration in drained water was affected by nitrogen and zeolite. The lowest and highest leached nitrate values were found in control without N and zeolite (N₀Z₀) and in treatments with the highest N supply without zeolite (N₂₇₀Z₀), respectively. In general, nitrogen-use efficiency decreased with an increase in N supply. Application of 9 t zeolite ha^?1 showed higher nitrogen use efficiency than other zeolite amounts. Also, application of more N fertilizer in soil reduced nitrogen uptake efficiency. In total, application of 270 kg N ha^?1 and 9 t zeolite ha^?1 could be suggested as superior treatment.     

Denitrification losses from 15N-labelled calcium nitrate fertilizer in a clay soil in the field

Calcium nitrate fertilizer containing 92.3 atoms % excess nitrogen-15 was applied on 5 May 1981 at a rate equivalent to 100 kg N ha^?1 to a clay soil in southern England cropped to winter wheat. Samples of the soil gases were collected frequently during the following 3 weeks. The soil oxygen concentration declined to 5% after 60 mm rain. A maximum of 1.5 ± 0.5 atom % N-15 enrichment in labelled N₂ gas (²⁹N₂) was detected in the soil atmosphere on 28 May. Total denitrification losses, calculated from air-filled pore space and rates of gas loss from the soil estimated using a Fick's law approximation, were 9.5 kg N ha^?1 with a daily rate of 0.30 ± 0.07 kg N ha^?1. Estimated total losses were greater than 30 kg N ha^?1, 93% in the form N₂, but the estimation depends on several assumptions about the amount of double labelled gas (³⁰N₂), rates of gas diffusion and flux.     

Effect of nitrogen fertilization, cropping and irrigation on soil air composition and nitrous oxide emission in a loamy clay

Most of the nitrous oxide (N₂O) in the atmosphere, thought to be involved in global warming, is emitted from soil. Although the main factors controlling the production of N₂O in soil are well known, we need more quantitative data on the interactions of soil and the environment in the soil that affect the emission. We therefore studied the effects of irrigation, cropping (fallow, barley with grass undersown) and N fertilization (unfertilized, 103 kg N ha^?1) on the composition of soil air and direct N₂O emission from soil (using the closed chamber method) in a factorial field experiment on a well‐structured loamy clay soil during 1 June?22 October 1993. The measurements were made weekly during the growing season and three times after harvesting. The composition of the soil air did not indicate severe anoxia in any treatment or combination of treatments, but the accumulation of N₂O in the soil air indicated that hypoxia was common. At the start of the irrigation the emissions were small, even though there was much ammonium and nitrate in the soil and therefore a potential for emission of N₂O produced by both nitrification and denitrification. Larger emissions occurred later. The largest emissions were found when 60–90% of the soil pore space was filled with water. Irrigation and fertilization with N both roughly doubled the cumulative N₂O emission. Growing a crop decreased it by a factor of 3–7. Most N₂O was lost from the irrigated fertilized soil under fallow (3.5 kg N ha^?1), and least from the unirrigated unfertilized soil under barley (0.1 kg N ha^?1).     

Einfluß von Bodeneigenschaften,Bodennutzung und Bodentemperatur auf die N-Mobilisierung von Kulturböden

Influence of soil characteristics, agricultural use and soil temperature on the N-mobilization of cultivated soils A new N-mobilization model, which considers also the short term and seasonal N-supplying capacity of soil is presented. At a fixed time the potential mobilizable N (N-MOB) is a sum of difficultly mobilizable N (N-MOB_s) originating from the pool of difficultly mobilizable N (N_s) and the easily mobilizable N (N-MOB₁) originating from the pool of easily mobilizable N (N₁). It is possible to characterize soil according to their M₁, N-MOB_s and v (N-MOB_s per day) values. Usefulness of these parameters in N-nutrition and ground water burden from N has been discussed. Basic parameters of this model have been experimentally determined independently with the help of two different experiments i. e. laboratory incubation and column lysimeter using surface soil samples. The easily mobilizable N pool (N₁) values were found in the range of 142 to 814 kg N ha^?1 which corresponded to 1.2 to 7.4 % of organic N content of these soils. The difficultly mobilizable N per day (i. e. v = N-MOB_s per day) in an incubation experiment (35°C) were found in the range of 1.5 to 24kg N ha^?1. However, in the column lysimeter experiment, in contrast, these values at 10°C ranged between 0.05 to 0.9 kg N ha^?1. These values correspond to N-MOB_s values in the range of 11–182 kg N·ha^?1 for a period of 200 days which approximate to a vegetation period. For practical purposes, the N₁ and v values could be calculated by just measuring 3–4 points after 14 days of incubation at 35°C. The results show that N-MOB_s values strongly correlated compared to N₁ values to total N, organic carbon and clay content and non significantly to pH and silt content. The results of an laboratory incubation experiment carried out to assess the effect of temperature on N-mobilization show that even at 0°C there was N-mobilization. The results revealed that in the temperature range of 0–8°C (a range of soil temp. usually observed in winter months) and in the range of 25–40°C (range of summer months temp. for surface arable soil), a small change in the soil temperature would result in enormous increase in the quantity of mobilized N. The highest mobilized N quantity was found above 60°C.     

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.     

Annual emissions of nitrous oxide and nitric oxide from a wheat–maize cropping system on a silt loam calcareous soil in the North China Plain

Nitrogen amendment followed by flooding irrigation is a general management practice for a wheat–maize rotation in the North China Plain, which may favor nitrification and denitrification. Consequently, high emissions of nitrous oxide (N₂O) and nitric oxide (NO) are hypothesized to occur. To test this hypothesis, we performed year-round field measurements of N₂O and NO fluxes from irrigated wheat–maize fields on a calcareous soil applied with all crop residues using a static, opaque chamber measuring system. To interpret the field data, laboratory experiments using intact soil cores with added carbon (glucose) and nitrogen (nitrate, ammonium) substrates were performed. Our field measurements showed that pulse emissions after fertilization and irrigation/rainfall contributed to 73% and 88% of the annual N₂O and NO emissions, respectively. Soil moisture and mineral nitrogen contents significantly affected the emissions of both gases. Annual emissions from fields fertilized at the conventional rate (600 kg N ha⁻¹ yr⁻¹) totaled 4.0 ± 0.2 and 3.0 ± 0.2 kg N ha⁻¹ yr⁻¹ for N₂O and NO, respectively, while those from unfertilized fields were much lower (0.5 ± 0.02 kg N ha⁻¹ yr⁻¹ and 0.4 ± 0.05 kg N ha⁻¹ yr⁻¹, respectively). Direct emission factors (EF_ds) of N₂O and NO for the fertilizer nitrogen were estimated to be 0.59 ± 0.04% and 0.44 ± 0.04%, respectively. By summarizing the results of our study and others, we recommended specific EF_ds (N₂O: 0.54 ± 0.09%; NO: 0.45 ± 0.04%) for estimating emissions from irrigated croplands on calcareous soils with organic carbon ranging from 5 to 16 g kg⁻¹. Nitrification dominated the processes driving the emissions of both gases following fertilization. It was evident that insufficient available carbon limited microbial denitrification and thus N₂O emission. This implicates that efforts to enhance carbon sink in calcareous soils likely increase their N₂O emissions.     

Effect of Alternating Furrow Irrigation and Nitrogen Fertilizer on Nitrous Oxide Emission in Corn Field

The objectives of this 2-year field study were to assess the effects of irrigation and nitrogen (N) application on nitrous oxide (N₂O). Soil N₂O flux was determined using open-bottomed chambers. Nitrous oxide concentrations were determined with gas chromatography. The results showed that in 2008, N₂O emission rates ranged from 2.0 to 50.0 g N ha^?1 d^?1 in the alternating furrow irrigation and N application treatments (AFINA) and from 2.4 to 68.4 g N ha^?1 d^?1 in the conventional every-furrow irrigation and fertilization treatment (CIF). In 2009, cumulative N₂O-N loss in the optimal combination with greater yields and lower N₂O emission in AFINA was 1277 g N ha^?1 compared to 1695 g N ha^?1 with CIF. The study indicated that AFINA practices combined with optimum N fertilizer and irrigation rates could reduce soil N₂O emission and water input compared to CIF practices without causing a decline in corn yield.     

Nitrous oxide emission from a grassland soil fertilized with slurry and calcium nitrate

Concentrations of nitrous oxide (N₂O) and oxygen were monitored over a 2-yr period in an imperfectly drained grassland soil receiving applications of N as cattle slurry or Ca(NO₃)₂. In both years N₂O concentrations in the different treatments were in the order nitrate > slurry > control. Gaseous diffusion coefficients were determined in soil cores by a krypton-85 tracer method and used to calculate approximate N₂O fluxes from the soil. Only 1–5 kg N ha^?1 was lost as N₂O after a single application of > 1200 kg N ha ^?1 as slurry compared with 3–11 kg N ha ^?1 lost after 100 kg was added as NO₃^?. Total gaseous losses (N₂O+N₂) could be expected to be higher in both cases.     

Effects of Conventional and Stabilized Urea Fertilizers on Soil Biological Status

Effects of stabilized urea fertilizers [Alzon 46 (A) and UREAstabil (US)] on soil microbiological and chemical parameters and also on grain yield, 1000-grain weight, and oil content were tested in a precise field study on Luvisol in 2010–2012. Winter rapeseed (Brassica napus L. cv. Californium) was fertilized both in autumn [45 kg nitrogen (N) ha^?1] and in spring (155 kg N ha^?1) with A [urea with DCD (dicyandiamide) plus pyrrodiazole (1,2,4-1H-triazole)], US {urea with NBPT [N-(n-butyl)-thiophosphoric acid triamide]}, and conventional N fertilizers (pure urea, calcium ammonium nitrate). Eleven parameters were used to evaluate the soil status: microbial biomass carbon (C; microwave method [MW]), dehydrogenase activity, arylsulfatase activity, available organic carbon, electroconductivity, C_org (MW method), and pH (in water, H₂O). None of the 11 parameters demonstrated significant difference between control, conventional N fertilizers, and stabilized urea fertilizers. The greatest yield significantly different from the control (zero kg N ha^?1; 2598 ± 881 kg ha^?1) was found for both stabilized urea fertilizers: A (200 kg N ha^?1; 3772 ± 759 kg ha^?1) and US (200 kg N ha^?1; 3764 ± 625 kg ha^?1). The control achieved the greatest oil content (46.0 ± 1.2%), which was significantly different from all N-fertilized variants, and also the greatest 1000-grain weight (5.62 ± 0.62 g).     

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%.     

Nitrous oxide emissions from artificial urine patches applied to different N-fertilized swards and estimated annual N2O emissions for differently fertilized pastures in an upland location in Germany

Abstract. Artificial urine containing 20.2 g N per patch of 0.2 m² was applied in May and September to permanent grassland swards of a long‐term experiment in the western uplands of Germany (location Rengen/Eifel), which were fertilized with 0, 120, 240, 360 kg N ha^?1 yr^?1 given as calcium ammonium nitrate. The effect on N₂O fluxes measured regularly during a 357‐day period with the closed‐chamber technique were as follows. (1) N₂O emission varied widely among the fertilized control areas without urine, and when a threshold water‐filled pore space >60% was exceeded, the greater the topsoil nitrate content the greater the flux from the individual urine patches on the fertilized swards. (2) After urine application in May, 1.4–4.2% of the applied urine‐N was lost as N₂O from the fertilized swards; and after urine application in September, 0.3–0.9% of the applied urine‐N was lost. The primary influence on N₂O flux from urine patches was the date of simulated grazing, N‐fertilization rate being a secondary influence. (3) The large differences in N₂O emissions between unfertilized and fertilized swards after May‐applied urine contrasted with only small differences after urine applied in September, indicating an interaction between time of urine application and N‐fertilizer rate. (4) The estimated annual N₂O emissions were in the range 0.6–1.6 kg N₂O‐N per livestock unit, or 1.4, 3.6, 4.1 and 5.1 kg N₂O‐N ha^?1 from the 0–360 kg ha^?1 of fertilizer‐N. The study demonstrated that date of grazing and N‐fertilizer application could influence the N₂O emission from urine patches to such an extent that both factors should be considered in detailed large‐scale estimations of N₂O fluxes from grazed grassland.     

Nitrous oxide emissions, cereal growth, N recovery and soil nitrogen status after ploughing organically managed grass/clover swards

The period after ploughing of grass–clover leys within a ley‐arable rotation is when nitrogen accumulated during the ley phase is most vulnerable to loss. We investigated how ploughing date and timing of cessation of grazing before ploughing affected nitrous oxide (N₂O) losses of the first cereal crop. Ploughing dates were July and October for a winter wheat pilot study and January and March for spring barley in the main experiment. Timings of cessation of grazing (main experiment only) were October, January and March. Spring barley yield, nitrogen uptake and soil mineral nitrogen were also assessed. A separate large‐scale laboratory incubation was made to assess the effect of temperature and rainfall on nitrous oxide emissions and nitrate leaching under controlled conditions. Nitrous oxide emissions in the 1‐ to 2‐month period after autumn or spring ploughing, or sowing were typically between 20 and 150 g N ha^?1 day^?1 and increased with temperature and rainfall. Tillage for crop establishment stimulated N₂O emissions with up to 2.1 kg N ha^?1 released in the month after spring tillage. Cumulative nitrous oxide emissions were greatest (～8 kg ha^?1 over 17 months) after cessation of grazing in March before March ploughing, and lowest (～5.5 kg ha^?1) after cessation of grazing in January before January ploughing. These losses were 1.2–3.9% of the N inputs. In the laboratory study, winter ploughing stimulated nitrate leaching more than nitrous oxide emissions. The optimum time of ploughing appears to be early spring when the cold restricts nitrogen mineralization initially, but sufficient nitrogen becomes available for early crop growth and satisfactory N offtake as temperature increases. Early cessation of grazing is advantageous in leaving an adequate supply of residues of good quality (narrow C:N ratio) for ploughing‐in. Restricting tillage operations to cool, dry conditions, being aware of possible compaction and increasing the use of undersown grass–clover should improve the sustainability of organic farming.     

Effect of biochar and nitrapyrin on nitrous oxide and nitric oxide emissions from a sandy loam soil cropped to maize

A field experiment was conducted to evaluate the combined or individual effects of biochar and nitrapyrin (a nitrification inhibitor) on N₂O and NO emissions from a sandy loam soil cropped to maize. The study included nine treatments: addition of urea alone or combined with nitrapyrin to soils that had been amended with biochar at 0, 3, 6, and 12 t ha^?1 in the preceding year, and a control without the addition of N fertilizer. Peaks in N₂O and NO flux occurred simultaneously following fertilizer application and intense rainfall events, and the peak of NO flux was much higher than that of N₂O following application of basal fertilizer. Mean emission ratios of NO/N₂O ranged from 1.11 to 1.72, suggesting that N₂O was primarily derived from nitrification. Cumulative N₂O and NO emissions were 1.00 kg N₂O-N ha^?1 and 1.39 kg NO-N ha^?1 in the N treatment, respectively, decreasing to 0.81–0.85 kg N₂O-N ha^?1 and 1.31–1.35 kg NO-N ha^?1 in the biochar amended soils, respectively, while there was no significant difference among the treatments. NO emissions were significantly lower in the nitrapyrin treatments than in the N fertilization-alone treatments (P?<?0.05), but there was no effect on N₂O emissions. Neither biochar nor nitrapyrin amendment affected maize yield or N uptake. Overall, our results showed that biochar amendment in the preceding year had little effect on N₂O and NO emissions in the following year, while the nitrapyrin decreased NO, but not N₂O emissions, probably due to suppression of denitrification caused by the low soil moisture content.     

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.     

Potential mineralization and nitrification in volcanic grassland soils in Chile

Abstract

A proportion of the nitrogen (N) applied to grasslands as organic or inorganic fertilizers can be lost to water courses as nitrate and to the atmosphere as nitrous and nitric oxides. Volcanic soils from Chile are not generally prone to leaching, possibly due to net immobilization of nitrate and/or ammonium, and/or due to inhibition of nitrification by either chemical or physical processes. In laboratory studies we found large mineralization potentials in soils from three different Chilean soils after 17 weeks of incubation, totalling 215 and 254 mg kg^?1 dry soil for two Andisols and 127 mg kg^?1 dry soil in an Ultisol. Nitrification occurred after a short period, and was lowest in the Ultisol. In addition, microbial analysis showed nitrifiers to be present in all three soils. Adsorption of ammonium was two-fold stronger than for nitrate, ranging from 29 to 180 kg N ha^?1. The highest potential for N adsorption in the 0–60 cm soil profile was with the Ultisol (398 kg N ha^?1), but was similar in both Andisols (193 and 172 kg N ha^?1, respectively). The combination of ammonium retention together with delayed nitrification could account for the low leaching rates in these soils.     

Simulation des Nitrataustrags im Winterhalbjahr aus Intensiv genutzten Ackerböden in der Geest

Modeling nitrate leaching during the winter halfyear from sandy arable soils under intensive cultivation Three years (1989–91) of post harvest and winter nitrogen dynamics (August to March) were simulated in 20 arable sandy soils to quantify nitrate leaching during winter time. Easily accessible soil, weather and management data were used for a simple but deterministic model. The calculated mineral N (N_min) content and distribution in the soil (0–90 cm) were compared to more than 100 measurements from September to March each season. An overall agreement of approximately 50% between measured and simulated N_min values was obtained. The simulation over- or underestimated the measured N_min depending on the rainfall and temperature distribution which varied from year to year. Practically, the effect of fertilizer application was largely (60%) responsible for deviations greater than ±20 kgN ha^?1 from the 1:1-line. Ignoring these instances, 80% of the simulated N_min contents were within these “confidence limits” of ±20 kgN ha^?1. Considering the nitrogen distribution in the profile, the N_min content is underestimated in the top soil, but overestimated in the subsoil. Based on the 95% confidence intervals (measured versus simulated) the estimate was better for the lower (30–90 cm) than for the upper part of the profile (0–30 cm). It is concluded that winter leaching can be reduced from 130 kgN ha^?1 (corn, winter grain) to about 10 kgN ha^?1 growing winter hard forage crops. Two major processes were identified as reasons for the disagreement and are proposed for further model improvement: (1) The simulation underestimates the short term transport velocity on the basis of field capacity derived from survey data. (2) Nitrogen is mineralized quickly in sandy soils, especially after catch crops, and sometimes due to freeze-thaw effects. Furthermore, as ammonium remains in the surface, nitrification needs to be explicitly simulated.     

Denitrifikationsverluste eines gemüsebaulich genutzten Bodens in Abhängigkeit von der mineralischen N-Düngung

Denitrification losses from a horticultural soil as affected by mineral N-fertilization To investigate denitrification in the A_p-horizon from a horticultural cambisol as affected by mineral N-fertilization, measurements of N₂O-release from the soil surface and N₂O-production in the upper 10 cm soil layer were carried out. The acetylene inhibition technique was used. The loamy sand was amended with 86 and 186 kg N·ha^?1 (ammonium nitratecalcium carbonate mixture). The field was cropped with celeriac (Apium graveolens L. var. rapaceum). Denitrification rates as well as soil temperature, moisture, nitrate and watersoluble carbon were measured from mid July until the end of October. In both N treatments denitrification rates were low, but higher rates could be measured in the higher N-treatment. They reached amounts of 0.6 to 134.3 g N₂O-N·ha^?1day^?1. Estimated N-loss by denitrification totalled about 3.5 in the low and 4.9 kg N·ha^?1 in the high N-treatment for the whole sampling period (107 days). Spatial variability of denitrification rates was high (39–283%). The relationship between soil temperature, moisture, nitrate content as well as watersoluble carbon and denitrification rate was shown by regression analysis.