黑垆土有机氮组分对可矿化氮的关系

Mineralizable N and organic N components in different layers (0-15, 15-30, 30-45, 45-60, 60-80 and 80-100 cm) of six soils with different fertilities sampled from Yongshou County, Shaanxi Province, China,were determined by the aerobic incubation method and the Bremner procedure, respectively. Correlation,multiple regression and path analyses were performed to study the relation of minerallzable N to organic N components. Results of correlation and regression analyses showed that the amounts of the N mineralized were parallel to, and significantly correlated with, the total acid hydrolyzahle N, but was not so with the acid-insoluble N. Of the hydrolyzable N, the amino acid N and the ammonia N had a highly consistent significant correlation with the mineralized N, and their partial regression coefficients were significant in the regression equations, showing their importance in contribution to the mineralizable N. The amino sugar N, on the other hand, had a relatively high correlation with the mineralized N, but their partial regression coefficients were not significant in the regression equations. In contrast, the hydrolyzable unknown N had no such relations.Path analysis further indicated that the amino acid N and ammonia N made great direct contributions to the mineralized N, but the contributions of the amino sugar N were very low. These strongly suggested tha tthe mineralized N in the soils tested was mainly from the hydrolyzable N, particularly the amino acid N and ammonia N which are the major sources for its production.     

Pedotransfer functions for the pool size of slowly mineralizable organic N in sandy arable soils

The major aim of this study was to evaluate how the pool size of slowly mineralizable, ‘old’ soil organic N can be derived from more easily accessible soil and site information via pedotransfer functions (PTF). Besides modeling, this pool size might be of great importance for the identification of soils with high mineralization potential in drinking‐water catchments. From long‐term laboratory incubations (ca. 200 days) at 35 °C, the pool sizes of easily mineralizable organic N (N_fast), mainly in fresh residues, and slowly mineralizable, ‘old’ soil organic N (N_slow) as well as their first‐order rate coefficients were obtained. 90 sandy arable soils from NW Germany served to derive PTFs for N_slow that were evaluated using another 20 soils from the same region. Information on former land‐use and soil type was obtained from topographical, historical, and soil maps (partly from 1780). Pool size N_slow very strongly depends on soil type and former land‐use. Mean pool sizes of N_slow were much lower in old arable lowland (105 mg N kg^–1) than upland soils (175 mg N kg^–1) possibly due to lower clay contents. Within lowlands, mean pool sizes in former grassland soils (245 mg N kg^–1) were 2 to 3 times larger than in old arable soils due to accumulation of mineralizable N. In contrast, mean pool sizes of N_slow were lowest in recently cleared, former heath‐ and woodland (31 mg N kg^–1) as a result of the input of hardly decomposable organic matter. Neither N nor C in the light fraction (density < 1.8 g cm^–3) was adequate to derive pool size N_slow in the studied soils (r² < 0.03). Instead, N_slow can be accurately (r² = 0.55 – 0.83) derived from one or two basic soil characteristics (e.g. organic C, total N, C : N, mineral fraction < 20 μm), provided that sites were grouped by former land‐use. Field mineralization from N_slow during winter (independent data set) can be predicted as well on the basis of N_slow‐values calculated from PTFs that were derived after grouping the soils by former land‐use (r² = 0.51***). In contrast, using the PTF without soil grouping strongly reduced the reliability (r² = 0.16).     

Determination of potentially mineralizable nitrogen in agricultural soil

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

Effect of burning on soil organic matter content and N mineralization under shifting cultivation system of Karen people in Northern Thailand

In the traditional shifting cultivation system practiced by the Karen people in northern Thailand, the effects of burning on the content of extractable organic matter, microbial biomass, and N mineralization process of the soils were studied. Five plots (5×5 m² quadrat) with 0, 10, 20, 50, and 100 Mg ha^-1 of slashed materials were arranged and burned. Ten to 20 Mg ha^-1 of slashed biomass corresponded to the amount commonly burned by the Karen people. During the burning process, the soil temperature at the depth of 2.5 cm in the 100 Mg ha^-1 plot almost evenly increased to 300°C while the temperature in the 10 to 50 Mg ha^-1 plots increased with large variations from 50 to 300°C. Burning caused a conspicuous increase in the contents of organic C and (organic + mineral)-N extracted at room temperature and a simultaneous decrease in the contents of microbial biomass C and N, especially in the soil of the 100 Mg ha^-1 plot. In the rainy season, the values of the changes induced by burning reverted to the values recorded before burning, except for the microbial biomass in the 100 Mg ha^-1 plot, which still remained lower. Based on an incubation experiment, N mineralization rate was higher in the soils taken just after burning, especially in the 100 Mg ha^-1 plot, than in the soils taken during the rainy season. However, the soil in the 100 Mg ha^-1 plot was considered to have the lowest ability to supply mineral N among the soils in the rainy season. Burning of 10 to 20 Mg ha^-1 biomass corresponding to the values recorded in Karen peoples' shifting cultivation system was more compatible with soil ecology in terms of N supply at the initial stage of crop growth and of microbial biomass recovery during the rainy season, compared to the burning of 100 Mg ha^-1 biomass corresponding to the value recorded in a natural forest. Thus, the shifting cultivation system implemented by the Karen people can be considered to be a well-balanced agricultural system.     

Extraction of nitrogen from soils

Summary A roller bed and rotary end-over-end shaker were compared for the extraction of mineral N from a variety of soil types; both were equally efficient with an optimum extraction time of 30 min. However, the roller bed permitted a greater operational capacity, a faster throughput of samples, and easier identification of sample bottles compared with the end-over-end shaker. More NH₄ ⁺-N and NO₃ ^–-N (P<0.001) was recovered from soil by 2 M KCl than by any other extractant, in a soil: extractant ratio of 1 to 5 (w:v), except water, which was equally efficient at removing NO₃ ^–-N from soils.     

Soluble organic nitrogen in agricultural soils

 The existence of soluble organic forms of N in rain and drainage waters has been known for many years, but these have not been generally regarded as significant pools of N in agricultural soils. We review the size and function of both soluble organic N extracted from soils (SON) and dissolved organic N present in soil solution and drainage waters (DON) in arable agricultural soils. SON is of the same order of magnitude as mineral N and of equal size in many cases; 20–30 kg SON-N ha^–1 is present in a wide range of arable agricultural soils from England. Its dynamics are affected by mineralisation, immobilisation, leaching and plant uptake in the same way as those of mineral N, but its pool size is more constant than that of mineral N. DON can be sampled from soil solution using suction cups and collected in drainage waters. Significant amounts of DON are leached, but this comprises only about one-tenth of the SON extracted from the same soil. Leached DON may take with it nutrients, chelated or complexed metals and pesticides. SON/DON is clearly an important pool in N transformations and plant uptake, but there are still many gaps in our understanding. Received: 10 June 1999     

不同形态氮肥对玉米产量和土壤浸提性有机质的影响

田间条件下,研究了不同形态氮肥(尿素、NH4+-N和NO3--N)对玉米产量、根际和非根际土壤氮和浸提性有机质的影响.结果表明,施氮处理的产量和吸氮量明显高于不施肥处理;施氮处理中,NO3--N和尿素处理开花前吸氮量显著高于NH4+-N处理,产量也略高于NH4+-N处理,但未达到显著水平;不同氮形态处理之间的土壤NH4+-N、NO3--N和浸提性有机碳(EOC)、氮(EON)没有差异;抽雄期EOC最高,与根系生长发育一致,而EON苗期相对最高.可见,在基础肥力较高的黑土上,不同形态氮肥对玉米产量、土壤养分影响不明显.     

Hot water extractable C and N in relation to microbiological properties of soils under beech forests

Hot water extraction is sometimes recommended as an easy method to estimate the readily mineralizable fractions of total C (C_t) and total N (N_t) in arable soils. However, the usefulness of this method for forest soils has not been adequately studied. The objectives of this study were to relate the hot water extractable C (C_hw) and N (N_hw) to microbiological and chemical properties of the forest soils under beech (Fagus sylvatica L.) stands and to test the ability of near infrared spectroscopy (NIRS) to predict chemical and microbial properties of these soils. Soils differing in humus type, soil type and soil texture were collected from five locations and five depths. In all soils the amount of C_hw was higher than the microbial biomass C (C_mic) indicating that a considerable part of C_hw was of non-microbial origin. The amount of C_hw in mineral soil correlated significantly (r =–0.30–0.53) with C_mic, basal respiration (BAS) and C_t/N_t ratio but was not related to C_mic/C_t ratio. The amount of N_hw was correlated with C_mic, BAS, C_mic/C_t ratio, and C_t/N_t ratio (r =–0.59–0.78). However, C_t and N_t values showed better relationships (r =–0.42–0.88) with all the parameters, indicating no advantage in using C_hw and N_hw in forest soils. NIRS predicted satisfactorily C_t, N_t, C_hw, N_hw, C_mic, C_mic/C_t ratio and BAS in the mineral soils [the regression coefficients (a) of linear regression (measured against predicted values) ranged from 0.84 to 1.17 and the correlation coefficients (r) ranged from 0.86 to 0.94] indicating the applicability of NIRS to estimate these properties.     

Effect of cropping systems on nitrogen mineralization in soils

 Understanding the effect of cropping systems on N mineralization in soils is crucial for a better assessment of N fertilizer requirements of crops in order to minimize nitrate contamination of surface and groundwater resources. The effects of crop rotations and N fertilization on N mineralization were studied in soils from two long-term field experiments at the Northeast Research Center and the Clarion-Webster Research Center in Iowa that were initiated in 1979 and 1954, respectively. Surface soil samples were taken in 1996 from plots of corn (Zea mays L.), soybean (Glycine max (L.) Merr.), oats (Avena sativa L.), or meadow (alfalfa) (Medicago sativa L.) that had received 0 or 180 kg N ha^–1 before corn and an annual application of 20 kg P and 56 kg K ha^–1. N mineralization was studied in leaching columns under aerobic conditions at 30  °C for 24 weeks. The results showed that N mineralization was affected by cover crop at the time of sampling. Continuous soybean decreased, whereas inclusion of meadow increased, the amount of cumulative N mineralized. The mineralizable N pool (N _o) varied considerably among the soil samples studied, ranging from 137 mg N kg^–1 soil under continuous soybean to >500 mg N kg^–1 soil under meadow-based rotations, sampled in meadow. The results suggest that the N _o and/or organic N in soils under meadow-based cropping systems contained a higher proportion of active N fractions. Received: 10 February 1999     

Labile organic matter fractions as early‐season nitrogen supply indicators in manure‐amended soils

Soil test indicators are needed to predict the contribution of soil organic N to crop N requirements. Labile organic matter (OM) fractions containing C and N are readily metabolized by soil microorganisms, which leads to N mineralization and contributes to the soil N supply to crops. The objective of this study was to identify labile OM fractions that could be indicators of the soil N supply by evaluating the relationship between the soil N supply, the C and N concentrations, and C/N ratios of water extractable OM, hot‐water extractable OM, particulate OM, microbial biomass, and salt extractable OM. Labile OM fractions were measured before planting spring wheat (Triticum aestivum L.) in fertilized soils and the soil N supply was determined from the wheat N uptake and soil mineral N concentration after 6 weeks. Prior to the study, fertilized sandy loam and silty clay soils received three annual applications of 90 kg available N (ha · y)^?1 from mineral fertilizer, liquid dairy cattle manure, liquid swine manure or solid poultry litter, and there was a zero‐N control. Water extractable organic N was the only labile OM fraction to be affected by fertilization in both soil types (P < 0.01). Across both test soils, the soil N supply was significantly correlated with the particulate OM N (r = 0.87, P < 0.001), the particulate OM C (r = 0.83, P < 0.001), and hot‐water extractable organic N (r = 0.81, P < 0.001). We conclude that pre‐planting concentrations of particulate OM and hot‐water extractable organic N could be early season indicators of the soil N supply in fertilized soils of the Saint Lawrence River Lowlands in Quebec, Canada. The suitability of these pre‐planting indicators to predict the soil N supply under field conditions and in fertilized soils from other regions remains to be determined.     

Contribution of α-amino N to extractable organic nitrogen (DON) in three soil types from the Scottish uplands

Organic nitrogen (DON) was extracted from two improved pasture soils, one of which had been re-colonized by acid heath vegetation, and a blanket peat. Although the quantities extracted in H₂O, 10 mM CaCl_2, 500 mM K₂SO₄ and 50 mM Na₂HPO₄ were not consistent, mean extractable DON as a proportion of total N was greater in the two grazed pastures (0.4%) than in the peat (0.2%). Averaged over the four extractants, free α-amino N was greater in the peat and least in the improved pasture soil and accounted for 26% of DON in the peat and less than 5% in the mineral soil. Amino N increased after 6 M HCl hydrolysis, and this combined N contributed 56% to DON in extracts of the mineral soil compared with only 36% in the peat This variation in the relative contributions of free and combined amino N to DON indicated qualitative differences in the composition of DON between the three soils.     

Potentially mineralizable nitrogen from organic materials applied to a sandy soil: fitting the one-pool exponential model

Abstract. Over the last three decades there has been a great increase in the production of waste from urban, industrial and agricultural activity that could be recycled as a source of plant nutrients, and used to enhance soil quality. The use of these materials could partially offset the need for mineral fertilizers, giving both economic and environmental benefits. An incubation experiment was carried out using different organic waste materials applied to a Cambic Arenosol. Air-dried soil was mixed with increasing amounts of composted solid municipal waste, secondary pulp-mill sludge, hornmeal, poultry manure, solid phase from pig slurry, and composted pig manure, resulting in applications equivalent to 0, 40, 80, 120, 160 and 200 kg ha⁻¹ of Kjeldahl nitrogen. The samples were incubated for 244 days under a controlled environment of 24 °C and 60% water holding capacity of the soil. The increasing amounts of waste applied always led to a greater amount of potentially available nitrogen present in the soil/waste mixture. Based on the proportion of their active N fraction, wastes were ranked: poultry manure>hornmeal>solid phase from pig slurry>composted pig manure>secondary pulp-mill sludge>composted municipal solid waste. The results were well described by a one-pool exponential mineralization model, and mineral N formation was proportional to the quantity of waste applied. Of the wastes tested, those from animal sources showed greater nitrogen mineralisation. Nitrification was rapid, and concentrations of ammonium nitrogen remained relatively small.     

Nitrogen pools and turnover in arable soils under different durations of organic farming: I: Pool sizes of total soil nitrogen,microbial biomass nitrogen,and potentially mineralizable nitrogen

Soil organic matter contents, soil microbial biomass, potentially mineralizable nitrogen (N) and soil pH values were investigated in the Ap horizons of 14 field plots at 3 sites which had been under organic farming over various periods. The objective was to test how these soil properties change with the duration of organic farming. Site effects were significant for pH values, microbial biomass C and N, and for potentially mineralizable N at 0—10 cm depth. The contents of total organic C, total soil N, and potentially mineralizable N tended to be higher in soils after 41 versus 3 years of organic farming, but the differences were not significant. Microbial biomass C and N contents were higher after 41 years than after 3 years of organic farming at 0—10 cm depth, and the pH values were increased at 10—27 cm depth. Nine years of organic farming were insufficient to affect soil microbial biomass significantly. Increased biomass N contents help improve N storage by soil micro‐organisms in soils under long‐term organic farming.     

洞庭湖水稻土有机氮组分及其与可矿化氮的关系特征

为深入理解土壤有机氮有效性,利用Bremner酸解法测定了洞庭湖区典型水稻土有机氮组分,采用淹水生物培养法测定了土壤可矿化氮,并分析了二者间的内在关系。结果表明,酸解氮是土壤有机氮素的主要存在形式,其占土壤全氮的比例为58.6%～83.8%,不同类型水稻土酸解氮含量总体上依潴育性水稻土、潜育性水稻土、淹育性水稻土的次序逐渐降低;酸解氮中,氨基酸氮、氨基糖氮、氨态氮与未知氮占土壤全氮的比例分别为25.6%～43.1%、2.6%～9.0%、11.9%～22.3%和8.0%～25.3%。土壤可矿化氮数量变化主要受有机碳、全氮及粘粒含量的影响。酸解氮各组分均与土壤可矿化氮显著正相关(R=0.427～0.858,P0.05),但多元逐步回归和通径分析表明,氨基酸氮是对可矿化氮有直接重要贡献的组分,是可矿化氮的主要来源。氨基酸氮、氨基糖氮、氨态氮、未知氮与氮矿化势的通径分析决策系数分别为0.685、0.251、0.028、-0.050,表明提升有机氮中除未知氮外的其它酸解组分特别是氨基酸氮的分配比例有利于增加土壤可矿化氮供应容量。     

Evaluation of the mineralizable organic nitrogen in soil using an immunological technique

Phosphate buffer-extractable organic nitrogen (PEON), which can be extracted from soil with a 67-mM neutral phosphate buffer solution, is considered to be a major source of mineralizable nitrogen (N) that is ubiquitous in soil. We have developed a Western blot analysis and enzyme-linked immune sorbent assay (ELISA) method for determining PEON. First, anti-PEON antibody (IgG) from a rabbit was produced using purified PEON from a volcanic ash soil. PEON was detected as a ladder-like staining pattern in the high-molecular-weight region and as a single band under 14 kDa in Western blot analysis using the anti-PEON IgG. In the ELISA assay, the anti-PEON IgG could specifically react with PEON irrespective of soil type and management. Furthermore, the absorbance at 450 nm in ELISA was highly correlated to the concentration of organic N (N_org) in phosphate extracts of different soils. We propose the immune assay using the anti-PEON IgG as a possible novel method for evaluating available N in soil.     

Effect of different soil cultivation systems,including no-tillage,on electro-ultrafiltration extractable organic nitrogen

The effect of different long-term soil-cultivation systems (ploughing, two types of cultivator, notillage) on organic N, extracted with the electroultrafiltration (EUF) technique, was studied in two arable soils, a Luvic Phaeozem derived from loess and a Eutric Cambisol. A modified EUF extraction procedure (the 80°C fraction extended from 5 to 90 min) was used to investigate the release of organic N from the ploughing and no-tillage treatment, and the content of hydrolysable N was measured in the combined filtrates. No-tillage and the two non-turning cultivation systems led to an accumulation of EUF organic N in the 0- to 10-cm depth compared to the ploughing treatment. In the lower horizon (15–25 cm) the reverse pattern was found in the loamy soil, with higher concentrations after ploughing than after reduced tillage. However, in the sandy soil all four cultivation treatments showed similar values in the 15- to 25-cm depth. During the time of investigation (May 1987 to February 1989) an EUF organic N accumulation occurred, which was about twice as high in the loamy as in the sandy soil. Therefore we conclude that in the sandy soil the mineralization of organic N was faster, and that reduced tillage retarded its degradation. In the total 0- to 25-cm depth, this delay was not observed in the loamy soil. The N release rates were much lower in the sandy than in the loamy soil and they were higher for the notillage than for the ploughing treatment. Only 30–40% of the total organic N desorbed was hydrolysable and the amino acid composition indicates that part of it originated from microbial Cells. The overall evaluation showed clearly that EUF-extractable organic N is a sitespecific factor.     

Long-term management impacts on soil carbon and nitrogen dynamics of grazed bermudagrass pastures

Managed pastures have potential for C and N sequestration in addition to providing forage for livestock. Our objectives were to investigate changes in soil organic C (SOC) and soil organic N (SON) concentrations and mineralizable C and N in cattle (Bos indicus) grazed bermudagrass [Cynodon dactylon (L.) Pers.] pastures up to 32 y after establishment. Management included low- and high-grazing intensity, fertilization, and winter overseeding with annual ryegrass (Lolium multiflorum Lam.) and clover (Trifolium sp.). Soil (0-15 cm) was sampled 7, 15, 26, and 32 y after establishment of Coastal and common bermudagrass pastures. No significant differences in SOC or SON concentrations were observed between Coastal and common bermudagrass pastures. Grazing strategies played important roles in C and N sequestration, as high-grazing intensity resulted in a lower increase in SOC and SON concentrations over time compared to low-grazing intensity. Increases in SOC were observed up to 26 y, while increases in SON were observed up to 32 y after establishment of bermudagrass pastures. Soil organic C increased 67 and 39% from 7 to 26 y at low-grazing intensity for bermudagrass+ryegrass and bermudagrass+clover pastures, respectively. SOC and SON concentrations did not increase beyond 15 y after bermudagrass establishment at high-grazing intensity. An exception was the Coastal bermudagrass+ryegrass pastures, which exhibited higher SON at 32 y than at 7 y at both grazing intensities. By 32 y, SON increased 83 and 45% in Coastal bermudagrass+ryegrass pastures at low- and high-grazing intensity, respectively, compared to 7 y. The introduction of clover to pastures decreased SOC and SON relative to ryegrass at high- but not at low-grazing intensity. Potentially mineralizable C increased from 7 to 15 y, while mineralizable N increased from 7 to 32 y. Potentially mineralizable N was also greater for bermudagrass+clover than bermudagrass+ryegrass pastures. Long-term increases in SOC and SON concentrations suggest that managed and grazed pastures have strong potential for C and N sequestration.     

Soluble organic nitrogen in temperate forest soils

Very few studies have been related to soluble organic nitrogen (SON) in forest soils. However, this nitrogen pool could be a sensitive indicator to evaluate the soil nitrogen status. The current study was conducted in temperate forests of Thuringia, Germany, where soils had SON (extracted in 0.5 M K₂SO₄) varying from 0.3 to 2.2% of total N, which was about one-third of the soil microbial biomass N by CFE. SON in study soils were positively correlated to microbial biomass N and soil total N. Multiple regression analysis also showed that mineral N negatively affected SON pool. The dynamics of the SON was significantly affected by mineralization and immobilization. During the 2 months of aerobic incubation, the SON were significantly correlated with net N mineralization and microbial biomass N. SON extracted by two different salt solution (i.e. 1 M KCl and 0.5 M K₂SO₄₎ were highly correlated. In mineral soil, SON concentrations extracted by 1 M KCl and 0.5 M K₂SO₄ solutions were similar. In contrast, in organic soil layer the amount of KCl-extractable SON was about 1.2-1.4 times higher than the K₂SO₄-extractable SON. Further studies such as the differences of organic N form and pool size between SON and dissolved organic N (DON) are recommended.     

Effect of increasing rates of 15N‐labelled fertilizer on recovery of fertilizer N in plant and soil N pools in a pot experiment with winter wheat

The effect of increasing rates of ¹⁵N‐labelled Ca(NO₃)₂ (N₀ = no N application, N₃₀₀ = 300 mg N/pot; N₆₀₀ = 600 mg N/pot; N₉₀₀ = 900 mg N/pot) on recovery of fertilizer N in winter wheat plants and soil (total soil N, soil microbial biomass N [N_mic], extractable organic N [N_org]) and on N mineralization (NM_soil) was investigated at milk‐ripe growth stage in a pot experiment. The N rates were equally split at tillering, stem elongation and ear emergence. Fertilizer N recovered in crops increased with increasing N rates (N₃₀₀: 223.5 mg N/pot [74.5% of applied fertilizer N], N₆₀₀: 445.6 mg N/pot [74.3%], N₉₀₀: 722.1 mg N/pot [80.2%]). NM_soil slightly increased from N₀ (43.8 mg N/pot) to N₉₀₀ (75.6 mg N/pot) indicating that N application enhanced availability of soil‐derived N for the plants. However, in fertilized treatments NM_soil is balanced by immobilization and losses (non‐recovered fertilizer N). Therefore the effective soil N mineralization is indicated by apparent net N mineralization (ANNM = NM_soil — fertilizer N immobilization — lost fertilizer N). Fertilizer N immobilization in soil increased from N₃₀₀ (38.7 mg N/pot) to N₆₀₀ (60.7 mg N/pot) and N₉₀₀ (65.5 mg N/pot). Lost fertilizer N increased from N₃₀₀ (14.8 mg N/pot) to N₆₀₀ (56.7 mg N/pot) and N₉₀₀ (62.1 mg N/pot). As a consequence negative ANNM values were calculated at N₆₀₀ and N₉₀₀. Due to the small differences between N₆₀₀ and N₉₀₀ fertilizer N immobilization and lost fertilizer N did not increase linearly with increasing N rates, i.e. both processes were limited by factors other than N rate. Only 5.6—7.4% of the immobilized fertilizer N was recovered in N_org and 5.4—9.3% in N_mic soil pools. It is assumed that most of the immobilized fertilizer N was in non‐extractable organic N forms. N_mic and N_org were weak indicators for the extent of fertilizer N immobilization.