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1.
Charcoal‐based amendments have a potential use in controlling NH3 volatilization from urea fertilization, owing to a high cation‐exchange capacity (CEC) that enhances the retention of NH . An incubation study was conducted to evaluate the potential of oxidized charcoal (OCh) for controlling soil transformations of urea‐N, in comparison to urease inhibition by N‐(n‐butyl) thiophosphoric triamide (NBPT). Four soils, ranging widely in texture and CEC, were incubated aerobically for 0, 1, 3, 7, and 14 d after application of 15N‐labeled urea with or without OCh (150 g kg?1 fertilizer) or NBPT (0.5 g kg?1 fertilizer), and analyses were performed to determine residual urea and 15N recovery as volatilized NH3, mineral N (as exchangeable NH , NO , and NO ), and immobilized organic N. The OCh amendment reduced NH3 volatilization by up to 12% but had no effect on urea hydrolysis, NH and NO concentrations, NO accumulation, or immobilization. In contrast, the use of NBPT to inhibit urea hydrolysis was markedly effective for moderating the accumulation of NH , which reduced immobilization and also controlled NH3 toxicity to nitrifying microorganisms that otherwise caused the accumulation of NO instead of NO . Oxidized charcoal is not a viable alternative to NBPT for increasing the efficiency of urea fertilization.  相似文献   

2.
Mobilization of non‐exchangeable ammonium (NH ) by hyphae of the vesicular‐arbuscular mycorrhizal (VAM) fungus Glumus mosseae was studied under controlled experimental conditions. Maize (Zea mays) and parsley (Petroselinum sativum) were grown either alone or in symbiosis with Glomus mosseae in containers with separated compartments for roots and hyphal growth. In one experiment, 15NH was added to the soil to differentiate between the native non‐exchangeable NH and the non‐exchangeable NH derived from N fertilization. Non‐exchangeable NH was mobilized by plant growth. Plant dry weight and N uptake, however, were not significantly influenced by mycorrhizal colonization of the roots. The influence of root infection with mycorrhizal fungus on the mobilization of non‐exchangeable NH was negligible. In the hyphal compartment, hyphal uptake of N resulted in a decrease of NH in the soil solution and of exchangeable NH . However, the NH concentration was still too high to permit the release of non‐exchangeable NH . The results demonstrate that, in contrast to roots, hyphae of VAM fungi are not able to form a non‐exchangeable‐NH depletion zone in the adjacent soil. However, under conditions of a more substantial depletion of the exchangeable NH in the mycorrhizal sphere (e.g., with longer growth), an effect of mycorrhiza on the non‐exchangeable NH might be found.  相似文献   

3.
The application of mineral nitrogen (N) fertilizers is one of the most important management tools to ensure and increase yield in agricultural systems. However, N fertilization can lead to various ecological problems such as nitrate () leaching or ammonia and nitrous oxide emissions. The application of N stabilizers (i.e., inhibitors) combined with urea fertilization offers an effective option to reduce or even prevent N losses due to their regulatory effect on ammonium () and release into the soil. The present field experiment therefore aimed at soil N speciation dynamics after urea spring fertilization (225 kg N ha?1) in the presence of a urease inhibitor (UI), a nitrification inhibitor (NI), both inhibitors (UI+NI) or when no inhibitor was applied at all. The study focused on the distribution of N species among soil matrix and soil solution. Plant cultivation was completely omitted in order to avoid masking soil N turnover and speciation by plant N uptake and growth dynamics. Application of UI clearly delayed urea hydrolysis in the top soil, but a complete hydrolysis of urea took place within only 10 days after fertilization (DAF). Nitrification was significantly reduced by NI application, leading to higher and lower concentrations in treatments with NI. Due to sorption of to the soil matrix a significantly larger fraction of was always detected in the soil extracts compared to soil solution. However, while in soil extracts the impact of NI application was less apparent and delayed, in soil solution a quick response to NI application was observed as revealed by significantly increased soil solution concentrations of . Because of the “asymmetric” soil phase distribution soil solution was predominant over only initially after fertilization even in inhibitor treatments (≈ 8 to 10 DAF). Nevertheless, inhibitor application tended towards closer ratios of to concentration in soil solution and hence, might additionally affect concentration dependent processes like plant N uptake and root development. Despite cold spring conditions urea application along with UI and/or NI did not indicate a limited supply of plant available and .  相似文献   

4.
The objective of this laboratory study with six loess soils (three Eutric CambisoIs and three Haplic Phaeozems) incubated under flooded conditions was to examine the effect of a wide range of NO doses under anaerobic conditions on soil redox potential and N2O emission or absorption. Due to the fact that loess soils are usually well‐drained and are expected to be absorbers during prevailing part of the season, the study aimed at determination of the conditions decisive for the transition from emission to absorption process. On the basis of the response to soil nitrate level, the two groups of soils were distinguished with high and low denitrification capacity. The soil denitrification activity showed Michaelis‐Menten kinetics with respect to soil nitrate content with KM in the range 50–100 mg NO ‐N kg–1. Percentage of nitrates converted to N2O increased linearly with nitrate concentration in the range from 25 to 100 mg NO ‐N kg–1 up to 43% and decreased linearly at higher concentrations reaching practically zero at concentrations about 600 mg NO ‐N kg–1. No denitrification was observed below 25 mg NO ‐N kg–1. Nitrous oxide absorption in soil occurred only at nitrate concentrations to 100 mg NO ‐N kg–1 and in this concentration range was proportional to the denitrification rate. Nitrous oxide was formed at redox potentials below +200 mV and started to disappear at negative Eh values.  相似文献   

5.
Citrus production in Florida accounts for ≈ 60% of national production in USA. The sandy soil characteristic (> 95% sand) makes water and nutrient management extremely difficult, raising concerns about environmental sustainability as a result of nutrient inputs in citrus producing regions where sandy soils dominate. Thus, laboratory column and field experiments were conducted to better understand the leaching patterns of and ions in Florida's sandy soils. The soil columns were first saturated from the bottom with two pore volumes of simulated Florida rain followed by pumping a pulse of fertilizer mixture at a steady Darcy flux of 14 cm h?1. Nitrate and Cl? appeared earlier in the effluent than in the A and Bh horizons, due to cation exchange of . Essentially identical breakthrough curves (BTCs) for and were observed in the E‐horizon, due to very low sorption of . The convective and dispersive equilibrium (CDE) model simulations were in good agreement with measured breakthrough curves (BTCs) for , , and Cl?. However, the sorption coefficient (KD) values used in the CDE model to simulate the BTCs for were about 10 times less than the batch isotherm KD values. This was attributed to differences in pH, cation composition, and ionic strength between batch (static) and dynamic (leaching) systems. The field experiment showed that under unsaturated flow, improved short‐pulse fertigation systems (drip and microsprinkler) limited and transport beyond the root zone (top 30 cm), which might have promoted nutrient and water uptake in citrus. The column study revealed that under extreme weather events such as hurricanes or storm surge in Florida, saturated soil conditions can trigger N mobility below the root zone to surficial or groundwater aquifers. In the field experiment, the use of judicious, minimal and split applications and accurate placement of N‐fertilizers reduced leaching of N especially during heavy storms in the summer rainy months of Florida. The field experiment demonstrated that it is possible to manage inorganic N forms for optimal residence time for uptake and minimal leaching concerns.  相似文献   

6.
Microbiological and biochemical characterization of agricultural soils Part. I. Determination of a soil microbiological index The intensity of soil microbial activity was determined by measuring the total microbial biomass, the activity of cellfree hydrolases (saccharase, protease and alkaline phosphatase) as well as mainly cellbound reductases (dehydrogenase and catalase). Testing 33 mixed samples of 11 different or differently treated, agricultural soils in Bavaria, a highly significant correlation (r = 0.77–0.99) between all individual microbiological soil properties was found. No correlations could be found with the additionally determined plate counts of bacteria or with nitrifications tests. This close relation between the tested biomass and enzyme activities could be used for calculating an over-all index (Bodenmikrobiologische Kennzahl) of soil microbial activity by transforming and combining the individual analytical soil properties according to the following equation:   相似文献   

7.
Alkaline soil is widely distributed and cultivated throughout the agricultural regions of the world. Organic carbon (OC) concentrations in alkaline soil are often small, partly because of the limitations of a high pH on the productivity of crops and pastures together with the effects of high pH on the chemistry of soil OC. Soil pH is often hypothesized to be a major factor in regulating OC turnover in agricultural soil, but there are few detailed studies on the effects of high pH on carbon cycling in alkaline soil. Sodium, K+, Mg2+ and Ca2+ are the major cations in alkaline soil, whereas Cl?, , and are the major anions. The effect of different combinations of these cations and anions on soil pH and OC is not well described in the literature. The objectives of this study were to evaluate the effect of cations and anions on soil pH and to quantify the dissolution of OC in relation to these changes in pH. The results showed that (Na+, K+ and Mg2+) salts and CaCO3 dominate in the pH range 7.0–8.5, and salts of Na+ and K+ dominate above pH 8.5. The amount of dissolved OC (DOC) increased significantly as pH increased. Therefore, the presence of large concentrations of and not only increased pH but also promoted the dissolution of soil OC. The concentration of Ca2+ modified this effect; large concentrations of Ca2+ increased the adsorption and reduced the concentration of DOC.  相似文献   

8.
The tomato (Solanum lycopersicum L.) cultivar Micro‐Tom (MT) is widely used in physiological studies, but the effects of nitrate ( ) and ammonium ( ) ratios ( : ratios) and, in particular, the effects of the accompanying ions in sources are unknown. To determine whether the accompanying ions in sources influence toxicity, the effects of : ratios on the physiology, electrolyte leakage index, nutrition, and dry weight were studied using hydroponics. The sources were ammonium chloride (NH4Cl) or ammonium sulfate [(NH4)2SO4], and five : ratios were used: 100 : 0, 75 : 25, 50 : 50, 25 : 75, and 0 : 100. The source was calcium nitrate [Ca(NO3)2], and the nitrogen (N) concentration was 15 mmol L?1. The results indicate that NH4Cl or (NH4)2SO4 can be used in studies on toxicity because the accompanying ions did not influence the tomato plants. In addition, : ratios of 100 : 0 and 75 : 25 resulted in the highest dry weight of tomato plants, whereas ratios of 25 : 75 or 0 : 100 were toxic.  相似文献   

9.
Translocation of nitrogen to the shoot of young bean plants after uptake of NO and NH by the root Phaseolus vulgaris plants (var. nana, cv. Saxa) at the primary leaf stage (without nodules) were fed during 6 hours with 15NO and 15NH, respectively. 24 hours after the absorption period more 15N from the absorbed NO was translocated from the root to the shoot. The presence of NH in the nutrient solution enhanced the translocation of 15NON, probably by an inhibition of nitrate reductase. NH4-+15N is mainly retained in the root by a high incorporation into the root protein. It can be concluded that nitrogen from newly absorbed NO is not retained and used for protein synthesis in the root according to the root's potential to synthesize protein. Nitrate reduction in the root is considered to be the limiting factor. This is supported by the fact that withdrawal of NO in the nutrient solution prior to the 15N-experiment increased NOtranslocation to the shoot as a consequence of a lowered level of nitrate reductase. In an experiment with 14NOsupply to the roots and 15NOapplication to the primary leaves (infiltration method) a considerable amount of 15N was translocated from the leaves to the roots. This indicates that an insufficient NOreduction in the root can be substituted by a retranslocation of reduced N-compounds from leaves to the roots. The proportion of NO reduced in the root influences also the pattern of primary distribution of nitrogen in the shoot of plants at the 4 leaf stage. At a concentration of 0,2 meq/l NO in the nutrient solution as compared to 20 meq/l NO during 10 hours a relative higher amount of 15N was transported from the root to the younger, growing leaves i.e. via the phloem to metabolic sinks.  相似文献   

10.
The objective of this study was to determine whether models developed from infrared spectroscopy could be used to estimate organic carbon (C) content, total nitrogen (N) content and the C:N ratio in the particulate organic matter (POM) and particle size fraction samples of Brookston clay loam. The POM model was developed with 165 samples, and the particle size fraction models were developed using 221 samples. Soil organic C and total N contents in the POM and particle size fractions (sand, 2000–53 µm; silt, 53–2 µm; clay, <2 µm) were determined by using dry combustion techniques. The bulk soil samples were scanned from 4000 to 400 cm?1 for mid‐infrared (MIR) spectra and from 8000 to 4000 cm?1 for near‐infrared (NIR) spectra. Partial least squares regression (PLSR) analysis and the ‘leave‐one‐out' cross‐validation procedure were used for the model calibration and validation. Organic C and N content and C:N ratio in the POM were well predicted with both MIR‐ and NIR‐PLSR models ( = 0.84–0.92; = 0.78–0.87). The predictions of organic C content in soil particle size fractions were also very good for the model calibration ( = 0.84–0.94 for MIR and = 0.86–0.92 for NIR) and model validation ( = 0.79–0.94 for MIR and = 0.84–0.91 for NIR). The prediction of MIR‐ and NIR‐PLSR models for the N content and the C:N ratio in the sand and clay fractions was also satisfactory ( = 0.73–0.88; = 0.67–0.85). However, the predictions for the N content and C:N ratio in the silt fraction were poor ( = 0.23–0.55; = 0.20–0.40). The results indicate that both MIR and NIR methods can be used as alternative methods for estimating organic C and total N in the POM and particle size fractions of soil samples. However, the NIR model is better for estimating organic C and N in POM and sand fractions than the MIR model, whereas the MIR model is superior to the NIR model for estimating organic C in silt and clay fractions and N in clay fractions.  相似文献   

11.
Remediation of an uranium‐mine soil from Settendorf (East Germany) includes phytoextraction under conditions which make its heavy metals more plant‐available but less leachable. A second way is active inhibition of heavy metal uptake by the plant. In a pot trial with Chinese cabbage (Brassica chinensis L.), planted and unplanted soil samples were daily irrigated with deionized water or aqueous solutions with a total of (g (kg soil)–1) CaCl2 (0.26 Ca), NH4Cl (1.39), casein, sucrose, citric acid (13), and an extract of rape (B. napus L.) shoots (13 DW) in a phytotron for 26 d. Water‐irrigated plants were also treated with a 50 mM citric acid solution (10.5 g (kg soil)–1) 6 and 7 d prior to harvesting. Total elements in plant tissue and soluble elements in aqueous extracts from control and postharvest soils were determined by ICP‐AES. Supplements of NH , and the NH ‐generating casein and rape extract reduced soil pH during nitrification, and increased plant uptake of Cd, Cu, Ni, and Zn. Citric acid at 50 mM adjusted soil to pH 4.5–6.0 and enhanced uptake of all elements. Long‐term application of sucrose and citric acid increased pH and inhibited uptake of Cd, Cr, Cu, Ni, and Zn. Contemporarily, leaching of heavy metals and humic substances was lowest with Ca and NH and highest with sucrose and citric acid amendments. It is concluded that Chinese cabbage grown for chelate‐assisted phytoextraction should be supplied with Ca and NH to obtain a high plant biomass on soil with a low hazard of leaching. Metal uptake should be stimulated by application of chelator 7 d prior to harvesting. Undesired uptake of heavy metals by Chinese cabbage determined as food should be inhibited with carbohydrate amendments. Long‐term application of NH or chelator, which reduces the solubility of certain elements but increases their uptake moderately, is recommended as a tool for continuous phytoextraction technologies.  相似文献   

12.
The amounts of N2O released in freeze‐thaw events depend on site and freezing conditions and contribute considerably to the annual N2O emissions. However, quantitative information on the N transformation rates in freeze‐thaw events is scarce. Our objectives were (1) to quantify gross nitrification in a Luvisol during a freeze‐thaw event, (2) to analyze the dynamics of the emissions of N2O and N2, (3) to quantify the contribution of nitrification and denitrification to the emission of N2O, and (4) to determine whether the length of freezing and of thawing affects the C availability for the denitrification. 15NO was added to undisturbed soil columns, and the columns were subjected to 7 d of freezing and 5 d of thawing. N2O emissions were determined in 3 h intervals, and the concentrations of 15N2O and 15N2 were determined at different times during thawing. During the 12 d experiment, 5.67 mg NO ‐N (kg soil)–1 was produced, and 2.67 mg NO ‐N (kg soil)–1 was lost. By assuming as a first approximation that production and loss occurred exclusively during thawing, the average nitrate‐production rate, denitrification rate, and immobilization rate were 1.13, 0.05, and 0.48 mg NO ‐N (kg soil)–1 d–1, respectively. Immediately after the beginning of the thawing, denitrification contributed by 83% to the N2O production. The ratios of 15N2 to 15N2O during thawing were narrow and ranged from 1.5 to 0.6. For objective (4), homogenized soil samples were incubated under anaerobic conditions after different periods of freezing and thawing. The different periods did not affect the amounts of N2 and N2O produced in the incubation experiments. Further, addition of labile substrates gave either increases in the amounts of N2O and N2 produced or no changes which suggested that changes in nutrient availability due to freezing and thawing are only small.  相似文献   

13.
Organic matter content was found to have a dominant effect on both the bulk and true densities of soil in the organic and eluvial horizons of the podzolic soils examined. The soils were stone-free, structureless, and of similar texture. The effects of organic matter on bulk density were described by the equation: A similar equation was devised for true density. Use of these equations indicated that, in the soils examined, total pore space could be predicted from organic matter content measured as per cent loss on ignition.  相似文献   

14.
Soil moisture affects the degradation of organic fertilizers in soils considerably, but less is known about the importance of rainfall pattern on the turnover of C and N. The objective of this study was to determine the effects of different rainfall patterns on C and N dynamics in soil amended with either biogas slurry (BS) or composted cattle manure (CM). Undisturbed soil cores without (control) or with BS or CM, which were incorporated at a rate of 100 kg N ha–1, were incubated for 140 d at 13.5°C. Irrigation treatments were (1) continuous irrigation (cont_irr; 3 mm d–1); (2) partial drying and stronger irrigation (part_dry; no irrigation for 3 weeks, 1 week with 13.5 mm d–1), and (3) periodic heavy rainfall (hvy_rain; 24 mm d–1 every 3 weeks for 1 d and 2 mm d–1 for the other days). The average irrigation was 3 mm d–1 in each treatment. Cumulative emissions of CO2 and N2O from soils amended with BS were 92.8 g CO2‐C m–2 and 162.4 mg N2O‐N m–2, respectively, whereas emissions from soils amended with CM were 87.8 g CO2‐C m–2 and only 38.9 mg N2O‐N m–2. While both organic fertilizers significantly increased CO2 production compared to the control, N2O emissions were only significantly increased in the BS‐amended soil. Under the conditions of the experiment, the rainfall pattern affected the temporal production of CO2 and N2O, but not the cumulative emissions. Cumulative NO leaching was highest in the BS‐amended soils (9.2 g NO ‐N m–2) followed by the CM‐amended soil (6.1 g NO ‐N m–2) and lowest in the control (4.7 g NO ‐N m–2). Nitrate leaching was also independent of the rainfall pattern. Our study shows that rainfall pattern may not affect CO2 and N2O emissions and NO leaching markedly provided that the soil does not completely dry out.  相似文献   

15.
Oat consumption has been rapidly increased worldwide because its high β‐glucan concentration may lower the level of blood cholesterol. The rates of β‐glucan accumulation in two husk and two nude oats were determined with an interval of 5 d after anthesis in a pot experiment. The results showed that a higher nitrogen level increased oat grain yield per plant, thousand‐grain weight, and concentrations of protein and β‐glucan. β‐glucan concentration generally increased with development of grain after anthesis, whereas the accumulation rate of β‐glucan was greater at the early stage of grain development and reached a maximum around 25 d after anthesis. We also found a larger β‐glucan concentration when plants were grown with NO ‐N as compared to NH ‐N. This study may suggest that the agronomic approaches such as nutrient management by optimizing the time and the level of nitrogen application and a higher ratio of NO ‐N to NH ‐N can play an important role in enhancing β‐glucan concentration in oat grains.  相似文献   

16.
The transfer function mode) (TFM) and convection-dispersion equation (CDE) were compared for predicting Cl ? transport through a calcareous pelosol during steady, nearsaturated water flow. Large, undisturbed soil cores were used at constant irrigation intensities (q0) between 0.3 and 3 cm h?1, with a step-change in Cl? concentration. The assumption of a lognormal distribution of travel times–characterized by the mean (μ) and variance (σ2)–permitted the flux-averaged breakthrough curves (BTCs) to be modelled very accurately by the TFM. The BTCs could be modelled equally well by the CDE when both the mean pore water velocity (v) and dispersion coefficient (D) were optimized simultaneously by the method of least squares, but not when v was put equal to q0/v, where V was the mean volumetric water content. The best estimate of v was consistently > q0/v, which suggested that not all the pore water was effective in chloride transport. An operationally defined transport volume (θst) was calculated from the mean () or median (τm) travel times derived from the TFM. Chloride exclusion was not solely responsible for θst() being <V: immobile water also contributed. The positive skewness of the travel time distributions meant that θst(τm) < θst(), indicating the effectiveness of macropore flow in solute transport. Dαv1.42 (from the CDE), and σ2αv (from the TFM), confirmed that Cl? dispersion increased as flow velocity increased. Flux-averaged concentrations were used to calculate the volume-averaged resident concentrations. They matched the measured Cl? concentrations most closely when there was a gradual decrease in measured Cl ? concentration with depth, but not when Cl ? decreased sharply below c. 10 cm. Calculations assuming that all the water was effective in chloride transport gave less accurate results. Comparison of the measured and predicted concentrations of solute demonstrated that this must be a critical part of the evaluation of any model of solute transport.  相似文献   

17.
The saturation percentage is related to the mechanical constituents of a soil: and is therefore a quantitative expression of soil texture. Profiles may be described in terms of the S.P.; thus Maps may be drawn showing quantitative changes in texture, and associated statements of the reliability of an S.P. estimate and the probable error of the position of a textural contour be made. Decomposition of the calcium carbonate component should be avoided in routine soil survey work.  相似文献   

18.
If an exchangeable ion in soil diffuses along a liquid and solid pathway, its diffusion coefficient may be expressed as where D, v, f, C are diffusion coefficient, volume fraction, impedance factor, and concentration terms and the suffixes l,S refer to liquid and solid. The self-diffusion coefficient of the ion is then where D′, D′t, and D′s, are self-diffusion coefficients. D and D′ will vary with concentration. In diffusion out of the soil to a zero sink, the appropriate average diffusion coefficient is, approximately, the self-diffusion coefficient in the undisturbed soil. Diffusion of one ion species is influenced by other ions diffusing in the system through the diffusion potential set up. When ions are diffusing to plant roots, the diffusion potential is likely to be small. A more likely, though more complicated, expression for D than the first equation above is derived by assuming the ion to follow solid and liquid pathways in series as well as in parallel.  相似文献   

19.
The calibration of soil organic C (SOC) and hot water‐extractable C (HWE‐C) from visible and near‐infrared soil reflectance spectra is hindered by the complex spectral interaction of soil chromophores that usually varies from one soil or soil type to another. The exploitation of spectral variables from spectroradiometer data is further affected by multicollinearity and noise. In this study, a set of soil samples (Fluvisols, Podzols, Cambisols and Chernozems; n = 48) representing a wide range of properties was analysed. Spectral readings with a fibre‐optics visible to near‐infrared instrument were used to estimate SOC and HWE‐C contents by partial least squares regression (PLS). In addition to full‐spectrum PLS, spectral feature selection techniques were applied with PLS (uninformative variable elimination, UVE‐PLS, and a genetic algorithm, GA‐PLS). On the basis of normalized spectra (mean centring + vector normalization), the order of prediction accuracy was GA‐PLS ? UVE‐PLS > PLS for SOC; for HWE‐C, it was GA‐PLS > UVE‐PLS, PLS. With GA‐PLS, acceptable cross‐validated (cv) prediction accuracies were obtained for the complete dataset (SOC, , RPDcv = 2.42; HWE‐Ccv, , RPDcv = 2.13). Splitting the soil data into two groups with different basic properties (Podzols compared with Fluvisols/Cambisols; n = 21 and n = 23, respectively) improved SOC predictions with GA‐PLS distinctly (Podzols, , RPDcv = 3.14; Fluvisols/Cambisols, , RPDcv = 3.64). This demonstrates the importance of using stratified models for successful quantitative approaches after an initial rough screening. GA selection frequencies suggest that the spectral region over 1900 nm, and in particular the hydroxyl band at 2200 nm are of great importance for the spectral prediction of both SOC and HWE‐C.  相似文献   

20.
Nitrate leaching depending on N fertilization and different crop rotations was studied at two sites with sandy soils in N Germany between 1995 and 2000. The leaching of NO was calculated by using a numerical soil‐water and N model and regularly measured Nmin values as input data. Also the variability of Nmin values on the sandy soils was determined along transects. They reveal the high variability of the Nmin values and show that it is not possible to confirm a significant Nmin difference between fertilizer treatments using the normal Nmin‐sampling intensity. Nitrate‐leaching calculations of five leaching periods showed that even strongly reduced N‐fertilizer applications did not result in a substantially lower NO leaching into the groundwater. Strong yield reductions of even more than 50%, however, were immediately measured. Mean NO concentrations in the groundwater recharge are >50 mg L–1 and are mainly due to mineralization from soil organic matter. Obviously, the adjustment of the N cycle in the soil to a new equilibrium and a reduced NO ‐leaching rate as a consequence of lower N inputs need a much longer time span. Catch crops are the most efficient way to reduce the NO concentrations in the groundwater recharge of sandy soils. Their success, however, strongly depends on the site‐specific development possibilities of the catch crop. Even with all possible measures implemented, it will be almost impossible to reach NO concentrations <50 mg L–1 in sandy soils. The only way to realize this goal on a regional scale could be by increasing areas with lower nitrate concentrations in the groundwater recharge like grassland and forests.  相似文献   

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