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Nitrogen fertilization for corn (Zea mays L.) production has relied extensively on yield-based recommendations that were developed to represent regional averages, yet are routinely applied to individual fields, on the assumption that fertilizer N serves as the major supply for crop N uptake. Using data from 102 on-farm N-response studies, an evaluation was conducted of the Illinois proven-yield (PY) method for accuracy and economic profitability on a site-by-site basis. As additional objectives, the Illinois soil N test (ISNT) was evaluated for detecting whether N fertilization was economical, and for quantifying crop response to N fertilization relative to soil and management factors. For 18% of the site-years studied, N recommendations by the PY method were accurate to within 20 kg [ha.sup.-1], whereas 13% were underfertilized by 25 to 129 kg [ha.sup.-1] (60 kg [ha.sup.-1] on average) at a current cost of $5 to $170 [ha.sup.-1] ($75 [ha.sup.-1] on average), and 69% were overfertilized by 21 to 235 kg [ha.sup.-1] (103 kg [ha.sup.-1] on average) at a cost of $12 to $130 [ha.sup.-1] ($57 [ha.sup.-1] on average). The latter group included 30 site-years that were completely nonresponsive to N fertilization, all but two of which were predicted by site-average ISNT values assuming a critical test level of 230 mg [kg.sup.-1] . This level was exceeded fur 19 of 69 responsive site-years, mostly during 2001-2003 when corn followed soybean (Glycine max L. Merr.) with high plant populations. A higher critical test level would have been required under such conditions, owing to more extensive residue inputs that would promote microbial N immobilization, and increased crop uptake of mineralized soil N. The ISNT was significantly related to crop N requirement, and was the most powerful predictor of error in PY recommendations (P < 0.001).

Denitrification losses are a possibility from turfgrass because of frequent irrigation, multiple applications of N fertilizers, and an abundance of readily decomposable organic C in thatch and verdure. Field experiments were conducted to directly measure [N.sub.2] and [N.sub.2]O evolved from a Flanagan silt loam soil under Kentucky bluegrass (Poa pratensis L.) or creeping bentgrass (Agrostis palustris Huds.). Mass spectrometric procedures were used to analyze atmospheric samples collected from replicated [sup.15]N fertilized turf (49 kg [ha.sup.-1]). Data showed that labeled fertilizer N (LFN) losses ranged from 2.1 to 7.3% for [N.sub.2] and from 0.4 to 3.9% for [N.sub.2]O; that large [N.sub.2] and [N.sub.2]O fluxes occurred after heavy rainfall events; and that more [N.sub.2] was evolved than [N.sub.2]O. Emission of gas was detected while standing water was visible within cylinders, suggesting the transfer of gases from the flooded soil to the atmosphere through the turfgrass plants. Evolution of [N.sub.2] and [N.sub.2]O was greater from creeping bentgrass treated with KN[O.sub.3] than urea through the first 3 wk of the experiment, whereas [N.sub.2] emission was greater for urea during the last 2 wk of the experiment, presumably because of N[O.sub.3] production through nitrification. Nitrous oxide was detected on the day of fertilization with the KN[O.sub.3] treatment, and the mole fraction of [N.sub.2]O decreased from 0.44 to 0.11 with each weekly application of N., DENITRIFICATION is an important process in the soil, plant, and atmosphere continuum because it is the primary mechanism for return of [N.sub.2] to the atmosphere (Stevenson and Cole, 1999). With [...]

Although the fate of fertilizer applied to turfgrass has been studied in the past, recovery of applied fertilizer N is typically low, and denitrification has been cited as the reason. The objectives of this research were twofold: (i) to examine the fate of [sup.15]N applied to Kentucky bluegrass (Poa pratensis L.) turf as KN[O.sub.3], including direct measurement of denitrification; and (ii) to determine whether and how plants affect fertilizer-N recovery. Polyvinyl chloride (PVC) cylinders, modified to permit atmospheric sampling, were used throughout field experiments during the spring and summer 1999 and a greenhouse experiment in 2000. Potassium nitrate (98.5 atom % [sup.15]N) was applied in solution at 49 kg N [ha.sup.-1] to replicated plots, and atmospheric samples were collected three times a day from 0800 to 1100, 1100 to 1400, and 1400 to 1700 h during a 6-wk period in the spring and a 4-wk period during the summer of 1999. Emission of [N.sub.2] or [N.sub.2]O ranged from 3.3 to 21.3% and from 0.3 to 5.9% of labeled fertilizer N (LFN), respectively. Recovery of LFN in the soil or plant, plus that emitted as [N.sub.2] or [N.sub.2]O, ranged from 57.4 to 73.2%. A 4-wk greenhouse experiment comparing LFN recovery for bare soil and turf, including gas emission and leachate, was initiated in the summer of 2000. Total emission of LFN as [N.sub.2] or [N.sub.2]O was 19.0% for the turfgrass, as compared with 7.3% for the bare soil. Corresponding values for total recovery of LFN were 70.6 and 84.2%, respectively., THE FATE OF N, specifically N[O.sub.3]-N leaching, has been studied in turfgrass systems during the past decades. These studies indicate that appropriate N fertilization of turf poses little risk to [...]

A technique was developed that permits the use of boric acid-indicator solution in carrying out diffusions for inorganic [sup.15]N analysis of soil extracts by direct combustion, so as to eliminate the need for a separate quantitative determination. In this technique, the titrated sample is acidified with 2.5 M KHS[O.sub.4] and subsequently treated with methanol to remove [H.sub.3]B[O.sub.3]. The N[H.sup+.sub.4]-N is dissolved in 1 mL of de-ionized water, concentrated after transfer to a microcentrifuge tube, and freeze-dried in a tin capsule. Isotope-ratio analyses were accurate to within 5% when diffusions were performed on 100 to 1000 [micro]g of N[H.sup.+.sub.4]-N (0.2-10 atom % [sup.15]N), whereas errors of 8 to 17% occurred with 25 to 50 [micro]g of labeled N, even after correction for isotopic dilution by atmospheric N[H.sub.3]. The technique described permits [sup.15]N analysis of any form of N that can be recovered by [H.sub.3]B[O.sub.3] diffusion of soil, soil extracts, soil hydrolysates, Kjeldahl digests, water, or wastewater.

Recent work indicates that accumulation of amino sugar N in soil reduces the yield response of corn (Zea mays L.) to N fertilization, and that nonresponsive sites are detectable by determination of amino sugar N in soil hydrolysates. Unfortunately, the hydrolysis process is too complicated and time-consuming for use in routine soil testing. A much simpler technique was developed to estimate amino sugar N without the need for acid hydrolysis. In this test, 1 g of air-dried soil is treated with 10 mL of 2 M NaOH in a 473-mL (1-pint) wide-mouth Mason jar, and the sample is heated for 5 h at 48 to 50 [degrees] C on a hot plate to liberate (N[H.sub.4] + amino sugar)-N as gaseous N[H.sub.3]. The N[H.sub.3] is collected in [H.sub.3]B[O.sub.3]--indicator solution, and subsequently determined by acidimetric titration. Recovery ranged from 97 to 102% when analyses were performed after treating samples with [sup.15]N-labeled [(N[H.sub.4]).sub.2]S[O.sub.4] or glucosamine, but did not exceed 6.5% with labeled glycine and was undetectable with labeled N[O.sub.3] or N[O.sub.2]. Comparative studies using 12 nonresponsive and 13 responsive soils showed a very high correlation between soil-test N and hydrolyzable amino sugar N (r = 0.90***). Test values were significantly higher (P < 0.001) for nonresponsive (237-435 mg N [kg.sup.-1]) than for responsive (72-223 mg N [kg.sup.-1]) soils. The soil test described has important economic implications for production agriculture, and also should be of value for controlling N[O.sub.3] pollution of ground and surface water.

Agricultural and natural N cycling systems have been intensively studied via the stable isotope (super 15)N. Tracing N translocation over time by applying (super 15)N-tagged fertilizer has been used extensively. Our objective was to quantify fertilizer (super 15)N translocation for an extended time in irrigated lysimeters containing sandy loam soil and cropped with corn and potato. Tagged fertilizer was applied to two lysimeters in 1989 and one in 1990. One lysimeter remained untreated. Breakthrough of (super 15)N, above the background level of 0.366 atom %, was detected in drain effluent from 2.3-m-deep drains on treated lysimeters one year after initial preplant (super 15)N application. Drainage water (super 15)N concentration then increased rapidly to about 0.48 atom %, followed by a gradual decrease. However, 9 years after application there was still elevated (super 15)N, 0.39 atom %, in the drainage water and 26-31% of the applied excess (super 15)N remained in the soil profile. Cumulative (super 15)N removed from lysimeters via drainage water during the first 7 years was between 3.0 and 3.7%. Estimated gaseous loss was 16%.

Serious interference can arise in carrying out quantitative or isotopic analyses of inorganic N in samples having a high content of labile organic N. Studies to evaluate existing Mason jar diffusion methods for interference by a high concentration of various amino acids and amino sugars showed the need to minimize the diffusion period. This was accomplished by increasing the volume of [H.sub.3]B[O.sub.3]-indicator solution (to 7 mL), and by carrying out diffusions from a fixed volume (10 mL) with a high salt concentration (4 M KCl). Quantitative recovery ([greater than or equal to]98%) of 4 mg of N[H.sub.4]-N was achieved in the presence of 10 mg of organic N, either in 18 h at 25 [degrees] C, or in 1.5 h by heating on a hot plate at 45 to 50 [degrees] C. Under the same conditions, complete recovery of N[O.sub.3]-N and N[O.sub.2]-N was achieved in the presence of 4 mg of organic N by increasing the amount of Devarda's alloy from 0.3 to 1.5 g. The modified diffusion methods were much more accurate and precise than conventional steam distillation techniques for inorganic N analysis of animal waste or other complex samples treated with labeled N[H.sub.4]-N, N[O.sub.3]-N, or N[O.sub.2]-N. Recovery of the labeled N by diffusion ranged from 96 to 107%, and the coefficient of variation was usually

Colorimetric methods based on the Berthelot reaction are used widely for quantitative determination of N[H.sub.4]-N in biological and environmental samples. Studies to evaluate phenol and salicylate, the most commonly used chromogenie substrates, revealed minor interferences by metallic cations, whereas up to a threefold shift in absorbance was observed with 38 diverse N-containing organic compounds. Interferences differed markedly between phenol and salicylate. The possibility of a simple correction was precluded by the fact that interferences were both positive and negative, and depended on the temperature during color development and the concentration of N[H.sub.4]-N. Fourteen compounds were evaluated as alternatives to phenol and salicylate, of which the Na salt of 2-phenylphenol (PPS) proved to be the most promising. Using PPS, macro- and microscale batch methods and an automated flow-injection method were developed. These methods are simple, convenient, and sensitive. Using the PPS microscale method, for which the limit of detection is 0.17 mg N[H.sub.4]-N [L.sup.-1], recovery of N[H.sub.4]-N added to soil extracts ranged from 98 to 104%, with a coefficient of variation of 1.4 to 2.7%. As with phenol and salicylate, precipitation of metal hydroxides was observed. Precipitation was controlled by chelation with citrate rather than ethylenediaminetetraacetic acid (EDTA), which suppressed color development by preventing monochloramine formation. Compared with Berthelot methods that use phenol or salicylate, interference by amino acids was decreased by up to 10-fold. Interference by other organic N compounds was virtually eliminated.

Diffusion methods are often employed to speciate inorganic N in soil extracts or water for N-isotope analysis with automated mass spectrometers. Diffusion is usually carried out in a plastic specimen container with an acidified filter disk to collect the diffused N[H.sub.3]. Owing to the small size of the container and the limited surface area of the acidified disk, a diffusion period of 6 to 14 d is generally required, and even then recovery may be incomplete. Simple diffusion methods were developed that use two acidified disks in a 473-mL (1-pint) wide-mouth Mason jar. Diffusions with MgO to recover N[H.sub.4]-N, or with MgO plus Devarda's alloy to recover (N[H.sub.4] + N[O.sub.3])-N or (N[H.sub.4] + N[O.sub.3] + N[O.sub.2])-N, were performed from 5 to 100 mL of either 2 or 4 M KCl. Quantitative recovery of 150 [[micro]gram] of N was achieved in 1 to 7 d at 20 to 25 [degrees] C, and in 2 to 14 h by heating on a hot plate at 45 to 50 [degrees] C. Isotopic analyses of labeled soil extracts were accurate to within 5%, as determined by isotope-dilution calculations. Incomplete diffusion led to

The major limitation of diffusion methods for N analysis is the time required to obtain the results - typically from one to several days. Methods were developed that involve a much shorter period for diffusion. In these methods, 10- to 100-mL samples of 2 or 4 M KCl soil extract or water were treated with MgO, or MgO plus Devarda's alloy, in a 473-mL (1-pint) wide-mouth Mason jar to liberate N[H.sub.4]-N, N[O.sub.3]-N, and/or N[O.sub.2]-N as N[H.sub.3]. The jar was placed on an electric griddle maintained at 45 to 50 [degrees] C. Gaseous N[H.sub.3] was collected in 5 mL of [H.sub.3]B[O.sub.3] indicator solution in a petri dish attached to the Mason jar lid, for quantitative determination by acidimetric titration. Complete recovery of 4 mg of N was achieved from 10 or 20 mL in 1.5 to 5 h. Recovery from 50 or 100 mL was complete in 5 to 8.5 h with 1 to 2 mg of N. The methods permit 15N analysis of the diffused N[H.sub.3]-N. Isotopic analyses of labeled soil extracts were accurate to within 3%, as determined by isotope-dilution calculations. Diffusions from 10 to 50 mL were subject to very little, if any, interference from decomposition of alkali-labile organic-N compounds.

An improvement in the nitrogen (N)-15 analysis of inorganic N in soil extracts is described. It is a modification of the Rittenberg technique, where the acidified glass fiber disks used in the diffusion step are digested using hydroflouric acid after being transferred to the sample tray. The results obtained using this method need to be corrected for isotopic dilution but they show good agreement with results obtained with conventional means.

A method initially developed for isotope-ratio analysis of inorganic nitrogen in forest soils was adapted for use with Kjeldahl digests of organic material. This involves diffusion of the digests using an automated Rittenberg apparatus and mass spectrometry. Results corrected for isotopic dilution were in agreement with findings obtained using standard steam-distillation and concentration techniques. Its main advantage is its ease of operation and ready availability of apparatus.

Radiotracer studies have provided indirect evidence that heterocyclic N in atrazine [2-chloro-4(ethylamino)-6-(isopropylamino)-1,3,5-triazine] may be utilized by microorganisms as a source of N; however, no data are available from investigations using 15N as a tracer. Studies were conducted to examine microbial utilization of atrazine ring-15N in soil and pure cultures of Pseudomonas sp. strain ADP, Agrobacterium radiobacter J14a, or bacterium M91-3. Atrazine [U-15N-ring] was synthesized from labeled urea. To investigate the effect of exogenous N on atrazine degradation, pure cultures were supplemented with unlabeled atrazine and labeled N as [(N[H.sub.4]).sub.2]S[O.sub.4], KN[O.sub.3], urea, or glycine. Under C-limiting conditions, cells of Pseudomonas sp. strain ADP incorporated side chain-N into biomass and liberated ring-N as N[H.sub.4]. When N was limiting, ring-N was also recovered in biomass. Degradation of atrazine by Pseudomonas strain sp. ADP and A. radiobacter was unaffected by the presence of exogenous N, whereas no degradation occurred with bacterium M91-3 in media containing urea or N[H.sub.4]-N. The fate of double-labeled [U-14C, U-15N-ring]-atrazine (15 mg [kg.sup.-1]) was examined after incubation of a Bloomfield soil (sandy, mixed, mesic Psammentic Hapludalf) amended with N[H.sub.4]- or N[O.sub.3]-N (75 mg [kg.sup.-1]), with or without an inoculum of Pseudomonas sp. strain ADP (1.06 > [10.sup.13] cells [kg.sup.-1]). ln uninoculated soil, mineralization of atrazine-14C was inhibited by inorganic N, whereas in the inoculated soil, 87% of the atrazine was mineralized, regardless of the N treatment. The C/N ratio was much lower for amino acids isolated from soil than for the atrazine ring, suggesting preferential assimilation of N over C by microorganisms.

Soil cation-exchange capacity (CEC) is often determined by NH4 saturation, using a 1 M solution of NH4C2H3O2 at pH 7. A study was conducted to ascertain whether this determination can be performed by employing a simple diffusion technique previously developed for direct inorganic-N analysis of soils. Values obtained for 10 diverse Illinois surface soils following overnight NH4 saturation were correlated very highly with CEC data collected for the same samples on the basis of NH4 analyses by steam distillation (r = 0.999, P < 0.001) or colorimetry (r = 0.999, P < 0.001), and also with data obtained by summing atomic absorption measurements of calcium (Ca), magnesium (Mg), and potassium (K) displaced during NH4 saturation (r = 0.811, P < 0.01). As a much more rapid and convenient alternative to existing methods for preparation of NH4-saturated soil, a simple saturation technique was developed whereby 0.500 g of soil was leached under vacuum with 15 mL of 1 M NH4C2H3O2 (pH 7) in a 10-mL disposable syringe containing a stainless-steel frit, and then with 30 mL of 2-propanol. After drying for a few minutes, the soil sample was transferred to a 473-mL (1-pint) wide-mouth Mason jar, treated with 10 mL of 2 M KCl, and analyzed for exchangeable NH4 by diffusion with MgO for 1.75 h at 45–50°C on a hot plate. Except for a calcareous soil, CEC measurements by the rapid saturation-diffusion approach did not differ significantly (P < 0.05) from diffusion data involving overnight NH4 saturation. This approach allows CEC determinations to be accomplished in a few hours instead of days, and will be especially useful for routine soil characterization and testing. [ABSTRACT FROM AUTHOR]

Denitrification losses are a possibility from turfgrass because of frequent irrigation, multiple applications of N fertilizers, and an abundance of readily decomposable organic C in thatch and verdure. Field experiments were conducted to directly measure N[sub 2] and N[sub 2]O evolved from a Flanagan silt loam soil under Kentucky bluegrass (Poa pratensis L.) or creeping bentgrass (Agrostis palustris Huds.). Mass spectrometric procedures were used to analyze atmospheric samples collected from replicated [sup 15]N fertilized turf (49 kg ha[sup -1]). Data showed that labeled fertilizer N (LFN) losses ranged from 2.1 to 7.3% for N[sub 2] and from 0.4 to 3.9% for N[sub 2]O; that large N[sub 2] and N[sub 2]O fluxes occurred after heavy rainfall events; and that more N[sub 2] was evolved than N[sub 2]O. Emission of gas was detected while standing water was visible within cylinders, suggesting the transfer of gases from the flooded soil to the atmosphere through the turfgrass plants. Evolution of N[sub 2] and N[sub 2]O was greater from creeping bentgrass treated with KNO[sub 3] than urea through the first 3 wk of the experiment, whereas N[sub 2] emission was greater for urea during the last 2 wk of the experiment, presumably because of NO[sub 3] production through nitrification. Nitrous oxide was detected on the day of fertilization with the KNO[sub 3] treatment, and the mole fraction of N[sub 2]O decreased from 0.44 to 0.11 with each weekly application of N. [ABSTRACT FROM AUTHOR]

Although the fate of fertilizer applied to turfgrass has been studied in the past, recovery of applied fertilizer N is typically low, and denitrification has been cited as the reason. The objectives of this research were twofold: (i) to examine the fate of [sup 15]N applied to Kentucky bluegrass (Poa pratensis L.) turf as KNO[sub 3], including direct measurement of denitrification; and (ii) to determine whether and how plants affect fertilizer-N recovery. Polyvinyl chloride (PVC) cylinders, modified to permit atmospheric sampling, were used throughout field experiments during the spring and summer 1999 and a greenhouse experiment in 2000. Potassium nitrate (98.5 atom % [sup 15]N) was applied in solution at 49 kg N ha[sup -1] to replicated plots, and atmospheric samples were collected three times a day from 0800 to 1100, 1100 to 1400, and 1400 to 1700 h during a 6-wk period in the spring and a 4-wk period during the summer of 1999. Emission of N[sub 2] or N[sub 2]O ranged from 3.3 to 21.3% and from 0.3 to 5.9% of labeled fertilizer N (LFN), respectively. Recovery of LFN in the soil or plant, plus that emitted as N[sub 2] or N[sub 2]O, ranged from 57.4 to 73.2%. A 4-wk greenhouse experiment comparing LFN recovery for bare soil and turf, including gas emission and leachate, was initiated in the summer of 2000. Total emission of LFN as N[sub 2] or N[sub 2]O was 19.0% for the turfgrass, as compared with 7.3% for the bare soil. Corresponding values for total recovery of LFN were 70.6 and 84.2%, respectively. [ABSTRACT FROM AUTHOR]

Evaluates a soil organic nitrogen (N) fraction that reduces the need for nitrogen fertilization. Yield response to N fertilization; Concentration of hydrolyzable N in soil; Correlations of soil chemical properties with check plot yield and N-fertilizer response; Production of mineral N during incubation of soils differing in N-fertilizer responsiveness.

Investigates whether Mason-jar diffusion methods for determination of inorganic nitrogen in soil extracts can be applied directly to the soil sample itself. Evaluation of the precision and analytical accuracy of the method; Comparison with inorganic nitrogen analysis by extract-diffusion.