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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 [...]

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]

Develops a technique to permit the use of boric acid indicator solution in carrying out inorganic nitrogen analysis in soil extracts. Accuracy of isotope-ratio analysis; Use of mass spectrometers for nitrogen isotope analysis; Determination of inorganic forms of nitrogen in soil extracts.

Focuses on the development of techniques to estimate amino sugar nitrogen in soils. Detection of nonresponsive soil sites to Nitrogen fertilization. Effects of amino sugar accumulation in soils; Implication of the test on production agriculture.

Presents diffusion methods to determine different forms of nitrogen (N) in soil hydrolysates. Reason for developing diffusion methods; Comparison of diffusion and steam-distillation methods; N-distribution analysis of soil hydrolysates by distillation and difffusion.

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 the applicability of the neon technique for atmospheric volume measurement of denitrification in soil cores. Description of the neon technique; Level of accuracy achieved in measuring the atmospheric volume inside a closed chamber containing saturated or unsaturated soil; Effect of pumping period on volume measurements for unsaturated soil cores in the field under turfgrass.

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.

Evaluates Mason jar diffusion methods for inorganic nitrogen analysis of organic-laded soil samples. Evaluation of modified diffusion methods; Protocol for the storage of complex samples.

Describes diffusion methods of determining inorganic nitrogen (N) in soil extracts or water. Materials and methods used; Evaluation of diffusion methods; Results and discussion; Analysis of statistical data compiled.

Examines accelerated diffusion methods for inorganic-nitrogen analysis of soil extracts and water. Limitation of diffusion methods for nitrogen analysis; Development of methods which involves shorter periods of diffusion.

Focuses on colorimetric analyses of nitrogen (N) based on the Berthelot method for determining ammonium in soil extracts and water. Materials and methods used; How color formation by the Berthelot reaction is influenced by potential hydrogen (pH); Functions of colorimetric methods; Results and discussion.

The diacetyl monoxime colorimetric method of determining urea in soil extracts was modified for microplate format. A 100‐μL aliquot of extract was treated with color reagent in a disposable plastic microtiter plate (96 wells/plate), and color was developed by heating the plate in a low‐temperature oven at 87°C for 55 min. After cooling for 20 min at ambient temperature, absorbance measurements were simultaneously performed on all 96 wells using a microplate reader. The microscale method was faster and more convenient than the conventional method; moreover, the volume of waste was markedly reduced. Studies to compare the two methods showed very little difference in accuracy, precision, or sensitivity. [ABSTRACT FROM PUBLISHER]