Abstract A common strategy for improving fertilizer N uptake efficiency by corn ( Zea mays L.) is to synchronize application with crop N demand during the growing season, which can be done using the Y Drop system recently developed for surface dribble placement. A 2‐yr field study was conducted using dual‐labeled urea‐ammonium nitrate (UAN) solution to compare fertilizer 15 N uptake efficiency (F 15 NUE) for surface and subsurface sidedress applications to soils of contrasting fertility under either second‐year corn or a corn–soybean [ Glycine max (L.) Merr.] rotation. Besides placement, treatments were designed to allow comparison of 15 N uptake from UAN applications made at planting vs. at the V9 growth stage. The importance of soil N supply was demonstrated by estimates of N derived from fertilizer that ranged from 17 to 47% in total aboveground biomass and never exceeded N derived from soil. Of the fertilizer N recovered in the crop at harvest, the majority originated from the 15 N applied at sidedressing rather than at planting. The range in F 15 NUE was from 12 to 42% (26% on average) for grain and from 14 to 51% (31% on average) for total aboveground biomass, the only significant difference occurring when the subsurface treatment outperformed Y Drop placement under conditions conducive to urea N loss through NH 3 volatilization. Both methods of application offer the same fundamental advantage, in that fertilizer N is supplied during the period of maximal crop uptake.
ABSTRACT Turfgrass managers frequently apply N as a foliar spray when low application rates are desired. This practice is believed to promote foliar N uptake that benefits turf; however, very little information is available concerning the quantity of N absorbed by turfgrass foliage or the effect of various spray parameters on foliar N uptake under field conditions. This research was conducted to evaluate fertilizer N uptake efficiency of foliarly applied 15 N to creeping bentgrass [ Agrostis stolonifera var. L. palustris (Huds.) Farw. ‘Pennlinks’] under field conditions. The effects of spray volume, N carrier, adjuvant addition, and tank mixing with commonly applied turf care products (e.g. chlorothalonil) on foliar N uptake were conducted to evaluate foliar uptake of fertilizer 15 N by creeping bentgrass. From 6 to 34% of foliar‐applied N was taken up mostly within 2 h and completely by 4 to 6 h after fertilizer application. Uptake efficiency increased significantly when spray volume was decreased but was unaffected by N carrier, adjuvant addition, or tank mixing.
Installation of subsurface drainage systems has profoundly altered the nitrogen cycle in agricultural regions across the globe, facilitating substantial loss of nitrate (NO3-) to surface water systems. Lack of understanding of the sources and processes controlling NO3- loss from tile-drained agroecosystems hinders the development of management strategies aimed at reducing this loss. The natural abundance nitrogen and oxygen isotopes of NO3- provide a valuable tool for differentiating nitrogen sources and tracking the biogeochemical transformations acting on NO3-. This study combined multi-years of tile drainage measurements with NO3- isotopic analysis to examine NO3- source and transport mechanisms in a tile-drained corn-soybean field. The tile drainage NO3- isotope data were supplemented by characterization of the nitrogen isotopic composition of potential NO3- sources (fertilizer, soil nitrogen, and crop biomass) in the field and the oxygen isotopic composition of NO3- produced by nitrification in soil incubations. The results show that NO3- isotopes in tile drainage were highly responsive to tile discharge variation and fertilizer input. After accounting for isotopic fractionations during nitrification and denitrification, the isotopic signature of tile drainage NO3- was temporally stable and similar to those of fertilizer and soybean residue during unfertilized periods. This temporal invariance in NO3- isotopic signature indicates a nitrogen legacy effect, possibly resulting from N recycling at the soil microsite scale and a large water storage for NO3- mixing. Collectively, these results demonstrate how combining field NO3- isotope data with knowledge of isotopic fractionations can reveal mechanisms controlling NO3- cycling and transport under complex field conditions.
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Abstract Public concern that agricultural use of N fertilizers may have adverse effects on environmental quality and human health has led to a growing need for reliable data concerning the concentration of inorganic N in ground and surface water. A study was conducted to compare the accuracy and precision of simple Mason‐jar diffusion methods for quantitative determination of NH + 4 and NO − 3 , in a wide variety of water and wastewater, relative to colorimetry, ion‐selective potentiometry, and steam distillation. Good agreement among methods was generally obtained with standard solutions prepared using deionized water; however, substantial differences often were observed with natural and anthropogenic samples, because of either Cl − interference in measurements with the NO − 3 electrode or CO 2− 3 interference in distillation. Analytical accuracy also was evaluated by measuring recovery of N added as (NH 4 ) 2 SO 4 or KNO 3 , (6 mg N L −1 ). With most of the samples studied, quantitative recovery (97–103%) was not achieved by potentiometry or distillation. Quantitative recoveries usually were achieved by a manual Berthelot method for colorimetric determination of NH + 4 , whereas recovery was often incomplete when NO − 3 analyses were performed with an automated flow‐injection system using Cd 2+ reduction. Regardless of the sample matrix, diffusion was always accurate in measuring recovery of NH + 4 or NO − 3 .
Abstract Rapid, sensitive analysis of NH4 ‐ NO3 ‐, and NO2 ‐ in 1–150 μL of soil extract or water was achieved using a modified indophenol blue technique adapted to microtiter plate format. The microplate technique was similar to conventional steam distillation in accuracy and precision. By varying aliquot volume, a wide linear dynamic range (0.05 to 1000 mg of NH4 +‐ or NO3 ‐‐NL‐1) was achieved without the need for sample dilution or concentration. High sample throughput (250–500 NH4 + analyses d‐1) was accomplished manually, but could be significantly increased by automation. Of considerable importance was the very low waste stream produced by the method. All equipment and supplies required are commercially available and need no modifications for this use. The microtiter plate format could be used for other soil colorimetric analyses with little or no down time for equipment setup, a major consideration for commercial soil‐testing laboratories. The method and equipment used are well suited to quality control and quality assurance programs, as required under FIFRA Good Laboratory Practices.
Abstract Inorganic nitrogen (N) in the form of exchangeable ammonium (NH 4 + ), nitrate (NO 3 − ), or nitrite (NO 2 − ) is normally extracted by shaking soil with a neutral salt solution and is subject to interference by soluble organic N (SON). After optimizing sequential diffusion methods to expedite recovery of NH 4 + –N and (NO 3 − + NO 2 − )‐N, 15 N‐tracer studies were conducted to ascertain whether extraction is quantitative when performed on soils amended with 2 g 15 N kg −1 using 0.2, 1, and 2 M potassium chloride (KCl) and can be carried out by a simple leaching method instead of conventional shaking‐filtration. The results verified a significant decrease in SON interference with the optimized diffusion procedures and showed that (a) interference is more serious for NH 4 + –N than for (NO 3 − + NO 2 − )‐N, (b) 2 M KCl is required for quantitative recovery of 15 NH 4 + –N, and (c) leaching virtually eliminates organic interference during diffusion of (NO 3 − + NO 2 − )‐N. The leaching‐diffusion approach minimizes the inflating effect of SON on soil inorganic N analyses and will be especially useful in N isotope studies.
Abstract In mass spectrometric procedures recently developed for determination of 15 N‐labeled dinitrogen (N 2 ) and nitrous oxide (N 2 O) evolved from soils, calculations are performed to determine the mole fraction of 15 N in the N pool from which this N 2 or N 2 O was derived ( 15 X N ), and a fraction proportional to the amount evolved ( d ). The equations originally derived for these calculations are based on several approximations and are so simple that they can easily be performed using a handheld calculator. Modern ratio mass spectrometers are usually equipped with an on‐line programmable calculator or computer to process the digital output from the integrating ratiometer, which has made it practical to calculate 15 X N and d using equations based on fewer approximations than the equations previously derived. Refined versions of the equations are derived in this paper. The refined equations are much more complicated than the original equations, but they are more accurate and permit the use of fertilizers containing <20 atom % 15 N in studies of denitrification.
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.
