E. G. Beauchamp

Denitrification rate relationships with soil parameters in the field

Abstract It has been recently shown that there is a large spatial variability in denltrification rates measured in the field. The objective of this study was to assign this variability to twelve measurable or determined soil parameters known or suspected to be Important to denitrification during the early part of the growing season. Relationships were sought with 16 cores at a grid spacing of 25 cm on three sites (dates) within a 0.07 ha area of a cultivated silt loam soil. The denitrification rate was estimated from the N2O production rate with the acetylene blockage technique. Only few statistical significant relationships were found with simple and multiple regression analyses and there was a lack of consistency from site to site. Plotting the data revealed a tentative negative relationship between the N2O production rate and percent air‐filled porosity. A few cores at each site showed a much greater N2O production rate for no discernable reason, but these rates were also negatively related to percent ...

Organic matter availability for denitrification in soils of different textures and drainage classes

Abstract Soils from the A, B, and C horizons representing three natural drainage classes and differing textures were chosen to study relationships between denitrification rate and estimates of available carbon. The highest correlation with denitrification rate was obtained with total organic C. Water‐extractable C, mineralizable C and 0.1 N Ba(OH)2‐extractable C produced less satisfactory correlations. When soils of the B and C horizons only were included in the regression analysis, 0.1 N Ba(OH)2‐extractable C was found to be unsatisfactory as a predictor of available C for soil denitrifiers. None of the four methods for estimating available C were found adequate for B and C horizon soils which were relatively low in available C. Coarser‐textured soils with relatively low C levels had correspondingly low denitrification rates. Regressions of denitrification rate on mineralizable C or water‐extractable C were nonsignificant with poorly drained soils whereas they were highly significant with well or imperfe...

Nitrous oxide emissions from soil amended with glucose, alfalfa, or corn residues

Abstract Nitrous oxide (N2O) emissions result from the nitrification and denitrification processes, the latter strongly affected by soil organic carbon (C) derived from plant residues. This study addressed two questions: (1) does plant residue C become less available to denitrifiers after a period of aerobic incubation, and (2) do plant residues with smaller particle sizes provide C for higher rates of N2O production due to a faster decomposition rate? Nitrous oxide fluxes from soil amended with alfalfa or corn residues, or glucose were measured in the laboratory using a gas flow‐through chamber system. Soil amended with these C substrates was also subjected to a 5‐d aerobic preincubation treatment. The significance of particle size on C availability was studied by comparing N2O released from soil amended with ground (particle size <1 mm) and large pieces (5‐cm lengths) of alfalfa residues. A 5‐d aerobic preincubation of soil amended with plant residues resulted in reduced N2O production during a subsequent anaerobic period. Results suggested that, due to consumption of the most available substrate, remaining C in plant residues is less available to denitrifiers after a period of aerobic incubation. Higher N2O losses were found with large alfalfa particles than with ground alfalfa.

Rapid extraction and analysis of volatile fatty acids in soil

Abstract The concentrations of volatile fatty acids (VFA) in soils are important in studies involving phytotoxicity and fermentation processes. Concentrations of acetic, propionic, and butyric acids as low as 0.21, 0.14, and 0.10 mmol kg‐1soil in water extracts were accurately determined. The extracts were filtered through 45 μm millipore disc filters and injected directly into a gas chromatograph following addition of purified formic acid. The formic acid eliminated ghosting of peaks. The gas chromatograph was equipped with a flame ionization detector and a 60/80 Carbopack C/0.3% Carbowax 20M/0.1% H3PO4packed precolumn (0.15 m) and column (1.83 m). The precolumn was changed after 150 to 200 sample injections when contaminated beyond acceptable limits. There was good separation of VFA with no interfering organic volatiles in extracts of soil containing glucose, cellulose or straw incubated anaerobically for as long as 4 weeks. The advantages of the procedure are relative rapidity and simplicity as well as...

NITROUS OXIDE PRODUCTION AND FLUX FROM SOIL UNDER SOD FOLLOWING APPLICATION OF DIFFERENT NITROGEN FERTILIZERS

Concern over contribution of nitrous oxide (N2O) to global warming and stratospheric ozone depletion has prompted measurement of nitrous oxide (N2O) emissions from agricultural soils and study of controlling factors. The objectives of this study were [1] to measure the magnitude of N2O emissions from application of (NH4)2SO4, Ca(NO3)2 or urea (each at 100 kg N/ha) to a Kentucky bluegrass (Poa pratensis L.) stand, and [2] to compare flux of N2O from the surface measured with covers to N2O production and denitrification in soil cores collected at a depth of 2.5–7.5 cm. Water, NH4 + and NO3 − contents of soil cores were also measured. Application of all three fertilizers increased N2O production by soil cores, and N2O flux from covers. The two measurements differed in temporal pattern and magnitude. Flux of N2O from the soil surface is a more complex and variable process than N2O production in a specific soil layer. The possibility of increased N2O production with urea requires further investigation under more controlled conditions. Nitrification of NH4 + appeared to be the principal source of N2O.

Denitrification and nitrous oxide production in soil fallowed or under alfalfa or grass

Abstract A field study was carried out to assess the effects of agronomic practices and crops on nitrous oxide (N2O) production and denitrification rates. Air‐filled porosity, moisture content, respiration rate, and ammonium (NH4) and nitrate (NO3) concentrations were also measured along with nitrogen (N2) gas production using the static soil core procedure with acetylene (C2H2). Agronomic practices included applications of liquid cattle manure, ammonium sulfate, sucrose, and irrigation water as well as the incorporation of alfalfa. Measurements were made on fallowed soil as well as soils under alfalfa (Medicago sativa L.) and Kentucky bluegrass (Poa pratensis L.). The temporal pattern of N2 gas production was dominated by episodic events caused by manure or sucrose application, or alfalfa incorporation in conjunction with irrigation or rainfall events. Rainfall or irrigation alone did not increase N2 gas production unless following upon a dry period. In wetted soil, the N2O production rate was lower than...

Soil tests for predicting the N requirement of corn

Several soil N tests were compared with the one currently used for predicting the N requirement for corn in Ontario. The current test involves a measurement of nitrate (NO3−, 0–30 cm) before N fertilizer sidedressing. The study was done to determine the efficacy of other tests for N fertilizer prediction. The tests chosen varied in the quantity of N “extracted” and included hot KCl-extractable NH4+, anaerobically released NH4+, extractable NH4+ following autoclaving in CaCl2 solution and total N of soil sampled to a depth of 30 cm. The 3-yr study was conducted on a sloped (simple) field site, which provided a wide range in soil organic matter (SOM) contents. A corn crop was grown each year following a barley crop with or without red clover cover crop residues incorporated in the spring and with or without N fertilization. Corn grain yields were obtained at the end of the growing season. Grain yields were lowest at the shoulder and backslope locations and highest at the footslope and toeslope locations. Co...

Relationships of Total Soil Nitrogen to Several Soil Nitrogen Indices

The usefulness of soil nitrogen (N) tests or indices for predicting crop N requirements has been controversial. This paper shows how the relationship between soil indices and total soil N varies using simple linear regressions. The soil N indices included measurement of extractable NH4 + following autoclaving or anaerobic incubation, or following “hot” (100°C) KCl extraction. Also, extractable NO3 − levels sampled four times during the early growing season (May/June) were correlated to total N. Total soil N was considered to be a relatively stable “bench mark” for this study. Soil samples (0–30 cm) were collected from field trials that focused on response of corn to N with different red clover cover crop management practices on different landscape locations over a 3-year period. Management practices included comparisons between no tillage and conventional tillage done in either the late fall or spring. It was observed that the correlations between total N and any of the soil N indices were extremely variable from year to year with each cover crop management practice. The correlations also varied with respect to slope location from year to year in an unpredictable manner. It was concluded that N indices only partially and variably reflect the N released from the large humus N pool in the soil, and are therefore unpredictably related to other more labile N pools (e.g., residues) in the soil.

Nitrogen mineralization and nitrifier activity in limed and urea‐treated soils

Abstract The effect of liming on mineralization and soil nitrifier activity (NA) was investigated with Brookston clay (pH 5.7) and Haldimand clay (pH 4.7). Liming increased the rate of mineralization in both soils but at a rate about 4‐times greater in Haldimand clay than Brookston clay. A significant increase in N mineralization due to liming occurred in both soils only when pH was raised above 6.0. The rate of mineralization was greater than nitrification in the Haldimand soil resulting in NH4 + accumulation. Nitrifier activity increased with liming of Brookston clay, but decreased in Haldimand clay after 15 days of incubation. There was a significant increase in nitrifier activity due to liming from 15 to 60 days in Haldimand clay. After 60 days nitrifier activity in limed treatments increased by five times over the unlimed control. The nitrification of urea powder (1000 mg N.kg‐1) mixed into the soil was also studied in several soils incubated at 15°C for 28 days. There was evidence up to 14 days that...

Fixed ammonium and potassium release from two soils

Abstract Release of native and added K+ and NH+ 4 from two soils was monitored during a 166 day incubation/leaching experiment. One soil (Brookston) represented a major soil series In Ontario whereas the other (Harriston) was suspected having a relatively large fixation capacity. Treatments were imposed involving addition of 50 μM g‐1 soil of K+(KCl) or NH+ 4 (NH4Cl) only or one added after the other on successive days. The addition of either K+ or NH+ 4 on day 2 tended to inhibit the release of the other added on day I. Also the addition of either K+ or NH+ 4 on day 1 tended to inhibit the sorption or fixation of the other on day 2. The release rate of K+ during the 10 to 166 day period was almost constant and not affected by the addition of NH+ 4. Alternatively, the addition of K+ on day 2 slowed the release rate of NH+ 4 measured by NO− 3 appearance from day 10 to 40 but had no effect thereafter. At the end of the experiment considerably more K+ than NH+ 4 was retained suggesting that K+ was more firml...