Dennis R. Keeney

Nitrous Oxide Emission from Soils

Nitrous oxide (N2O) constitutes only 350 parts per billion (ppb) of the atmosphere. Its production by biochemical processes in soils has long been recognized (Delwiche, 1981; Payne, 1981a, b). However, recent concern about the involvement of N2O in promoting destruction of the stratospheric ozone layer, which protects the biosphere from harmful ultraviolet radiation (Crutzen, 1970, 1971, 1974, 1981; Johnston, 1971, 1977; CAST, 1976; McElroy et al., 1977; Liu et al., 1977), and also the concern that the increased N2O may contribute to the “greenhouse effect” caused by increased CO2 concentration (Yung et al., 1976), have resulted in extensive research on how N2O emissions are affected by fertilizer N usage for meeting food, feed, and fiber requirements of the world (Delwich, 1981; Payne, 1981b; Keeney, 1982; Firestone, 1982; Freney and Simpson, 1983).

Sources of nitrate to ground water

There are a multitude of sources of nitrate to ground waters. Nitrogen undergoes a complex series of biochemical, chemical, and physical reactions in soils and waters, and thus the source of nitrate in ground waters is often difficult or impossible to ascertain with any degree of certainty. However, highly contaminated ground waters often have local sources that can be controlled. Sources of nitrate most often linked with contamination problems include septic tanks, animal and human wastes, and commercial fertilizers.

Potentiometric titration of chloride in plant tissue extracts using the chloride ion electrode

Abstract Use of the chloride specific ion electrode to determine chloride in plants was evaluted. Direct potentiometric determination of chloride by the electrode resulted in unreproducible and extremely high chloride values. However, use of this electrode to indicate the end point in titration of the tissue‐extract mixture with AgNO3 gave results nearly identical to those obtained by the Mohr procedure. The potentiometric titration procedure developed was found to be a rapid, simple and accurate method of determining the chloride concentration in plants.

Nitrogen and phosphorus release from decaying water milfoil

To evaluate the net N and P contribution to water from herbicide-killed aquatic weeds, water milfoil containing 1.5% N and 0.30% P was killed with endothal and allowed to decompose, in the dark, in water only or sediment-water systems. Changes with time in dry weight, total N and P, and organic C in the plant material, and organic and inorganic forms of N and P in the water were determined. Plant decompostion was limited by N. Inorganic N was released by the sediment, and decomposition was more rapid when sediment was present. A smaller N requirement for decomposition under conditions of low O2 was postulated as a possible explanation of the more rapid decomposition observed in the absence of aeration. The presence of plant P in excess of decomposition requirements resulted in rapid accumulation of organic P, followed by inorganic P, in the water. Organic N appeared in the water early in the experiments, but was depleted rapidly, and inorganic N was apparently immobilized as soon as it was formed. In the presence of sediment, organic N and inorganic P levels were much lower. On treating of water milfoil with herbicide, rapid P release can be expected. This P can either be utilized in further biomass production or be sorbed by the sediment. Insufficient data were available to reach definite conclusions regarding N. It would appear, however, that N release from decaying weeds is much slower than P.

Soil nitrogen mineralization as affected by water and temperature interactions

SummaryThe hypothesis that water and temperature interact to influence the rate of soil N mineralization was studied in laboratory incubation experiments with two contrasting soils. Small sample rings (10 mm tall, 50 mm diameter) were packed to uniform bulk density with 1–2 mm aggregates of Plano silt loam and Wacousta silty clay loam. Samples were brought to five different water potentials (−0.1, −0.33, −0.5, −1.0, −3.0 bars) using pressure-plate techniques, and the undisturbed sample rings were then incubated at 10–35°C for 3, 10 or 14 days. The concentration of soil exchangeable NH4+-N and NO3−-N was measured at the end of each incubation period on replicate samples. The Q10 of N mineralization was approximately 2 for all tested water potentials. Soil N mineralization was linearly related to water content or log water potential, but no water-temperature interaction was evident. The Q10 was constant with water content, and the scaled water content-N mineralization relationship was constant with temperature. We recommend the use of scaling approaches for assessing interactive effects between water and other environmental factors on N turnover in soils.

Site of nitrous oxide production in field soils

SummaryNitrous oxide (N2O) fluxes at the soil surface and concentrations at 0.1, 0.2, and 0.3 m were determined in a 40-year-old planted tallgrass (XXX) prairie, a 40-year-old white pine (Pinus strobus) plantation, and field plots treated annually for 18 years either with 33 metric tons of manure ha−1 (330 kg N ha−1) and NH4NO3 (80 kg N ha−1) or with only NH4NO3 (control). Nitrous oxide fluxes from the prairie, forest, manure-amended, and control sites from 13 May to 10 November 1980 ranged from 0.2 to 1.3, 3.5 to 19.5, 3.7 to 79.0, and 1.7 to 24.8 ng N2O-N m−2s−1, respectively. We observed periods when there was no apparent relationship between the N2O flux from the surface and N2O concentrations in the soil profile. This was generally the case in the prairie and in the field sites following the application of N fertilizer. The N2O concentrations in the soil profile increased markedly and coincided with increased soil water content following periods of heavy rainfall for all sites except the prairie. Nitrous oxide concentration gradients indicate that following heavy rainfalls the site of N2O production was moved from the surface deeper into the soil profile. We suggest that the source of N2O production near the surface is nitrification and that N2O is produced by denitrification of NO3 leached into the soil following heavy rainfall.

Arsenic-phosphorus interactions on corn

Abstract Samples of two widely divergent soils, a Waupun silt loam and a Plainfield sand, deficient in P, were treated with 0, 20 or 80 ppm As and 0, 50, 100 or 300 ppm P in all possible combinations and cropped twice for 40 days to corn in the greenhouse. Arsenic had a much more pronounced toxicity to corn in the sand than on the silt loam. At the 80 ppm As level, P had little effect on As toxicity with the silt loam but enhanced toxicity with the sand and increasing rates of P increased As uptake by corn. At the 20 ppm As level, P did not affect As toxicity or uptake. Soil As extracted by N NH4OAc (pH 7.0) decreased with time but increased with increasing levels of applied P. Bray Pl extractable As was not greatly affected by applied P or time, and appeared to be a more suitable “available”; soil As test. From the results obtained, it would appear that P applications are not the solution to an As toxicity problem.

Sample preparation for and nitrogen isotope analysis by the noi-4 emission spectroscope

Abstract A sample preparation unit was developed for use in emission spectrometric analysis of 15 N, and the unit and the NOI-4 spectroscope were evaluated. The sample preparation unit was designed to permit use of reusable discharge tubes, monitoring of pressure in the tube, and flushing with and addition of an inert gas to the tube. It utilizes the hypobromite oxidation approach for production of nitrogen gas. Instrument problems and sources of error included nonlinear gain settings, baseline determination, overlapping bandheads and nonlinearity of the standard curve. Problems in the sample preparation method adopted were limited to memory in the discharge tube ; this was reduced by prolonged baking of the tubes at 700°. Minimum sample size is about 10 μg N. In the normal to 5 atom% 15 N range, the overall method (sample preparation and analysis) gave 0.01 confidence intervals of ±0.03 atom% 15 N.

Perspectives for research on development of nitrification inhibitors

A brief review of the present status and scope of research on nitrification inhibitors pertaining to agricultural production and environmental pollution is presented. An approach is advanced for identification and evaluation of nitrification inhibitors from indigenous resources. Concurrently, research to identify functional groups retarding nitrification would be conducted. These approaches will aid in developing inexpensive and effective materials for nitrification inhibition. Future research needs relating to nitrification inhibitors are also examined.

Distribution and background levels of mercury in sediment cores from selected wisconsin lakes

The vertical distribution of Hg in sediment cores from a range of hard- and soft-water lakes in Wisconsin was evaluated in terms of potential sources of Hg during the nineteenth and twentieth centuries. For the Madison lakes, the trends in Hg distribution were related to variations in sewage inputs during the last 80 yr. It is unlikely that either inputs of sewage or erosional products are responsible for the observed accumulation of Hg in the most recent sediments from three lakes in northeastern Wisconsin. Background levels varied from 0.01 to 0.24 ppm of Hg (intact sediment basis) in precultural sediments from the Wisconsin lakes investigated. There was no consistent relationship between the concentration of Hg and other sediment components of potential importance in the retention of Hg.