2.3 Changes in soil temperatures after fire 3. Influence of the products of vegetation burning (ash and heat), on the soil environment, and their relation to nutrient availability 3. 1 The soil as an environment for biological activities and nutrient transformations 3.2 The ash component 3.2.1 Relationship between ash deposition and soil fertility 3.2.2 Effects of ash on nutrient cycling and soil chemical and biological processes 3.2.2.1 Ash formation 3.2.2.2 Ash return and properties 3.2.2.3 Nutrient return in ash, and the effect of ash on soil chemical properties 3.2.2.4 Influence of ash on soil biological processes 3.3 The heat component 3.3.1 General introduction 3.3.2 Plant growth in heated and sterilized soils 3.3.3 Effect on soil physical properties 3.3.4 Influence of heat on soil chemical properties 3.3.4.1 Changes in properties other than N compounds 3.3.4.2 Non-biological changes in soil N fractions 3.3.5 Biological changes in heated soils 3.3.6 Non-biological gas exchange in heated soils

Modification of the soil environment by vegetation fires, with particular reference to nitrogen transformations: A review

Effects of acute gamma irradiation on chemical, physical and biological properties of soils

The effects of sterilizing a silt loam by γ-irradiation or autoclaving on direct counts of bacteria, CO 2 production, and mineral nitrogen content during storage at 5° C for 98 days were studied. After autoclaving, 55% of the bacterial population lysed rapidly and by 56 days only 10% of the initial population could be seen. Irradiated bacteria remained intact for longer, with over 70% being visible after 98 days. CO 2 production increased after irradiation and then declined to a stable rate after 21 days. Autoclaving reduced CO 2 production to near zero. The irradiated soil responded to the addition of glucose but there was no response from the autoclaved soil. There was a flush of NH 4 + -N production after both autoclaving and irradiation. The concentration of NH 4 + -N increased in the irradiated soil throughout the 98 days' storage, but remained constant in the autoclaved soil. NO 3 − -N was reduced by both means of sterilizing. The time needed for the soil to stabilize after sterilizing is discussed.

Effects of sterilization and storage on respiration, nitrogen status and direct counts of soil bacteria using acridine orange

Agricultural soils are the primary anthropogenic source of atmospheric nitrous oxide (N2O), contributing to global warming and depletion of stratospheric ozone. Biochar addition has shown potential to lower soil N2O emission, with the mechanisms remaining unclear. We incubated eucalypt biochar (550 °C) – 0, 1 and 5% (w/w) in Ferralsol at 3 water regimes (12, 39 and 54% WFPS) – in a soil column, following gamma irradiation. After N2O was injected at the base of the soil column, in the 0% biochar control 100% of expected injected N2O was released into headspace, declining to 67% in the 5% amendment. In a 100% biochar column at 6% WFPS, only 16% of the expected N2O was observed. X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N2O and the biochar surfaces. We have shown increases in -O-C = N /pyridine pyrrole/NH3, suggesting reactions between N2O and the carbon (C) matrix upon exposure to N2O. With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents. Evidence suggests that biochar has taken part in redox reactions reducing N2O to dinitrogen (N2), in addition to adsorption of N2O.

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Lowering N2O emissions from soils using eucalypt biochar: The importance of redox reactions

Determination of free fatty acids in beer.

Five Hawaiian soils were irradiated at various levels of gamma irradiation and analysed for available (NH4 and NO3) nitrogen content immediately after irradiation, and after periods of incubation. The release of NH4-N generally increased with increasing dosages in all soils, while NO3-N decreased in some soils. Incubation studies showed that the loss of NO3-N continued even after several days of irradiation. The rate of NH4-N mineralisation in irradiated soils was highest during the first seven days and declined later on.

Effects of gamma irradiation on the available nitrogen status of soils

Nitrification of mineralised NH4-N was enhanced by long-term laboratory storage in polyethylene bags. Such storage caused a slight decrease in soil pH, possibly due to release of acids from decomposing organic matter. Long-term oven-drying of soils released substantial amounts of NH4-N; the NO3-N remained practically unchanged. The magnitude of released NH4-N was noted to be dependent upon the organic matter content of soils. It was speculated that the released NH4-N came from the splitting of ammonium from N-bearing organic compounds in these soils.

Y. Kanehiro

Papers

Effects of gamma irradiation on the available nitrogen status of soils

Changes in available nitrogen content of soils during storage.