This study was conducted to determine the effect of soil compaction and N fertilization on the fluxes of N2O and CH4 in a soil (fine‐silty Dystric Eutrochrept) planted with potato (Solanum tuberosum L.). Fluxes of N2O and CH4 were measured weekly for 1 yr on two differently fertilized (50 and 150 kg N ha‐1) fields. For the potato cropping period (May–September) these fluxes were quantified separately for the ridges (soil bulk density ρb = 1.05 Mg m‐3) covering two‐thirds of the total field area, and for the uncompacted (ρb = 1.26 Mg m‐3) and the tractor‐traffic‐compacted (ρb = 1.56 Mg m‐3) interrow soils, each of which made up one‐sixth of the field area. The annual N2O‐N emissions for the low and the high rates of N fertilization were 8 and 16 kg ha‐1, respectively. The major part (68%) of the total N2O release from the fields during the cropping period was emitted from the compacted tractor tramlines; emissions from the ridges made up only 23%. The annual CH4‐C uptake was 140 and 118 g ha‐1 for the low and high levels of fertilization, respectively. The ridge soil and the uncompacted interrow had mean CH4‐C oxidation rates of 3.8 and 0.8 µg m‐2 h‐1, respectively; however, the tractor‐compacted soil released CH4 at 2.1 µg CH4‐C m‐2 h‐1. The results indicate thas soil compaction was probably the main reason for increased N2O emission and reduced CH4 uptake of potato‐cropped fields.

No abstract

Regular application of slurry manurc in large quantities is thought to degrade soil structure and increase erodibility. One hypothesis links this to the large input of potassium which increases the exchangeable potassium percentage (EPP) and, thereby, dispersion. The effect of EPP on erodibility was quantified in three experiments. In the laboratory, eleven rainfall experiments were conducted using a silty topsoil from a typic Hapludalf which was fertilized to EPPs of 4 to WYO. Field rainfall experiments on 22 Inceptisols and Alfisols were used to examine whether the long-term application of monovalent cations (Naf, K+ and NH,') with slurry manure had changed soil properties, especially erodibility. In addition, erodibilities of 32 soils determined with natural and simulated rains were taken from literature. The experiments on these 65 soils together covered a wide range of soils, slopes and rainfalls. Dispersion by a large percentage of highly hydrated ions ( K f , Naf) reduced the infiltration rate faster, caused runoff up to 5 min earlier, and increased sediment concentrations by 15 g/I compared to low EPP soils. These changes increased soil erodibility of the Universal Soil Loss Equation (USLE) by 0.021 t x h/N x ha (where N = Newtons) for each 1 O/O increase in EPP + ESP (exchangeable sodium percentage). The ESP contributed little to this increase as ESP was less than 1/10 of EPP in the experiments.Fields with long-term manure application had similar chemical, physical and microbiological soil properties as fields without slurry manure except for slightly greater pH ( + 0.6) and P ( + 17 mg/kg) values. We conclude that, as long as the potassium input and output are balanced, the long-term use of slurry manure does not increase erodibility.

Monospecific polyclonal antisera raised against Rhizobium leguminosarum bv. trifolii R39, a bacterium which was isolated originally from red clover nodules, were used to study the colonization of roots of leguminous and nonleguminous plants (Pisum sativum, Lupinus albus, Triticum aestivum, and Zea mays) after inoculation. Eight weeks after inoculation of soil-grown plants, between 0.1 and 1% of the total bacterial population in the rhizospheres of all inoculated plants were identified as R. leguminosarum bv. trifolii R39. To characterize the associative colonization of the nonleguminous plants by R. leguminosarum bv. trifolii R39 in more detail, a time course study was performed with inoculated roots of Z. mays. R. leguminosarum bv. trifolii R39 was found almost exclusively in the rhizosphere soil and on the rhizoplane 4 weeks after inoculation. Colonization of inner root tissues was detected only occasionally at this time. During the process of attachment of R. leguminosarum bv. trifolii R39 to the rhizoplane, bacterial lipopolysaccharides were overexpressed, and this may be important for plant-microbe interaction. Fourteen weeks after inoculation, microcolonies of R. leguminosarum bv. trifolii R39 were detected in lysed cells of the root cortex as well as in intracellular spaces of central root cylinder cells. At the beginning of flowering (18 weeks after inoculation), the number of R. leguminosarum bv. trifolii R39 organisms decreased in the rhizosphere soil, rhizoplane, and inner root tissue.

The effect of soil sterilization by chloroform fumigation on the release of fallout radiocesium incorporated in the fungal biomass of the organic layer of two forest soils was investigated by applying a sequential extraction procedure for radiocesium. The amount of the biomass in all soil samples was estimated by determination of the dissolved organic carbon (DOC) before and after fumigation, and qualitatively also by the ergosterol test. The five fractions obtained by sequential extraction (modified Tessier procedure) were: (I) easily exchangeable, (II) bound to oxides, (III) bound to organic matter, (IV) persistently bound, (V) residual. For the samples from the soil under spruce trees, no significant effects were apparent in any of these five fractions as a result of chloroform fumigation, indicating that the amount of radiocesium in the biomass of this soil was obviously negligibly small compared with the radiocesium associated with other soil constituents. The results obtained for the soil samples from the beech stand, however, reveal that the destruction of the biomass by chloroform fumigation modified considerably the extent of the association (i.e., binding) of radiocesium with the various other soil constituents (especially the clay minerals). As a result of this rapid redistribution of radiocesium released by the fungal biomass, it is not possible, in general, to attribute the observed increase of radiocesium in fraction I (easily exchangeable) after soil sterilization quantitatively to radiocesium released by the biomass. A reliable method to determine the amount of radiocesium incorporated in the fungal biomass of the soil samples which also contain clay minerals has, therefore, still to be developed.