Per Berg

Inhibitory effect of low partial pressures of acetylene on nitrification

Abstract The inhibiting effect of C 2 H 2 on nitrification was investigated in two agricultural soils. Nitrification was totally inhibited at 10 Pa partial pressure of C 2 H 2 which is lower than previously reported for soils. There were no differences in rates of nitrate production between flasks without C 2 H 2 and flasks with C 2 H 2 at 0.01 Pa, while there was an effect on nitrification at 0.1 PaC 2 H 2 . At 0.1 Pa no inhibition was noted during the first 3 days; after this period nitrification was partially inhibited. The inhibiting effect did not cease until 7 days after removal of C 2 H 2 . The sensitivity of nitrification to low concentrations of C 2 H 2 should be noted when denitrification rates are determined by the use of the acetylene inhibition method (usually C 2 H 2 at 10kPa).

Microbial nitrogen transformations in the root environment of barley

Abstract To determine the influence of barley roots on microorganisms and N-transfonning processes in soil, numbers of nitrifiers and potential nitrification and denitrification rates were measured every week for 5 wks. The barley plants were grown in growth chambers in which the root-containing soil layer (A) was separated from three outer soil layers (B, C, D). The numbers and biomass of bacteria, numbers of flagellates and amoebae, total and FDA-active hyphal lengths, microbial biomass carbon and respiration were also determined. The numbers of ammonium oxidizers were positively correlated with root biomass but did not differ significantly between soil layers. Potential ammonium oxidation was stimulated in the root-layer, while potential nitrite oxidation was stimulated in the B- and C-layers. The denitrification activity (measured anaerobically in the presence of excess No − 3 ) was positively correlated with root biomass in the A-layer. Denitrification activity in the B-layer was positively correlated with the water content of the soil. When roots grew near the nets separating the root layer from the other layers, denitrification activity was stimulated in the next layer (B). We propose that nitrite oxidation in the root zone partly depends on the reduction of nitrate. This would explain why nitrite-oxidizer numbers were usually several orders of magnitude higher than ammonium-oxidizer numbers. Bacterial numbers decreased between wks 1 and 5. Increases in bacteria, naked amoebae and flagellates in all layers between wks 2 and 3 indicated that bacteria were produced until wk 3. There were no signs of bacterial production after wk 3. The total length of hyphae and the length of FDA-active hyphae were not significantly different between layers. However, both of these parameters, as well as total microbial biomass carbon and respiration, were consistently highest in the A-layer.

Seasonal Variations in Abundance and Activity of Nitrifiers in Four Arable Cropping Systems

Ammonium and nitrite oxidizers were counted with the most probable number (MPN) method and potential ammonium- and nitrite-oxidation rates were determined with a chlorate inhibition technique in an arable soil over a 3-year period. Samples were taken from the topsoil once a month for 2 years and a few times during a third year in four cropping systems: unfertilized lucerne ley and barley, and nitrate fertilized grass ley and barley. The distribution of nitrifiers was determined and their activities measured at various soil depths and between and within plant rows of fertilized barley.The numbers and activities of ammonium oxidizers were highest in the spring and autumn samples. Numbers of ammonium oxidizers ranged from 0.2 to 19×104 and nitrite oxidizers from 3 to 870×104 cells g−1 dry soil. Potential ammonium-oxidizer activities ranged from 120 to 1,060 and nitrite-oxidizer activities ranged from 280 to 680 ng N g−1 dry soil hour−1. Lucerne and grass leys generally showed the highest, whereas unfertilized barley had the lowest, abundances and activities.Abundance estimates and activities were 10–20 times higher in the plow layer than in underlying sand and clay layers. A strong correlation was found between organic matter content vs numbers and activities of both ammonium and nitrite oxidizers. Only nitrite oxidizer counts were significantly higher within plant rows compared to between plant rows.

The Sounds of Two Landscape Settings: Auditory concepts for physical planning and design

Sonic aspects relevant to landscape architects and planners are examined in order to show that soundscapes can be acknowledged and developed as an aesthetic resource for sustainable development. This auditory approach aims at an inter-sensory understanding of human perception and its significance for the design of physical environments. Two settings—a pasture landscape and a city garden—were studied by skilled listeners on site. They contributed to a preliminary terminology for the design of sonic environments, sonotopes. Clarity emerged as one cardinal principle for auditory refuges, and it was found to be related to the balance of particular sonic features and their background sounds. A figure/ground model described these proportions. The distances to sonic events and the tempo of sonotopes defined refuges. Sonic events mirrored the land use and constituted acoustic space according to the distribution of sound sources. Distant sources were suggested as a practical pointer and design tool for overall conditions together with tempo, which is described as the pace of interplay of figures that fade in and out of a background.

Sustainability resources in Swedish townscape neighbourhoods: Results from the model project Hågaby and comparisons with three common residential areas

Seven dynamic aspects of sustainability—resources—were described and monitored thoroughly in a small model community—Hagaby—in west Uppsala, Sweden. The residents’ use of local and distant physical resources, such as heat, electricity, fuel and clean water or production of solid waste and wastewater in the model project were lower than the Swedish average, while the utilisation of local material resources like soil and ground water was higher. Economic resources like houses, equipment, greenery and technical infrastructure were administered and used to minimise costs for construction, maintenance, rents and fees. Social and organisational resources were outlined and managed to facilitate relations between residents and between local professionals in the area. Other goals in the planning of Hagaby, were to facilitate an efficient local as well as distant mobility (transportation and communication) and to organise space for social contact as well as for privacy for individuals and households. Biological, cultural and aesthetic resources were important indirect factors affecting the inhabitants’ feeling of rootedness and their sense of place. All seven resources were managed in its site context to optimise the sustainability of the unique local community. The results from Hagaby were also compared with preliminary data from a new research project investigating sustainability conditions in three common Swedish townscape types in four municipalities. Preliminary results showed that sustainability strengths and weaknesses in several cases indeed differ quantitatively and qualitatively between different typical parts of the city. The results support that the dynamic resource model presented in this paper, should be helpful in establishing place and situation adapted sustainability strategies in any type of Swedish local community.