Arne Sæbø

A simple method for measuring oxygen level in the root zone of plants growing in non-saturated humidity conditions is presented. The oxygen concentration of soil air under layers of compost mulch was measured using galvanic oxygen sensors mounted in diffusion chambers and the results were compared with infrared gas analyses of soil air samples. Two trials showed that a moderate

ABSTRACT Low soil temperatures limit nutrient uptake with negative consequences for growth and foliage quality. A better understanding of the temperature sensitivity of root N uptake is required to improve the best management practices for fertilization of conifers. Uptake of 15N in saplings of Abies lasiocarpa (Hook) Nutt and Abies nordmanniana (Steven) Spach was studied at root temperatures of 3–15°C in hydroponics. 15N accumulation in shoots increased with temperature, showing accelerated accumulation from 7°C upward. At 3°C, uptake rates were low for both species. Between 7 and 12°C, 15N accumulation in shoots increased by a factor of 5 in A. lasiocarpa and by a factor of 3 in A. nordmanniana. The temperature response of N uptake was similar to root growth responses to temperature documented by previous studies. The results have implications for early season fertilization, where fertilization of both species should be withheld until soil temperatures reach 10–12°C.

ABSTRACT The influence of irradiance and light quality on in vitro cultures was studied at the rooting stage, and subsequently as it affected the field performance of birch (Betula pendula Roth.). Forty‐five μmol m−2 s−1 during the rooting stage reduced the rooting time compared with 30 μmol m−2 s−1. The light quality treatments of the cultures, from which the microcuttings were harvested, had a larger effect on the rooting than the treatments during the rooting stage. The fastest rooting was observed in microcuttings pre‐treated with blue light (6 days), and the slowest rooting after treatments with red light (12 days), which also, respectively, gave the highest (5.1) and lowest (3.5) mean number of roots per microcutting. The largest growth rate in the field was observed in plantlets harvested from cultures subjected to blue and cool white light.

... Present Address: Ø. M. Edvardsen The Norwegian Forest Seed Center, 2301 Hamar, Norway 123 ... ex Hildebr and Abies magnifica Murray. The black plastic may have caused less evaporation and a better water supply to the plants, but the higher soil temperature (Fig. ...

ABSTRACT The fertilizing effect of P in different sewage sludges was investigated in a pot experiment. Five different sludge types were applied to rye grass growing in either a moraine or a clay soil. The flocculating agents used to precipitate P in the sludges were aluminium chemicals, iron chloride or biological P-reduction without use of chemicals. The total P content in the sludges varied approximately from 7500 to 30,950mgkg−1, and the pH varied between 5.45 and 12.4. Biological purification without chemical additives and lime treatment produced sludges with a P fertilizing effect comparable to inorganic fertilizers. P precipitated by use of Fe and Al chemicals and without liming treatment produced sludges with very low P fertilization values. Sewage sludge P applied in combination with water-soluble inorganic P increased the availability of the sewage sludge P. Sewage sludge application significantly influenced soil pH, and may therefore indirectly influence the plants’ general access to essential soil nutrients. Repercussion values of P in the sewage sludge were calculated indicating the amount of plant available P left in the soil at the end of the first growing season. This unused surplus of plant-available P may be utilized by the plants in the subsequent growing season. The repercussion was highest for the biological and lime treated sludges and low in the sludges treated with Fe and Al flocculating agents.Although low concentrations of water-extractable P were measured after addition of sewage sludge, considerable accumulation of P took place in the soil (50–95% increase). This accumulation must be considered as a potential environmental risk due to the possibility of erosion and subsequent surface runoff.