ISHS Acta Horticulturae 450: International Symposium Growing Media and Plant Nutrition in Horticulture
AIR-FILLED POROSITY OF EIGHT GROWING MEDIA BASED ON SPHAGNUM PEAT DURING DRYING FROM CONTAINER CAPACITY |
| Author: | J. Heiskanen |
| Keywords: | aeration, hypoxia, density, irrigation, mixture, perlite, sand, Scots pine seedlings, substrate, waterlogging, water retention |
| Abstract:
Temporal changes in the water content and air-filled porosity (AFP) of eight growing media composed of medium-textured sphagnum peat, coarse perlite and fine sand were studied during drying from container capacity. The media were dried using three types of containers and two levels of evaporation, with and without Scots pine (Pinus sylvestris L.) seedlings. It was shown that in the growing media studied AFP usually can rise above critical levels (>20 %) within days after heavy irrigation. However, the results suggest that under prolonged conditions of low evaporation, and especially with small slightly transpiring plants, more than a week of drying may be required to achieve favorable AFP (>40 %), which may lead to hypoxia and loss of growth in the plant stock. Because high containers and those that narrow towards the bottom produced increased AFP, the risk of waterlogging can be reduced by using these kinds of containers instead of shallow ones. By adding large enough proportions (>25 % by volume) of coarse perlite to peat, the number of coarse pores, AFP and thus aeration can also be elevated. In addition, when the risk of waterlogging is especially high, such as after removal of tree seedlings from greenhouses to open fields in autumn, it may be necessary to prevent waterlogging by protecting seedlings from frequent rain and by carefully adjusting the frequency of irrigation. | |
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