Spatial and temporal oxygen distribution measured with oxygen microsensors in growing media with different levels of compaction

Oxygen microsensors were used to determine oxygen profiles in situ from the top to the bottom layer of the growing medium for potted plants of Rosa sp. ‘Dior’. The growing medium was peat- based and compacted uniformly to 3 different bulk densities of 0.14, 0.18 and 0.23 g cm−3 (0, 20 and 40% compacted, respectively). The water distribution in the pot was determined as water content (g cm−3) in the top, middle and bottom layers of the peat. Oxygen content was also determined after a standard subirrigation cycle and after excessive irrigation where the bottom of the pots were left waterlogged for 24 h. Measurements were carried out at 5.5 weeks during the production phase and at 12 weeks at the end of the production. The results showed that with increasing compaction and density, more water was transported to the upper layers of the pot. After a standard irrigation cycle there was no effect of the level of medium compaction on the oxygen distribution, whereas after excessive irrigation, the oxygen contents at the bottom of the pots were strongly reduced and the level of compaction significantly affected oxygen availability. The most compacted medium had the lowest oxygen content at 5.5 weeks, with anoxic conditions in the bottom 30 mm. Plant quality measured as fresh weight, dry weight, height and number of shoots with flowers and buds was not affected by the different levels of compaction. The use of oxygen microsensors provided a new insight into the spatial and temporal distribution of oxygen in growing media and how this was affected by the physical characteristics of the growing media.

Research highlights▶ Oxygen profiles in growing media can be determined by micro sensors. ▶ Detailed knowledge of oxygen distribution in time and space can be obtained. ▶ Compaction affected the oxygen profiles but not the overall plant quality. ▶ Increased compaction led to increased water content and improved water distribution without resulting in prolonged anoxic conditions or negatively affecting plant growth.