Biodegradable mulch effectiveness under different conditions of water and weed management

The aim of this research was to evaluate the effectiveness of two biodegradable mulches on weed control in container-grown Photinia × fraseri 'Red Robin' and their effect on evaporation and substrate temperature. The experiment was repeated in 2008 and 2009. Two biodegradable mulching materials were tested and compared with both chemical control (oxadiazon) and non-mulched and non-treated control. Two levels of overhead irrigation were evaluated: 1) daily irrigation to container capacity (well watered); 2) daily irrigation to 30% of container capacity (water stressed). Two weed managements were planned: 1) hand weeding three times during the growing season; 2) no weeding until the end of the growing season. One-year-old seedlings of Photinia were potted in 3-L containers and arranged using a split-split plot design, where irrigation was the main plot, weed managements were the subplots and weed control strategies were the sub-subplots. Photinia growth (shoot dry weight) was measured at the end of each growing season. Weed shoot dry weight per container was recorded in each assessment. Water content per pot (as a percentage of water holding capacity) was measured by weighing containers every two hours during the day. Fv/Fm ratio and substrate temperature were measured only in the second experiment. Weed growth was statistically limited by mulches, but was unaffected by the irrigation level. In the first experiment, mulched plants resulted in a higher shoot dry weight than non-treated and non-mulched plants, while in the second year no differences were observed. The black colour of containers was probably the main factor driving substrate temperature increase, indicating that mulching materials do not screen the substrate from sunlight effects. In both experiments, container water content was not affected by mulching materials. Transpiration was the main component of water loss from container-grown Photinia plants.