This project was started in May 2014 on a USGA-spec. green with a one year old cover of creeping bentgrass Bioforsk Landvik, Norway. The trial followed a split plot design with four replicates; two irrigation regimes on main plots and surfactants (No surfactant control, Qualibra and Revolution) on subplots. The irrigation regimes were ‘FC x 1’ (=irrigation to field capacity once a week) , and ‘Excess x 2’ (=irrigation twice per week with 50% more water than needed to replenish FC). The plots were irrigated using a manually operated irrigation boom, the amount of water to being calcaluated from TDR measurements (20 cm depth) and an anticpated soil water content at FC of 20 %. Both surfactants were applied at a rate 20 L in 800 L water ha-1 at monthly intervals from 1 May to 1 September.
The first part of the growing season 2014 was dry with only 84 mm natural rainfall from 15 May to 31 July. The dry period perod culminated with a very warm week with daily maximums close to 30 °C in late July. In contrast, August and September had more than 300 mm rainfall. For this reason, the experimental data were analysed seperately for the two periods. The irrigation treatment ‘Excess x 2’ improved visual turf quality significantly over ‘FC x 1’ during the first ‘dry’ period, but this tended to be reversed during the latter ‘wet’ period.
Both surfactants acted as penetrants and reduced the soil water content by 10-20 % during the ‘dry’ as well as during the ‘wet’ period. The reduction occurred regardless of irrigation regime and was stronger in the top 5 cm (5 cm TDR probes) than on average for the top 20 cm rootzone. The reduction was slightly, but not significantly, stronger with Revolution than with Qualibra. It was unexpected that the surfactants reduced the soil water content even during the warm and dry period in June and July.
Both surfactant caused significant reductions in potential hydrophobilcity at 5, 15, 30 and 50 mm depth as indicated by water droplet penetration tests. However, distinct dry spots did not appear and visual turf quality was not signifcantly affected by the surfactants, even during the dry period, Stimpmeter readings were also not affected, but the green surface tended to be harder after use of either Qualibra or Revolution.
The project will continue until observations of snow mold and other winter damages in spring 2015.
