Large scale evaluation of a LEPA/LESA system compared with MESA on spearmint and peppermint

摘要

Most large-scale mint growers are using center pivot irrigation systems with mid elevation sprinkler application (MESA) sprinklers that have a water application efficiency close to 80 %. Modifications of the sprinkler systems like low elevation spray/precision application (LESA/LEPA) that apply water close to the ground can save a lot of water throughout the season. However, improving or maintaing the current oil yield is a main priority for satisfying these producers. A two-year study was conducted in the field near Toppenish, Washington, USA to evaluate and compare the effect of LESA/LEPA, MESA, and hand line (HL) irrigation systems on the hay yield, oil yield, and oil concentration on spearmint and peppermint. Due to the higher application efficiency of the LESA/LEPA systems, they were designed at 15 % less liters per second per hectare than the MESA systems. The HL treatments were irrigated by the grower without any changes. The soil water content (SWC) of each plot was measured continously throughout the growing season using neutron probe soil moisture sensor. The results of the two-year study showed that despite using 15 % less water, there were no significant differences in the SWC, hay yield, oil yield, and oil concentration between the LESA/LEPA and MESA treatments. However, the HL in spearmint had significantly greater hay yield (30.8 tons/ha) and the lowest oil concentrations (31 mL per 10 Kg fresh hay) compared with the other two treatments. From this research study it can be concluded that large water savings are possible by using LESA/LEPA without significantly impacting oil yields in both peppermint and spearmint. Pumping energy savings are also possible because less pumping is required to get an equivalent amount of water to the soil, and because LESA/LEPA sprinklers require less pressure to operate properly. It also showed that hand-line sprinkler-irrigated spearmint had significantly lower oil concentrations than the LEPA/ LESA treatments, or the MESA treatments.