Sustained Deficit Irrigation Effects on Peppermint Yield and Oil Quality in the Semi-Arid Pacific Northwest, USA

Abstract

A field experiment was conducted from 2008-2010 to evaluate sustained deficit irrigation impacts on biomass, oil yields, and oil components of peppermint (Mentha piperita L. Black Mitchum) in the semi arid Pacific Northwest, USA. A line-source sprinkler design was used to create gradually increasing deficit irrigation treatments. Irrigation scheduled using a soil water balance method so as to replenish the soil water deficit in a 100cm deep managed root zone two to three times a week in the fully irrigated treatment plots adjacent to the sprinkler lines. The plots furthest from the sprinkler line received minimal supplemental irrigation. The results show that biomass hay yield was significantly affected by water availability. Oil yields also decreased with increasing deficit irrigation from 103 to 26 kg/ha in the only harvest obtained from all test plots. Peak water use of peppermint was about 580 mm per harvest with significant inter-year variation. Of the two harvests per year the peak water use for the second harvest was considerably lower than that for the first harvest due to a shorter growth period. The second harvest was significantly less than the first harvest suggesting that under sustained deficit irrigation a second harvest is not profitable. Hay water productivity of 2.55 to 6.04 kg/m3 was realized while oil water productivity of 0.01 kg/m3 was realized across all treatments. The major peppermint oil components were significantly affected by irrigation level. There is potential to improve water use efficiency and crop productivity using sustained deficit irrigation but the significant loss of plant stand makes the practice inadvisable for peppermint.