Container Grown Lavender Affected by Oxygenated Irrigation Water

Watering crops can be one of the most difficult jobs in nursery production and requires careful attention.  Underwatering crops can lead to cell dehydration, while overwatering can reduce the oxygen content of the substrate and lead to reduced root respiration.  In addition, root respiration can be limited by plastic containers where gas diffusion is restricted to the surface and drain openings.  Reduced root respiration can limit nutrient uptake, reduce energy production, and suppress plant growth.  By elevating the dissolved oxygen level of irrigation water, roots would be exposed to more oxygen in the root zone, which could improve root growth.  On 16 March 2012, twenty Lavendula angustifolia 'Provence' liners were potted into 5" azalea containers and topdressed with Osmocote 18N-2.6P-10K, 8 to 9 month control release fertilizer at a rate of 5 grams per container on 9 April 2012.  To determine the effects of elevated dissolved oxygen levels of irrigation water there was a control level (7.2 mg·L^-1 average over the experiment) and an elevated dissolved oxygen level (13.3 mg·L^-1 average over the experiment).  Irrigation water was elevated using a portable oxygenator (The Oxygenator, O₂ Marine Technologies, Shorewood, MN).  Dissolved oxygen levels were determined with a LDO101 dissolved oxygen probe attached to a portable dissolved oxygen meter (HQ30d, HACH Company, Loveland, CO).  Experiment was initiated on 10 May 2012, and ended 2 November 2012.  Data collected included initial and final growth indices [GI = (height + width + perpendicular width) ÷ 3], shoot biomass (all plant material above the first root) and root biomass (all plant material below the first root).  Shoot and root biomass were oven dried for 72 hours at 55 °C.   Experiment was a randomized complete-block design with 10 single pot replications.  There were no differences in growth indices or shoot biomass of lavender irrigated with elevated dissolved oxygen compared to lavender irrigated with the control level.  However, root biomass (P = 0.0401) was greater for lavender irrigated with elevated dissolved oxygen compared to plants irrigated with the control level.  Based on these results, elevating the dissolved oxygen level of irrigation water can improve root growth of container grown lavender.