Irrigation return flow and nutrient movement mitigation by irrigation method for container plant production

The production of nursery crops demands substantial irrigation, with overhead irrigation the most common method of application; however, this method is inefficient with respect to water used and the precision with which it is applied, resulting in the generation of irrigation return flow and concomitant agrochemical export. Microirrigation systems such as individual container spray stakes provide water directly to crops thus applying water more efficiently than overhead systems but may be more costly in terms of installation (smaller pipes and components; however, a greater quantity of pipes and components) and maintenance. The study was conducted at the Michigan State University Research Nursery, where four ornamental shrub taxa were produced in #3 (11.3 L) containers using a control with 19 mm overhead irrigation per day and a conventional phosphorus fertilizer (Conv) (19-2.16-6.64), compared with four treatments: a static, daily (2 L per container) spray stake irrigation (SS2Lpd) and conventional phosphorus fertilizer; a static daily (2 L per container) spray stake irrigation and low phosphorus fertilizer (LowP) (19-1.62-6.64); spray stake irrigation based on substrate volumetric water content (θ) (up to 2.4 L per container) (SSθ) and conventional fertilizer; and spray stake irrigation based on θ (up to 2.4 L per container) and low phosphorus fertilizer. Spray stakes reduced irrigation by 76–80% compared to the overhead control, and reduced the generation of both surface and subsurface irrigation return flow (IRF), mitigating the movement of both N and P (over 98% reduction in surface IRF). Plant growth index (GI) was measured on 12 June 2017 and 6 October 2017, followed by a destructive harvest to measure shoot dry weight, and shoot nutritional content. For all four taxa, microirrigation systems were capable of producing plants of equivalent GI and shoot nutritional concentration; however, plants receiving the low phosphorus fertilizer produced less shoot biomass. Microirrigation is effective in reducing water use, water lost to IRF (particularly surface IRF), and associated fertilizer movement, while maintaining crop size.