Summary
Container crop production is an input intensive agricultural sector, oftentimes demanding frequent, typically daily irrigation, substantial fertilizer use, and multiple pesticide applications throughout the production cycle. The combination of these factors increases the risk for agrochemical movement in irrigation return flow (IRF). Over the course of two studies, a model nursery designed to collect surface and subsurface IRF was used to investigate water use and agrochemical movement in a... Show moreContainer crop production is an input intensive agricultural sector, oftentimes demanding frequent, typically daily irrigation, substantial fertilizer use, and multiple pesticide applications throughout the production cycle. The combination of these factors increases the risk for agrochemical movement in irrigation return flow (IRF). Over the course of two studies, a model nursery designed to collect surface and subsurface IRF was used to investigate water use and agrochemical movement in a model nursery. An overhead control was compared to micro-irrigation (SS) and substrate volumetric moisture content (θ) sensor based overhead irrigation (OH) in the volume of water applied, volume of water lost to IRF, and associated fertilizer and pesticide content transported. Irrigating using OH and SS reduced the volume of irrigation applied by 49% and 78% compared to the control. Surface IRF was reduced by 80% using OH and was largely eliminated using SS; however, subsurface IRF was generally equivalent between the control and treatments. Surface IRF movement of nitrate and phosphate was reduced by 72% - 76% when irrigating using OH, and up to 98% when irrigating using SS. Pesticide mobility in irrigation return flow was reflective of pesticide physiochemical properties, with more soluble pesticides exhibiting greater movement than less soluble pesticides, particularly in subsurface IRF. OH reduced surface IRF movement of the 10 pesticides by 43-89%, while SS reduced surface IRF movement by 77-100%. There were typically no differences in subsurface IRF pesticide movement between the control and treatments. For all studied taxa (Cornus obliqua 'Powell Gardens', Cornus sericea 'Farrow', Hydrangea paniculata 'Limelight', Physocarpus opulifolius 'Seward', Rosa x'Meipeporia', Spiraea japonica 'SMNSJMFP', and Weigela florida 'Elvera') an equivalent growth index to the control was achieved when irrigating based on θ. Irrigation treatments were capable of producing an equivalent weight of shoot dry biomass for all taxa except C. obliqua, P. opulifolius, and S. japonica where the control was greater than all treatments. For the three species where root dry biomass was investigated (H. paniculata, R. x., and S. japonica), only S. japonica exhibited reduced root dry biomass under the OH and SS treatment compared to the control. Irrigating based on θ, regardless of the delivery method, can produce woody ornamental species of equivalent quality, while also reducing water use and agrochemical export in irrigation return flow; however, bioactive concentrations of agrochemicals may still be present. Woodchip bioreactors (WB) and adsorbent aggregate filters (AF) are treatment technologies that are capable of remediating or sequestering contaminants from IRF via biological and sorptive processes, provided a sufficient hydraulic retention time (HRT). A 72 hour HRT reduced over 99% of influent nitrate in WB and up to 87% of phosphate in AF; whereas, an HRT of 21 minutes was insufficient for nutrient remediation. An HRT of 21 minutes was effective in reducing the movement of bifenthrin, chlorpyrifos, and oxyfluorfen by 76%, 63%, and 31%, respectively, using WB. Microbial analysis of WB identified shifts in species composition when exposed to pesticides, enriching for a number of species within the Pseudomonas and Exiguobacterium genus, while decreasing the number and diversity of Bacillus species compared to the nutrient only control. Show less
