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Title: Integrating moisture characteristic curves with gravimetric data in the management of substrate moisture content for annual vinca

Author
item NEWBY, ADAM - THE OHIO STATE UNIVERSITY
item Altland, James
item STRUVE, DANIEL - THE OHIO STATE UNIVERSITY
item PASIAN, CLAUDIO - THE OHIO STATE UNIVERSITY
item LING, PETER - THE OHIO STATE UNIVERSITY
item JOURDAN, PABLO - THE OHIO STATE UNIVERSITY
item KESSLER, RAYMOND - AUBURN UNIVERSITY
item CARPENTER, MARK - AUBURN UNIVERSITY

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2018
Publication Date: 8/1/2018
Citation: Newby, A., Altland, J.E., Struve, D., Pasian, C., Ling, P., Jourdan, P., Kessler, R., Carpenter, M. 2018. Integrating moisture characteristic curves with gravimetric data in the management of substrate moisture content for annual vinca. HortScience. 53:1197-1202. https://doi:10.21273/HORTSCI13030-18.
DOI: https://doi.org/10.21273/HORTSCI13030-18

Interpretive Summary: Nutrient leaching and runoff due to excessive irrigation have detrimental environmental impacts, and emerging regulations require growers to minimize these impacts. Automated on-demand irrigation systems that apply irrigation based on water use have been used successfully to provide adequate irrigation to bedding plants and nursery crops with little to no leachate using a variety of approaches. Basing irrigation decisions on volumetric water content is the most common approach. However, volumetric water content necessary to trigger irrigation systems may differ between substrate types. We hypothesize that substrate matric potential could be used uniformly across substrate types. The objective of this experiment was to determine the effects of two substrates and two substrate matric potential ranges on annual vinca growth, applied irrigation, leachate volume, and plant water use. The results of our study demonstrate that differences in airspace between substrate mixes affect plant response even when volumetric water content between the substrate mixes is similar and that airspace could be controlled in real time through irrigation management. Although volumetric water content was very similar between the two substrates used in our study, differences in plant size, plant dry weight, and flower number occurred depending on substrate.

Technical Abstract: Greenhouse growers must use water more efficiently. One way to achieve this goal is to monitor substrate moisture content to decrease leaching. A systems approach to irrigation management would include knowledge of substrate matric potentials and airfilled pore space (AS) in addition to substrate moisture content. To study the relationship between substrate moisture and plant growth, annual vinca (Catharanthus roseus L.) was subject to a 2 3 2 factorial combination of two irrigation treatments and two substrates with differing moisture characteristic curves (MCCs). A gravimetric on-demand irrigation system was used to return substrate moisture content to matric potentials of L2 or L10 kPa at each irrigation via injected drippers inserted into each container. Moisture characteristic curves were used to determine gravimetric water content (GWC), volumetric water content (VWC), and AS at target substrate matric potential values for a potting mix consisting of sphagnum moss and perlite and a potting mix consisting of sphagnum moss, pine bark, perlite, and vermiculite. At each irrigation event, irrigation automatically shut off when the substrate-specific weight of the potted plants associated with the target matric potential was reached. Irrigation was triggered when the associated weight for a given treatment dropped 10% from the target weight. VWC and AS differed between substrates at similar matric potential values. Irrigating substrates to L2 kPa increased the irrigation volume applied, evapotranspiration, plant size, leaf area, shoot and root dry weight, and flower number per plant relative to irrigating to L10 kPa. Fafard 3B had less AS than Sunshine LB2 at target matric potential values. Plants grown in Fafard 3B had greater leaf area, shoot dry weight, and root dry weight. Leachate fraction ranged from 0.05 to 0.08 and was similar across all treatment combinations. Using data from an MCC in conjunction with gravimetric monitoring of the container–substrate–plant system allowed AS to be determined in real time based on the current weight of the substrate. Closely managing substrate matric potential and AS in addition to substrate water content can reduce irrigation and leachate volume while maintaining plant quality and reducing the environmental impacts of greenhouse crop production.