I recently gave a talk for the Ohio Turfgrass Foundation Grounds and Greens Lunch and Learn on environmental and plant health sensors to improve decision making. Click here for a PDF of my slides, and please reach out if you want more information on the topic.
Students in the irrigation and drainage class at The Ohio State University Agricultural Technical Institute (OSU ATI) have been learning about the tools available to them to conserve water. Water conservation has been a central focus in the class because 1) water is a precious resource, 2) future regulations will lead to more irrigation restrictions on turf, 3) water can be expensive, 4) sometimes there might not be any water available for irrigation, and 5) sloppy wet soils are a no-no for golf and other sports activities.
We have discussed traditional approaches to irrigation decision making like watering based on gut-feel as well as using data to decide on irrigation timing/amount such as using evapotranspiration rates (ET) to determine how much irrigation to apply, irrigating to stay around a certain soil volumetric water content (%VWC), and using soil water potential to guide decisions on whether to water or not. Irrigating based on data such as ET or by %VWC are great ways to save on water and keep the turfgrass healthy and playable, and both have become pretty standard in the turfgrass industry. On the other hand, the use of water potential has been highly underused.
Figure 1: A) As sandy soils dry down, not much water is left in the rootzone binding to the sand particles, but in B) high clay soils a large volume of water can be left in the rootzone that is tightly bound to clay particles and not available to roots to take up. Because of this, a certain %VWC in sandy soils and high clay soils do not mean the same thing, but a water potential of -800 kPa will indicate how much water is available to the plant regardless of the soil type.
Water potential, measured in Pascals (Pa), describes where water will move to within what’s called the soil-plant-atmospheric-continuum (SPAC). Water will always move from areas of high water potential towards areas of low water potential. Soil water potential, also called soil water suction, can indicate whether or not the soil is binding the water at a level that’s tighter than what the plant can pull back at (Figure 1). Soils can have water in them that’s not available to the plant to take up, and this is often the case of soils with high amounts of clay and silt. A soil water potential of -1,500 kPa is at what is called the permanent wilting point, and indicates that the soil is binding the water at a level that is tighter than what the plant can “pull back at”. At this water potential, any water in the soil is being held so tightly, roots cannot absorb the water, even if there is water in the soil. Soil moisture release curves describe the relationship between %VWC and water potential, and show how different soil types will get to the PWP at different %VWC (Figure 2).
Figure 2: Soil moisture release curves of a loamy fine sand (grey line), a fine sandy loam (light blue line), and a silt loam (dark blue line). The loamy fine sand reaches it’s PWP at approximately 2%, but the silt loam doesn’t reach it’s PWP until about 15%. The greater proportion of fine soil particles (clay and silt) hold on to water very tightly, and even if there is water within the soil, it’s being held to tight for the plant to take up.
The water potential that a given turfgrass will show wilt or stress at will not change from soil type to soil type. If a Kentucky bluegrass lawn mowed at 3.0 inches on a high clay root zone shows wilt at -1,000 kPa, it will also show wilt in a sandy loam at -1,000 kPa. Unlike, %VWC, there is less guesswork on when to apply water if you’re using water potential. Therefore, you can be more consistent and use less water if you’re making irrigation decisions based on water potential. For more information on water potential read Measurement of the matric potential of soil water in the rhizosphere by Whalley, Ober, and Jenkins (2013; https://doi.org/10.1093/jxb/ert044).
The problem is that we currently don’t have enough data to say at what soil water potentials various turfgrasses show stress and need supplemental irrigation. Part of this is because the sensors to measure soil water potential haven’t been as practical and affordable as they are now. We are currently trying to learn more about turfgrass responses to various water potentials in an effort to use water more efficiently.
On March 24th 2022, students in the irrigation and drainage class setup a small experiment to compare the amount of water needed to maintain healthy turfgrass using 1) a gut-feel irrigation strategy, 2) 60% of ET deficit irrigation, 3) a %VWC threshold, and 4) a soil water potential based threshold using data loggers and sensors that were sponsored by Meter Group (http://metergroup.com) (Figure 3). We will not water %VWC plots until the sensors read 10% or less, and water potential sensors plots will not be watered until -800 kPa.
Figure 3: Irrigation and drainage students at their plots with sensors and data logging equipment sponsored by Meter Group. An all-in-one weather station (ATMOS 41) is being used for ET calculations, and ZL6 data loggers are being used to collect and upload data from the sensors to the cloud.
Students spent the morning trenching in wires and installing TEROS 21 water potential sensors and TEROS 12 %VWC sensors at a depth of 3.0 inches on a Kentucky bluegrass athletic field on a clay loam soil (Figure 4). Data from the sensors will be used to determine when water should be applied and how much water should be applied to restore water levels to plant available levels.
Figure 4: Students installed all TEROS 21 and TEROS 12 sensor 3.0 inches below the soil surface. TEROS 21 water potential sensors were first encased in wet native soil to ensure no air gaps were present around the ceramic matrix, and TEROS 12 %VWC sensors were installed horizontally to take data at the same depth as the water potential sensors.
After all the sensors were applied, students measured 6-foot by 12-foot plots that were centered around their sensors (Figure 5). Using this, students will be able to apply a precise volume of water determined by the irrigation treatment. We will track every drop of water applied, to evaluate which irrigation treatment used the least amount of water. Students will also rate turfgrass plots for their quality, color, and density to see if they can use less water than they thought to maintain healthy turfgrass.
Figure 5: Students measured 6-foot by 12-foot plots that were centered around their sensors to help precisely apply volumes of water that will be tracked over the course of the project.
This project will continue over the coming year to help us better understand how we can decrease water use using in-ground data. We will also start to gain some insight into water potential thresholds we can use to more precisely apply irrigation. If you’re interested in coming to see the plots, the sensors, or the data, please reach out and we’d be more than happy to show you around.
My name is Dominic Petrella, and I’m the new program coordinator of the Ohio State University Agriculture Technical Institute (OSU-ATI) Turfrgass Management Program [Turfgrass Management | Ohio State ATI (osu.edu)]. I’m originally from Girard Ohio, a suburb of Youngstown that is located in southern Trumbull county. My connection to the turf industry started when my dad started taking me golfing around the age of 8. For those of you from the Mahoning Valley, I grew up playing golf at Mahoning Country Club, Tamer Win, Hubbard Golf Course, Candywood Golf Course (R.I.P), Mill Creek Metro Parks North and South Courses, Old Avalon, Avalon Lakes Country Club, Squaw Creek Country Club, Yankee Run Golf Course, and many many more. The game of golf is at the heart of why I am here at OSU-ATI, and this is something I’m looking to continue for both our teaching and research programs.
Growing up, I had no clue that studying turfgrass management was an option at Ohio State, let alone at Ohio State ATI; I only knew about the Penn State program. Instead, after graduating from Girard High School, I attended Youngstown State University (YSU) to study Biology in hopes of going into a medical field. After graduating from YSU, I soon realized medicine wasn’t for me, and after squandering around for a bit it was my dad who searched and found the turfgrass program at Ohio State main campus. I studied as both an undergraduate and graduate student in the turfgrass program at Ohio State main campus, working with both Dr. Ed Nangle and Dr. Dave Gardner during my previous tenure at OSU. My primary area of research during graduate school was turfgrass responses to high-intensity light and response to specific wavelengths of light. This is what I love working on; light has a massive impact on turfgrass growth and development, and this is something I will continue working on for years to come.
After finishing graduate school, I went and worked as a Postdoctoral Researcher in the University of Minnesota (UMN) Turfgrass Science Program under Dr. Eric Watkins for around 4.5 years [Turfgrass Science News | Turfgrass Science (umn.edu)]. At UMN I learned more about turfgrass breeding, turfgrass seed production, low-input turfgrass management, and continued my research on turfgrass responses to light and shade. Learning how to collaborate and write grants to obtain research funding was a key are of my postdoctoral education at UMN, and this is something I look to bring onboard at Ohio State.
My role at OSU-ATI is both one of teaching and research. Alongside Dr. Ed Nangle, I am teaching, advising, and getting students setup with summer internships. I am looking to bring fresh ideas to the teaching program such as training students how to best use technology in their day-to-day work. As an example, this will include teaching students how to monitor and use soil volumetric water content data for irrigation decisions; teaching students how to use the equipment, manage data, analyze data, and use that data for decision making. I am also looking to incorporate more low-input turf management education into our program; low-input species selection, management with reduced resources, and adjusting expectations with a low-input attitude.
Doing research is also very much a part of who I am, and I’ll be doing as much research as possible in my role at OSU-ATI. This research will heavily involve students to help inform them of how the practices they use are developed, but I also believe that including the students in an everyday role in our research program will make them more apt to trust academic research in the future. Going forward our research program will be two pronged; one arm aimed at working with industry to develop research projects that will impact their jobs right now, and the second arm devoted to fundamental questions that will impact the industry in the future years. This will include optimizing fertility programs for new cultivars, development of new cultural practices, and better understanding turfgrass responses to environmental stress to help us develop improved cultivars. If you’re an industry professional with turf problems that need addressed through research, please don’t hesitate to reach out so we can develop projects together as we move forward.
I’ll be using this blog to post research updates, educational tidbits, and information about our teaching program. Be on the lookout for bi-weekly articles and updates.