Final report for GNC17-243
Groundwater pumped from a shallow, unconfined aquifer for irrigation supports the farms, vegetable processing plants, and supplemental businesses that the Wisconsin Central Sands (WCS) economy hinges on. Groundwater from this aquifer simultaneously replenishes the lakes, streams, and wetlands in the region, supporting aquatic habitats valued by residents and tourists. Declining surface water levels and a declining trout population in the late 2000s stress the importance of balancing the needs of agriculture and aquatic ecosystems in the WCS. Two relatively untapped resources are available to growers to reduce consumptive groundwater use: irrigation scheduling and precision irrigation.
The two primary goals of proposed research are: (1) to quantify the effectiveness of irrigation management strategies (precision irrigation and irrigation scheduling) for reducing consumptive groundwater use while maintaining acceptable crop productivity in the WCS and (2) to identify key barriers to irrigation scheduling and precision irrigation adoption by improving our understanding of how WCS growers make irrigation decisions. This project will be conducted on and in partnership with Isherwood Family Farms, a sixth-generation, 1500-acre farm with 250 acres of woodland and 7 km of stream edge located near Plover, WI: the center of the water-stressed WCS. Paired field experiments, field observations, and remotely sensed landscape imagery will be used to compare spatiotemporal differences in water budget partitioning, crop growth, and yield between scheduled and intuitively-managed irrigation regimes, among precision irrigation management zones, and across model complexities. Grower interviews will provide insight into how growers use experience, intuition, or objective measurements to make irrigation decisions. Project outcomes will be evaluated using academic and outreach indicators and surveys.
Growers need to know if investing time and resources in these irrigation technologies will lead to reduced agricultural groundwater consumption (reserving more water to support aquatic habitats) and improved crop water use efficiency, while still maintaining the yields necessary to support grower livelihoods and the WCS economy.
Understanding the value of irrigation scheduling and precision irrigation strategies requires clear knowledge on the how and why behind intuitive irrigation decisions. This knowledge is crucial for scientists, conservation professionals, and legislatures in order to direct research, resources and policy in a way that balances the water needs of WCS stakeholders.
Short term learning outcomes are (1) increased knowledge of how use of the Wisconsin Irrigation Scheduling Program (WISP) compares to intuitively managed irrigation practices in terms of yield and groundwater recharge on a commercial farm. Target audiences will (2) learn how precision irrigation management zones relate to intrafield differences in crop growth, evapotranspiration, and groundwater recharge. Research will (3) improve understanding of how WISP operates on-farm and guides irrigation management compared to a more complex agroecosystem model (Agro-IBIS). During the research process, I will (4) acquire knowledge of how growers make irrigation decisions, identify any barriers to WISP/precision irrigation adoption, and identify information that growers want to know about WISP/precision irrigation to iteratively inform field data collection.
On-farm irrigation scheduling and comparison of data collected among precision irrigation management zones will inform the action outcomes of this project. Data collected will provide growers on-farm evidence to decide if irrigation scheduling and/or precision irrigation technologies are a worthwhile investment in the coarse WCS soils. In the long-term, research results may lead to actions by growers, residents, and legislators regarding strategies to conserve groundwater that we cannot concretely predict.
WCS growers are the primary target audience, with applicability to growers in areas of humid, irrigated agroecosystems with shallow depth to groundwater (e.g. Minnesota and Michigan). WCS residents, tourists, government, and researchers will also benefit from this project, as it ultimately explores how to produce more food with less water.
Data collection for this project occurred over three field seasons (2017-2019). Measurements were taken at ~12 locations per field, across six fields, each year. The 12 sample points chosen span the “management zones” for each field, which were determined by soil electrical conductivity mapping in 2015-16. By taking plant, soil, and water measurements in each management zone, we hope to say something about the potential of precision irrigation technologies to improve crop water use efficiency and conserve water in the Wisconsin Central Sands agricultural context.
Crop growth was monitored by measuring Leaf Area Index (LAI), percent canopy cover, growth stage, and plant height at each sample point every 1-2 weeks over the season. Measurement frequency was dependent on how fast the crop was growing at that time. End-of-season yield and peak biomass production were collected at the end of a crop growth cycle.
A network of 25 previously installed passive capillary wick lysimeters and pressure transducers, distributed across management zones, measured drainage flux below the root zone every five minutes. Soil moisture probes measured soil water content and temperature at four depths within the root zone near each lysimeter. Three meteorological stations collected precipitation, wind speed, air temperature, and relative humidity data near fields. Irrigation inputs were measured using in-field rain gauges to verify grower application rates near lysimeters. In 2019, an additional uniformity test was conducted on the irrigation systems to verify the spatial distribution of water application. All of this data will be used to estimate evapotranspiration, drainage, and crop water use efficiency, and if there are significant within-field differences that warrant precision irrigation.
Spectral reflectance of fields was measured with multi-band and thermal cameras via airplane three times on average during each summer. Multi-band reflectance will be used to estimate surface albedo and crop canopy characteristics, and thermal reflectance will measure canopy surface temperature across field space. The HRMET model (High Resolution Mapping of EvapoTranspiration, Zipper and Loheide II, 2014) will use this data, along with meteorological inputs to estimate spatial variability in ET. This will be used for ET and water use comparisons among precision irrigation management zones and between irrigation regimes.
A paired field experiment was conducted each year where one set of fields was irrigated using the Wisconsin Irrigation Scheduling Program (WISP), and a matching set of fields was irrigated according to farmer experience and intuition, in order to test the accuracy and usefulness of WISP. The required WISP data inputs were also collected on the remaining study fields in order to conduct a sensitivity analysis of WISP inputs and accuracy assessment of WISP predictions compared to measured data.
Overall, data collection was successful. See the Materials and Methods section for how data was measured.
Data analysis regarding Objective 2 (intrafield differences in crop growth characteristics for precision irrigation management) is near completion. Preliminary results suggest that there is limited, but existing, potential for precision irrigation interventions in the WCS. Correlations between EC and yield vary by year, field, and crop type. Final results will be ready to report by spring 2021.
Data analysis regarding the remaining objectives will be conducted over the next year. All results will be reported by the end of 2021 at the latest.
Educational & Outreach Activities
2018: I gave an oral presentation and a poster presentation at the annual American Society of Agronomy meeting in November. The oral presentation showed preliminary data comparing yield and leaf area index among soil management zones to an audience of primarily agricultural professionals (scientists, government, etc), and won second place in the graduate student competition. The poster presentation showed the preliminary data assessing the accuracy of WISP and its potential for improved water use efficiency, and won first place in the graduate student competition. A pdf of the poster is attached.
2019: I attended the Wisconsin and Potato Vegetable Growers’ Association (WPVGA) Grower Education Conference where I connected with farmers about my work to understand what information would be most useful for them in deciding how to irrigate. I also attended the American Geophysical Union (AGU) annual conference where I presented and lightening talk and e-poster. In April of 2019, I showed my research plan to the WPVGA’s Water Task Force, a group of farmers and educators (~15 total), to let them know what data I am collecting, what questions I’m asking, and see if there is any information I can collect that would be especially helpful to them. I have also attended these Water Task Force meetings several times a year over the last three years to get to know the farmers better and hear their perspectives.
2020: I was invited to present at the WPVGA Grower Education Conference in February. My talk was titled “Understanding the Potential of Irrigation Scheduling and Precision Irrigation to Improve Water Use Efficiency,” and was part of the main session of the conference, so the room was full of farmers and agricultural professionals. I received interesting questions, feedback, and stories from participants after the talk, which (I hope) signifies there was some dissemination of information.
As the data continues to be analyzed, results will be disseminated through more scientific conferences, publications, grower meetings, and grower groups. I am an invited speaker in the “Use of Modeling in Crop Irrigation Management” symposium at the 2020 ASA-CSSA-SSSA International Annual Meeting (Nov 9-13, 2020), where I will present some of the results of this work.
This project will result in increased knowledge of how use of the Wisconsin Irrigation Scheduling Program (WISP) compares to intuitively managed irrigation practices in terms of yield and groundwater recharge on a commercial farm. We will learn how precision irrigation management zones relate to intrafield differences in crop growth, evapotranspiration, and groundwater recharge. Research will improve understanding of how WISP operates on-farm and guides irrigation management compared to a more complex agroecosystem model (Agro-IBIS). On-farm irrigation scheduling and comparison of data collected among precision irrigation management zones will provide growers with on-farm evidence to decide if irrigation scheduling and/or precision irrigation technologies are a worthwhile economic and environmental investment in the coarse WCS soils.
WCS growers are the primary beneficiaries of this work, with applicability to growers in areas of humid, irrigated agroecosystems with shallow depth to groundwater (e.g. Minnesota and Michigan). WCS residents, tourists, government, and researchers will also benefit from this project, as it ultimately explores how to produce more food with less water.
Every field season, grower meeting, or farmer interaction increases my knowledge about the Central Sands context, the challenges farmers face, and potential sustainable agriculture solutions. I have gained a better understanding of how farmers perceive irrigation scheduling technology, specifically the Wisconsin Irrigation Scheduling Program, and the current industry initiatives and investment happening in irrigation scheduling programs. I also have a better awareness of what farmers factor into their decisions to irrigate. For example, while much of my work focuses on irrigating according to crop evaporative demand, the most limiting factor for irrigation decisions appears to be the time it takes for the pivot to water a field. So, a grower may water field X today, even though it doesn’t need water until tomorrow, because they know that tomorrow they HAVE to water field Y, and both pivots are hooked up to the same well. This project, and the time I have spent with farmers and thinking about farmers, has, for me, uncovered more of the complicated decision webs that farmers have to navigate.
It is my understanding that one of the goals of the SARE graduate student grants is to give graduate students experience managing a grant. I think that this is an AWESOME idea! Unfortunately, at my university the financial/grant management aspect of the university doesn’t work that way. There is no dashboard where I can see how much is left in the SARE account or what my spending has been. To keep track of it, I have to email my PI to email the finance person for our department. This makes the process more cumbersome and less like I am gaining grant management experience. I assume that at other universities there is a more direct avenue between the graduate students and the grant management. My suggestion is that SARE request that UW makes a more direct pipeline for grad student grant management or issues the graduate student to be the PI. I’m so grateful for the support I’ve received from SARE and the work it has allowed me to do for farmers and our food system! Thank you for considering this feedback.