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.
I have completed two seasons of data collection, with one season remaining in summer 2019. The following measurements were taken within each water management zone on six fields (water management zones were determined by soil electrical conductivity mapping in 2015). 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 multiple 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. Leaf area index and percent crop cover were collected one per week on average. Yield was determined by harvesting from five 1-m2 locations in each management zone at the end of a crop growth cycle. 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 during the 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 in 2018 where one set of fields (one potato and one peas) 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. This will be continued with another set of fields in 2019. The required WISP data inputs were also collected on the remaining study fields, so I can conduct a sensitivity analysis of WISP inputs and accuracy assessment of WISP predictions compared to measured data.
I am still analyzing the data and do not have reportable results at this time. Overall, data collection was successful.
Educational & Outreach Activities
I gave one oral presentation and one poster presentation at the annual American Society of Agronomy meeting in November 2018. 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.
As the data continues to be analyzed, results will be disseminated through more scientific conferences, publications, and grower meetings.
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. This past year 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.