Location: Dairy Forage Research
Project Number: 5090-21500-002-028-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Apr 1, 2023
End Date: Dec 31, 2025
Objective:
The goals of this project are 1) to evaluate and demonstrate innovative establishment and termination strategies for alfalfa to improve soil health and field carbon (C) balances
Project objectives are to:
1). Evaluate the impacts of tillage, nurse crops, and alfalfa-grass mixtures on field-scale carbon dioxide (CO2) fluxes, mineralizable carbon, and soil organic carbon during the establishment and termination periods using on-farm alfalfa stands (ARS objective). Management practices to evaluate include: Cover or nurse crops for alfalfa establishment (e.g. oat, barley, triticale, Italian ryegrass)
Tillage management for alfalfa establishment and termination (no-till/herbicide, chisel till, undercutting, strip tillage).
Approach:
ARS scientists in St. Paul, MN, and Madison, WI, will lead research on Objective 1. Research will be conducted at two on-farm locations in Minnesota and Wisconsin. At each measurement site, two adjacent fields with at least 200 m fetch (~40 acres) in the prevailing wind direction will be identified for establishment of the experiment. One field will be managed with a “business as usual” (BAU) approach that represents standard approaches to establishment or termination of alfalfa with respect to tillage, grass mixtures, and cover/nurse cropping. As a contrast to the BAU field, a second field at each site will be managed as the “treatment” field where alternative approaches to establishment and termination are employed with a goal of improving the field C balance relative to the BAU approach. Practices that may be evaluated include no-till or strip-till seeding and herbicide/no-till termination of alfalfa; cover or nurse crops for alfalfa establishment such as oat, barley, tritcale, or Italian ryegrass; alfalfa-grass mixtures (e.g, seeded in biculture with meadow fescue). The specific management practices chosen for the treatment field will be selected based on each producer’s ability to implement the selected practices at the field scale. Treatments may be combined for an individual field (e.g. no-till + cover crop). In this case, the impacts of individual management practices may be confounded, so the treatments will be considered as a “system” for comparison with the BAU approach. All other management practices will be held consistent between fields to the extent possible. This “paired-field” design will allow for a treatment vs BAU contrast at each farm.
Eddy covariance towers will be installed in both fields at each measurement site and monitored for a two year period (2023 - 2024). Year-round, field-scale eddy covariance flux measurements will allow for continuous monitoring of CO2, water, and energy exchange of each alfalfa management system throughout the duration of this project. Additional meteorological data will be collected including incident photosynthetically active and net radiation; air temperature and relative humidity; precipitation; soil moisture and temperature. We will also work with producers at each site to record any additions of C to each field via manure application (manure C) and removals of C in harvested forage (crop harvest C). From these data we will calculate the net ecosystem production (NEP, or the net CO2-C flux in each field), and the net ecosystem C balances (NECB) for each management system, where NECB = NEP + manure C – crop harvest C. The NECB accounts for all major C flows from the field, both gaseous and non-gaseous, and represents the implied change in soil organic carbon (SOC). Soil samples will also be collected at each measurement site at the beginning and end of the experiment and analyzed for total, inorganic, and organic C for comparison with NECB estimates.
