Evaluation of tillage and manure application practices on soil quality and greenhouse gas emissions

Evaluation of tillage and manure application practices on soil quality and greenhouse gas emissions

Summary

Minimum and no tillage practices have tremendous potential to reduce farmer expenses and the potentially negative impacts of intensive agriculture on soil quality and the environment. An important co-benefit of these tillage practices may be reducing regional to national greenhouse gas (GHG) emissions by storing carbon in the soil and reducing emissions of carbon dioxide, methane, and nitrous oxide. In minimum tillage systems, however, a persistent problem is how to apply and retain nutrients stored in manure: without incorporation, more than 50% of manure nitrogen may be lost through runoff and volatilization (Jokela et al. 2004).

Our ongoing goal is to study the benefits and/or drawbacks different tillage and manure application methods in the Manure Injection No Till (MINT) farm trial. We are examining three tillage practices (vertical-till, strip-till, no- till) under two manure treatments (broadcast, injected). Our primary objective is determining the manure and soil management practices best suited for reducing GHG emissions and N losses, while increasing carbon storage.

During June – November 2015 and March – November 2016 we took in-field carbon dioxide, nitrous oxide, and mineral nitrogen measurements approximately bi-weekly during the growing season (May-November). In 2015 we also took 1-m deep soil cores from each treatment to examine total soil carbon and nitrogen storage. Overall, we found that no-till decreased CO₂ emissions and manure injection increased N₂O emissions. We also found some evidence that manure injection decreased soil carbon storage at depth, but these results are preliminary and will require resampling after the treatments have been established for more than two years (this work will be funded by a USDA CARE grant).

During 2015, we had the opportunity to present our preliminary results to farmers and service providers at the 2015 Annual Northwest Crops and Soils Field Day (July 2015, Borderview Farm, Alburgh, VT). We also presented preliminary results during a Gund Tea seminar entitled “The Potential for Agriculture to Mitigate Climate Change” and related podcast (https://soundcloud.com/gundinstitute/carol-adair-the-potential-for-agriculture-to-mitigate-climate-change; December 2015, Burlington VT). During 2016, we presented our results during a SARE Farm Tour (July 27, Borderview Farm, Alburgh, VT) and at the 2016 Annual Northwest Crops and Soils Field Day (July 28, Borderview Farm, Alburgh, VT).

Objectives/Performance Targets

Our research was conducted within the on-going Manure Injection No Till (MINT) farm trial on Borderview Farm in Alburgh, VT. This trial is in a continuous corn system. There are three tillage treatment plots (vertical till, strip till, no till) and two manure application methods: broadcast and injected. Each tillage and manure treatment combination is replicated four times.

Within each treatment combination we measured soil C and N (this work was funded separately) to a depth of 1-meter. Soil cores were sectioned into 5 sections (0-10, 10-20, 20-30, 30-60, and 60-100 cm) and analyzed for total C and N (by dry combustion elemental analysis at UVM’s Agricultural and Environmental Testing Lab). This work was completed in 2015.

We measured mineral soil nitrogen, soil moisture, soil temperature and carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions at least bi-weekly, but more frequently after manure spreading. We planned on measuring methane emissions, but the instrument for measuring all three gases (CO₂, N₂O and CH₄) failed unexpectedly (a GC: Shimadzu Gas Chromatograph-17A equipped with a Flame Ionization Detector for quantifying CH₄ and with an Electron Capture Detector for quantifying CO₂ and N₂O), so we instead used a new instrument (Photoacoustic Spectroscopy (PAS) gas analyzer, Innova Air Tech Instruments, Ballerup, Denmark), to quantify in-field CO₂ and N₂O emissions. The PAS does not accurately measure methane (CH₄), but while the GC did work, we found methane emissions from farm fields to be extremely low or negative. Accurate measurements of CO₂ and N₂O using the PAS were taken from late May through November 2015. At each sampling date we measured CO₂, N₂O, soil nitrate, soil temperature and soil moisture in one location per treatment combination. This work was completed from June – November in 2015 and March – November in 2016.

Analysis of the CO₂ and N₂O emissions data indicated that no till decreased CO₂ emissions compared to other tillage treatments, while manure injection increased N2O emissions compared to broadcast. We also found some evidence that manure injection decreased soil carbon storage at depth (below 50 cm), but these results are preliminary and will require resampling after the treatments have been established for more than two years (this work will be funded by a current USDA CARE grant).

Accomplishments/Milestones

Proposed Project Timetable

Field data collection began in April after snow melt (winter was long), but accurate data was not collected until early June, due to the failure of UVM’s GC (Shimadzu Gas Chromatograph-17A). We began using an alternative instrument (Photoacoustic Spectroscopy (PAS) gas analyzer) in early June. Using this instrument, we sampled at least every other week from this point until the end of November, but more frequently after manure spreading events. Each sampling event included in-field CO₂ and N₂O emissions, soil nitrate, soil temperature, and soil moisture measurements taken in each manure-tillage treatment combination. We also collected 1-meter deep soil cores for measuring total soil carbon and nitrogen from each manure-tillage treatment combination. Because our sampling began so late in the 2015 growing season, we obtained a no-cost extension to continue sampling through the 2016 growing season. We therefore completed in-field CO₂ and N₂O emissions, soil nitrate, soil temperature, and soil moisture measurements from March – November in 2016.

Soil samples were processed and analyzed for soil nitrate and total carbon and nitrogen at UVM’s Agricultural and Environmental Testing Lab from May – December 2015.

Data analyses for all 2015 data were conducted on in-field CO₂ and N₂O emissions from August 2015 – April 2016. The 2015 results were incorporated into Tyler Goeschel’s MS thesis, which was successfully defended in July 2016.

Dissemination of results: During 2015, we had the opportunity to present our preliminary results to farmers and service providers at the 2015 Annual Northwest Crops and Soils Field Day (July 2015, Borderview Farm, Alburgh, VT). We also presented preliminary results during a Gund Tea seminar entitled “The Potential for Agriculture to Mitigate Climate Change” and related podcast (https://soundcloud.com/gundinstitute/carol-adair-the-potential-for-agriculture-to-mitigate-climate-change; December 2015, Burlington VT). During 2016, we presented our results during a SARE Farm Tour (July 27, Borderview Farm, Alburgh, VT) and at the 2016 Annual Northwest Crops and Soils Field Day (July 28, Borderview Farm, Alburgh, VT). Tyler Goeschel also presented the 2015 data during his MS defense in July 2016 at the University of Vermont.

Impacts and Contributions/Outcomes

GHG emissions data indicate that no-till decreased CO2 emissions compared to strip, vertical or conventional tillage, while manure injection increased N2O emissions compared to broadcast spreading. In the coming months, I will combine our full data set with concurrent data collected by Heather Darby (e.g., including corn silage yield, corn quality, and plant nitrogen content) to gain a more complete picture of the benefits/disadvantages of these practices. I hope to publish these data within the next year.

Moving forward from this research, we have added an ammonia gas detector to our PAS, which will provide us with a more complete picture of how manure application method (e.g., injection versus broadcasting) impacts gaseous nitrogen losses. These data are not yet analyzed. With Heather Darby and others, we have recently obtained funding via a USDA CARE grant to continue this work and expand on it by incorporating the impacts of cover crops and manure application timing.

Collaborators: