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.

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 2015 we took in-field carbon dioxide, nitrous oxide, and mineral nitrogen measurements approximately bi-weekly during the growing season (May-November). We also took 1-m deep soil cores from each treatment to examine total soil carbon and nitrogen storage. Laboratory analyses are now complete and we are analyzing the results for incorporation with ongoing UVM Extension measurements (e.g., crop productivity and quality). Our results will provide a more complete understanding of the benefits and disadvantages of these different management practices.

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, 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).

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. We also compared measurements taken from these treatments to measurements taken in conventional agricultural management plots: conventional tillage with broadcast manure (four replicates).

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).

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 methane, 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, 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.

Preliminary analysis of May-August CO₂ and N₂O emissions data indicated that no till decreased CO2 emissions compared to other tillage treatments; manure injection increased N₂O emissions compared to broadcast.

Accomplishments/Milestones

Proposed Project Timetable:
Field data collection: March – October 2015
Data analysis: July – December 2015
Dissemination of preliminary & final results: July 2015 – February 2016

Field data collection began in April after snow melt, but accurate data was not collected until late May, due to the failure of UVM’s GC (Shimadzu Gas Chromatograph-17A). We began using an alternative instrument (Photoacoustic Spectroscopy (PAS) gas analyzer) in late May. 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.

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.

Preliminary data analyses were conducted on in-field CO₂ and N₂O emissions from August – current. We expect the final results to be analyzed and incorporated into Tyler Goeschel’s MS thesis and associated publications by May 2016.

Dissemination of results: Preliminary results were presented to farmers and service providers at the 2015 Annual Northwest Crops and Soils Field Day (July 2015, 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).

Impacts and Contributions/Outcomes

GHG emissions data from May through early August suggest that no till decreased CO₂ emissions compared to strip, vertical or conventional tillage, while manure injection increased N₂O emissions compared to broadcast spreading. We are in the process of compiling and analyzing data from across the entire season, from May through November.

In the coming months, we will combine our results with data collected by Heather Darby during the past year (including corn silage yield, corn quality, and plant nitrogen content) to gain a more complete picture of the benefits/disadvantages of these practices.

Moving forward from this research, we are adding 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.

Collaborators: