Greenhouse gas fluxes from a dairy cropping system at the Wisconsin Integrated Cropping System Trials

This experiment was designed to measure the greenhouse gas (GHG) fluxes and related agronomic characteristics of a dairy forage cropping system. The cropping system rotation consisted of one year of corn (Zea mays) followed by three years of alfalfa (Medicago sativa). Liquid dairy manure was applied in the fall following corn and the final year of alfalfa. The primary purpose of this study was to gain insight into GHG dynamics of corn and alfalfa crops receiving manure as fertilizer. These observations have also been used for parameterization and validation of computer simulation models of GHG emissions from dairy farms (Gaillard et al., in preparation), and for evaluation of the effects of biomass manipulation within static chambers on nitrous oxide emissions from soil (Collier et al., 2016). These activities were performed as part of the Dairy CAP, described below.

The experiment was conducted at the Wisconsin Integrated Cropping System Trials (http://wicst.wisc.edu/) at the University of Wisconsin’s Arlington Agricultural Research Station in Arlington, WI. WICST is a long-term study of the productivity, profitability and environmental impact of six representative Wisconsin cropping systems. The site's conversion from prairie vegetation to cropland began in the mid-1800s, primarily for the production of wheat. From the 1860's until ~ 1960 the land was used to produce feed for dairy cattle; from 1960 until the initiation of WICST the predominant crop rotations were corn (Zea mays L.) and alfalfa (Medicago sativa L.) with dairy manure serving as the primary source of nutrients. The treatments in the current experiment corresponded with the four phases of the rotation. Each of the three blocks used at WICST contained all four phases every year, so that twelve plots were used in total. Please note that some of the field operations included in the “Experimental_Set-up” section of the data set, especially tillage and manure application, were made in the fall in preparation for the next growing season. Weather data for WICST are available at (http://agwx.soils.wisc.edu/uwex_agwx/awon).

The soil at WICST is “Plano silt loam” (Mollisol, Typic Argiudoll) according to the USDA-NRCS soil classification system. Soil slope is 0-2%, with no impermeable layers at less than 1 meter depth. Samples for soil carbon, nitrogen and bulk density analysis were taken in 2009, prior to this experiment (n=12, see Sanford et al., 2012). Soils were sampled on April 27, 2015 for pH, phosphorus, potassium, cation exchange capacity (K+, Ca+ and Mg2+ only), soil organic matter, and soil texture. At this latter sampling, two cores per plot were taken between the GHG-measurement chambers (n=24) and composited by block before analysis at the University of Wisconsin Soil & Forage Analysis Laboratory (https://uwlab.soils.wisc.edu/). Soil chemical and physical characteristics are given on a dry soil basis (0% water).

The manure applied in this experiment was liquid / slurry manure from the dairy herd at the University of Wisconsin’s Blaine Dairy Cattle Research Center (W6723 Badger Ln., Arlington, WI 53911). The herd had 430 milking cows, 100 dry cows and more than 50 calves in a free-stall barn with sand bedding. Manure was stored in an earthen pit. In 2013, three manure samples were collected: one each at the beginning, middle and end of the field application day. In 2014 and 2015, two samples were taken. Sampling in 2012 was similar to 2014 and 2015, but only averages were retained by field management. Samples were frozen until analysis at the UW Soil & Forage Analysis Laboratory. Manure chemical and physical characteristics are given on a dry manure basis (0% water).

GHG fluxes (CO2, CH4, N2O) were measured using vented static chambers as described in Collier et al. (2014). Soil temperature, moisture, NO3- and NH4+ contents were also measured. Chamber dimensions were 40.5 cm diameter in 2013, and 76.2 cm long by 42.2 cm wide in 2014 and 2015, with variable height including extensions for alfalfa and accounting for uneven soil surface. Chamber deployment time was 20-36 minutes to yield 4-5 time points. Gas samples were analyzed by gas chromatography (7890A GC System, Agilent). Linear regression of gas concentrations (with visual inspection for quality control) was used to calculate GHG flux rates. Soil samples for nitrate + nitrite and ammonium contents were collected on selected gas sampling dates during 2014 and 2015.

This experiment was part of “Climate Change Mitigation and Adaptation in Dairy Production Systems of the Great Lakes Region,” also known as the Dairy Coordinated Agricultural Project (Dairy CAP), funded by the United States Department of Agriculture - National Institute of Food and Agriculture (award number 2013-68002-20525). The main goal of the Dairy CAP is to improve understanding of the magnitudes and controlling factors over GHG emissions from dairy production in the Great Lakes region. Using this knowledge, the Dairy CAP has improved life cycle analysis (LCA) of GHG production by Great Lakes dairy farms, developing farm management tools, and conducting extension, education and outreach activities. Support was also provided by National Science Foundation grant number 1215858, “Translating agricultural greenhouse gas emissions modeling into decision making on landscapes.”