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.”

本实验旨在测量乳牛牧草作物系统的温室气体（GHG）通量和相关的农业特性。作物轮作包括一年种植玉米（Zea mays），随后三年种植紫花苜蓿（Medicago sativa）。液态乳牛粪便在玉米种植后及紫花苜蓿种植的最后一年秋季施用。本研究的首要目的是深入了解接受粪便作为肥料的玉米和紫花苜蓿作物的GHG动态。这些观察结果亦被用于参数化和验证计算机模拟模型，以评估乳牛农场GHG排放（Gaillard等人，待发表），以及评估在静态室内对生物质进行操控对土壤中氧化亚氮排放的影响（Collier等人，2016年）。这些活动均为Dairy CAP项目的一部分，下文将予以描述。

实验于威斯康星大学阿灵顿农业研究站（http://wicst.wisc.edu/）的威斯康星综合作物系统试验（WICST）进行。WICST是一项长期研究，旨在探讨六种代表性威斯康星作物系统的生产力、盈利能力和环境影响。该地点从19世纪中叶开始从草原植被转变为耕地，主要用于生产小麦。从1860年代到大约1960年，该土地被用于生产乳牛饲料；从1960年到WICST的启动，主要的作物轮作是玉米（Zea mays L.）和紫花苜蓿（Medicago sativa L.），而乳牛粪便则是主要的营养来源。当前实验中的处理措施与轮作的四个阶段相对应。WICST使用的三个区块每年都包含所有四个阶段，因此总共使用了十二个地块。请注意，数据集中“实验设置”部分包含的一些田间操作，特别是耕作和粪便施用，都是在秋季进行的，为下一生长季节做准备。WICST的天气数据可在（http://agwx.soils.wisc.edu/uwex_agwx/awon）找到。

WICST的土壤根据美国农业部自然资源保护局（USDA-NRCS）的土壤分类系统被归类为“Plano壤质粘壤土”（Mollisol，Typic Argiudoll）。土壤坡度为0-2%，在1米深以下没有不透水层。在2009年，即本实验之前，采集了土壤碳、氮和容重分析的样本（n=12，参见Sanford等人，2012年）。2015年4月27日，在测量GHG的室之间采集了两个地块的样本，用于pH值、磷、钾、阳离子交换能力（仅K+、Ca+和Mg2+）、土壤有机质和土壤质地分析。在此次后者采样中，每个地块采集了两个核心样本（n=24），并在分析前按区块进行混合。土壤的化学和物理特性以干燥土壤为基础（含水量为0%）。

本实验中施用的粪便来自威斯康星大学布莱恩乳牛研究中心的乳牛群（W6723 Badger Ln.，Arlington，WI 53911）。该群有430头挤奶牛、100头干奶牛和50多头小牛，在带有沙床的开放式牛舍中。粪便储存在土坑中。2013年，在田间施用当天收集了三个粪便样本：分别在开始、中间和结束时各一个。2014年和2015年，各采集了两个样本。2012年的采样与2014年和2015年相似，但仅保留了平均值。样本在分析前被冷冻。粪便的化学和物理特性以干燥粪便为基础（含水量为0%）。

使用通风静态室（如Collier等人（2014年）所述）测量了GHG通量（CO2、CH4、N2O）。还测量了土壤温度、水分、NO3-和NH4+含量。2013年的室直径为40.5厘米，2014年和2015年为76.2厘米长、42.2厘米宽，高度可变，包括为紫花苜蓿准备的延伸部分，并考虑到不规则的土壤表面。室部署时间为20-36分钟，以获得4-5个时间点。气体样品由气相色谱（7890A GC System，Agilent）分析。通过线性回归（辅以视觉检查以进行质量控制）气体浓度来计算GHG通量速率。在2014年和2015年的选定气体采样日期收集了土壤样本，用于测定硝酸根+亚硝酸根和铵含量。

本实验是“大湖地区乳牛生产系统气候变化缓解与适应”项目的一部分，也称为乳牛协调农业项目（Dairy CAP），该项目由美国农业部国家粮食与农业研究所（资助编号2013-68002-20525）资助。Dairy CAP的主要目标是提高对大湖地区乳牛生产GHG排放规模及其控制因素的理解。利用这些知识，Dairy CAP改善了大湖地区乳牛农场GHG生产的生命周期分析（LCA），开发了农场管理工具，并开展了扩展、教育和外展活动。此外，该项目还得到了国家科学基金会资助编号1215858的“将农业温室气体排放建模转化为景观决策”项目的支持。