Data from: Mitigating nitrogen pollution with under-sown legume-grass cover crop mixtures in winter cereals

This study was part of a cover crop-based, organic rotational no-till cropping systems experiment conducted from 2015-2017. The study site was at Pennsylvania State University’s Russell E. Larson Agricultural Research Center in Rock Springs, PA, USA. This site represents a deep (1.8 m), well-drained Hagerstown silt loam soil (Fine, mixed, semiactive, mesic Typic Hapludalf). The experiment used a randomized complete block, full-entry design with four blocks. Each block contained three crop entry main-plots (110 x 18 m) with four cropping system treatment subplots (49 x 9 m). Two of the four systems included microplots (2 x 2 m) within the treatment subplot where weeds and cover crops were manually removed following emergence to provided a no cover crop control. The experiment employed a corn (Zea mays subsp. mays L.), soybean (Glycine max (L.) Merr.), spelt (Triticum spelta L.) rotation that is typical for feed and forage farmers in the Mid-Atlantic USA.
Plot numbers are three digit codes where the first digit indicates the block, the second digit indicates the crop entry main plot, and the third digit indicates the system subplot. Year indicates the year the measurements were taken. System indicates the cropping system treatment for that plot. The system for a plot is consistent throughout the entire experiment. However, the crop changes for that entry point depending on the year of the rotation (corn, soybean, or spelt). Certain datasets include an 'excl' or 'x' subplot, which is the cover crop removal microplot inside of the main plot. The plots.csv data file provides a reference for the crop and system for each plot in each year and the Cropping_Systems.pdf figure provides an overview of the major differences between the four systems.
The data include:

Nitrate leaching from anion resin bags
Nitrous oxide fluxes from static chambers and isotopomers
Soil inorganic N including ammonium and nitrate
Soil moisture and temperature
Cover crop biomass as well as carbon and nitrogen content and nitrogen isotope ratios
Cash crop yields
Resources in this dataset:Resource Title: Corn grain yield. File Name: corn_grain_yield.csvResource Description: Corn grain yield in pounds per acre (lbs_ac) and bushels per acre (bu_ac).Resource Title: Corn silage yield. File Name: corn_silage_yield.csvResource Description: Corn silage yield in pounds per acre (lbs_ac) and tons per acre (tons_ac).Resource Title: Forage yield. File Name: forage_yield.csvResource Description: Yield from a forage cutting of the clover timothy cover crop in pounds per acre (yield_lbac).Resource Title: Nitrogen derived from atmosphere. File Name: ndfa.csvResource Description: Cover crop nitrogen derived from fixation of atmospheric nitrogen calculated from the delta15N of the grass cover crop and the delta15N of the legume cover crop in a legume-grass cover crop mixture. 'legume' indicates which cover crop species was sampled. This table includes the d15N of the grass in permil (grass_d15n), the d15N of the legume in permil (legume_d15n), beta which is the d15N of the legume grown in nitrogen-free media so that all of the nitrogen was derived from the atmosphere obtained from literature averages, and nitrogen derived from the atmosphere (ndfa) as a percent. Resource Title: Soil inorganic nitrogen. File Name: soil_n.csvResource Description: Soil inorganic nitrogen and gravimetric water content.
gwc = Gravimetric water content as a fraction
no3_mgkg = Nitrate in milligrams per kilogram of soil
nh4_mgkg = Ammonium in milligrams per kilogram of soil
totn_mgkg = Sum of ammonium and nitrate in milligrams per kilogram of soilResource Title: Spelt yield. File Name: spelt_yield.csvResource Description: Spelt yield in pounds per acre (yield_lbac).Resource Title: Cropping system diagram. File Name: crop_system.pdfResource Description: Cropping systems diagram. The dashed vertical line marks spelt harvest. White boxes represent spelt growing season. Dark gray boxes represent hairy vetch and triticale growing season. Light gray boxes represent red clover and timothy growing season. BM = Broadcast manure; IM = Injected manure; MP = Moldboard plow; CP = Chisel plow; NT = No-till.

S1 = Post-harvest + Manure
S2 = Post-Harvest
S3 = Underseeded
S4 = Underseeded NT
Resource Title: Cover crop biomass, carbon, and nitrogen. File Name: covercrops.csvResource Description: Cover crop biomass in grams per meter squared (wt_gm2) as well as percent nitrogen (per_n), percent carbon (per_c), and nitrogen in grams per meter squared (n_gm2). Measurements are from cover crop mixtures with two species and so each plot is represented by two rows in the table.Resource Title: Plot reference. File Name: plots.csvResource Description: This table presents the plot number for every plot as well as the block number (block), the cropping system (system), and the crop for each year of the study (entry_15 for 2015; entry_16 for 2016).Resource Title: Nitrate leaching. File Name: leaching.csvResource Description: Nitrate leaching measured from nitrate accumulated in anion resin bags buried at 25 cm below the soil surface. Leaching is measured in kilograms of nitrogen per hectare (leached_kgha).Resource Title: Nitrous oxide flux. File Name: n2o_flux.csvResource Description: Nitrous oxide flux data captured as four time point samples over 45 minutes from static chambers. Fluxes are in grams of nitrogen per hectare per day (ghad).Resource Title: Nitrous oxide site preference. File Name: n2o_sp.csvResource Description: Nitrous oxide site preference calculated as the difference in delta15N isotopes between the central and terminal nitrogen atoms within nitrous oxide isotopomers. 'smp' indicates samples from the chamber, 'amb' indicates ambient samples from the open air, and 'soil' indicates site preference for soil nitrous oxide calculated from the chamber and ambient samples. 'sp' indicates site preference and 'd18o' indicates delta18O oxygen isotopes.Resource Title: Ancillary soil data. File Name: n2o_ancillary.csvResource Description: Ancillary soil measurements associated with nitrous oxide flux measurements taken at the same time and location as nitrous oxide flux. Soil temperature (soil_temp) and air temperature (air_temp) in degrees celsius, and soil moisture as percent volumetric water content (vwc).Resource Title: Data Dictionary. File Name: mitigating-n-data-dictionary-2019-08_ahm.csvResource Description: Defines the variables, their units, data type, and allowed values for each table.

本研究系一项基于覆盖作物轮作制度的有机免耕作物轮作系统实验的一部分，该实验于2015年至2017年间进行。实验地点位于美国宾夕法尼亚州立大学拉塞尔·E·拉森农业研究中心，位于宾夕法尼亚州洛克溪市。该地点代表了一片深层（1.8米）、排水良好的哈格城壤质壤土（细粒、混合、半活跃、湿润的典型表土Hapludalf）。实验采用随机完全区组设计，共分为四个区组。每个区组包含三个作物入口主区（110 x 18米），以及四个作物系统处理子区（49 x 9米）。在四个系统中，有两个包含微区（2 x 2米），位于处理子区内，在杂草和覆盖作物出现后手动去除，以提供无覆盖作物对照。实验采用玉米（Zea mays subsp. mays L.）、大豆（Glycine max (L.) Merr.）、黑麦（Triticum spelta L.）轮作，这种轮作在中大西洋美国的饲料和牧草农民中较为典型。

地块编号为三位数代码，第一位数字表示区组，第二位数字表示作物入口主区，第三位数字表示系统子区。年份表示测量值所对应的年份。系统表示该地块的作物系统处理。在整个实验过程中，地块的系统保持一致，但根据轮作年份（玉米、大豆或黑麦），该入口点的作物会发生变化。某些数据集包括一个'excl'或'x'子区，即主区内的覆盖作物去除微区。plots.csv数据文件提供了每个地块在每年作物和系统的参考，而Cropping_Systems.pdf图形提供了四个系统之间主要差异的概述。

数据包括：

- 阴离子树脂袋中硝酸盐的淋溶
- 静态室中的氧化亚氮通量及同位素异构体
- 土壤无机氮，包括铵和硝酸盐
- 土壤水分和温度
- 覆盖作物生物量以及碳和氮含量及氮同位素比
- 经济作物的产量

数据集中的资源包括：

资源标题：玉米籽实产量。文件名：corn_grain_yield.csv。资源描述：玉米籽实产量以每英亩磅（lbs_ac）和每英亩蒲式耳（bu_ac）表示。

资源标题：玉米青贮产量。文件名：corn_silage_yield.csv。资源描述：玉米青贮产量以每英亩磅（lbs_ac）和每英亩吨（tons_ac）表示。

资源标题：牧草产量。文件名：forage_yield.csv。资源描述：牧草切割覆盖作物（三叶草和雀麦）的产量以每英亩磅（yield_lbac）表示。

资源标题：大气氮来源。文件名：ndfa.csv。资源描述：通过草覆盖作物和豆科覆盖作物混合物中草覆盖作物和豆科覆盖作物中的δ15N差值计算的大气氮固定得到的覆盖作物氮。

资源标题：土壤无机氮。文件名：soil_n.csv。资源描述：土壤无机氮和重量水含量。

资源标题：黑麦产量。文件名：spelt_yield.csv。资源描述：黑麦产量以每英亩磅（yield_lbac）表示。

资源标题：作物系统图。文件名：crop_system.pdf。资源描述：作物系统图。虚线垂直线标记黑麦收获期。白色框代表黑麦生长季节。深灰色框代表羽状巢菜和大麦生长季节。浅灰色框代表红三叶草和雀麦生长季节。BM = 播撒粪便；IM = 注射粪便；MP = 铲形犁；CP = 钻孔犁；NT = 免耕。

S1 = 收割后 + 粪便
S2 = 收割后
S3 = 间种
S4 = 间种 NT

资源标题：覆盖作物生物量、碳和氮。文件名：covercrops.csv。资源描述：覆盖作物生物量以每平方米克（wt_gm2）表示，以及百分比氮（per_n）、百分比碳（per_c）和每平方米克氮（n_gm2）。

资源标题：地块参考。文件名：plots.csv。资源描述：该表格展示了每个地块的地块编号以及区组编号（block）、作物系统（system）和每年的作物（entry_15 为 2015 年；entry_16 为 2016 年）。

资源标题：硝酸盐淋溶。文件名：leaching.csv。资源描述：通过在土壤表面下25厘米处埋入阴离子树脂袋中积累的硝酸盐测量的硝酸盐淋溶。淋溶以每公顷千克氮（leached_kgha）表示。

资源标题：氧化亚氮通量。文件名：n2o_flux.csv。资源描述：通过静态室在45分钟内采集四个时间点的样本捕获的氧化亚氮通量。通量以每公顷每天克氮（ghad）表示。

资源标题：氧化亚氮位置偏好。文件名：n2o_sp.csv。资源描述：通过氧化亚氮同位素异构体中中心氮原子和末端氮原子的δ15N同位素差值计算的氧化亚氮位置偏好。

资源标题：辅助土壤数据。文件名：n2o_ancillary.csv。资源描述：与氧化亚氮通量测量在同一时间和地点进行的辅助土壤测量。土壤温度（soil_temp）和空气温度（air_temp）以摄氏度表示，土壤湿度以体积水含量百分比（vwc）表示。

资源标题：数据字典。文件名：mitigating-n-data-dictionary-2019-08_ahm.csv。资源描述：定义了每个表中的变量、它们的单位、数据类型和允许值。