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.csv

    Resource 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.csv

    Resource Description: Corn silage yield in pounds per acre (lbs_ac) and tons per acre (tons_ac).

  
  

  • Resource Title: Forage yield.

    File Name: forage_yield.csv

    Resource 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.csv

    Resource 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.csv

    Resource 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 soil

  
  

  • Resource Title: Spelt yield.

    File Name: spelt_yield.csv

    Resource Description: Spelt yield in pounds per acre (yield_lbac).

  
  

  • Resource Title: Cropping system diagram.

    File Name: crop_system.pdf

    Resource 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.csv

  Resource 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.csv

  Resource 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.csv

  Resource 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.csv

  Resource 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.csv

  Resource 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.csv

  Resource 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.csv

  Resource Description: Defines the variables, their units, data type, and allowed values for each table.