The data included here are for the WQFS maize grain yields only; see companion publications for other data including yields of rotation crops, maize stover biomass, nitrate loss in drainage water and other environmental impact data.
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The Water Quality Field Station (WQFS), a Purdue University Core Facility, is an in-field laboratory dedicated to the study of productivity and environmental impacts of rainfed, maize-based production systems, system variants and emerging alternatives. The data included here are for the facility’s maize (''Zea mays'' L.) grain yields only; other data including yields of soybean (''Glycine max'' Merr.) grown in rotation with maize, maize stover biomass (selected years only), nitrate loss in tile drainage water, seasonal greenhouse gas emissions, soil nutrient status and other carbon and nitrogen (N) cycling data are reported in companion publications. All yields are reported as dry weight (0 kg H,,2,,O per kg grain following drying at 60 ^o^C to constant weight). Protocols for WQFS standard operating procedures (SOPs) for harvesting, drying and calculating yield are provided as supporting documents. Relevant information on the overall facility and specific treatments are given below. Established in 1992, the WQFS emphasizes synergies and tradeoffs between crop productivity, soil microbial diversity, and air and water quality as influenced by crop rotation and fertilizer N management. The facility is located at Purdue University’s Agronomy Center for Research and Education (ACRE), West Lafayette, IN (40° 29’ 55.20” N; 86° 59’ 53.23” W; elevation 215 m). The soil series are Drummer silty clay loam (fine-silty, mixed, superactive, mesic Typic Endoaquoll) and Raub silt loam (fine-silty, mixed, superactive, mesic Aquic Argiudoll). The mean air temperature and annual precipitation at the site are 12°C and 950 mm, respectively (data from 1977 to 2006). Companion daily weather data are available from ACRE’s weather station. A hallmark attribute of the WQFS is that within every treatment plot (10.8 by 48 m), a large drainage lysimeter (10.8 by 24.4 m) was constructed as a bottomless clay box to allow the collection of drainflow from a hydrologically isolated area of soil thereby permitting analyses of management impacts on losses of nutrients and other crop inputs to surface waters. Bentonite slurry was used to construct the walls of the clay box to a depth of 1.5 m; 0.1 m diameter agricultural drain tiles are installed at 0.9 m depth and all drainage water from a given plot is monitored continuously for drainage volume with composite samples collected on a 24-hr interval for constituent analyses. The experimental design for the facility is a randomized complete-block design with four replicates and 12 treatments (48 separately drained treatment plots). Eleven agricultural treatments are complemented by a restored prairie grass (PG) treatment, which serves as an analog for a natural ecosystem (Trt 1). The predominant species in Trt 1 is big bluestem (''Andropogon gerardii'' Vitman). Between 1995 and 2006, all agricultural treatments include maize grown annually with no rotation to another crop (continuous corn (CC)) or maize grown in rotation with soybean (corn-soybean rotation (C/S)); in 2007/2008, a subset of treatments (Trt 2-5) were transitioned to candidate bioenergy systems (described elsewhere) with only one treatment retained in a maize-based system (Trt 3). Fertilizer N treatments feature varying rates, sources and application timings. For CC, inorganic N fertilizer management systems are generally as follows: (i) 202 kg N ha^-1^ applied preplant (Trt 3, 1995 – 2006), (ii) 179 kg N ha^-1^ applied preplant (Trt 12, 1995 – 2012), and (iii) 157 kg N ha^-1^ applied in a sidedress application after stand establishment and before the V6 growth stage (Trt 5, 1995 – 2007). For C/S rotations, the inorganic N fertilizer management systems require pairs of treatment plots so that both crops are present every study year; N managements are generally as follows: (i) 179 kg N ha^-1^ applied preplant (Trt 2 and 4, 1995 – 2007/2006), (ii) 157 kg N ha^-1^ applied preplant (Trt 6 and 7, 1995 – 2012), and (iii) 135 kg N ha^-1^ applied in a sidedress application after stand establishment and before V6 (Trt 8 and 9, 1995 – 2012). From 1997 onward, the source of inorganic N fertilizer was urea ammonium nitrate (UAN, 28% N) knifed in. Two additional CC treatments receive swine manure effluent as their source of N fertilizer with approximately 250 kg N ha^-1^ injected in the spring and fall to Trt 10 and 11, respectively. Liquid starter fertilizer containing N and P is applied to all corn plantings at a rate of 22 kg ha^–1^ N and 8 kg ha^–1^ P placed 5 cm to the side and 5 cm below the seed. Some deviation in these N managements occurred prior to 1997 and these deviations are noted in the data record. Thereafter, the management is maintained as described. The best commercial hybrids for the region are used in conjunction with best management practices for other nutrients and pest/pathogen and weed control.
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The results reported here would not be possible without a host of faculty, staff and student contributions to the design and implementation of treatments and to the careful collection, analysis and preservation of treatment data, which dates back more than two decades and includes a myriad of obsolete formats and software technologies. We are particularly grateful to David B. Mengel and Agronomy colleagues for bringing the WQFS to life and to Brenda S. Hofmann for the initial stewardship of the facility. This publication would not be possible without the efforts of Jerry Schmerier in preparing the historical data record, Marianne Stowell Bracke in standardizing its description, and colleagues in the Purdue University Research Repository (Courtney Matthews, Michael Witt and many others) to operationalize the data publication process at Purdue. The following funding organizations have all contributed to this data record, which spans the life of the facility: Purdue University College of Agriculture, Purdue University Center for the Environment, Purdue University Department of Agronomy, USDA-NRI, USDA-NIFA/AFRI, USDA/DOE Northcentral Sungrant Program, National Pork Producers, Purdue University Showalter Trust, US Environmental Protection Agency, US National Science Foundation, USDA Consortium for Agricultural Soils Mitigation of Greenhouse Gasses, USDA CSREES National Integrated Water Quality Program, International Plant Nutrition Institute, USDA Special Grants Program, Eli Lilly Foundation, US Department of Energy, Indiana Department of Environmental Management.