1. USDA/ARS, Beltsville Agricultural Research Center, Instrumentation and Sensing Laboratory, Beltsville, MD 20705-2350. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable.
2. Corresponding author. E-mail: delwiche@ba.ars.usda.gov.
3. Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE.
4. USDA/ARS at Department of Agronomy and Horticulture, University of Nebraska, Lincoln, NE.