THE EFFECT OF PREPLANT NITROGEN AND SOIL-TEMPERATURE ON YIELD AND NITROGEN ACCUMULATION OF ALFALFA

Recommendations for the use of preplant N in alfalfa establishment are controversial. Growth chamber experiments were conducted to examine the effect of preplant N and soil temperature on yield and N accumulation of alfalfa (Medicago sativa L.). Alfalfa was grown in river sand at three day/night soil temperatures (18/12-degrees-C, 24/16-degrees-C, and 27/21-degrees-C), and at five levels of preplant N (0, 10, 20, 40, 80 kg ha-1). At 18/12-degrees-C, 40 kg ha-1 preplant N resulted in a 69% increase in shoot dry matter yield. Dry matter and N accumulation rates were greatest at 40 and 80 kg ha-1. Preplant N effects on dry matter and N accumulation at 18/12-degrees-C were expressed primarily between the early bud and early flowering stages. Assessment of soil temperature and soil N availability is necessary to determine the potential for a yield response of alfalfa to preplant N.