Alfalfa Establishment and Production with Continuous Alfalfa and Following Soybeans1

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AbstractAlfalfa (Medicago sativa L.) is commonly grown in rotation with other crops but land can be continuously cropped with alfalfa. The purpose of this study was to determine the stand establishment and production of alfalfa cultivars that differed in disease resistance in a continuous alfalfa cropping situation, with limited supplemental irrigation. Two alfalfa cultivar experiments were spring‐seeded in 1970 at the Nebraska Agric. Exp. Stn. Mead Field Lab. on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) soil with no known prior alfalfa cropping. The area was plowed in late May 1975 after the first cutting and fallowed. Soybeans (Glycine max L. Merr.) were seeded in 1976 on subareas reserved for seeding alfalfa in 1977 and 1978, and in 1977 on the subarea reserved for seeding alfalfa in 1978. Two alfalfa experiments were spring‐seeded per year in 1976, 1977, and 1978, a foliar fungicide and a fungicide seed treatment experiment. Forage yields did not differ among foliar fungicide treatments or between ‘Arc’ and ‘Ranger’ in the year of seeding or in subsequent years. Anthracnose (caused by Colletotrichum trifolii Bain) and foliar diseases were at subeconomic levels. Stands in the year of seeding did not differ among fungicide seed treatments or between ‘Agate’ and ‘Dawson’. Anthracnose and phytophthora root rot (caused by Phytophthora megasperma Drechs) were factors in stand decline and yield reduction of susceptible cultivars after the year of seeding. Stands in the year of seeding were excellent on the same land area where alfalfa was seeded in 1970 with no known previous alfalfa cropping, after plowing the 5‐year‐old stand of alfalfa in 1975 and seeding in 1976, and after 1 or 2 years of soybeans and seeding alfalfa in 1977 and 1978, respectively. Average forage yields of the experiments seeded in 1970 were 26% higher in the year of seeding, and 40 and 35% higher in the 1st and 2nd year after seeding, respectively, than in the experiments seeded in 1976 to 1978.