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Potassium Effects on Improved Growth, Nodulation, and Nitrogen Fixation of Hairy Vetch¹

ABSTRACT

Symbiotic N fixation by forage legumes presents practical means for improved pasture productivity. However, soil fertility and plant nutrient deficiencies may greatly limit legume growth, nodulation, and nitrogenase activity levels.

Results from 3 years' field and greenhouse experiments were evaluated to determine the influence of K and P levels with and without Ca on growth, nodulation, nitrogenase (C₂H₂ reduction) and nodule cytosol components of ‘Madison’ hairy vetch (Vicia villosa Roth) grown in a siliceous thermic Psammentic Paleustalf (Eufaula). Significant increases in both growth and seed yield resulted from application of 50 mg P and 100 mg of K/kg soil. Nodulation and nitrogenase activity (C₂H₂ reduction) at anthesis (248 day age) were significantly increased with both P and PK treatments. Nitrogenase activity levels correlated with nodule mass with highly significant increases resulting from the K treatment. Phosphorus content of nodule cytosol was significantly increased with 0, 50, 100, 150 mg P/kg soil in factorial combinations with 100 mg of K and 400 mg of Ca/kg soil. Nitrogenase activity levels were increased with all K treatments and effects of K were highly significant influencing every parameter except cytosol Ca. Cytosol Na was reduced inversely to increased K content. Growth increased in quadratic response to 0, 100, 200, and 300 mg of K applied with and without 100 mg of P/kg soil. Highly significant linear increase in nodule weight, nitrogenase activity, and nodule cytosol K resulted with increased K levels without P interaction. Cytosol Ca, Mg, and P were significantly increased, and highly significant decreases in Na resulted with increased K applications. The most reliable response surface by multiple regression with R² = 0.738 was: nitrogenase = 48.36 nodule weight + 0.1 K – 1.44 top weight – 0.04 Na + 0.01 Ca, C.V. = 27.4%. Nodule weight x nitrogenase correlations were highly significant with negative correlations existing for cytosol Na and every other parameter.

¹ Journal article 3823 Oklahoma Agric. Exp. Stn., Stillwater, OK 74078.

² Professor; Supervisor, Agronomic Service Laboratory (Agronomy); and Professor (Biochemistry), respectively, Oklahoma State Univ., Stillwater, OK 74078.

Received for publication July 21, 1980. Accepted for publication October 15, 1980.