Soil pH and Calcium Effect on Nitrogen Fixation and Growth of Board Bean
1990
Nitrogen fixation and growth of broad bean (Vicia faba L.) are adversely affected by low soil pH. This investigation was conducted to determine whether pH effects can be alleviated by Ca, and whether low pH primarily limits growth of the host plant or symbiotic N₂ fixation. The Vicia faba L. cv. Kristall was grown in pots on a Dystrochrent at different pH and Ca levels. Dinitrogen fixation was measured using a nondestructive acetylene reduction method. Exchangeable soil Ca had no major effect on yield, total N uptake, or nitrogenase activity. At low pH (pH 4.7 and 5.4), dry matter production, seed yield, and N₂ fixation were significantly lower than at the higher pH levels (pH 6.2 and 7.0). Low pH delayed the development of nitrogenase activity. Rates of acetylene reduction correlated significantly with plant N content. The N concentrations in the various plant parts of pH 5.4 treatment were as high as in treatments with higher pH levels. The slight yield depression found at this moderately low pH is therefore assumed to be a direct effect of H⁺ activity in the soil on the growth of the host plant. However, at pH 4.7, plants showed N deficiency symptoms during early growth, which suggests pH limitation of N₂ fixation. Dry matter production of young plants not dependent on rhizobial N₂ fixation was significantly decreased at low pH 4.7, 5.6, and 6.2 relative to pH 7.0. Contribution from the Inst. of Plant Nutrition, Justus Liebig Univ., Suedanlage 6, D-6300 Giessen, F.R.G.
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