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This article in AJ

  1. Vol. 79 No. 5, p. 926-928
    Received: Nov 10, 1986

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Infuence of Calcium, Nitrogen, and pH on Alfalfa Root Growth and Nitrogen Fixation Using the Implanted Soil Mass Technique1

  1. J. E. Rechcigl,
  2. K. L. Edmisten,
  3. D. D. Wolf and
  4. R. B. Reneau Jr.2



Soil acidity is a major growth-limiting factor responsible for stunting roots, reducing forage yield, and limiting N2 fixation in alfalfa (Medicago saliva L.). The implanted soil mass technique was utilized to investigate the influence of subsurface amendments on root systems. It consisted of mixing a study soil with chemical treatments of interest, burying the mixture in mesh bags 15 cm below an existing alfalfa stand, removing the bags after 1 yr, and determining root mass and N2 fixation via acetylene reduction. A Tatum clay loam (clayey, mixed, thermic Typic Hapludult) soil with an initial pH of 4.4 and amended with either CaSO4, NH4NO3, CaSO4, + NH4NO3, KOH, or Ca(OH)2 was buried in the mesh bags, in an Ernest silt loam (fine-loamy, mixed, mesic Aquic Fragidult) that had received either 0 or 6.7 Mg ha−1 of surface-applied dolomitic limestone. After liming, the pH of the soil surface (0–5 cm) increased from 5.3 to 6.3. Surface liming increased the root mass in only the implanted soil mass receiving a Ca(OH)2 or KOH amendment and did so by 7.5- and fivefold, respectively. With the unlimed soil, only Ca(OH)2 increased root mass in the implanted soil mass. With the exception of Ca(OH)2, treatments had no influence on N2 fixation in the implanted soil mass. For the Ca(OH)2 amendment there was a fourfold increase in N2 fixation in the surface-limed soil and a 20-fold increase in the unlimed soil.

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