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Agronomy Journal Abstract -

Influence of Tillage Practices on Phosphorus Distribution and Forms in Three Ultisols


This article in AJ

  1. Vol. 80 No. 3, p. 503-509
    Received: Mar 9, 1987

    * Corresponding author(s):
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  1. R. R. Weil ,
  2. P. W. Benedetto,
  3. V. A. Bandel and
  4. L. J. Sikora
  1. Soil-Microbial Systems Lab., USDA-ARS-NRI, Beltsville, MD 20705



Many studies have indicated that organic matter levels in soils tend to rise when no-till (NT) management replaces plowing. It was hypothesized that organic P may thus play a more important role in the plant availability of P in NT soils. A laboratory study was conducted to investigate the organic and inorganic forms of P and their cycling in NT and conventionally tilled (CT) silt loams. Soils from three long-term field experiments were sampled in the fall of 1984, obtaining core segments from 0 to 2, 2 to 4, 4 to 8, 8 to 12, 16 to 20, and 24 to 28 cm. Soil analyses indicated significant differences in the distribution with depth of macro-nutrients between tillage systems. Total P, dilute acid-extractable P (DA-P), total N, and organic matter were more concentrated in the 0- to 2-cm layer under NT compared to CT management. Organic P did not accumulate to the same extent as did organic N and C, resulting in a lower organic P/organic C ratio under NT than under CT management. With increased rates of P fertilization on one soil, total P and DA-P increased dramatically in the upper soil layers, but a similar increase and stratification of organic P was not observed. Samples taken in the spring of 1985 indicated that, despite significantly higher microbial respiration in NT cores, there was no consistent change in the solubility of P over a 75-d incubation period. Thus, it was concluded that the incubation procedure inadequately measured P mineralization in these soils. However, water-soluble P was significantly greater in the upper 5 cm under NT, even where no P fertilizer had been applied. This may have been a result of interference with P-adsorption reactions by accumulated organic matter. This study provided no evidence that organic P is of more importance to plant P availability under NT.

Contribution from the Dep. of Agronomy and the Maryland Agric. Exp. Stn., Univ. of Maryland, College Park, and the Soil-Microbial Systems Lab., USDA-ARS-NRI, Beltsville. Scientific Article no. A4620, and Contribution no. 7616 of the Maryland Agric. Exp. Stn.

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