Abstract
A new method allowing control of rhizosphere pH and mineral nutrition was applied to study depletion of various organic and inorganic phosphorus fractions extractable sequentially with 0.5M KHCO3 (pH 8.5), 0.1M NaOH and residual P extractable with 6M H2SO4 from the rhizosphere soil.
Soil pH was affected about 2 mm from the root mat. Depletion zones of inorganic P (KHCO3-Pi) extractable with 0.5M KHCO3 extended up to about 4 mm but the depletion zones of all other P fractions were about 1 mm only. The root-induced decrease of soil pH from 6.7 to 5.5 increased the depletion of total P from all fractions by 20% and depletion of KHCO3-Pi and residual P by 34% and 43%, respectively. Depletion of organic P (KHCO3-Po) extractable with 0.5M KHCO3 was not affected by a change in rhizosphere pH. With constant or increased pH, depletion of inorganic P (NaOH-Pi) was 17% and organic P (NaOH-Po) was 22% higher than with decreased pH. Only 54–60% of total P withdrawn from all fractions was from KHCO3-Pi. Substantial amounts of KHCO3-Po and NaOH-Po were mineralized and withdrawn from the rhizosphere within 1 mm from the root mat, as 11–15% of total P withdrawn originated from the organic P fractions. A remaining 11–16% was derived from NaOH-Pi, and 15–18% from residual P fractions likely to be rather immobile. Thus, 40–46% of the P withdrawn near the root mat of rape originated from non-mobile P fractions normally not included in 0.5M NaHCO3 extraction used to obtain an index of plant-available soil P.
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Gahoonia, T.S., Nielsen, N.E. The effects of root-induced pH changes on the depletion of inorganic and organic phosphorus in the rhizosphere. Plant Soil 143, 185–191 (1992). https://doi.org/10.1007/BF00007872
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DOI: https://doi.org/10.1007/BF00007872