Effect of Citric Acid, Glucose and Organic Matter on Plant P Uptake and Soil P Fractionations in a Highly Weathered Ultisol
Chin J Plan Ecolo. 1996, 20 (2):
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The effect of eitrie acid and glucose on P uptake by different species of Cultivated and wild plants, and P fraetlonations of the soil was investigated in an acid Ultisol. Experiments were conducted in the greenhouse, using continuous addition of citric acid and glucose solutions, and a complete budget study designed to examine the changes of soil phosphorus in various fractions employing a P fraetionation procedure. Without inorganic P additions, citric acid increased P uptake by soybean (Glycine max (L.) Merr.) and sorghum (Sorghum bicolor), indicating that citric acid solubilized the P bound by A1 and Fe oxides. The addition of P (20mg P kg-1 soil)in combination of a continuous addition of citric acid solution resulted in higher P uptake by soybean and sorghum. The addition of glucose, with and without addition of P, did not change the P uptake by plants. However, the addition of glucose increased the organic P in NaOH fraction, and a decrease in inorganle NaOH fractions. A negative microbial P was obtained for all the treatments, especially when glucose was added. This suggests that the method described by Hedley is not suitable for determination of microbial P in very acid soils having little orgame matter content. The increase of P uptake by sorghum and a decrease of P in the NaOH fractions in the soil with the addition of inorganie P and citric acid suggests that organic llgands can prevent P from being fixed by soil particles. The addition of oak (Quercus spp.) and red clover (Trifolium pratense) litter to a similar acid soil resulted in a higher P uptake by pokeweed (Phytolacea americana). After a period of 7 months, the resin-P and inorganic bicarbonate P decreased substantially compared with the P at the beginning of experiment. This can be attributable to the P uptake by plant, P taken up by microbial organisms, an increase in organic P,and an increase in HC1 fraction.The results also showed thatboth clover and oak litter did not increase the inorganle P in NaOH fractions. This indicates that products of organic matter decomposition might have prevented the mineralized P from being immobilized by clay partleles and Fe- and Al-oxides. An attempt was also made to elucidate the mechanisms involved in the P solubilization by the products of organic matter decomposition, and the resuetion of P adsorption by Al- and Fe-compounds in the presence of organic ligands.