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Status and Behavior of Phosphorus in Major Acid Agricultural Soils in Lampung, Indonesia
Dissertation Abstract:
Two Red Yellow Podzolic soils and one Andosol from Lampung in Southern Sumatra were studied in a laboratory and greenhouse to determine some chemical and mineralogical properties and the influence of some soil management practices on soil phosphorus (P) in terms of extractable P and selected inorganic P fractions as well as P uptake and dry matter yield of soybean.
The soils differed in their acidity (pH and total exchangeable acidity), minera logical properties, total P content, extractable P, P sorption capacity, and their P fractions (A1-P, Fe-P, and Ca-P).
The laboratory study showed that add it ion of Iime, rock phosphate, and rice straw increased pH and extractable P of the three soils. The three soi ls differed in their response to addition of lime, rock phosphate, and rice straw with regard to their pH, extractable P, A1-P, Fe-P, and Ca-P.
The effect of treatments also differed depending on whether the samples were leached or unleached during incubation and depending on the time the samples were collected during incubation. The extractable Pin leached samples was lower than in unleached samples. Addition of silicated lime to the Podzolic soils resulted in higher extractable P. However, in the Andosol, the two sources did not differ in extractable P.
The effect of treatments on A1-P, Fe-P. and Ca-P fluctuated with time of sampling but A1-P and Fe-P decreased and Ca-P increased although the soils differed in the sampling period when the increase or decrease occurred and depended on whether the sample was leached or unleached.
The greenhouse study showed that dry matter yield and P uptake of soybean were much higher in Andosol than in Podzolic soil. The effects of lime, rock phosphate, and rice straw were significant for dry matter yield and P uptake of soybean. However, the effect of the three treatments interacted with each other in the Podzolic soil. For Andosol, the interactions were only: lime x rock phosphate, lime x rice straw, and rock phosphate x rice straw. Added lime increased the pH in both the Podzolic and Andosol but beyond the expected value. The results were consistent with those in the laboratory experiment. Addition of rock phosphate to Podzolic soil inc reased extractable P but rice straw decreased the value s lightly when recommended lime rate was applied.
In the Andosol, the extractable P at harvest increased from its initial level. The increase appeared to be associated with addition of rice straw, particularly in samples that received lime. A1-P in Podzolic soil decreased in pots applied with sil icate lime but increased with addition of carbonate lime. In Andosol, A1-P differed only s lightly among the treated samples. Fe-P decreased sharply at harvest in Podzolic soil due to addition of rock phosphate. The increase, however, was greater in Andosol due to addition of rice straw.
