The aim of the study was to examine the effect of combined use of organic residue with inorganic fertiliser-P on organic residue decomposition, P transformations and utilisation by upland rice. Five agroforestry tree prunings (organic residues) were incubated without and with inorganic fertiliser-P for 56 days using soil as inoculum only. Decomposition and P release were in the same order i.e. Gliricidia sepium > Senna siamea > Leucaena leucocephela > Paraserienthus falcataria > Acacia mangium. The lignin, polyphenol and cellulose contents and their ratios to the P content of the residue influenced decomposition and hence P release. Added inorganic fertiUser-P had no effect on decomposition. A greater proportion of inorganic fertiliser-P was recovered when applied with low quality residue and less with high quality residue. Gliricidia sepium and Acacia mangium prunings were incubated without and with morganic fertiliser-P for 56 days in high and low P status soils. Gross mineralisation was estimated by isotopic dilution. Unlike Acacia, Gliricidia increased gross mineralisation in the low P status soil with weaker P sorbing capacity although net mineralisation was not attained. Inorganic fertiliser-P had no effect on gross mineralisation. Organic residue influenced both the inorganic and organic labile soil P fractions while inorganic fertiliser-P influenced only the labile inorganic P fractions. Upland rice (ROK 16) grown on the two soil types treated without and with Gliricidia and inorganic fertiliser-P indicated increased dry shoot weight and total P uptake in the low P soil and not the high P soil. With a double isotopic labelling technique, it was observed that in the low P status soil, Gliricidia P-accounted for over 50% of the total rice P uptake followed by organic-P (25%). Over 80% of the total P uptake in the high P status soil was soil-P. Organic residue increased the quantity of inorganic fertiliser-P utilised but not the native soil P.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:502488 |
| Date | January 2002 |
| Creators | Baggie, Idriss |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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