Contents & Foreword, Characterizing And ... - IRRI books

● acidic pH (< 6)● low organic matter content● high clay content, particularly kaolinite, gibbsite, or goethite● high concentrations of Fe, Al, or Mn ions in soil solutionThe variability in response of rice to P applications because of P fixation in redyellowpodzolic soils has been demonstrated in several P trials. P response trials withupland rice in Lampung have shown an increase in grain yield with P application atsome sites with relatively low soil P, particularly in newly cleared areas (Effendi et al1982). However, a two-year trial with upland rice in Pekalongan, Lampung, gave noresponse to P (Makarim 1990), whereas upland rice grown on a clayey Typic Paleudultproduced 90–100% maximum grain yields at 20 kg P ha –1 (Palmer and Sudjadi 1984).A trial on a newly cleared site in Central Lampung showed that grain yields could bedoubled by applying P fertilizer at rates similar to those recommended for irrigatedrice in Java (Effendi et al 1982).The dual effects of extractable soil P and P sorption capacity are exemplified intwo upland P trials conducted in Lampung during the 1998-99 wet season as part ofthe Acid Soils Project. Site selection was based on soil P maps produced by CSARand 1998 soil surveys. Phosphorus was applied at four rates, the maximum rate beingdetermined through the soils’ P sorption curve to be adequate to give 0.02 µg mL –1soil P in solution. Rice crops grown at both sites gave a positive response to SP-36application (P