The incubation experiment (experiment C) included two treatments: straw retention (SRT) and straw removal (SRM). In a 500-ml wide-mouthed bottle, 150 g dry soil (supplemented with 8 g chopped rice straw [P:1.82 ± 0.01 g kg-1] in the straw retention group) and 250 ml available P solution were added, and the water line was marked on the bottle.