At all sites, the fields were prepared by plowing with hand
tractor. Commercial biochar from wood residues (e.g., teak (Tectona
grandis L.) and rosewood (Pterocarpus macrocarpus Kurz)) of a local
lumbermill was used in these experiments. Wood residues were
processed into biochar by the earth mound method (FAO, 1983).
Biochar was ground to 2 mm particle size, then applied and carefully
mixed with the soils after plowing. A third of N fertilizer was
broadcasted before sowing, at 40 days after sowing (DAS) and at 80
DAS, respectively. All the P fertilizer was applied just before sowing.
Sowing and harvesting were conducted in mid-May and early
October, respectively. Planting density was 16 hills m2
.
In Exp. 1, saturated hydraulic conductivity (SHC) of the surface
soil wasmeasured at 60 DAS for one undisturbed soil sample from 0–
5 cm depth in each plot. At 70 DAS, rice plants were cut at 10 cm
above the ground and the xylem sap flow (XSF) was estimated by
collecting sap flow from the cut rice culm with a ball of cotton wool
between 16:00–4:00. In Exp. 1 and 2, the leaf chlorophyll
concentration (SPAD-value; SPAD502, KONICAMINOLTA. Inc.,
Tokyo) was determined at 90 DAS for the three youngest completely