Biochar amendment techniques for upland rice production in Northern Laos: 1. Soil physical properties, leaf SPAD and grain yield

The objective of this study was to investigate the effect of biochar application (CA) on soil physical properties and grain yields of upland rice (Oryza sativa L.) in northern Laos. During the 2007 wet season, three different experiments were conducted under upland conditions at 10 sites, combining variations in CA amounts (0–16 t ha−1), fertilizer application rates (N and P) and rice cultivars (improved and traditional) in northern Laos.CA improved the saturated hydraulic conductivity of the top soil and the xylem sap flow of the rice plant. CA resulted in higher grain yields at sites with low P availability and improved the response to N and NP chemical fertilizer treatments. However, CA reduced leaf SPAD values, possibly through a reduction of the availability of soil nitrogen, indicating that CA without additional N fertilizer application could reduce grain yields in soils with a low indigenous N supply. These results suggest that CA has the potential to improve soil productivity of upland rice production in Laos, but that the effect of CA application is highly dependent on soil fertility and fertilizer management.