Soil mapping for improved phenotyping of drought resistance in lowland rice fields

• Soil electrical conductivity was related to the severity and timing of drought stress.
• Soil electrical conductivity correlated with rice grain yield under drought.
• Mapping soil electrical conductivity could improve rice drought screening.

Phenotyping of drought resistance traits in rice is challenging at the field level due to the spatial variability of soil characteristics linked to soil water content. Apparent soil electrical conductivity (ECa) mapping may therefore be useful for characterizing spatial variability and improving phenotyping efforts in drought screening trials. ECa mapping was conducted over two seasons in lowland rice drought phenotyping trials. ECa was positively correlated with clay content and soil depth, and negatively correlated with volumetric soil water content during periods of moderate to severe drought. In addition, ECa was negatively correlated with indicators of plant performance including canopy temperature, normalized difference vegetation index, biomass, plant height, and grain yield. The results suggest that clay content and topsoil depth were the primary factors influencing the timing and severity of the drought response during the dry down of the field. Overall, the results illustrate the usefulness of ECa mapping for the spatio-temporal characterization of soil heterogeneity that influences plant performance under drought in lowland rice fields. ECa mapping can be useful for optimizing experimental plot layouts to ensure their uniformity and to improve validity of drought phenotyping and breeding trials.