Assessing root growth and water extraction for rainfed rice

In drought-prone rainfed lowland, rice encounters fluctuating water conditions in the same season, ranging from anaerobic soils with ponded water to aerobic soils with water deficit (Wade et al 1998, 1999a,b). Other rainfed environments encounter varying combinations of stresses over a related range of hydrology and oxygen status, from submergence to saturated soils to severe water deficit. Whichever ecosystem is the target, rice fields are variable, especially in rainfed, and field measurements of root systems are difficult. Controlled environments offer the opportunity to provide repeatable conditions which mimic those likely to be encountered in the field, but in circumstances in which reliable measurements on root growth and water extraction can be obtained. Water uptake can readily be monitored by weighing the pots. For more complete understanding, water extraction by soil layer can be measured using a time-domain reflectometer. Field validation is essential for correct results.