Rice root response to water stress in rainfed lowland
Thangaraj, M. | O'Toole, J.C.
In a greenhouse experiment, water stress for 16 days increased the soil mechanical impedance and consequently decreased the rice root growth in the 0-20 cm soil layer by 47% below the continuously flooded control. Rice root growth decreased with decreasing soil moisture and increasing soil mechanical impedance. Soil mechanical impedance values around 1.0 to 1.5 MPa appeared to be critical and decreased the root growth consistently and inhibited further elongation. Under wetland field conditions, approximately 70% of the total root length and root dry weight were found distributed in the 0 to 10 cm soil profile. Irrespective of the water regimes, the physical size of the root system in terms of length and dry weight increased progressively with time and reached its maximum at flowering and decreased toward harvest. The adverse effects of water stress on soil mechanical impedance and root growth were more pronounced in the 0-10 cm soil profile where significant proportion of the root system of transplanted rice is present. In a simulated rainfed lowland condition, soil moisture content below 60% and soil mechanical impedance as low as 0.05 MPa were found to be sufficient to inhibit the root growth below control. Values greater than 0.3 to 0.5 MPa consistently decreased the root growth and extension to 25% of the control level. The root length density in the 0 to 10 cm soil layer at flowering was positively and linearly related to the yield and yield components. The new root sampling technique provides a rapid, and quantitative approach for measuring rice root responses to water and nutrients in wetland soil
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