ROOT-GROWTH AND WATER-UPTAKE BY WHEAT DURING DRYING OF UNDISTURBED AND REPACKED SOIL IN DRAINAGE LYSIMETERS

The availability of water to crops depends on both soil properties and root distribution. The dynamics of root development and water uptake in undisturbed and repacked clay soil were studied during increasing soil water deficit pre- and post-anthesis to find how root distribution, soil type and plant development affect plant available water (PAW). Volumetric water fraction was measured with a neutron probe, while root distribution was measured non-destructively using a series of horizontal perspex observation tubes. Soil modification affected the downward root growth which changed little over time for undisturbed (W) soil (6.7-13.6 mm/day-1) compared with the repacked (R) soil (7.5-42.9 mmday-1). In the well-watered treatments root distribution was mostly above the 0.55 m depth in U soil, while there was a reasonably uniform vertical distribution in R soil. The rate of root growth during post-anthesis drying was 61% of that during pre-anthesis drying. The specific root water uptake rate (vol./unit root length/time) was linearly related to the relative root growth rate, indicating the importance of root growth in supplying water during soil drying. Estimated PAW values reflected effects of soil hydraulic properties, root distribution and a propensity to grow new roots during soil drying. Differences in grain yield between treatments were thought to result from the effects of different root distributions and the propensity to grow roots during soil drying. © 1990 CSIRO. All Rights Reserved.