Agriculture and Food Systems - Theses

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    Root and top growth of the wheat plant as affected by water supply
    Alamoodi, Ahmed S ( 1987)
    Two experiments were conducted to study the growth, particularly the root growth, of wheat in relation to moisture supply. One was conducted in an igloo house at the Mt Derrimut Field Station of the School of Agriculture and Forestry, University of Melbourne and the other in a glass house on the main campus. The plants were grown in a mixture of soil, sand and ligna peat contained in plastic bags to give columns about 0.8 m deep. In the first experiment the effects on both above-ground and below-ground growth of withholding water at different stages of growth and for different times were studied on three cultivars of wheat. In the second experiment effects of supplying different amounts of water were studied. Plants were harvested periodically for measurement of dry weights of the various plant parts, measurement of leaf area and root length and counts of tillers, heads, grains and roots. The soil columns were dismantled 20 cm at a time to enable the distribution of roots in the profile to be observed. Withholding water at any stage of growth and for any period reduced the above-ground dry matter at maturity; the longer the period of non-watering the greater the reduction. Reduction in above-ground dry matter resulted from reductions in number of tillers, leaf area and grain yield. Tillering was most affected by non-watering during early and mid-season growth, and yield by non-watering after anthesis, especially when it occurred during the first two weeks after anthesis. Non-watering after anthesis reduced yield mainly by reducing grain size (1000 grain weight). The quantity of recoverable roots, measured either by weight or by length, reached a maximum about the time of anthesis and then declined as roots died and were lost during harvest. The quantity of roots formed was reduced when non-watering was imposed during early or mid-growth. The distribution of roots in the profile was also affected by the watering treatments. Withholding water during early and mid-growth resulted in a greater proportion being located in the deeper soil zones. However, with the soil initially below field capacity, withholding water from sowing onwards resulted in shallow rooting presumably because an absolute lack of water limited the plants' ability to produce deep roots. Watering the soil to field capacity every three days in Experiment 2 resulted in less above-ground dry matter than watering to field capacity once a week. It resulted also in a greater proportion of the roots being in the upper part of the profile suggesting that root penetration of the lower part was inhibited by poor aeration as a consequence of overwatering. Watering to field capacity once a week resulted in less above-ground dry matter than giving half the amount of water needed to restore the whole soil column to field capacity. Moreover, the proportion of roots in the bottom zone of the rofile was less under the former treatment than under the latter suggesting that watering to field capacity once a week was causing some restriction of root growth in the bottom zone, presumably through poor aeration. These two facts taken together suggest that in this experiment watering to field capacity once a week even amounted to over-watering.