| Summary: | A knowledge of root growth and the activity of separate members of the root system is necessary before a comprehensive understanding of plant water and nutrient uptake is possible. The literature describing the developmental characteristics of wheat root systems is first reviewed. Methods of examining root systems in the field are compared, and studies of the contribution of seminal and nodal roots, and the effects of soil environment are discussed. Finally, nutrient and water uptake are considered mainly from the literature concerned with soil processes supplying nutrients to the root surface. The literature survey highlights the scarcity of field studies of water and nutrient uptake compared to laboratory studies and the poor understanding of the ways in which soil water status affects root growth and activity. An experiment in which spring wheat was grown in soil columns in a controlled environment is reported. Water was withheld during growth and the consequences for root growth and nutrient and water uptake followed. Nodal root growth was also restricted but this treatment was largely inconclusive because of the limited time during which conditions comparable to those in the field could be maintained. It was decided from these experiments to work with a field crop; a major study of the micro-climate and growth of winter wheat was in progress, so it was appropriate to examine in detail the growth and functioning of the crop's root system. A number of experiments were set up but this thesis mainly describes the root growth, and associated nutrient and water uptake of the normal field-grown crop. Measurements of root dry weight and length, plant nutrient content and water use are reported in early sections, with subsequent calculations of nutrient and water inflow; the possible contribution of mass-flow to plant nutrient is considered. A pattern of nutrient inflow not previously reported was found and possible explanations are discussed. The influence of soil properties, root distribution and atmospheric conditions on water inflow are also examined. The work shows the importance of field studies in understanding root growth and activity, and puts forward a number of suggestions for future progress.
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