TAILIEUCHUNG - Mechanical impedance to root growth: a review of experimental techniques and root growth responses

It may not seem strange to us today that there is a thing called energy that is conserved in all physical interactions. Energy is a concept we have all grown up with. A hundred and fifty years ago it was not so evident that there should be an intimate, quantitative relationship between such appar- ently unrelated phenomena as motion and heat. The discovery that heat and motion can be seen as different forms of the same thing—namely energy—was the first and biggest step toward understanding the concept of energy and its conservation. Count Rumford of Bavaria, in 1798, was the first to realize that work and heat. | Journal of Soil Science 1990 41 341-358 Mechanical impedance to root growth a review of experimental techniques and root growth responses A. G. BENGOUGH C. E. MULLINS Cellular and Environmental Physiology Department Scottish Crop Research Institute Dundee DD2 5DA and Department of Plant and Soil Science University of Aberdeen Aberdeen AB9 2UE UK SUMMARY Mechanical impedance to roo t growth is one of the most important factors determining root elongation and proliferation within a soil profile. Penetrometers overestimate resistance to root growth in soil by a factor of between two and eight and although they remain the most convenient method for predicting root resistance careful interpretation of results and choice of penetrometer design are essential if improved estimates of soil resistance to root elongation are to be obtained. Resistance to root growth through pressurized cells containing ballotini considerably exceeds the confining pressure applied externally to these cells. Results from this work are reappraised. Existing models of soil penetration by roots and penetrometers are reviewed together with the factors influencing penetration resistance. The interpretation of results from mechanical impedance experiments is examined in some detail and root responses including possible mechanisms of response are discussed. INTRODUCTION The type of soil strength characteristic . the variation of soil strength with soil water content favourable to crop growth depends on both the amount and the distribution of the annual rainfall and on the nature of the crop. The soil must have sufficient mechanical strength to provide adequate anchorage for the plant throughout its development and to prevent the collapse of soil water and air pathways by soil overburden pressure and the weight of vehicle and animal traffic. Dense regions of high strength may limit root growth and crop yield Jamieson et al. 1988 Oussible 1988 by creating a large mechanical resistance to root growth

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