Page 146 - Biosystems Engineering
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CHAPTER 4






                                           Models for Heat


                                      Transfer in Heated



                                                    Substrates





               Manuel Ramiro Rodriguez and
               Maria Dolores Fernandez
               Universidad de Santiago de Compostela
               Galicia, Spain





          4.1  Heat Transfer in Soils


               4.1.1 The Soil Thermal Regime
               Soil temperature is one of the factors that most influence physical,
               chemical, and biological processes in soil and plants. Generally, the
               importance of the effects of soil temperature on plants lies in the role
               of soil temperature as a controlling factor of the intensity of a series of
               processes (Buchan 1991; Jury et al. 1991) that usually reach a maxi-
               mum within a given temperature range (Porta et al. 1999).
                   Temperature affects plant growth and development to such an
               extent that plant growth has often been described by a linear approx-
               imation dependent on temperature and time (thermal time). This
               approach can be used to predict seedling emergence time when soil
               temperature is taken into consideration (Finch-Savage et al. 2001).
               The dependence between the accuracy of soil temperature estimation
               and the prediction of the rate of germination has been studied for
               a number of species, such as Geranium carolinium (Washitani 1985),
               Pinus densiflora (Washitani and Saeki 1986), chickpeas (Covell et al.
               1986; Ellis et al. 1986), lentils, soybeans, and cowpeas (Covell et al. 1986),
               millet (García-Huidobro et al. 1982), or soybeans (Andales et al. 2000).
               In fact, from among the wide range of factors that affect preemergence
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