A model to estimate the temperature of a maize apex from meteorological data

During early growth, when the apical meristem of a maize plant is close to the soil surface, its temperature may be very different from air temperature. A model is proposed to estimate apex temperature from meteorological data, when the leaf area index is less than 0.5. This model is based on the energy balance of the apical meristem, considered as a vertical cylinder close to the soil surface, called 'apex'. Soil surface temperature was calculated from an energy and water balance of the soil. Input data were hourly standard meteorological data and soil texture. Stomatal conductance was calculated from solar radiation and water vapor deficit. Five field experiments with different soil and climatic conditions were conducted to calibrate and validate the model. The roughness length of the soil surface was used as a calibrating factor. The selected value was 0.3 mm, and was used on all datasets, The agreement between observed and calculated apex temperatures was fairly good, with residual standard deviations between 0.8 and 1.9 K in five experiments, while apex temperature was generally higher than air temperature at screen level by more than 5-7 K during the day. This study showed that the main problem to overcome in estimating apex temperature, is to calculate air temperature at apex height, i.e. at several centimeters from the soil surface. This requires development of precise soil surface temperature models. (C) 2000 Elsevier Science B.V. All rights reserved.