Measuring and modelling the radiation balance of an orange tree

Abstract

The crop radiation balance is related to plant transpiration and photosynthesis, being important in practical applications and theoretical studies envolving these two processes. For sparse and in hedgerows-forming crops, it is interesting to quantify the all-wave radiation absorbed by the canopy of single plants. In practice, direct measurement of radiant energy absorbed by a single plant is not an easy procedure requiring the positioning of several sensors incompassing the crown, whose measurements using the weight sum of radiation recorded by each sensor. Models to assess radiation balance of trees are the alternatives. Despite its simplifications, the model simulated reasonably well the all-wave net radiation of a citrus tree, tested for differente leaf area conditions on 15min-time (Willmott index of agreement, D from 0.95 to 0.97; RMSE from 0.33 to 0.77 MJ tree^-1 15 min^-1 and BIAS from 0.09 to -0.41 MJ tree^-1 15min^-1). On a day-time the performance of the model kept reasonably well (D = 0.95; RMSE = 13.91 MJ tree^-1 15 min^-1 and BIAS = -0.03 MJ tree-¹ 15 min^-1).