Influence of leaf area index on canopy energy partitioning and greenhouse cooling requirements

Abstract

Canopy transpiration, which represents the major cooling process in greenhouses, depends strongly on the crop leaf area index I-LA. In this paper, the influence Of I-LA on canopy and greenhouse energy balance of a soilless rose canopy (Rosa hybrida, cv. First Red) was studied during summer in a greenhouse located in the coastal area of eastern Greece. Measurements were carried out during two periods: (i) in summer 1998, under a whitened greenhouse, with a value for ILA (With reference to ground area) of about 2 (dense canopy) and (ii) in summer 1999, under the same greenhouse, before and after whitening, with a value for ILA of about 1 (open canopy). Under whitening, the transpiration rate per unit leaf area was significantly higher for the dense canopy. The canopy stomatal conductance referred to unit leaf area was about 30% higher for the dense canopy than for the open canopy, and the crop water stress index was found significantly lower in the case of the dense canopy. The analysis of the greenhouse energy balance through the classical design formula for ventilation indicated that the evaporation coefficient epsilon (defined as the ratio of latent heat to radiation load) varies in the range of about 0.25-1.25, the lower value being observed in the case of open canopy and non-whitened greenhouse, and the higher value for dense canopy and whitened greenhouse. These results confirm the beneficial effects of a high value for I-LA on both greenhouse environment and crop behaviour under the conditions prevailing during summer in warm Mediterranean and and climates. They also stress the need to account for both leaf area index and radiation load when designing greenhouse-cooling systems. (C) 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved.