How mulching and canopy architecture interact in trapping solar radiation inside a Mediterranean greenhouse

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This work evaluates roles and interactions of ground albedo (ag) and canopy architecture in capturing solar radiation inside Mediterranean greenhouses. Both incident and reflected solar radiation were measured over the ground surface and the greenhouse roof cover during a series of greenhouse experiments where common types of mulch and crop architecture were combined. In the experiments without crop around winter, changes in the daily mean ag from 0.06 to 0.38 induced changes in the greenhouse cover albedo (ac), which ranged from about 0.20 to 0.42. In measurements carried out around winter, both the ag and ac decreased when the ratio of the outdoor diffuse-to-solar radiation increased, independently of the ground surface, indicating that a higher percentage of solar radiation was trapped by the greenhouse under diffuse than under sunny conditions. In crops grown horizontally (not vertically trained), the effect of ground mulching over ag vanishes progressively with the increase in leaf area of the crops, resulting in an asymptotic trend of ag close to 0.23 at full ground covering, independently of the mulch type. In crops grown with high-wire production systems (plants grown in separated rows with the canopy distributed vertically up to 1.5–4.0 m high), asymptotic ag values were also reached but they were lower and dependent on the mulch type and the canopy architecture (0.08 for with black mulch and 0.12 to 0.19 with a gravel mulch). Then, crops with high-wire production systems, common in greenhouses, presented a higher efficiency in trapping solar radiation inside greenhouses. A model, which predicts fairly well the ac from the knowledge of ag and the cover shortwave reflectance, was proposed and used.