Penetration of Radiation into Cotton Crop Canopies
1985
Marani, A. | Ephrath, J.
The penetration of radiation into cotton (Gossypium hirsutum L., ‘Acala SJ-2’) canopies was investigated in two field experiments in Negba (1980, irrigated by sprinklers), and in Nahal-Oz (1981, three irrigation treatments by a drip system). Photosynthetically active radiation (PAR) below the canopy was measured by a sensor moving on a 2 at track across the rows and integrated for periods of 30 min. The PAR was also measured above the canopy, and the percent of penetration was calculated. Plant height and leaf area index (LAI) were measured together with the radiation measurements. A high correlation was found between plant height and LAI, and both were highly correlated with radiation penetration. Plant height was found to be more useful than LAI as a predictor of radiation penetration, because its measurement in the field is more convenient. During periods of moisture stress, radiation penetration was usually lower than predicted by plant height. An examination of our data by using a model revealed that plant width was an important factor determining radiation penetration. The model accurately predicted radiation penetration into the canopy, provided that reliable estimates of essential plant parameters (e.g., plant height and width, LAI, and leaf angle distribution) had been input. Increased growth in height was usually associated with high rates of irrigation, whereas plant width was not. Plant width increased abruptly as soon as the first bolls began to develop, and this was followed by a rapid decrease in radiation penetration.
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