Diurnal and seasonal light transmission to cowpea in sorghum-cowpea intercrops in Mali
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abstract
Tall cereal-short legume intercropping is ubiquitous in the semiarid tropics of West Africa, yet little is known regarding the dynamics of light interception in these systems. A field study was conducted in Cinzana, Mali, to characterize light transmission to cowpea in sorghum [Sorghum bicolor (L.) Moench]-cowpea [Vigna unguiculata (L.) Walp] intercropping systems. Different sorghum-cowpea planting configurations were used to examine photosynthetically active radiation (PAR) incident on the cowpea. The 4-m tall sorghum cultivar CSM 219E intercepted > 60% of incoming PAR from 2 m height to harvest (50 days). Consequently, total seasonal PAR received by intercropped cowpea was 60-66% that of the unshaded monocrop. Thirty-minute averages of PAR transmitted around solar noon had poor agreement (R 2 = 0.53) with fractional daily light interception and overestimated seasonal PAR received by cowpea by 17% in the north-south row orientation used. Thirty-minute averages at 1100 h (R 2 = 0.93) and 1430 h (R 2 = 0.91) had the closest correlation to diurnal average PAR incident on cowpea. This study indicates that tall guineense sorghum captures significant amounts of light at low leaf area index (LAI) (< 2.0). Row orientation, time of measurement, plant height and LAI should be considered in calculating light interception in these intercropping systems.
