The effects of population density, row spacing and intercropping on the interception and utilization of solar radiation by Sorghum bicolor and Vigna unguiculata in semi-arid conditions in Botswana.
The effects of population density and row spacing on the growth and solar radiation interception of sorghum were measured from 1980-81 to 1983-84 in increasingly arid conditions in Botswana. The growth and radiation interception of low and medium density sorghum/cowpeas intercrops were measured in the dry 1982-83 and 1983-84 seasons. In moist conditions increasing sorghum density resulted in large increases in LAI, DW and light interception. As conditions became drier, these effects of density were progressively reduced. Intercropping sorghum and cowpeas in dry conditions resulted in small increases in LAI and DW of the combined crops, but small decreases in interception. Persistence of senescent leaf material in the canopy considerably reduced the transmission of radiation to the soil surface in the latter part of each season. Solar radiation extinction coeff. were affected by density, row spacing and the dryness of each season. Extinction coeff. of the cowpeas were lower than those of the sorghum, and intercropping resulted in reduced extinction coeff. of the mixture compared with the sorghum. The efficiency of conversion of intercepted radiation to DW was not measurably affected by population density, row spacing or intercropping.