Broomcorn [Sorghum bicolor (L.) Moench] responses to shade: an agroforestry system interface simulation

Abstract

Broomcorn is a sub-species of sorghum principally cultivated for its inflorescences, which take the form of panicles from which brooms are manufactured. Broomcorn cultivation is common on small properties, occupying marginal areas or grown in rotation with traditional crops. Despite the generalized use of plastics, there is a wide and increasing market for hand-made products fabricated from natural materials, which can represent a good opportunity for additional revenue to low-income families. There have been few studies on broomcorn, and, in particular, there are no reported scientific studies of the performance of this species of sorghum in agroforestry systems. In the present study, production into various organs of broomcorn (stem, leaves, panicle, and seeds) has been evaluated as a function of the availability of solar radiation, in order to assess the adaptive capacity of broomcorn. In a field study, broomcorn plants were submitted to solar radiation moderated by shading provided by adjacent trees, corresponding to different levels (IR) of full-sun irradiance, varying from 42 to 95%. The evaluated plant biomasses displayed close relationships with the available radiation. Out to distances slightly greater than their height, the shading trees had a negative influence on plant biomass production. Once the quantity of received radiation exceeded about 83% of that provided by full sun, the sorghum production displayed only small changes with further increases in available radiation. It did appear that a small reduction in the available radiation was beneficial, for production at IR = 88–92% was observed to be between 2 and 22% greater than under IR = 95%, depending on the production parameter considered. In response to a decrease in the irradiance, broomcorn showed an increased capacity to exploit solar radiation. Consideration of the current methods of agricultural production of broomcorn and the poverty of the small properties on which it is raised indicates that there are excellent prospects for success from the future cultivation of broomcorn within agroforestry systems. Additional beneficial factors are crop protection by the trees and conservation of forested areas. An agroforestry system will offer increased production from the broomcorn crop together with new products coming from the trees, and the start of small agriculture-based industries.