A nice study reminding agricultural experts to be modest about what is known and unknown about complex cropping systems in West Africa.
Parkia biglobosa and Vitellaria paradoxa are known to improve soil fertility and redistribute water under their crowns in parkland systems. A field experiment was conducted to separate above and below-ground interactions between these species and associated Sorghum bicolor using root trenching and crown pruning during three cropping seasons. Trenching increased soil water availability because Sorghum plants displayed higher leaf water potential -0.73 ± 0.11 MPa in the trenched plots than control plots -1.32 ± 0.14 MPa. There were no significant differences in grain 315 ± 80 kg ha-1 versus 217 ± 48 kg ha-1 and straw biomass 1639 ± 295 kg ha-1 versus 1307 ± 278 kg ha-1 yields between trenched and control plots. Crown pruning increased sorghum grain yield in the trenched plots in 2008 and 2009 under P. biglobosa while the opposite happened under V. paradoxa. Better performance of Sorghum in the trenched plots under unpruned V. paradoxa trees than pruned trees could be an indication that light was less limiting under this species as previously thought but also that crown removal induced soil water evaporation and decreased soil water content under this species. An implication of this is that recommendations for including trees in cropland, or for management of existing trees within cropland, must be context and species specific.
Michael Kevane 