Germinable weed seed-bank response to plant residue application and hand weeding under two contrasting tillage systems in a granite-derived clay loam soil in Zimbabwe

Abstract

High levels of weed infestation are among the major reasons for the limited adoption of conservation agriculture techniques by farmers in sub-Saharan Africa. This study investigated the effects of plant residue application (zero: NR, low: LR, medium: MR and high: HR) and hand weeding (twice: TWI, thrice: THR, four times: FOU and clean weeding: CLE) under two tillage systems (basin planting: BASIN, and conventional tillage: CT) on weed seed density in a clay loam soil at Chinhoyi University of Technology experimental farm, Zimbabwe. During 2014/15, the number of germinable Amaranthus hybridus L. seeds was higher in BASIN+NR+THR and BASIN+MR+TWI than other treatments. Germinable propagules of Cyperus L. spp. were fewer in NR+FOU and NR+CLE than NR+TWI and NR+THR plots. In 2015/16, TWI resulted in an increase of 52.3−79.5% of the number of germinable A. hybridus seeds compared to THR, FOU and CLE. Germinable weed seeds increased by 67.1% for Alternanthera pungens Kunth and 164.8% for Galinsoga parviflora Cav. in the surface compared to the subsurface layers of BASIN but were evenly distributed in CT. The results suggest that cultural practices exert selection pressure on individual weed species which may change the weed species composition in the soil seed bank.