Soil dwelling beetle community response to tillage, fertilizer and weeding intensity in a sub-humid environment in Zimbabwe

Abstract

Soil dwelling beetles contribute greatly to biodiversity and offer important services in agroecosystems including predation, weed herbivory and decomposition. An experiment was conducted in the 2013/2014 and 2014/2015 cropping seasons at Chinhoyi University of Technology experiment station, Zimbabwe, to investigate the impact of tillage system (conservation tillage and conventional tillage), fertilizer application rate and weeding intensity on beetle communities in maize. The experiment was laid out in a split-split plot using a randomized complete block design and replicated three times. Beetles were sampled using un-baited pitfall traps. A total of 6020 beetles were collected comprising 53 species, nine families and four functional groups. Tillage system had the strongest effects on beetle diversity. Advanced constrained analysis using principal response curves revealed that the abundances of Anchophthalmus oncotipes decreased under conservation tillage. In contrast, abundances of Zophosis boei, Gonocephalum simplex, Renatiella reticulata and Stenethmus tentyriniformis increased under conservation tillage relative to conventiona tillage (CT). Detritivore abundances were 50.8% and 45% greater under rip line seeding than CT during the hot dry season of 2014 and cold dry season of 2015, respectively. Predator abundances were almost double in basin planting relative to CT during the cold dry season of 2014 and hot humid season of 2015. In the 2014/2015 cropping season, maize grain yield significantly increased (P < 0.05) from 4963 kg ha−1 in CT to 7848 kg ha−1 in basin planting tillage. Application of a high rate of fertilizer increased maize grain yield by 31.2% compared to the low and medium fertilizer application rates. Weeding twice resulted in the highest maize grain yield but there was no yield benefit in increasing weeding intensity more than twice per season. Our results suggest that there is potential for increasing density and diversity of beneficial beetle species through conservation tillage with crop residue retention.