Weed growth and labor demand under hand-hoe based reduced tillage in smallholder farmers’ fields in Zimbabwe

Conservation agriculture based on hand hoe dug planting basins has been widely promoted for the last decade or two in the smallholder farming sector of southern Africa targeting resource constrained households without access to draft power. In Zimbabwe planting basins are used by about one hundred thousand households but on small plots (<0.5ha) although most are unable to adopt soil surface mulching and crop rotation due to competing uses for crop residues as livestock feed and poorly developed markets for other crops, respectively. We report on the effects of reduced tillage based on hand-hoe dug planting basins (PB) on weed growth (20 farms), and labor demand and returns to investment (50 farms) compared with animal-drawn mouldboard plough based conventional tillage (CONV) in maize (Zea mays L.) fields, across selected districts located in contrasting agro-ecological zones in Zimbabwe. Weed growth was assessed through a survey conducted at the end of the 2009/10 and 2010/11 cropping seasons. Labor demand and returns to investment were measured on 50 farms across five districts using direct observations during the 2011/12 cropping season. The survey showed that farmers on average weeded their PB plots 2.7 times per season compared to 1.7–1.9 times in CONV plots (P<0.001), and timing was often delayed in the former. Reduced tillage plots had 17% (P<0.001) more weed ground cover and 9% (P<0.05) more weed dry matter compared with CONV plots in the 2009/10 season, and differences in 2010/11 were not significant. Weed growth was highest in semi-arid areas (natural regions III and IV) compared with wetter sub-humid areas (natural region II) and arid areas (natural region V). Farmers planted their PB plots 12–23 days earlier, weeding frequency was 42.1–58.9% higher in PB plots, compared with CONV. Labor demand was more than double under PB (84.7mandaysha−1, weeding 48.1mandaysha−1) compared to CONV (38.6mandaysha−1). However, returns to investment were 42.7% higher under PB (U$1.77) compared with CONV (U$1.24). Weed growth and labor demand remained high under PB tillage even after several years, interventions such as the use of alternative weed control methods need to be introduced to farmers to reduce labor demand and consequently increase its adoption both in terms of number of farmers and cultivated area in southern Africa.