Abstract:
The study was carried out to evaluate the impact of tillage system in combination with different herbicides
on weed density, diversity, crop growth and yields on 18 farms in Kadoma, Zimbabwe. Experiments
were set up as a split plot design with three replications on each farm. Tillage was the main plot
(Conservation Tillage (CT), Conventional Tillage (CONV)) and weeding option (hand weeding, cyanazine,
atrazine, glyphosate only and mixture of cyanazine þ alachlor and atrazine þ alachlor) as the sub-plots.
Due to the heterogeneous nature of farmers’ resource base, the farms were grouped into three farm
types: high (Type 1), medium (Type 2) and poorly resourced farmers (Type 3). The hand hoe weeded
treatments had 49 percent higher total weed densities in CT relative to CONV, and was statistically
similar to the glyphosate treatment. The mixed pre-emergence herbicides reduced the diversity indices
by 69 and 70 percent when compared to the hand hoe weeded treatment under CT in cotton and maize,
respectively. The effectiveness of all pre-emergence herbicides were not influenced by tillage but were
affected by farmers resource endowments with pronounced effect in Farm Type 1. Maximum plant
heights of 85 and 238 cm were recorded for mixed pre-emergence herbicides under CT for cotton and
maize, respectively. Minimum plant heights of 75 and 217 cm were recorded for the respective hand hoe
weeded treatments. The hand hoe weeded treatments resulted in average cotton lint yield of 1497 and
2018 kg ha 1 for maize. The mixed pre-emergence herbicides treatments gave yields of 2138 and
2356 kg ha 1 of cotton and maize, respectively. The higher weed densities in CT under hand weeded
treatments underscored the need for other weeding options. Similarly, a mixture of cyanazine þ alachlor
in cotton and atrazine þ alachlor in maize is recommended for suppressing broad and grass weed
populations and enhancing yields in CT systems.
