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Wageningen Universiteit (2004)

Improving weed management and crop productivity in maize systems in Zimbawe

Mashingaidze, A.B

Titre : Improving weed management and crop productivity in maize systems in Zimbawe

Auteur : Mashingaidze, A.B

Université de soutenance : Wageningen Universiteit

Grade : PhD thesis 2004

Résumé partiel
In the tropics, weeds cause more crop losses and farmers spend more of their time weeding crops than in any other part of the world. Weeds form a major factor which contributes to the miserable quality of life of smallholder farmers, especially of women and children, in rural areas of sub-SaharanAfrica. The effects of maize-pumpkin and maize-bean intercropping and, narrow row planting and precise basal fertilizer placement in monocrop maize, on crop and weed radiation interception (RI), crop yields, weed emergence, growth and fecundity were investigated in this study. The effects of leaf stripping (removal of the lowest 2-6 leaves) and detasselling maize at anthesis on the radiant environment and crop yields in a maize monocrop and maize-pumpkin and maize-bean intercrops were also studied to determine the impact of these interventions on yield of component crops. The aim of the studies was to generate technologies that could be integrated into the production practices of smallholder farmers to suppress weeds and alleviate the severe weeding burden faced by these farmers while ensuring high crop productivity. Maize-pumpkin and maize-bean intercropping reduced weed biomass by 50-66% when established at a density of 12,300 plants ha-1for pumpkins equivalent to 33% of the maize density (37,000 plants ha-1), and 222,000 plants ha-1for beans. Lower densities of pumpkins than 33% of the maize density failed to reduce weed biomass more than that achieved by sole maize. Sole maize crops were weeded twice or thrice to achieve the same weed biomass as intercrops weeded once showed that intercropping could reduce the weeding requirements of maize by 33 to 67%. Maize grain yield was reduced by 20% in one out of four seasons in the first study on maize-pumpkin intercropping. Maize grain yield was not reduced in three seasons when the maize-pumpkin intercropping treatments were leaf stripped and/or detasselled and the trend of leaf stripping and detasselling alleviating the effects of companion crop competition on maize grain was shown in the maize-bean intercrop experiments as well. Intercrop productivity increased with leaf stripping and detasselling as a result of greater penetration of radiation to the companion crop and their effects of increasing dry matter distributed to the maize cob (indicated by 1000-grain weight, cob weight, and kernel weight cob-1). Leaf stripping maize at anthesis focused on the removal of leaves that were beginning to senesce. If they would remain on the plant they would compete with the cob for assimilates as they senesce further, until necrosis. Detasselling is known to remove apical dominance and to increase radiation penetration to the middle leaves on the maize plant that produce most assimilates destined for the cob. Leaf stripping did not affect the ability of the intercrop to suppress weed growth and seed production. In maize monocrops more weed biomass and weed seeds were produced with leaf stripping and detasselling. Maize grain yield decreased with an increase in maize density from 30,000 plants ha-1to 36,000 and 42,000 plants ha-1and weed growth suppression increased with an increase in maize density in a semi arid location in Zimbabwe. Planting maize using narrow row (60 cm × 45 cm) and (75 cm × 36 cm) spatial arrangements increased radiation interception by maize plants by 16 to 24% and maize grain yields by 15 to 26% compared to wide row (90 cm × 30 cm) spatial arrangement commonly used by smallholder farmers. Weed biomass was reduced by 20 to 80%, dependent on weed species, in narrow row spatial arrangements compared to normal farmer planting patterns. The duration of the weed free period required to attain maximum yield increased from 6 weeks after emergence (WAE) in the 60 cm × 45 cm spatial arrangement to 9 WAE in the wider row spatial arrangements. It is, therefore, risky for smallholder farmers to increase maize density to suppress weeds as this will lead to maize grain yield reductions. The use of narrow rows proved to be a better option.

Mots clés : zea mays / maize / weed control / manual weed control / herbicides / cropping systems / intercropping / zimbabwe

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Page publiée le 27 mars 2008, mise à jour le 14 janvier 2018