The predominant use of manual weeding means that farming in Zimbabweis highly labour-intensive. Herbicides are expensive for farmers and weedsare responsible for the loss of a large proportion of each year's harvest.In addition, agriculture is going through great difficulties due to a radicalland reform programme implemented by the government and an AIDS pandemic thatis having disastrous effects on the availability of labour for weeding. ArnoldB. Mashingaidze will be awarded a doctorate at Wageningen University on 12October for the thesis titled Improving weed management and crop productivityin maize systems in Zimbabwe that was written from the results of thiswork.
Intercropping of maize and pumpkin, narrow row planting and precise feriltilizerplacement and use of reduced herbicide dosages are potential solutions tothe problems of weeds and low crop productivity currently being experiencedin Zimbabwean’ agriculture. In a joint research project between theUniversity of Zimbabwe and Wageningen University, Arnold B. Mashingaidze hasexamined the potential of cultural practices, which increase radiation interception(RI) by the crop and reduce RI by weeds, to increase crop yields while simultaneouslysuppressing weeds.
Mashingaidze assessed the effect of production (cultural) practices thatcan easily be adopted by smallholder farmers on crop yields and weed growthand seed production. Among other things, he looked at the effect of intercroppingmaize and pumpkin on land use efficiency and weeds. The results showed thatpumpkin, a creeper plant with large leaves, reduces weed growth and seed productionby intercepting a greater proportion on incoming radiation and thefore reducingthe amount of light incident on the weeds. Yield was equal to or higher thanthat of maize monocultures in three out of the four seasons in the study,while time spent on manual weeding was reduced by a factor of two to three.
In order to increase the yield of both maize and pumpkin, the lowest 4-6leaves (leaf stripping) and tassel (detasselling) of the maize plants wereremoved at flowering to allow the pumpkin plants to receive more light. Resultsshowed that leaf stripping and detasselling increased maize grain yield by10-12% and 16-28%, respectively, in maize monocrops. In intercropping, leafstripping and detasselling improved the productivity of the system by increasingmaize grain yield and the yield of the minor crop. Experiments involving narrowplanting and precise fertilizer placement methods in maize also produced beneficialeffects. These two interventions were shown to increase radiation interceptionby the crop resulting in increased maize grain yield and lower weed growthand seed production, when compared to normal farmer practice.
Mashingaidze also experimented with the use of reduced herbicide dosagesin maize. He showed that reduced doses ( as low as 12.5% of recommended) werecapable of suppressing the competitiveness of weeds during the critical first4-5 weeks after emergence and prevented weeds from causing yield loss. However,a greater number of moderately tolerant weed species survived and producedseeds with lowering of dosages, meaning that reduced doses need to be followedwith hoe- or mechanical- weeding to prevent resistance development.
By providing insights into practicises that can reduce the manual weedingburden while simultaneously increasing crop productivity, the results of thisstudy can make an important contribution to improving the quality of lifeand food secuity for smallholder farmers in Zimbabwe.
NOTE FOR THE EDITOR
Arnold B. Mashingaidze will be defending his thesis Improving weed managementand crop productivity in maize systems in Zimbabwe on 12 October 2004at 16.00in the auditorium of Wageningen University at Generaal Foulkesweg1a in Wageningen.
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