Researcher finds solutions to problems in troubled Zimbabwean agriculture cultural practices and reduced herbicide dosages in a bid to increase crop productivity while at the same time suppressing weeds

The predominant use of manual weeding means that farming in Zimbabwe is highly labour-intensive. Herbicides are expensive for farmers and weeds are responsible for the loss of a large proportion of each year's harvest. In addition, agriculture is going through great difficulties due to a radical land reform programme implemented by the government and an AIDS pandemic that is having disastrous effects on the availability of labour for weeding.

Intercropping of maize and pumpkin, narrow row planting and precise feriltilizer placement and use of reduced herbicide dosages are potential solutions to the problems of weeds and low crop productivity currently being experienced in Zimbabwean' agriculture. In a joint research project between the University of Zimbabwe and Wageningen University, Arnold B. Mashingaidze* has examined the potential of cultural practices, which increase radiation interception (RI) by the crop and reduce RI by weeds, to increase crop yields while simultaneously suppressing weeds. Arnold B. Mashingaidze will be awarded a doctorate at Wageningen University on 12 October for the thesis titled Improving weed management and crop productivity in maize systems in Zimbabwe that was written from the results of this work.

Mashingaidze assessed the effect of production (cultural) practices that can easily be adopted by smallholder farmers on crop yields and weed growth and seed production. Among other things, he looked at the effect of intercropping maize and pumpkin on land use efficiency and weeds. The results showed that pumpkin, a creeper plant with large leaves, reduces weed growth and seed production by intercepting a greater proportion on incoming radiation and thefore reducing the amount of light incident on the weeds. Yield was equal to or higher than that 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 4-6 leaves (leaf stripping) and tassel (detasselling) of the maize plants were removed at flowering to allow the pumpkin plants to receive more light. Results showed that leaf stripping and detasselling increased maize grain yield by 10-12% and 16-28%, respectively, in maize monocrops. In intercropping, leaf stripping and detasselling improved the productivity of the system by increasing maize grain yield and the yield of the minor crop. Experiments involving narrow planting and precise fertilizer placement methods in maize also produced beneficial effects. These two interventions were shown to increase radiation interception by the crop resulting in increased maize grain yield and lower weed growth and seed production, when compared to normal farmer practice.

Mashingaidze also experimented with the use of reduced herbicide dosages in maize. He showed that reduced doses ( as low as 12.5% of recommended) were capable of suppressing the competitiveness of weeds during the critical first 4-5 weeks after emergence and prevented weeds from causing yield loss. However, a greater number of moderately tolerant weed species survived and produced seeds with lowering of dosages, meaning that reduced doses need to be followed with hoe- or mechanical- weeding to prevent resistance development.

By providing insights into practicises that can reduce the manual weeding burden while silmutaneously increasing crop productivity, the results of this study can make an important contribution to improving the quality of life and food secuity for smallholder farmers in Zimbabwe.

The Plant Sciences Group of Wageningen UR is a collaboration between
* Wageningen University, Plant Sciences
* Plant Research International
* Applied Plant Research (PPO)

* Arnold B. Mashingaidze will be defending his thesis Improving weed management and crop productivity in maize systems in Zimbabwe on 12 October 2004 at 16.00 in the auditorium of Wageningen University at Generaal Foulkesweg 1a in Wageningen.