Zimbabwe case study
Zimbabwe Cereal Postharvest Losses
In Zimbabwe, farmers cultivate maize, millet, sorghum, wheat and barley. The climate in provinces 1-4 and 8 (Fig. 1) is humid sub-tropical (Cwa and Cfa of the Köppen code) while provinces 5-7 are hot and semi-arid (Bsh). Maize, millet and sorghum are grown by smallholders in all provinces. Wheat and barley are grown under irrigation but data are not currently available to allow them to be included in the loss calculations. Some maize is grown on large farms.
In Zimbabwe, maize and other cereal crops are normally grown in only one season with harvests in April/May for maize, sorghum and millet while wheat and barley are winter crops and harvested in October/November. Most of the harvesting occurs in May which normally marks the commencement of the dry season so that damp weather at harvest is not usually a problem. The Larger Grain Borer (LGB) is known to be present as a pest in Zimbabwe and causes losses specially in the major maize producing areas of the Mashonaland provinces. Although some farmers are taking action to prevent losses (such as admixing insecticide or selling their grain early) losses are believed to be significant.
In 2012, cereal production of maize, millet and sorghum was about 1.4 million tonnes of which an estimated 18.2% (or about 0.25 million tonnes) was lost in postproduction activities. Most of this loss is contributed by maize both in absolute terms, i.e. because it has by far the largest production, and also in relative terms as it suffers a greater proportion of weight loss (Fig. 1).
Figure 1: Losses maps for eight provinces of Zimbabwe in 2012
In the case of maize, the postharvest loss profiles (PLPs) that are used by the APHLIS calculator to estimate losses, are reasonably specific to the situation in Zimbabwe. They are less specific for millet and sorghum. For all cereals only in the case of farm storage are loss values derived from mostly measured estimates. Other loss estimates are derived from questionnaire surveys which tend to be less accurate.
In the case of maize there has been some variation in loss values since 2008 largely due to differences in whether or not LGB was reported as a significant pest. In the case of millet and sorghum the values since 2008 have remained static since there has been no annual variation in seasonal factors used in the APHLIS calculation. There are however differences between provinces. In the case of maize the losses are on average 2% to 3.5% lower in Province 8 (Midlands) because the farm storage period is estimated to be only 5 months rather than 8 months; the longer period leading to significantly more damage by insect pests. In the case of millet and sorghum there is also a consistent difference between provinces 5, 6 and 7, which have a hot dry climate, and the others since the hot dry climate is associated with lower storage losses.
For all three cereals there is little difference between provinces in the contribution each link in the postharvest chain makes to the overall cumulative loss. The largest single contribution is harvesting and field drying, followed by platform drying and storage which are broadly similar in magnitude.