Rwanda Cereal Postharvest Losses
In Rwanda, smallholder farmers cultivate maize, rice, sorghum and wheat and there is a little large-scale maize farming in the Northern province. The climate of all provinces is tropical savannah (Aw of the Köppen code). Maize and sorghum are grown in all provinces, rice is grown in all but Northern and wheat is grown in only three of the five provinces (Western, Northern and Southern).
In 2012, total cereal production was about 0.88 million tonnes of which an estimated 17.6% (or 0.15 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 in relative terms as it suffers greater weight loss values (Figure 1). Rwandan cereals may be grown in two (or more) seasons. In Season A, the maize and rice crop may be affected by rain close to harvest time which results in difficulty in crop drying and consequently losses due to mould damage. However, to date farmers have not complained about Larger Grain Borer, an important pest of stored maize which is prevalent in neighbouring Tanzania.
Figure 1: Losses maps for the five provinces of Rwanda in 2012
The postharvest loss profiles (PLPs), used by the APHLIS calculator to estimate losses, are strongly specific to the situation in Rwanda in the case of maize and rice, reasonably specific for sorghum, but much less so for wheat. Specific PLPs give more reliable loss estimates.
In a 2012 questionnaire survey of maize losses at harvest/field drying found that weight loss in harvesting/field drying without rain at harvest is slightly higher than APHLIS (7.8% instead of 6.4%). But with rain at harvest the Rwandan estimate is considerably lower (9.6% instead of 16.3%). There was also an investigation of farm storage but this was not based on a questionnaire survey but supported by a visual scale study by the survey teams. APHLIS returns a weight loss value of zero (0%) if storage is less than four months. However, the Rwanda study observed losses on average 3.2 months after harvest and suggested that the farm weight loss was 4.9%. However, such a high loss so early in storage suggests that probably this damage occurred at previous steps in the postharvest chain and was only then being estimated once the grain had reached storage. The major cause of damage appears to have been rats (2.9%) which is likely to have occurred during harvesting/field drying and platform drying, rather than when the crop is stored in sacks.
Overall the final postharvest loss estimates, with APHLIS defaults and with the new Rwanda figures, are quite similar. Compared to APHLIS estimates, the final estimates when weighted for regions with and without rain at harvest were 17.5 and 16.1%. Notably, key parameter differences are cancelled out in a disguised way. This difference would be greater if there was 1) a greater instance of ‘rain at harvest’ (i.e. in Season A), and/or 2) longer maize storage periods on-farm.