Pilot projects on use of waste products in periurban agriculture

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The results from Bamako indicate that the the use of compost made from urban solid waste can be agronomically and economically attractive for farmers. Average yield improvements ranged from about 20% to almost 60% when compost was applied at 6 kg/m2 as compared to using manure at the same application rate (see Figure 11). Indeed, on average, yields did also not differ signficantly from the manure control plots when compost was applied at the lower rate of 5 kg/m2, a hypothesis that the farmers had proposed themselves. The improved performance of the compost is probably partly due to the use of the same type of manure as co-composter, ensuring that organic matter and nutrient content were higher.

In general, farmers in Bamako were very pleased with the results of the experiment. They recognised that the increased cost of the compost, in comparison to manure, was more than compensated by the performance. Most interestingly, the farmers had ideas about how to vary the application rates of the compost and to conduct trials with different crops and crop rotations, to make best use of the longer-term nutrient release and improvement in soil structure. It appeared that farmers in Bamako were planning to continue experimenting with the technique and with materials themselves.

In Ouagadougou, the agronomic results of the use of compost as a soil conditioner were more promising for the staple crops in the peri-urban site of Kamboinse than for the urban horticultural crops. Yields declined on average more than 20% with respect to the control of manure (see Figure 12). In contrast to Bamako though, the dosage rate of the compost was much lower (2 kg/m2), although the average dose of manure applied by farmers was also lower than in Bamako. In addition, the compost used for the experiments in Ouaga was based on a poorer combination of compostable materials.

The results with the staple crops show, on the other hand, an average yield gain approximately 20% across the three crops in the experimental plots (see Figure 13). As a whole, the Kamboinse trials indicate the agronomic value of compost over non-composted waste. But economic analysis shows that the use of the compost, at a price of approximately 15 FCFA/kg is not attractive to the those staple crop farmers, particularly since most of them are producing for subsistence. At a price of 1-5 FCFA/kg, the compost becomes economically interesting (depending on the crop) and maybe feasible for these cash-constrained farmers.

Figure 10: Farmer with experimental cabbage plots, Djelibougou, Bamako

Figure 10: Farmer with experimental cabbage plots, Djelibougou, Bamako

Figure 11: Improvement in yields from compost use

Figure 12: Horticultural experiments, Ouagadougou

Yield change with compost - horticultural crops (Ouagadougou)

Lettuce — Paspanga

1 1

Cauliflower Paspanga

Hib. sabd. Kossodo

Carrot —I Kossodo

Crops

The further analysis of soil samples from the Kamboinsé experimental plots revealed no evidence of different accumulation of heavy metals due to the addition of the compost. Almost all of the samples, whether from the plots with uncomposted or composted waste fell within acceptable norms for heavy metal content. Thus there is not yet any indication that the application of either untreated or composted municipal solid waste is leading to a contamination of soil with heavy metals in the peri-urban zone of Ouagadougou.

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