Effects of mulching with Azadirachta indica and Albizia lebbeck leaves on the yield of sorghum under semi-arid conditions in Burkina Faso.
From 1988 to 1990, leaves from Azadirachta indica and Albizia lebbeck were used as mulch for sorghum (Sorghum bicolor) grown at a site on the central plateau in Burkina Faso. The site had previously been a fallow and the soil was a luvisol. The most common production system in this region is the cropped parkland savanna and Azadirachta indica is often found in clusters close to houses or in nearby fields. Five different application modes were evaluated, each representing a different combination of application timing and mulch composition. In one of the modes leaves were combined with sorghum straw. Leaf quantities applied corresponded to dosages of 25, 50 and 75 kg N ha-1 in all five modes. Dosage had a significant influence on yield all three years. The mulching effect increased progressively over the years and was more pronounced the higher the dosage. Mean grain yields obtained with the highest dosage, relative to an unmulched control, were 203, 364 and 422%, respectively, for the three years. Application timing had a significant influence on yields in 1988 and 1989, but the response was not consistent. Differences in response were attributed to variation in the rainfall distribution. Mulch composition did not have a significant influence on yield during any of the three years. Of the five modes evaluated, the ones producing the highest yields over the three-year period of study were leaves of Azadirachta indica applied (i) at sowing and (ii) 4-6 weeks after sowing. Yields decreased on both the treated and untreated plots between 1988 and 1989. On the treated plots, yield generally increased again in 1990. This increase was attributed to a residual effect of the mulch. The residual effect probably only explained part of the large difference in yield between treated and untreated plots. It is, therefore, suggested that most of the nutrients released from the mulch were used by the plants during the same season, which increased production. Furthermore, the mulch layer could have reduced evaporation and thus increased the retention of soil water.