Effect of ramial wood amendment on sorghum production and topsoil quality in a Sudano-Sahelian ecosystem (central Burkina Faso)

In Sudano-Sahelian agriculture, organic amendments are often limited by resource availability. Small branches (ramial wood, RW) represent an organic resource found in many landscapes but little is known about their effects. This field trial (2007–2009) studied the effects of RW or straw at low application rate (0.69 Mg C ha −1 year −1 ) on topsoil carbon (C), nitrogen (N) and available phosphorus (P, P av ), termite cast abundance, and sorghum yield. Straw and RW were chopped and either buried (StBu, WoBu) or mulched (StMu, WoMu). Mineral fertilizers were added to straw so that RW- and straw-amended plots received similar applications of C, N, P, and potassium. Another treatment had RW buried with additional N (WoBuN), and there was a control (Ctrl). Branches came from Piliostigma reticulatum , very common in the area. The treatments had little significant effect on topsoil and crop, owing to the low application rate and spatial variability. However, P av was significantly lower with buried than mulched amendments in 2009, and decreased significantly over time in Ctrl and with buried amendments. Topsoil C also decreased significantly with time in WoMu. Significantly more termite casts were observed with RW. The sorghum yield averaged 0.87 Mg DM ha −1 in 2007 and then decreased. The treatments affected yield significantly in 2008 only: it was higher in WoBuN and StBu than in Ctrl. In 2009, the yield was mainly affected by initial topsoil P av . These results suggest that RW stimulated biological activity, leading to P immobilization and C mineralization, but had little effect on yields.