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

Abstract

Erratum paru dans Agroforestry Systems = ISSN 0167-4366. - (2015)vol.89:n°1 p. 95-96. 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, Pav), 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, Pav 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 Pav. These results suggest that RW stimulated biological activity, leading to P immobilization and C mineralization, but had little effect on yields. (Résumé d'auteur

Ramial wood amendments (Piliostigma reticulatum) mitigate degradation of tropical soils but do not replenish nutrient exports

“…Synthetic fertilizers were added to the straw treatments so that nutrient supply in wood and straw treatments was the same (2007–2009). One additional treatment with buried woody material received extra synthetic N (WoBu3t+N), and there was an untreated control plot (results reported in Barthès et al, ). From 2010 through 2013, the experimental layout remained the same, but the focus of the experiment shifted from an objective of comparing effects of two sources of organic amendments (straw vs. wood) to an objective of comparing two different rates of the same source of organic matter (only woody material), featuring a “low‐RW” rate of 3 Mg FM·ha −1 ·yr −1 (3t) versus “high‐RW” rate of 12 Mg FM·ha −1 ·yr −1 (12t).…”

“…Hochst.) on soils and crops, Barthès et al () reported no significant yield differences with application of 3 Mg fresh mass (FM) ha −1 ·yr −1 of buried or mulched material on sorghum yields, as compared with control or crop residue application. From that experience, conducted between 2007 and 2009 at Gampéla, Burkina Faso, the experiment described in this paper was partly modified by introducing higher rates of ramial wood (RW) application in 2010 (12 Mg FM·ha −1 ·yr −1 ), incorporated or as mulch, and continued until 2013.…”

Typologie et logique socio-économique des systèmes de culture associant céréales et légumineuses dans les agro-écosystèmes soudano-sahéliens du Burkina Faso

“…Les faibles rendements ici rapportés pour le sorgho ou le mil ne sont pas étonnants puisqu'on se situe en général sur des sols très pauvres, tandis que 57% des EA utilisent des quantités de fumier inférieures à 0,5 t ha -1 ; les doses apportées ne dépassent guère 2 t ha -1 . Barthes et al (2015) rapportent qu'une amélioration du nombre de grains induite par un apport de nutriments peut entraîner une compétition pour l'eau en fin de cycle, affectant le nombre de grains et l'efficience des nutriments vis-à-vis du rendement du sorgho dans ces agro-systèmes.…”

Restoration of soil microbes and organic matter through tropical reforestation

“…In addition, attempts to increase SOM by adding more organic residue to agricultural systems should not have failed (Barthès et al, 2015;Page et al, 2013) if energy limitation were responsible for SOM decomposition. Arguing that SOM decomposition is incentivised by nutrient limitation rather than energy limitation leads to the prediction that SOM will increase with fertilisation, which occurs in some situations Liu and Greaver, 2010) but is at odds with the general trend of lower SOM in fertilised agricultural systems, including low-intensity pasture, when compared with old-growth forest.…”

“…This in turn explains SOM loss in agricultural systems as partially caused by limited input of organic substrate inducing energy starvation of soil microbes, incentivising them to invest in SOM attack. However, low C/N/P/S ratios of SOM make it a better source of nutrients than energy (Kirkby et al, 2011), so if soil microbes have the capacity to decompose SOM under energy-starved conditions and gain energy in the process, they ought to break it down under old-growth forest where more energy is available to fuel SOM decomposition, and nutrients are comparatively more limiting.In addition, attempts to increase SOM by adding more organic residue to agricultural systems should not have failed (Barthès et al, 2015;Page et al, 2013) if energy limitation were responsible for SOM decomposition. Arguing that SOM decomposition is incentivised by nutrient limitation rather than energy limitation leads to the prediction that SOM will increase with fertilisation, which occurs in some situations Liu and Greaver, 2010) but is at odds with the general trend of lower SOM in fertilised agricultural systems, including low-intensity pasture, when compared with old-growth forest.…”