Trade-offs in maize seedling losses in African grasslands

In central Cameroon, there are strongly defined savanna-forest boundaries. Imperata cylindrica, a pantropical Poaceae weed, is also one component of these savannas. There is a well-known discourse that I. cylindrica presence indicates poor soils and smallholder farmers report low crop establishment rates on land dominated by I. cylindrica. Yet, according to farmers one of the major limiting constraints is not soil fertility but seedling damage from birds, rodents and stem-cutting termites. It was hypothesised that losses might vary depending on both agronomic techniques used and vegetation management. In a two-factorial randomised complete block design, the effects of glyphosate herbicide clearance versus manual machete clearance and burning of plant residues versus mulching were assessed on Zea mays (maize) post-emergence seedling losses by birds, rodents and termites. Overall, birds caused greatest post-emergence losses in the first three weeks after planting (on average, 29%), followed by rodents (14%) and termites (11%). Glyphosate use significantly reduced seedling losses from birds (by 16%) suggesting that either birds avoided areas with lower vegetation cover or that such weedy vegetation is an attractant. For termites, glyphosate use significantly increased damage (13% damage in glyphosate plots compared with 8% in no-herbicide plots). Seedling damage by termites was greater in the burnt plots and where herbicide was applied. One compromise would be to avoid burning, so ensuring mulch cover to provide alternative food for termites, yet ensure vigorous weeding.