Impact of season, fuel load and vegetation cover on fire mediated nutrient losses across savanna agro-ecosystems: the case of northern Ghana

Abstract

In the subsistence-based, nutrient-poor soils, and fertilizer-limited agriculture of northern Ghana, 45–65 % of land cover is annually burned for purposes of hunting and agricultural land preparation. The effects of burn-season, fractional nutrient losses, combusted plant parts and vegetation type on the fire-mediated nutrient cycling are unclear. We estimate and compare the plant nutrient losses associated with different savanna covers in the early and late burn-seasons and fractionate the losses into actual losses, which should be the cause for concern and the losses due to particulate redistribution. The tissue-moisture and fuel-load elemental concentrations are predominant factors that determine the quantity of fire-induced nutrient losses. About 50 % of total combusted phosphorus, potassium, calcium and magnesium load; and ~99 % of the carbon and nitrogen loads are directly lost from burned sites during burns. Generally, calcium and magnesium are redistributed in particulate forms (~100 and ~90 % respectively) and not lost from the region, phosphorus and potassium are lost in both particulate (~50 and ~75 % respectfully) and non-particulate forms (~50 and ~25 % respectively), whereas the carbon and nitrogen are mostly lost in gaseous forms (~95 %). In the early-burn season high tissue-nitrogen concentration and low phosphorus-concentration renders burn vulnerable to high nitrogen-losses/emissions and low phosphorus-losses per unit burnt biomass. A comparatively high tissue moisture, however, impedes the early burns, resulting in patches of burned and unburned vegetation that reduce the occurrence of late burns and the total losses of plant-nutrients. Early burns reduce the quantity of nutrient losses towards a more secured food production.