'Formiguers', a historical system of soil fertilization (and biochar production?)

▶ 'Formiguers' increase labile phosphorus in the soil cover. ▶ Mineral nitrogen recovers in the soil cover of 'formiguers' after initial depletion. ▶ 'Formiguers' provide significant inputs of potassium from ashes and char. ▶ A net loss of organic carbon occurs in 'formiguers'. ▶ Over 15 Mg of biomass were burnt in 'formiguers' per hectare of agricultural land.