Balance of nitrogen in plant-soil system with the presence of Compost+Charcoal

The benefit of charcoal for growing crops has been well established. In a tropical suboptimal soil, however, use charcoal only may not provide sufficient nutrient to crops. Therefore, adding compost with charcoal is expected to not only provide nutrition also improve soil biology and chemical properties. A greenhouse experiment was carried out to investigate the effect of Compost+Charcoal (CC) on soil properties and their effect on plant top biomass of maize (Zea mays) and cowpea (Vigna unguiculata). The treatments were maize and cowpea grown on a) soil only, and b) treated with CC only. In order to estimate the N balances in the plant-soil system, main parameters were measured, namely the amount of nitrogen (N) from soil mineralisation, leached N and N uptake. The results showed that the use of CC caused the net N balance in the plant-soil system to decrease. The negative N balance may be due to N loss via denitrification resulting from higher water holding capacity of the soil treated with CC than soil only. The N loss due to denitrification might be minimised by managing the watering system when charcoal is present in the soil. It was also found that CC application only significantly increased dry matter yield and N uptake of maize, but, it did not have the same result with cowpea. The effect of CC in decreasing the leaching of N was only noticed in the early growth of maize and cowpea. However, the significant decrease of N leaching was affected by maize and cowpea