Nutrient cost of soil carbon sequestration and its implication in nutrient turnover

Abstract

Soil carbon sequestration is an underexplored potential of soils, which are capable of acting as carbon sinks and locking carbon to mitigate the impacts of global warming. Both agroforestry and agricultural systems hold significant potential for carbon sequestration. However, the conversion of added carbon into a stable humified fraction requires not only carbon but also essential building blocks such as nitrogen (N), phosphorus (P), sulfur (S), and several micronutrients. It is estimated that for the sequestration of 10,000 kg of carbon in stable humus, approximately 833 kg of nitrogen, 200 kg of phosphorus, and 143 kg of sulfur are needed, based on a carbon-to-nitrogen ratio of 12:1, a carbon-to-phosphorus ratio of 50:1, and a carbon-to-sulfur ratio of 70:1. A lack of these nutrients can not only limit plant biomass production but also restrict the assimilation of carbon into the stable fraction of soil organic matter (SOM) in the absence of the additional nutrients required beyond those needed for crop growth. Therefore, to fully harness the potential of soil carbon sequestration, additional nutrients must be supplied to the soil to facilitate the conversion of added carbon from residues into more stable and humified products. Unfortunately, the cost of these nutrients is often overlooked in studies on carbon sequestration. This article highlights the importance of carbon sequestration, its potential, and the nutrient inputs required alongside residue addition to ensure the effective conversion of carbon into the stable, humified fraction in the soil.