Soil management for regulating C pools: Perspective in tropical and subtropical soils

Abstract

Worldwide tropical region covers an area of about 8 billion ha. Tropics are increasingly threatened by intensive and inappropriate land use. According to some global data, land use change has resulted in losses of 25-50% of SOC in topsoil. The objective of this chapter is to highlight and synthesize the soil management options, which help to sequester carbon in tropical and subtropical regions. Some improved soil management practices for capturing and storing carbon with favourable impact on capturing carbon include growing cover crops, sowing crops with conservation tillage, maintaining balance level of soil fertility, and converting marginal and degraded lands to restorative land uses. A meta-analysis of 137 studies largely from tropical countries showed that the cover crop has the capability of annual change rate of 0.32 ± 0.08 mg ha-1 year-1 in the topsoil. Long-term conservation tillage experiments revealed that the improvement in soil organic C was proportionately higher in poorer soils than in soils with inherently higher organic C content. Integrated nutrient management involving addition of organic manures/composts along with inorganic fertilizers results in improved soil aggregation and greater carbon sequestration, especially in macroaggregates. Agricultural intensification also enhanced C-sequestration as increase in one tonne productivity of rice and wheat, resulting in a C-sequestration of 0.85 mg ha-1. Likewise, conversion of degraded croplands to grassland can result in an annual increase of 3% or more SOC concentration. Through this conversion, C-sequestration rate of 0.3-0.8 mg ha-1 year-1 was achieved in tropical West Africa. Some researchers even reported a higher sequestration rate between 1.2 and 1.7 mg ha-1 year-1 in the case of land conversion from degraded cultivated land to grassland. Maximizing the productivity of existing agricultural land and applying best management practices to that land would slow the loss of soil C. Soil C management needs to be considered within a broader framework of sustainable development. Widespread adoption of RMPs by resource-poor farmers of the tropics is urgently warranted.