Soil Carbon Dynamics under Intensive Cropping Systems

摘要

Soil organic matter is of fundamental importance in maintaining soil fertility. It is a storehouse of essential plant nutrients; affects soil physical, chemical and biological properties; provides energy material for the soil organisms; and plays a vital role for sustainable crop productivity. It also acts as a sink for green house gases between land surface and the atmosphere (Swarup 2008a). The soil organic carbon (SOC) constitutes one of the five principal global C pools, others being oceanic, geologic, atmospheric and biotic. The rate of depletion of SOC in soils of the tropics is exacerbated by the onset of degradation processes including decline in soil structure, leading to crusting/ compaction and accelerated runoff and erosion, reduction insoil biotic activity, leaching of bases and depletion of soil fertility. Although the amount of SOC in soils of India is relatively low, ranging from 0.1 to 1% and typically less than 0.5%, its influence on soil fertility and physical condition is of great significance (Swarup et al. 2000). The cause of low level of organic carbon in Indian soils is primarily due to high temperature prevailing throughout the year. Organic carbon level of soil reaches a fixed equilibrium that is determined by a number of interacting factors such as precipitation, temperature, soil type, tillage, cropping systems, fertilizers, type and quantity of crop residues returned to the soil, and method of residues management. Conversion of land from its natural state to agriculture generally leads to losses of SOC. It may take up to 50 years for the organic carbon of soils in the temperate climate to reach a new equilibrium level following a change in management but this period is much shorter in a semi-arid and tropical environment like India (Swarup 2008b). Considering the nutrient removal by crops and supply through different sources under intensive cropping systems, removal is far greater than supply. It is, therefore, extremely important to maintain SOC at a reasonable stable level, both in quality and quantity by means of suitable addition of organic materials or crop residues. Long-term experiments conducted in different agroecoregions of India involving a number of intensive cropping systems and soil types have provedthat even balanced use of NPK fertilizers helps in maintaining SOC. The encouraging results obtained by integrated use of fertilizers, organic and green manures and bio-fertilizers are providing the leads for future strategies for rational use for continuously enhancing productivity without detriment to the environment. Increasing soil organic carbon content enhances soil quality, reduces soil erosion and degradation, improves surface water quality and increases soil productivity. Thus, carbon sequestration in soils i.e. increasing SOC in agricultural lands through proper management practices provides several environmental benefits in general and sustainability of agriculture in particular. In this paper, attempt has been made to review the work doneon various aspects of land use and management practices under intensive cropping systems on organic carbon dynamics in soils of India.