Soil Organic Carbon Dynamics Under Tropical Garden Land Systems

ABSTRACT The organic carbon (OC) status of three continuously cropped permanent manurial experiments, under different cropping systems, over a period of time is discussed in this paper. The Old Permanent Manurial Experiment (OPME) was originally an irrigated experiment started in 1909 and in 1937, converted into a rainfed experiment (at this time the cropping system was converted from two crops per year into a single crop per year). The New Permanent Manurial Experiment (NPME) was started in 1925 and was conducted in an irrigated system with one set of treatments receiving 2 t ha-1 of cattle manure since its inception. These two experiments were conducted with different nutrient input management systems of single inorganic nutrients and their combinations. The effect of these treatments on the OC status of the soil was evaluated. Along with these, the changes in the OC status of another irrigated long term fertilization trial which has been conducted since 1972 under the intensive cultivation system with three crops per year were studied. The results obtained in the three experiments showed that there was a build up in the OC status of the soil for the balanced application of N, P, and K combined with an organic manure. Among the inorganic fertilizer treatments, the combined application of all the three major nutrients (N, P and K) resulted in a higher OC status, compared to the application of single nutrients. This may be due to better growth and a higher amount of root residues added after the harvest of each crop, over a period of time. But, in both OPME and NPME, there was a decline in the OC content after seven years and a build up has happened in the last nine years. Under the intensive cropping system of cultivation, the soil organic carbon build up occurred in all the treatments, including the unmanured control, and was the maximum for the combined application of inorganics and organics (100% NPK + Farm Yard Manure (FYM)). The increase in OC is attributed to enhanced root biomass over a period of 30 years.