THE CATION-EXCHANGE PROPERTIES AND MICROBIAL CARBON, NITROGEN AND PHOSPHORUS IN SAVANNA ALFISOL UNDER CONTINUOUS CULTIVATION

The study reports on the impact of inorganic fertilisers with or witho ut farmyard manure on the cation exchange capacity (CEC), cationic bal ance and microbial biomass carbon (C), nitrogen (N) and phosphorus (P) in a savanna Alfisol after 45 years of cultivation. Soils for the stu dy were fertilised with N or N + P + K, cow dung (D), D + N and D + N + P + K for 45 years. Inorganic fertiliser significantly reduced CEC, exchangeable cations and upset the cationic balance. The reduction in CEC and exchangeable cations seemed to operate via organic matter depl etion and pH reduction. Similarly inorganic fertiliser stressed microb ial activity evidenced by the low amounts of microbial biomass C, N an d P compared to the soil under native vegetation and the soils fertili sed with D + N and D + N + P + K. From the perspective of the flows of C, N and P through soil microbial biomass, and cation exchange proper ties and prevention of nutritional imbalances involving basic cations, a rational fertilisation program for savanna Alfisols is one that com bines inorganic fertilisers with farmyard manures.