Nutrients limiting microbial growth in a tropical forest soil of Ghana under different management

Respiration profiles were analysed following addition of a carbon source (glucose), nitrogen (NH4NO3), and phosphorus (H2PO4-/HPO42-) to three different soils from the tropical forest belt of West Africa. In all stands (virgin forest, rubber, and cocoa plantation) microbial growth was limited by C whereas N did not limit growth in either C- or C + P-amended soil. The P-limitation indicated in C-as well as C + N-amended incubations was significant for virgin and cocoa soil. In soil from the cocoa stand. microbial growth started earlier when P was added together with C as compared to C-addition alone. This difference in timing of microbial growth caused by P-addition not observed in the other stands suggests that the microbial community in the cocoa soil differed functionally from that in the other soils in accordance with the high nutrient demand of cocoa as compared to rubber trees. The study therefore provides direct evidence for the P-limitation often claimed in tropical soils as opposed to a N-limitation found in temperate soils. (C) 1998 Elsevier Science B.V. All rights reserved.