Interrelationships between microbial and soil properties in young volcanicash soils of Nicaragua

The activity and biomass of soil microorganisms were measured in soils from 25 different arable sites in the Pacific region of Nicaragua with the obje ctive of elucidating their interrelationship with soil textural and soil ch emical properties. All soils developed from recent volcanic deposits but di ffer in their particle size distribution. Short-term phosphorus fixation ca pacity varied widely and was, on average, 11% of added P. In contrast, long -term P fixation capacity varied within a small range of around 55%. Mean b asal respiration was 8.6 mug CO2-C d(-1) g(-1) soil, average contents of bi omass C, biomass P, and ergosterol as an indicator of fungal biomass were 1 16, 1.95, and 0.34 mug g(-1) soil, respectively, They were all, except biom ass P, significantly lower in the sandy than in the loamy soils. The mean b iomass C-to-soil C ratio was 0.69%, the mean metabolic quotient 95 Mg CO2-C d(-1) g(-1) biomass C, the mean ergosterol-to-biomass C ratio 0.31% and th e mean biomass C-to-P ratio 107. The very low ergosterol-to-biomass C ratio indicates that fungi contribute only a relatively small percentage to the microbial biomass. The biomass C-to-P ratio exceeded considerably the soil C-to-total P ratio. Metabolic quotient qCO(2) and ergosterol-to-biomass C w ere both negatively correlated with biomass C-to-soil C ratio and clay cont ent, indicating positive correlations between qCO(2) and ergosterol-to-biom ass C ratio and between biomass C-to-soil C ratio and clay content. Key pro blems of soil fertility and soil quality in Nicaragua are low availability of soil organic matter and phosphorus to soil microorganisms, which are mag nified by a low percentage of fungi, probably reducing the ability of soil to provide nutrients for plant growth. (C) 2001 Elsevier Science Ltd. All r ights reserved.