Impact of ecological and conventional arable management systems on chemical and biological soil quality indices in Nicaragua

We measured the activity and soil microbial biomass in volcanic ash soils f rom 10 sites under ecological fanning (no pesticides, shallow ploughing, mu lching, organic fertilizers, crop rotation) and 15 sites under conventional farming (pesticides, mineral fertilizers, deep ploughing). Our aim was to determine the effects of management system on soil quality and soil fertili ty in tropical Nicaragua in relation to soil type. None of these sites were irrigated. Conventional management led to significantly increased amounts of total soil P and a significantly larger biomass C-to-P ratio compared to ecological management. Almost all of the other microbial properties, i.e. soil basal respiration, ergosterol and biomass C were significantly improve d by ecological management. Also the biomass C-to-soil C ratio was signific antly increased, but not the metabolic quotient qCO(2) or the ergosterol-to -biomass C ratios, indicating that the positive effects of ecological manag ement were mainly due to increased C input rates. Biomass C, ergosterol, an d basal respiration rate were significantly larger at the loamy sites than at the sandy sites, The same was true for the biomass C-to-soil C ratio, bu t the ergosterol-to-biomass C ratio and the metabolic quotient qCO(2) were larger at the sandy sites. Our results demonstrate that ecological manageme nt is an important tool for soil conservation and sustainable management of arable land in Nicaragua. However, the decline in total P and the low P av ailability to soil microorganisms need attention as a precaution against P deficiency. The improvement was greatest at the loamy sites, although the e ffects of management system were in most cases independent of the soil type . For this reason, ecological management should be preferably promoted on l oamy soils. (C) 2001 Elsevier Science Ltd. All rights reserved.