Designer compost with biomass ashes for ameliorating acid tropical soils: Effects on the soil microbiota

In a greenhouse study we investigated the potential of wood ash amended composts to ameliorate acid tropical soils. Three composts (produced with 0%, 8% and 16% wood ash admixture, respectively), and two acid tropical soils, an Oxisol and an Ultisol from Cameroon were used for that purpose. In this paper we report the effects on the soil microbiota at the end of the cropping cycle (100 days soybean plus 100 days fallow). Principal coordinate analysis of denaturing gradient gel electrophoresis patterns of ammonium oxidizing bacteria (AOB) indicated that they were stimulated by addition of compost. AOB communities of the compost treated soils differed from the control ones, and no significant differences among the different composts were found in both soils. Soil type clearly influenced the AOB community. Ester-linked phospholipid fatty acids increased in compost treated soils, up to an ash amendment of 8%. The ratio of cyclopropyl-to-monoenoic precursor (cy19:0 to 18:1 omega 7), which has been proposed as an indicator of stress conditions, decreased upon compost addition and did not differ among the treated soils. Community level physiological profiling indicated an increase in activities after addition of compost, the effect was most distinct for the compost with 16% ash. Based on these results, compost with moderate close of wood ash is considered beneficial to the soil microbiota and could thus be used for ameliorating tropical acid soils. (C) 2010 Elsevier B.V. All rights reserved.