REGULAR ARTICLE Organic amendments and land management affect bacterial community composition, diversity and biomass in avocado crop soils Nuria Bonilla & Francisco M. Cazorla & Maira Martínez-Alonso & José M. Hermoso & Jorge J. González-Fernández & Núria Gaju & Blanca B. Landa & Antonio de Vicente Received: 21 September 2011 / Accepted: 30 January 2012 / Published online: 23 February 2012 # Springer Science+Business Media B.V. 2012 Abstract Background and aims The avocado-producing area of southern Spain includes conventional orchards and organic orchards that use different organic amend- ments. To gain insight into the effects of these amend- ments, physicochemical properties and microbial communities of the soil were analysed in a represen- tative set of commercial and experimental orchards. Methods The population size of several groups of culturable microorganisms was determined by plating on different selective media. Bacterial community structure was studied by denaturing gradient gel elec- trophoresis (DGGE) Results Commercial composts showed the largest effects, especially the animal compost, enhancing the population sizes of some microbial groups and affect- ing bacterial community structure in superficial and deep soil layers. Moreover, animal and vegetal com- post, manure and blood meal addition are related to high bacterial diversity in the superficial soil layer. Conclusions All of the organic amendments used in this study affect soil properties in one or more of the characteristics that were analysed. Culturable microbi- al population data revealed the most evident effects of some of the organic treatments. However, molecular analysis of soil bacterial communities by DGGE allowed the detection of the influence of all of the analysed amendments on bacterial community com- position. This effect was stronger in the superficial layer of the avocado soil. Plant Soil (2012) 357:215–226 DOI 10.1007/s11104-012-1155-1 Responsible Editor: Harsh P. Bais. Electronic supplementary material The online version of this article (doi:10.1007/s11104-012-1155-1) contains supplementary material, which is available to authorized users. N. Bonilla : F. M. Cazorla (*) : A. de Vicente Instituto de Hortofruticultura Subtropical y Mediterránea “La Mayora” (IHSM-UMA-CSIC). Departamento de Microbiología, Facultad de Ciencias, Universidad de Málaga, 29071 Málaga, Spain e-mail: cazorla@uma.es M. Martínez-Alonso : N. Gaju Departamento de Genética y Microbiología, Facultad de Biociencias, Universidad Autónoma de Barcelona, 08193 Bellaterra, Spain J. M. Hermoso : J. J. González-Fernández IHSM-UMA-CSIC, Departamento de Fruticultura, EE “La Mayora”, 29750 Algarrobo costa, Spain B. B. Landa Departamento de Protección de cultivos, Instituto de Agricultura Sostenible (IAS-CSIC) Finca Alameda del Obispo, 4084-14080 Córdoba, Spain