Influence of a six-year organic and inorganic fertilization on the diversity of the soil culturable microrgansims in the Indian mid-Himalayas

•Highest microbial diversity was estimated with PM6 amendment, which was 73% higher than inorganic fertilizer (IF) application.•PM₆ moderated soil temperature better than IF.•Highest soil organic carbon (SOC) was recorded under PM6, which was 9% higher than IF.•SOC was found to greatly influence soil microbial diversity and other soil properties.

Industrial agriculture inputs can diminish soil microbial biodiversity. The use of organic soil amendments may foster beneficial microorganisms. Organic production systems have increased in recent years, but we know little about the effect of these production practices on soil culturable microbial diversity compared to inorganic fertilization. Therefore, the objective of our research was to evaluate the effect of two levels (high and low) of three organic amendments (poultry manure, vermicompost and cattle manure) versus inorganic fertilization (IF) on soil culturable microorganism diversity and selected soil properties after six years under a gardenpea (Pisum sativum var. hortense L.)-french bean (Phaseolus vulgaris L.) system in a sub-temperate soil of the mid-Himalayas. There was at least 31% greater population of beneficial microorganisms with application of high level (6 Mg ha−1) of poultry manure (PM6) than IF in the surface soil layer (0-15 cm depth). The highest soil culturable microbial diversity index was recorded with PM6 (0.562). Application of high level (6 Mg ha−1) of vermicompost (VC6) yielded the highest Trichoderma species count, and PM6 plots had similar values to VC6. The morning and afternoon surface soil temperature moderation during the coldest and hottest weeks with PM6 amendment was 0.50 and 1.73 °C higher over IF, respectively. The soil cracking surface area under PM6 was 112% less than IF (0.311 m2 m−2 area). Application of PM6 provided 38 and 29% higher gardenpea and french bean pod yields than IF, respectively. The soil organic carbon under PM6 in the surface layer was about 9% greater than IF. Soil organic carbon markedly influenced soil culturable microbial diversity, moderation of soil temperature and other soil properties. Thus, application at 6 Mg ha−1 poultry manure for each crop is recommended over inorganic fertilizer for higher soil culturable microbial diversity under gardenpea-french bean system in this region and similar agro-ecologies.