Impact of Organic Amendments and the Microbial Inoculants on the Population of Soil Microorganisms and Their Influence on the Growth of Manilkara hexandra (Roxb)

Abstract

Soils containing a high microbial diversity are characteristic of a healthy ecosystem. Becausesoil microbial communities are the driving force behind regulating soil processes it isimperative to have a better understanding of the impacts of organic amendment and microbialinoculant addition on the population of soil microorganisms and also their influence of plantgrowth. A pot experiment was carried out in the greenhouse at the Rajarata University,Mihinthale, Sri Lanka. The 2.5 kg of surface soils (0-15 cm in depth) of the field inMihinthale was collected into each pot. Water content was set to 75% of total water capacity.Ten treatments were applied in randomized complete block design with four replicates andthe control. Treatments included applications of field soil only as control,arbuscularmycorrhizal fungi (AMF), “Jeewamurthum”, biochar, compost and inorganicfertilizer, combinations with AMF and all microbial inoculants together.

Five seeds of Manilkara hexandra were sown per pot and three seedlings were removed afterthree weeks. Seed germination rate and relative growth rate of Manilkara hexandra wereestimated. Total bacterial and fungal counts (CFUs) in 1 g of dry soil samples werecalculated by following standard total plate counts. Seedlings were uprooted after 21 weeksand percentage AMF colonization of roots was estimated and shoot dry biomass wasmeasured. According to Generalized test result (P<0.05), statistically significant treatmenteffect was established for total bacterial counts (P=0.01) and there was no significanttreatment effect for fungal counts (P=0.086) of the soil. Further mean comparison resultsshowed that compost with AMF added treatment had the highest bacterial population.Significantly different treatment effect of percentage AMF colonization (P=0.022) wasobserved, further mean comparison results revealed that AMF added treatment had thehighest performance in this category. Generalized test result revealed that there was asignificant treatment effect (P<0.05) from treatments to the percentage seed germination rateof Manilkara hexandra and AMF and compost addition treatments showed the highestperformance. However, AMF and compost together treatment showed significantly high(P<0.05) relative growth rate. AMF added treatment established significantly high (P<0.05)shoot dry biomass after 21 weeks of seedling growth. Organic amendments and microbialinoculants enhance soil microbial communities and also have positive impact on the seedgermination and seedling establishment of Manilkara hexandra.