Microbial activities in soil cultivated with corn and amended with sewage sludge

Rosana Faria Vieira,Ricardo Antônio Almeida Pazianotto

doi:10.1186/s40064-016-3502-9

Abstract

Background One of the main concerns related to the increasing use of sewage sludge in the soil is the possible presence of excess nutrients, which could cause environmental problems and detrimental effects on the soil microorganisms, considered essential to soil nutrient cycling. Thus, the objective of this work was to evaluate the microbial biomass and activity and some chemical characteristics of one specific tropical soil, classified as Dark Red Distroferric Latosol, of a loamy/clayey texture, in a long-term field experiment using anaerobically digested household sludge amendment. The sludge doses applied were the recommended dose and 2, 4 and 8 times the recommended dose. The authors hypothesized that the frequent application of this compound to the soil, even when using the recommended dose, could affect the available phosphorus (Pav) and heavy metal contents of the soil, resulting in concentrations above the needs of the culture as well as negatively affecting the activity of the soil microorganisms.ResultsThe results demonstrated that successive applications of sludge, calculated considering the recommended dose of N for corn, did not increase the soil Pav contents in relation to the treatment in which the fertilizer was applied considering the nutrient needs of the culture, contrary to what happened with the highest sludge doses. The Cr, Ni and Cu contents increased with increase in sludge dose, but did not surpass the limits considered inadequate. There were no accentuated differences between the treatments with respect to microbial biomass C. Basal respiration and the FDA hydrolysis were considered to be the parameters that most differentiated the effect of increasing sludge doses on the microbial activity.ConclusionThe application of a sludge dose to a tropical soil, based on the recommended dose, did not affect the Pav or heavy metal contents of the soil even after years of application. Since there were no differences between the treatments with respect to the Cmic values, to the contrary of what happened with the other microbiological parameters evaluated, the possibility of changes in the composition of the microbial community with the higher sludge doses was considered.

Highlights

One of the main concerns related to the increasing use of sewage sludge in the soil is the possible presence of excess nutrients, which could cause environmental problems and detrimental effects on the soil microorganisms, considered essential to soil nutrient cycling
The greatest impact caused by the application of increasing sludge doses to the soil was the accentuated increase in the Pav and heavy metal contents, these latter elements were below the mandatory limits allowed by Brazil (2006)
There were no differences between the MF and 1FS treatments with respect to the heavy metal contents or the Pav of the soil, which fails to confirm the initial hypothesis that continued sludge applications, even when using doses considered adequate, could increase the P and heavy metal contents of the soil

Summary

Introduction

One of the main concerns related to the increasing use of sewage sludge in the soil is the possible presence of excess nutrients, which could cause environmental problems and detrimental effects on the soil microorganisms, considered essential to soil nutrient cycling. As a result of various inconveniences in dumping sewage sludge in landfills or incinerating it, its application in agriculture has emerged as a promising technique The incorporation of this residue into the soil allows for better use of the nutrients by the plants, since they are in the organic form and are liberated gradually, providing the nutritional requirements of the plants in the most adequate way throughout the cycle of the culture (Claassen and Carey 2007). Other benefits associated with the use of sewage sludge in agricultural areas are improvements in the physical properties of the soil (Claassen and Carey 2007) Such residue acts as a cementing agent for aggregate formation and stabilization (Sundermeier et al 2011)

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