Organic Amendments and Elemental Sulfur Stimulate Microbial Biomass and Sulfur Oxidation in Alkaline Subtropical Soils

Kouser Majeed Malik,Naeem Khan,Khalid Saifullah Khan,Motsim Billah,Asia Munir,Muther Mansoor Qaisrani,Azhar Mahmood Aulakh,Shah Rukh,Mohammad Saleem Akhtar,Majid Rahim,Sadia Alam

doi:10.3390/agronomy11122514

Abstract

Sulfur deficiency arising due to intensive cultivation, use of sulfur free fertilizers and reduction in atmospheric sulfur depositions has become a major issue limiting crop production in many parts of the world. Elemental sulfur could be a good source of available S, but its slow oxidation is a problem for its efficient use as a sulfur fertilizer. Main objective of the study was to assess the effect of organic amendments (OA) and elemental sulfur (ES) on microbial activities, sulfur oxidation and availability in soil. A laboratory incubation experiment was carried out for a 56 days period using two sulfur deficient alkaline soils. Organic amendments (OA), i.e., farmyard manure (FYM), poultry litter (PL) and sugarcane filter cake (SF), were applied (1% w/w) with or without elemental sulfur (ES) at 50 mg kg−1. Application of ES alone or in combination with OA significantly increasedCO2-C evolution, microbial biomass, and enzyme activities in the soils, except dehydrogenase activity (DHA) which was not affected by ES application. Combined application of OA and ES had a more pronounced effect on microbial parameters compared to ES or OA applied alone. Ratios of dehydrogenase activity-to-microbial biomass C and arylsulfatase activity-to-microbial biomass C were high in ES+FYM and ES+SF treatments, respectively. Elemental sulfur got sufficiently oxidized resulting in significant improvement in plant available S. Relatively more ES was distributed into C-bonded-S than ester bonded-S. Increase in sulfur availability in ES+OA amended soils was the combined function of sulfur oxidation and mineralization processes through improved microbial activity.

Highlights

Sulfur (S) is an essential macronutrient required for normal growth and metabolic functions in plants
Total N, total phosphorus and total zinc contents were higher in poultry litter (PL) while the total iron and total manganese contents were higher in farmyard manure (FYM) as compared to the other two amendments
The ratio of total organic C to total S was lowest in sugarcane filter cake (SF), whereas the ratio of total organic C to total N, and total organic C to total P was lowest in the P

Summary

Introduction

Sulfur (S) is an essential macronutrient required for normal growth and metabolic functions in plants It is an integral part of many biological and structural compounds of living entities and is directly involved in protein synthesis as a constituent of S containing amino acids like methionine and cysteine [1]. Sulfate form is readily available to crop plants but being mobile in nature is susceptible to leaching losses in alkaline and sandy soils which inherently have low sulfate retention [5]. Under these conditions, elemental S attains importance as a fertilizer resource due to its high S content, slow S releasing property and low leaching. Knowledge of sulfur oxidation and its distribution into various forms in soil is important for efficient use of elemental sulfur as a fertilizer

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