Redox Chemistry and Nutrient Release from Organic Amended Terrace Soil under Anaerobic Incubation

Aims: To examine the changes in pH and Eh values of terrace soils during anaerobic incubation when amended with different organic materials, and to study N, P and S release from different manure and bio-slurry in terrace soil under anaerobic condition.

Study Design: The experiment was carried out following Complete randomized design (CRD) with two replications.

Place and Duration of Study: A laboratory incubation study was conducted in Soil Science Laboratory, Bangladesh Agricultural University, Mymensingh in December 2014 for 98 days.

Methodology: The surface (0-15 cm) soil sample was collected from rice growing field of a selected area of Bhaluka, Mymensingh. The incubation study was carried out using four different sources of organic manures with two replications and five treatment combinations. The changes in soil pH, Eh and release pattern of N, P, and S from some organic materials in terrace soil under anaerobic incubation were investigated during December 2014 to April 2015. The soil was amended with all the treatments at 2g 100 g-1 (air dry basis) soil and incubated for 14 weeks at 25° C. The N, P and S release were determined by the measurement of NH4-N, phosphate P and SO4-S on destructive sampling at every two weeks.

Results: The pH values increased at initial stage but gradually decreased over time to neutral and the soil became reduced with the advancement of incubation, it varies (1-3 weeks) depending on the quality of organic matter used. The reduction potential showed a significant variation among the treatments. Overall, when the pH values were averaged over the weeks, the highest pH value was measured in poultry bio-slurry (PB) amended soil followed by poultry manure (PM), cow dung bio-slurry (CDB) and cow dung (CD) amended soils and the lowest was in control. In case of Eh, the most negative (-133.08) Eh value was measured in PM amended soil followed by poultry bio-slurry (PB), CD and CDB amended soils. Control soil had comparatively positive Eh value. At the end of incubation, the highest amount of NH4-N found in CDB followed by CD, PM, PB and the lowest was in control; the highest amount of phosphate P found in PB followed by PM, control, CDB and CD; the highest amount of SO4-S found in PB followed by PM, CD, CDB and the lowest was in control.

Conclusion: PB is the best source of organic amendment with respect to release of P and S, whereas CDB showed the best performance in release of N. Nutrient release and availability in reduced environment in terrace soil are a function of soil redox chemistry which is influenced by the quality and quantity of organic matter.