Effect of Pesticides and Chemical Fertilizers on the Nitrogen Cycle and Functional Microbial Communities in Paddy Soils: Bangladesh Perspective.

The concept of the Nitrogen (N) cycle has been modified over the years based on certain new pathways, including comammox, anammox, and DNRA (dissimilatory nitrate reduction to ammonium). Comammox, nitrification, anammox, denitrification, DNRA, and nitrogen fixation pathways play key roles in the N cycle in paddy soils. Pesticides and chemical fertilizers' effects on the N cycle in paddy soils together with the possible manifestation of these newly discovery pathways are the focus of this review. Both chemical fertilizers and pesticides' overuse affect nitrifying archaea/bacteria and denitrifying and anammox bacteria, while heavy metals affect the nitrification rates in paddy soils. To add extra value to this study, we quantified the comammox amoA single copy gene from the Nitrospira strain 'Nitrospira inopinata'. This review will help researchers access the latest information on the N cycle, particularly in the light of the most recent discoveries.

Effect of Manure Application on Net Nitrification Rates, Heavy Metal Concentrations and Nitrifying Archaea/Bacteria in Soils.

In this study, we determined the effect of manure application on net nitrification rates (NNRs), heavy metal concentrations (HMCs), and abundance of ammonia-oxidizing archaea (AOA)/bacteria (AOB), and nitrite-oxidizing bacteria (NOB) in soil. HMCs were measured by atomic absorption spectroscopy. Abundance of AOA, AOB, and NOB was enumerated by q-PCR. NNRs ranged from 2.8 to 14.7 mg kg-1 h-1 and were significantly (p < 0.05) increased in manure soils as compared to control soils. NNRs were affected by pH 7 and temperature 30°C. Cd, Fe and Pb concentrations were classified as excessively polluted, moderate contamination and slight pollution, respectively, in the manure soils. NNRs and concentrations of Fe and Pb were significantly (p < 0.00) positive correlated, but Cu and Cd were significantly (p < 0.00) negative correlated with NNRs. Application of manure significantly (p < 0.05) increased HMCs (Fe, Cu, and Pb), which have indirect and direct effects on NNRs and nitrifying bacteria.