Straw returning and nitrogen fertilizer application to paddy soil influence hydroxyl radical formation in the soil surface water

PurposeIn paddy field environment, reactive oxygen species could be produced in surface water by light illumination, because large amounts of photoactivated species exist in the surface water, which could be affected by agronomic measure. In this study, hydroxyl radical ((OH)-O-center dot) formation affected by straw returning and nitrogen fertilizer application in paddy soil was investigated in the soil surface water.MethodsIn this study, laboratory simulation experiments were conducted to investigate the effect of straw returning (wheat straw and rape straw, 1% w/w) and nitrogen fertilizer application (urea, 130 mg/kg) on (OH)-O-center dot production in the surface water of paddy field. The amount of (OH)-O-center dot was quantified via chemical probes.Results and discussionIt found that straw returning, regardless of straw type, decreased the formation of (OH)-O-center dot, while nitrogen fertilizer application increased (OH)-O-center dot formation. Correlation analysis showed that dissolved organic matter (DOM) and NO3- affected (OH)-O-center dot production during the early stage of incubation (0-14 days), whereas NO2- produced by denitrification had a great effect on (OH)-O-center dot production at the later stage (14-63 days). Although DOM content increased after straw return, NO3- and NO2- decreased sharply, which possibly accounted for the lower (OH)-O-center dot formation in the straw-amended paddy soil.ConclusionThis study provides a theoretical basis for (OH)-O-center dot formation in the surface water of paddy fields, which is essential for understanding the transformation of pollutants in such environments.