Amendment with industrial and agricultural wastes reduces surface-water nutrient loss and storage of dissolved greenhouse gases in a subtropical paddy field

Paddy fields are important ecosystems for supporting human life. They are frequently fertilized more than necessary for providing high yields of rice (Oryza sativa), so nutrients are lost by leaching into aquatic ecosystems, which become eutrophic. Rice production is also an important source of greenhouse gases (GHGs). Mitigation of the nutrient losses and GHG emissions from paddy fields is crucial both for the sustainability of rice production and the reduction of adverse environmental effects. We examined the effects of the application of biochar, steel slag, shell slag, gypsum slag and silicate and calcium slag (produced from steel slag) on water nutrient concentrations and dissolved GHGs in a paddy field in subtropical southeastern China, one of the most important areas of rice production in the world. The concentrations of total dissolved nitrogen (TN) and total dissolved phosphorus (TP) in the surface water were lower in plots amended with shell slag than the control plots. Mean porewater TN and TP concentrations, however, were higher, and the mean porewater dissolved CO₂ concentration was 68% lower in the plots amended with silicate and calcium slag than the control plots. Mean dissolved CH₄ concentrations were 92 and 70% lower in the plots amended with gypsum slag and silicate and calcium slag, respectively. Mean dissolved N₂O concentrations did not differ significantly among all plots. The concentrations of dissolved CO₂ and CH₄ were correlated with their production and emission. The concentration of dissolved CO₂ was negatively correlated with porewater concentrations of NH₄+, NO₂−, NO₃−, TN, TP and Cl−. The concentration of dissolved CH4 was negatively correlated with porewater concentrations of NH₄+, TN, TP, dissolved organic carbon (DOC), SO₄²− and Cl−. The concentration of dissolved N₂O was correlated positively with the concentrations of NO₂−, NO3−, DOC and SO₄²− and negatively with the porewater concentration of NH₄+. These results support the use of these fertilizers alone or in combination for the mitigation of water nutrient losses and GHG production in rice agriculture and will provide a scientific basis for continuing the search for an easy, economical and optimum management of fertilization