No abstract

No abstract

Herein, we introduce continuous sub-irrigation with treated municipal wastewater (tWW) as a novel cultivation system to promote resource recycling and cost-effective forage rice production in Japan. However, both tWW irrigation and forage rice cultivation were previously considered to intensify cH 4 and n 2 O emissions. In the present study, therefore, we evaluate the emissions of greenhouse gases (GHGs) and yielding capacity of forage rice between conventional cultivation and continuous sub-irrigation systems employing different water supply rates. Results indicated that continuous subirrigation with TWW resulted in high rice yields (10.4-11 t ha −1) with superior protein content (11.3-12.8%) compared with conventional cultivation (8.6 t ha −1 and 9.2%, respectively). All TWW irrigation systems considerably reduced cH 4 emissions, while higher continuous supply rates significantly increased n 2 O emissions compared with the conventional cultivation. Only the continuous irrigation regime employing suitable supply rates at appropriate timings to meet the n demand of rice plants decreased both cH 4 and n 2 O emissions by 84% and 28%, respectively. Overall, continuous sub-irrigation with tWW provides high yields of protein-rich forage rice without the need for synthetic fertilisers and effectively mitigated GHG emissions from paddy fields. Cultivation of forage rice (Oryza sativa L.) has been promoted by the Japanese government to reduce the cost of domestic animal husbandry by reducing the use of imported feedstuffs, which can be of unstable supply and highly priced depending on global markets 1. As a result, there has been a recent increase in forage rice cultivation. However, this has been accompanied by high levels of N fertiliser use to ensure high-yield production, which might lead to inefficient N use and considerable N loss to the environment 2. Effluents from wastewater treatment plants (WWTPs) contain high concentrations of organic and inorganic nutrients beneficial for plant growth and development. Thus, reusing these effluents for agricultural irrigation has major advantages for crop production and environmental management 3. Paddy rice cultivation generally demands large amounts of irrigation water and synthetic fertilisers, and thus, would greatly benefit from recycling water and valuable nutrients from WWTPs. To promote forage rice production and establish an effective resource circulation model for the management of agricultural water, we developed new cultivation systems, and treated municipal wastewater (TWW) was effectively reused in paddy fields to produce high yields of forage rice without applying synthetic fertilisers 1,4,5. The reuse of wastewater or TWW for rice cultivation has been intensively investigated and is widely practiced owing to its undeniable benefits. For instance, prior studies have demonstrated that rice grain yield from fields irrigated with treated wastewater could be 35-55% higher than that from groundwater-irrigated fields 6. Furthermore, reusing wastewater could lower the...

No abstract

In full-scale sewage treatment plants, long-term and high-frequency monitoring is required to mitigate nitrous oxide (N 2 O) emissions. In this study, the profile of the dissolved N 2 O concentration in a full-scale oxidation ditch reactor was investigated to determine the variation of the N 2 O emission factor. It was found that the concentration of dissolved N 2 O depended on microbial activity, which is affected by water temperature, dissolved oxygen concentration, and the dimensional relationship between the rotator and the inflow point. In the reactor, higher transcription levels of amoA mRNA and lower transcription levels of clade II type nosZ mRNA may be associated with N 2 O production. The emission factor for removed dissolved inorganic nitrogen presented a mean value of 0.86% and a median of 0.19%. When N 2 O production was promoted, gasification from the water surface was the most significant emission source, accounting for 52% of the total N 2 O emitted, on average. The N 2 O emission factor was often lower than 0.01% during stable operation; however, this factor was subject to sudden increases caused by nitrite accumulation.