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Exchange of nitrogen and phosphorus across sediment-water interface plays an important role in the management of nutrient recycling in the aquaculture pond. In this study, a plot experiment was conducted to study the effect of rice-catfish/shrimp co-culture on the micro-profile of oxygen (O2), pH and nutrient exchange across sediment-water interface in the intensive culture ponds. The results showed that rice-catfish co-culture increased the concentration and penetrating depth of O2, but decreased the pH value across the sediment-water interface, compared with catfish monoculture. Additional rice cultivation significantly reduced the flux rates of ammonium (NH4+) and nitrate (NO3−) across sediment-water interface in the catfish and shrimp ponds. The flux rates of NO2− and soluble phosphorus (PO43−) showed no significant difference between rice-catfish/shrimp co-culture ponds and catfish/shrimp monoculture ponds. Rice only affected the dissolved inorganic nitrogen and phosphorus fractions in the sediment. The concentrations of NH4+ were significantly lower in the sediment of co-culture ponds than in the monoculture ponds. Additional rice cultivation also significantly reduced the content and percentage of dissolved inorganic phosphorus in the sediment of catfish ponds. Keywords: sediment-water interface, rice-fish co-culture, eutrophication, nitrogen and phosphorus recycling, aquaculture

Vegetable production is recognized as an important anthropogenic source of nitrous oxide (N2O) emission. An improved understanding of yield-scaled N2O emission from vegetable production can promote innovation for climate smart cropping. In this study, we performed a meta-analysis to quantify yield-scaled N2O emission from six types of vegetable crops, to elucidate the effects of greenhouse cultivation and different types of nitrogen (N) fertilizers on yield-scaled N2O emission from vegetable crops. Significant differences were observed in N2O emission factor (EF) and area- and yield-scaled N2O emissions among the six vegetable types. Stem and seed vegetables showed the lowest and highest area- and yield-scaled N2O emissions, respectively. The average yield of all of the vegetables was significantly higher in greenhouses than in open fields. However, only leafy vegetables were observed to have significantly lower yield-scaled N2O in greenhouses than in open fields. Emissions of yield-scaled N2O in response to inorganic N application rate differed among the different vegetable types. The replacement of inorganic N fertilizer with manure significantly reduced yield-scaled N2O emission from leafy vegetables, but significantly enhanced that from fruit vegetables. Enhanced-efficiency N fertilizer (EENF) significantly increased yield, and significantly reduced area- and yield-scaled N2O emissions from all of the vegetable types; however, it was less effective for root vegetables and open field cultivation.

Rice-fish co-culture has gained increasing attention in the restoration of water quality of intensive aquaculture. However, the effect of rice-fish co-culture on sediment resuspension, a key proces...

How to reduce the gaseous nitrogen (N) pollution (N2O and NH3) of intensive aquaculture ponds to atmosphere has gained increasing attention for the sustainable development of aquaculture. In this study, we constructed a new rice-fish/shrimp co-culture system in aquaculture ponds by using a specially developed high-stalk rice variety, and performed a 2-year field experiment to investigate the effect of this system on the N2O and NH3 emissions from yellow catfish and freshwater shrimp ponds. The results showed that the mean emission factors of N2O and NH3 to the total N input in feed was 0.18% and 0.89% for catfish monoculture pond, and 2.46% and 13.45% for shrimp monoculture pond, respectively. Rice-fish/shrimp co-culture not only reduced the N2O and NH3 emission from rice platform of catfish and shrimp ponds, but also mitigated the N2O and NH3 emission from the ditch without rice planted. The total amount of N2O and NH3 were respectively mitigated by 85.6% and 26.0% for catfish pond, and by 108.3% and 22.6% for shrimp pond, as compared with that of monoculture ponds. Co-culture system was more effective on the mitigation of gaseous N loss in the catfish than shrimp ponds.

Rice-fish co-culture has gained increasing attention to remediate the negative environmental impacts induced by intensive aquaculture. However, the effect of rice-fish co-culture on oxygen depletion has rarely been investigated. We constructed a rice-fish co-culture system in yellow catfish (Pelteobagrus fulvidraco) and freshwater shrimp (Macrobrachium nipponense) ponds using a new high-stalk rice variety, and conducted a field experiment to investigate the effect of rice-fish co-culture on water parameters and oxygen consumption. The results showed that rice-fish co-culture reduced the nutrients (total nitrogen, ammonia-N, total phosphorous and potassium) and the dissolved oxygen content in fish and shrimp ponds. However, they showed similar seasonal change of dissolved oxygen in the water of fish and shrimp ponds. Rice-fish co-culture reduced the total amount of oxygen consumption and optimized the oxygen consumption structure in pond. The respiration rates in water and sediment were significantly reduced by 66.1% and 31.7% in the catfish pond, and 64.4% and 38.7% in the shrimp pond, respectively, by additional rice cultivation. Rice-fish co-culture decreased the proportions of respiration in sediment and water, and increased the proportion of fish respiration. These results suggest that rice-fish co-culture is an efficient way to reduce hypoxia in intensive culture pond. Keywords: rice-fish co-culture, oxygen depletion, respiration, pond aquaculture, yellow catfish, freshwater shrimp

Greenhouse gas (GHG) emissions from aquaculture have gained widespread attention. However, the effect of phosphorus (P) and potassium (K) on GHG emissions from aquaculture systems has rarely been studied. In this study, we conducted a laboratory-scale experiment to investigate the effect of P and K addition on CH4 and N2O emissions and nutrient use efficiency in a rice-fish co-culture system. The results showed that the CH4 flux rate did not differ between the rice-fish co-culture (RF) and fish monoculture (F) systems. Phosphorus addition did not affect CH4 emission from the RF. In contrast, K addition significantly increased the CH4 emission from the RF by 148.4%. Dual P and K addition greatly increased the CH4 emission from the RF by six times, indicating an interactive effect of P and K on the stimulation of CH4 emission. Phosphorus addition strengthened the restorative effect of the RF on N2O emission, while K addition weakened the restorative effect of the RF on N2O emission. The combination of P and K did not affect the N2O emission from the RF. The application of P and K strengthened the restorative effect of rice on nitrogen (N) pollution in aquaculture water. Phosphorus and K addition significantly increased the rice biomass and nutrient in the harvested rice, but did not affect the fish biomass and nutrient in the harvested fish. Dual P and K addition increased the nutrient use efficiency in the rice-fish system. These results provide a reference for adjusting nutrient management to reduce GHG emissions and improve nutrient use efficiency in the rice-fish system.

To better understand the effects of tillage on the spatial heterogeneity of CH4 and N2O in the soil profile of late rice fields, we conducted a field experiment to investigate the impacts of tillage methods (rotary tillage (RT) and no-tillage (NT)) on the spatial patterns and influential factors of CH4 and N2O in the soil pore water under different fertilization treatments (inorganic fertilizer with straw (FS) and no fertilizer (CK)). The results showed that great spatial variation was observed in the concentrations of CH4 and N2O in the soil profile. The content of CH4 in the soil pore water was significantly higher in the deep layer (−17.5 cm ∼ −22.5 cm) than the upper layer (−2.5 cm ∼ −7.5 cm) for NT-CK; but it was opposite for NT-FS. RT significantly increased the content of CH4 in the soil pore water at depths of −7.5 cm, −12.5 cm, and −17.5 cm as compared with NT irrespective fertilization. High values of N2O were observed in the deep layer (−17.5 cm ∼ −22.5 cm) for NT-CK, middle layer (−7.5 cm ∼ −15 cm) for RT-CK, upper layer (−2.5 cm ∼ −10.0 cm) for NT-FS, and across the whole profile for RT-FS. The horizontal distribution of CH4 did not show a significant difference at different distances from the rice plant, whereas the horizontal distribution of N2O showed a general pattern where high values of N2O occurred at a distance from the rice plants. The results of classification and regression tree (CART) analysis showed that K+ and PO43− presented relatively higher importance to the spatial heterogeneity of CH4 and N2O in the soil profile of late rice fields, in contrast to the contents of carbon and nitrogen. These results provide detailed insight into the spatial distribution and influential factors of CH4 and N2O in the soil profile of rice fields.

Life cycle assessments (LCA) of staple food (rice, wheat and corn) production and assessments of the associated greenhouse gas (GHG) and reactive nitrogen (Nr) releases from environmental and ecological perspectives help to develop effective mitigation options. Therefore, carbon (C) and nitrogen (N) footprint reductions in agroecosystems have become an increasingly popular topic related to global climate change and agricultural adaptation. The LCA method was used to calculate the product and farm C footprint (CF) and N footprint (NF) of double rice, rice-wheat and wheat-maize production based on governmental statistical datasets and published results. The spatial and temporal patterns of CF and NF were analyzed in China during 2004–2017, and their driving factors were analyzed to identify potential mitigation strategies. The results showed that of the various inputs, fertilizer application and diesel oil consumption contributed the most to both GHG and Nr emissions from farm inputs in the grain crop production process. The CFs for double rice, rice-wheat and wheat-maize were 0.83, 0.74, and 0.37 kg CO2-eq kg−1 year−1 at the yield scale, respectively. In addition, the NFs were 11.6, 13.4, and 15.4 gN-eq kg−1 year−1 at the yield scale for double rice, rice-wheat and wheat-maize, respectively. The largest fraction of CF and NF was the share of CH4 emissions and NH3 volatilization from the field soil, respectively. The annual CFs and NFs of the multiple crop in the southwestern provinces were higher than those in the central and northern provinces. The annual GHG and Nr emissions from the multiple crop maintained a relatively stable state from 2004 to 2017. The proportion of CO2/Nr production was partly reflected a soil C/N ratio, suggesting a higher C abundance for the double rice production, which could be used as a reference parameter for crop structure adjustment in the future. Based on our results and other studies, some effective solutions, especially optimized fertilization, farm machinery operation efficiencies and changes in regional allocation of grain cropping areas, are needed to mitigate the impacts of climate change and eutrophication on the main grain crop production in China.