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

Factors related with CH4 and N2O emissions from a paddy field : clues for management implications

Paddy fields are major sources of global atmospheric greenhouse gases, including methane (CH₄) and nitrous oxide (N₂O). The different phases previous to emission (production, transport, diffusion, dissolution in pore water and ebullition) despite well-established have rarely been measured in field conditions. We examined them and their relationships with temperature, soil traits and plant biomass in a paddy field in Fujian, southeastern China. CH₄ emission was positively correlated with CH₄ production, plant-mediated transport, ebullition, diffusion, and concentration of dissolved CH₄ in porewater and negatively correlated with sulfate concentration, suggesting the potential use of sulfate fertilizers to mitigate CH₄ release. Air temperature and humidity, plant stem biomass, and concentrations of soil sulfate, available N, and DOC together accounted for 92% of the variance in CH₄ emission, and Eh, pH, and the concentrations of available N and Fe³⁺, leaf biomass, and air temperature 95% of the N₂O emission. Given the positive correlations between CH4 emission and DOC content and plant biomass, reduce the addition of a carbon substrate such as straw and the development of smaller but higher yielding rice genotypes could be viable options for reducing the release of greenhouse gases from paddy fields to the atmosphere

Effect of simulated acid rain on CO₂, CH₄ and N₂O fluxes and rice productivity in a subtropical Chinese paddy field

The need of more food production, an increase in acidic deposition and the large capacity of paddy to emit greenhouse gases all coincide in several areas of China. Studying the effects of acid rain on the emission of greenhouse gases and the productivity of rice paddies are thus important, because these effects are currently unknown. We conducted a field experiment for two rice croppings (early and late paddies independent experiment) to determine the effects of simulated acid rain (control, normal rain, and treatments with rain at pH of 4.5, 3.5 and 2.5) on the fluxes of CO₂, CH₄ and N₂O and on rice productivity in subtropical China. Total CO₂ fluxes at pHs of 4.5, 3.5 and 2.5 were 10.3, 9.7 and 3.2% lower in the early paddy and 28.3, 14.8 and 6.8% lower in the late paddy, respectively, than the control. These differences from the control were significant for pH 3.5 and 4.5. Total CH₄ fluxes at pHs of 4.5, 3.5 and 2.5 were 50.4, 32.9 and 25.2% lower in the early paddy, respectively, than the control. pH had no significant effect on CH₄ flux in the late paddy or for total (early + late) emissions. N₂O flux was significantly higher at pH 2.5 than 3.5 and 4.5 but did not differ significantly from the flux in the control. Global-warming potentials (GWPs) were lower than the control at pH 3.5 and 4.5 but not 2.5, whereas rice yield was not appreciably affected by pH. Acid rain (between 3.5 and 4.5) may thus significantly affect greenhouse gases emissions by altering soil properties such as pH and nutrient pools, whereas highly acidic rain (pH 2.5) could increase GWPs (but not significantly), probably partially due to an increase in the production of plant litter

Effects of steel slag and biochar amendments on CO₂, CH₄, and N₂O flux, and rice productivity in a subtropical Chinese paddy field

Steel slag, a by-product of the steel industry, contains high amounts of active iron oxide and silica which can act as an oxidizing agent in agricultural soils. Biochar is a rich source of carbon, and the combined application of biochar and steel slag is assumed to have positive impacts on soil properties as well as plant growth, which are yet to be validated scientifically. We conducted a field experiment for two rice paddies (early and late paddy) to determine the individual and combined effects of steel slag and biochar amendments on CO₂, CH₄, and N₂O emission, and rice productivity in a subtropical paddy field of China. The amendments did not significantly affect rice yield. It was observed that CO₂ was the main greenhouse gas emitted from all treatments of both paddies. Steel slag decreased the cumulative CO₂ flux in the late paddy. Biochar as well as steel slag + biochar treatment decreased the cumulative CO₂ flux in the late paddy and for the complete year (early and late paddy), while steel slag + biochar treatment also decreased the cumulative CH4 flux in the early paddy. The biochar, and steel slag + biochar amendments decreased the global warming potential (GWP). Interestingly, the cumulative annual GWP was lower for the biochar (55,422 kg CO₂-eq ha⁻¹), and steel slag + biochar (53,965 kg CO₂-eq ha⁻¹) treatments than the control (68,962 kg CO₂-eq ha⁻¹). Total GWP per unit yield was lower for the combined application of steel slag + biochar (8951 kg CO₂-eq Mg⁻¹ yield) compared to the control (12,805 kg CO₂-eq Mg⁻¹ yield). This study suggested that the combined application of steel slag and biochar could be an effective long-term strategy to reduce greenhouse gases emission from paddies without any detrimental effect on the yield

Responses of greenhouse-gas emissions to land-use change from rice to jasmine production in subtropical China

We studied the impacts of an increasingly common change in land use from paddy field to jasmine fields on the emission of greenhouse gases (GHGs), which have supposed the transformation of more than 1200 ha only in the last decade in the surroundings of Fuzhou city in response to economic changes. The possible increases that this can suppose constitutes and environmental concern in China. We studied areas dedicated to rice crop that have been partially converted to jasmine cultivation with some parts still kept as rice fields. Emissions of CO2, CH4 and N2O varied significantly among the seasons. CO2 and CH4 cumulative emissions and the global-warming potential (GWP) of these emissions were significantly lower in the jasmine than the paddy field. N2O emission, N2O cumulative emission, however, were higher in the jasmine than the paddy field, despite in some concrete studied periods the differences were not statistically significant. The total decrease in GHG emissions from the conversion from rice to jasmine production was strongly influenced by the indirect effects of various changes in soil conditions. The expected changes due to the great differences in water and fertilization use and management and organic matter input to soil between these two crops were in great part due to modified soil traits. According to structural equation models, the strong direct effects of the change from rice to Jasmine crop reducing the emissions of CO2 and N2O were partially decreased by the indirect effects of crop type change decreasing soil pH and soil [Fe2+] for CO2 emissions and by decreasing soil salinity and soil [Fe3+] for N2O emissions. The negative effects of the crop conversion on CH4 emissions were mostly due to the globally negative indirect effects on soil conditions, by decreases in soil salinity, water content and [Fe2+]. Soil salinity, water content, pH, [Fe2+], [Fe3+] and [total Fe] were significantly lower in the jasmine than the paddy field, but temperature had the opposite pattern. CO2 emissions were generally correlated positively with salinity, temperature, and water content and negatively with [Fe3+] and [total Fe] in both fields. CH4 emissions were positively correlated with salinity, temperature, water content and pH in both fields. N2O emissions were positively correlated with temperature and were negatively correlated with water content, pH, [Fe2+], [Fe3+] and [total Fe] in both fields. CO2 was the most important GHG for the GWPs, and the total GWP was significantly lower for the jasmine than for the rice cropland field. The change in the land use in this area of paddy fields will decreased the global GHG emission, and the effect on the GWPs was mostly due to changes in soil properties

Effects of steel slag application on greenhouse gas emissions and crop yield over multiple growing seasons in a subtropical paddy field in China

Asia is responsible for over 90% of the world's rice production and hence plays a key role in safeguarding food security. With China being one of the major global producers and consumers of rice, achieving a sustainable balance in maximizing crop productivity and minimizing greenhouse gas emissions from paddy fields in this country becomes increasingly important. This study examined the effects of applying steel slag, a residual product derived from the steel industry, on crop yield and CH4 and N2O emissions over multiple growing seasons in a Chinese subtropical paddy field. Average CH4 emission was considerably higher during the periods of rice crop growth compared to that during the periods of fallowing and vegetable crop growth, regardless of the amount of steel slag applied. When compared to the controls, significantly lower mean emissions of CH4 (1.03 vs. 2.34 mg m−2 h−1) and N2O (0.41 vs. 32.43 μg m−2 h−1) were obtained in plots with slag addition at a rate of 8 Mg ha−1 over the study period. The application of slag at 8 Mg ha−1 increased crop yields by 4.2 and 9.1% for early and late rice crops, respectively, probably due to the higher availability of inorganic nutrients such as silicates and calcium from the slag. Slag addition had no significant effect on the concentrations of heavy metals in either the soil or the rice grains, although a slight increase in the levels of manganese and cobalt in the soil and a decrease in the levels of manganese and zinc in the rice grains were observed. Our results demonstrate the potential of steel slag as a soil amendment in enhancing crop yield and reducing greenhouse gas emissions in subtropical paddy fields in China, while posing no adverse short-term impacts on the concentrations of heavy metals in the soil or the rice grains. However, long-term implications of this management practice and the cost/benefit remain unknown, so further studies to assess the suitability at large scale are warranted

Shifts in plant and soil C, N and P accumulation and C:N:P stoichiometry associated with flooding intensity in subtropical estuarine wetlands in China

Flooding caused by rising sea levels can influence the biogeochemistry of estuarine wetland ecosystems. We studied the relationships of higher flooding intensity with soil carbon (C), nitrogen (N) and phosphorus (P) concentrations in communities of the native sedge Cyperus malaccensis var. brevifolius Boecklr. in the wetlands of the Minjiang River estuary in China. The aboveground and total biomasses of C. malaccensis were higher in high-flooding habitats than in intermediate- and low-flooding habitats. These differences in plant biomass were accompanied by a lower N:P ratio in the aboveground biomass and a higher N:P ratio in the belowground biomass. Higher intensities of flooding were associated with higher soil N and P concentrations in intermediate and deep soil layers. The higher P concentration under flooding was mainly associated with the higher clay content, whereas the higher N concentration was associated with higher salinity. Flooding intensity did not have a net total effect on soil total C concentration. The positive direct effect of flooding intensity on total soil C concentration was counteracted by its positive effects on CH4 emissions and soil salinity. The results suggest that C. malaccensis wetlands will be able to maintain and even increase the current C, N and P storage capacity of the ecosystem under moderate increases of flooding in the Minjiang River estuary

Industrial and agricultural wastes decreased greenhouse-gas emissions and increased rice grain yield in a subtropical paddy field

Imbalance P paper. Contact with Jordi Sardans: [email protected] the emissions of greenhouse gases (GHG) from paddy fields is crucial both for the sustainability of rice production and mitigation of global climatic warming. The effects of applying industrial and agricultural wastes as fertilizer on the reduction of GHG emissions in cropland areas, however, remain poorly known. We studied the effects of the application of 8 Mg ha⁻¹ of diverse wastes on GHG emission and rice yield in a subtropical paddy in southeastern China. Plots fertilized with steel slag, biochar, shell slag, gypsum slag and silicate and calcium fertilizer had lower total global-warming potentials (GWP, including CO₂, CH₄ and N₂O emissions) per unit area than control plots without waste application despite non-significant differences among these treatments. Structural equation models showed that the effects of these fertilization treatments on gas emissions were partially due to their effects on soil variables, such as soil water content or soil salinity. Steel slag, biochar and shell slag increased rice yield by 7.1%, 15.5% and 6.5%, respectively. The biochar amendment had a 40% lower GWP by Mg⁻¹ yield production, relative to the control. These results thus encourage further studies of the suitability of the use waste materials as fertilizers in other different types of paddy field as a way to mitigate GHG emissions and increase crop yield

Multiple trade-offs between maximizing yield and minimizing greenhouse gas production in Chinese rice croplands

Globally, paddy fields are a major anthropogenic source of greenhouse gas (GHG) emissions from agriculture. There is, however, limited understanding of relationships between GHG production with fertilizer management, rice varieties, and soil variables. This information is crucial for minimizing the climatic impacts of rice agriculture. Here, we examined the relationships between soil GHG production and management practices throughout China. The current doses of N-fertilizer (73-272 kg ha−1) were negatively correlated with rice yield and with CO2 or CH4 production and positively correlated with N2O production, thus suggesting N-overfertilization. Impacts on soil traits such as decreasing pH or the availabilities of other nutrients could be underlying these relationships. Rice yield was highest, and GHG production was lowest at sites using intermediate levels of P- and K-fertilization. CO2 and CH4 production and emissions were positively related with soil water content. The yield was higher, and N2O productions were lower at the sites with japonica rice. Our results strongly suggest that current high doses of N-fertilizers could be reduced to thus avoid the negative effects of excessive N input on GHG production without any immediate risk of rice production loss. Current intermediate doses of P- and K-fertilization should be adopted across China to further improve rice production without the risk of GHG emissions. The use of different rice varieties and strategies of water management should be reexamined in relation to crop production and GHG mitigation