C. W. Lindau

Effect of urea fertilizer and environmental factors on CH4 emissions from a Louisiana, USA rice field

Methane emissions from a flooded Louisiana, USA, rice field were measured over the first cropgrowing season. Microplots contained the semidwarf Lemont rice cultivar drill seeded into a Crowley silt loam soil (Typic Albaqualfs). Urea fertilizer was applied preflood at rates of 0, 100, 200 and 300 kg N ha−1. Emissions of CH4 from the plots to the atmosphere were measured over a 86-d sampling period until harvest. Methane samples were collected in the morning hours (07∶30–09∶30) using a closed-chamber technique. Emissions of CH4 were highly variable over the first cropping season and a significant urea fertilizer effect was observed. Two peak CH4 emission periods were observed and occurred about 11 d after panicle differentiation and during the ripening stages. Maximum CH4 emmissions from the 0, 100, 200 and 300 urea-N treatments were 6.0, 8.9, 9.8 and 11.2 kg CH4 ha−1 d−1, respectively. These flux measurements corresponded to approximately 210, 300, 310 and 360 kg CH4 evolved ha−1 over the 86-d sampling period for the 4 treatments.

Methane production from anaerobic soil amended with rice straw and nitrogen fertilizers

Laboratory experiments were conducted on the effects of rice straw application and N fertilization on methane (CH4) production from a flooded Louisiana, USA, rice soil incubated under anaerobic conditions. Rice straw application significantly increased CH4 production; CH4 production increased in proportion to the application rate. Urea fertilization also enhanced CH4 production. The maximum production rate was 17% higher, and occurred 1 week earlier, than that of soil samples which did not receive urea, possibly due to the increase in soil pH following urea hydrolysis. The increase in soil pH following urea hydrolysis may have stimulated CH4-generating bacteria by providing more optimal soil pH conditions or contributed to the drop in redox potential (Eh). The significant decrease in both the production rate and the total amount of CH4 by application of NH4NO3 was associated with increases in soil Eh after addition of this oxidant. Addition of 300 mg. kg−1 NO3--N increased soil Eh by 220 mV and almost completely inhibited CH4 production. However, this inhibitory effect was short-termed. Soon after the applied NO3--N was reduced through denitrification, CH4 production increased. When (NH4)2SO4 was applied, the inhibition of CH4 production was not associated with an increase in soil Eh which did not change significantly. A direct inhibitory effect of sulphate on methanogenesis might have been more important.

Methane emission and entrapment in flooded rice soils as affected by soil properties

Laboratory incubation experiments were conducted to study the effects of soil chemical and physical properties on CH4 emission and entrapment in 16 selected soils with a pH range of 4.7–8.1, organic matter content of 0.72–2.38%, and soil texture from silt to clay. There was no significant correlation with CH4 emission for most of the important soil properties, including soil aerobic pH (measured before anaerobic incubation), total Kjeldahl N, cation exchange capacity, especially soil organic matter, and soil water-soluble C, which were considered to be critical controlling factors of CH4 emission. A lower CH4 emission was observed in some soils with a higher organic matter content. Differences in soil Fe and Mn contents and their chemical forms contributed to the this observation. A significant correlation between the CH4 emission and the soil organic C content was observed only after stratifying soils into subgroups according to the level of CH4 emission in soils not amended with organic matter. The results also showed that the soil redox potential (Eh), anaerobic pH, anerobic pH, and biologically reducible Fe and Mn affected CH4 emission significantly. Urea fertilization promoted CH4 emission in some soils and inhibited it in others. This result appeared to be related to the original soil pH. CH4 entrapment was positively correlated with soil clay content, indicating the importance of soil physical characteristics in reducing CH4 emissions to the atmosphere.

Methane mitigation in flooded Louisiana rice fields

SummaryA field experiment was conducted to determine whether selected nitrification inhibitors (encapsulated calcium carbide and dicyandiamide) and SOinf4sup-2-containing compounds [(NH4)2SO4 and Na2SO4] had mitigating effects on CH4 emissions from flooded rice. Microplots were established within a rice bay drill-seeded with the Texmont rice cultivar and CH4 fluxes were measured over the main rice cropping season. Methane emissions over the 77-day sampling period were approximately 230, 240, 260, 290, 310, and 360 kg CH4 ha-1 from the calcium carbide, Na2SO4-rate II, Na2SO4-rate I, (NH4)2SO4, dicyandiamide, and urea (control) treatments, respectively. Reductions in CH4 evolution, compared to the control, ranged from 14 to 35%, depending on treatment. The selected inhibitors and SOinf4sup-2-containing compounds appear to be effective in reducing the CH4 emitted from flooded rice fields.

Production of dinitrogen and nitrous oxide in soil suspensions as affected by redox potential

The effect of soil redox potential on N2O and N2 emission from soil suspensions was studied under laboratory conditions. Crowley silt loam soil suspensions were equilibrated under controlled (−200, −100, 0, +100, +200, +300, and +400 mV) redox levels, and the amounts of N2 and N2O evolved quantified. At higher redox levels (+300, and +400 mV) nitrification was the dominant soil biological process controlling N chemistry. A small amount of N2O evolved during nitrification. A redox value between +300 and +200 mV was found critical for denitrification to occur. Both N2 and N2O were produced during denitrification. The maximum amount of N2O evolved at a redox value of 0 mV. Dinitrogen emission increased at lower redox levels. The highest N2/N2O evolution ratio was observed at −200 mV and the ratio decreased with increasing redox. A lack of N-balance during denitrification at redox levels of +100, and +200 mV is also reported.

Effect of rice variety on methane emission from Louisiana rice

Abstract A field experiment was conducted to determine the effect local cultivars of Oryza sativa L. (rice) had on methane evolution from flooded plots. Semidwarf and tall varieties were drill-seeded into a Crowley silt loam (Typic Albaqualf) and methane fluxes were measured twice a week over the first and ratoon cropping seasons. Semidwarf varieties evolved significantly less methane over both growing seasons. Over the main cropping season, semidwarfs emitted an average 185 kg CH4 ha−1 to the atmosphere compared with 300 kg CH4 ha−1 for the tall varieties. During the ratoon sampling season, semidwarf and tall varieties evolved 540 and 830 kg CH4 ha−1, respectively. Compared with tall cultivars, semidwarfs evolved 36% less methane over both seasons.

Methane sources and sinks in paddy rice soils: relationship to emissions

Abstract Methane sources and sinks in a Louisiana rice soil and how they relate to atmospheric emissions were quantified. Total methane emission from the plant-soil system was compared with methane emission from surface soil between drill rows of rice (Oryza sativa L.). Results showed that over 95% of methane emitted to the atmosphere was through the rice plant. Average emission through the plant-soil system was 300 mg CH4 m−2 day−1 and 826 mg CH4 m−2 day−1 for the first and ratoon crops, respectively. By comparison average methane emission from soil between drill rows was 2.1 mg CH4 m−2 day−1 for the first crop and 12.7 mg CH4 m−2 day−1 for the ratoon crop. Significant methane oxidation was measured in the surface oxidized layer in the soil profile between drill rows. Treatment with methylfluoride inhibitor showed that methane emission from the soil would be five to ten times greater if oxidation did not occur in the surface layer. Laboratory studies of methane oxidation (also using methylfluoride) showed that approximately 30% of the methane in the rice root rhizosphere was being oxidized by methanotrophs. Results showed that methane oxidation in the surface oxidized soil layer and in the root rhizosphere play an important role on limiting atmospheric methane emissions from Louisiana paddy soils.

Sensitivity of US Gulf of Mexico coastal marsh vegetation to crude oil: Comparison of greenhouse and field responses

Greenhouse and field studies were conducted to evaluate the effect of crude oil on selected US Gulf of Mexico coastal marsh species. Species showed different levels of sensitivity to oiling between greenhouse and field conditions. In greenhouse studies, two crude oils were used: South Louisiana crude oil (SLC) and Arabian Medium crude oil (AMC). The majority of Spartina patens plants died within one month following oiling with little or no recovery after three months. Panicum hemitomon and Spartina alterniflora were also adversely affected by oiling under greenhouse conditions but to a lesser extent than S. patens. The SLC or AMC oiling led to biomass reductions in S. alterniflora and S. patens. The dry biomass was not affected by oiling in P. hemitomon, Sagittaria lancifolia, Typha latifolia, and Scirpus olneyi. Results showed that S. patens plants were more sensitive to SLC as compared to AMC oil. Gross CO2-C fixation data collected in the greenhouse indicated no differences in recovery among species across oiling treatments for S. lancifolia, S. olneyi, and T. latifolia. Field studies with S. alterniflora, S. patens and S. lancifolia demonstrated initial sensitivity of these species to oiling, and recovery following oiling with SLC. Our data also showed that caution must be employed whenever results from greenhouse studies are extrapolated to predict oil impact on vegetation under field conditions. Development of any sensitivity index of plant responses to oiling should not be based on greenhouse experiments only. Field evaluations should be included which best depict plant responses to oiling. Thus, restoration measures of US Gulf of Mexico coastal marshes following oiling should rely primarily on field studies. The field research suggests that the US Gulf of Mexico coastal marsh vegetation are likely to recover from oil spills naturally without the need for remediation procedures.

Nitrification and Denitrification Estimates in a Louisiana Swamp Forest Soil as Assessed by 15N Isotope Dilution and Direct Gaseous Measurements

The transformations of applied (100 kg N ha-1)15 N labelled NO3 and NH4 in Mississippi River deltaic plain swamp forest soil which receives agriculture run-off from adjacent sugarcane fields were determined. Using an isotopic dilution technique, the rates of NO3 production (nitrification) and reduction in the 15NO3 treated soil-water-columns were approximately 240 and 2,320 g N ha-1 d-1, whereas NH4 production (mineralization) and removal rates in the 15NH4 treated soil-water-columns were 270 and 2160 g N ha-1 d-1, respectively. It was shown that if nitrification and NH4 assimilation were the primary processes responsible for NH4 removal, average NH4 assimilation would be 145 g N ha-1 d-1. Based on labelled N2-emission, denitrification was 3 fold greater in the NO3 treatment compared to the NH4 treated soil water-columns with rates of 818 and 266 g N ha-1 d-1 respectively. Even though the rate was lower in the NH4 treatment, results show that nitrification-denitrification of NH4 is a significant process. Nitrogen losses determined by15 N2 emissions were 20.4 and 6.4% and N2O emissions were 0.10 and 0.03% of the applied NO3-N and NH4-N, respectively, over 32 days of incubation. Fertilizer loss through N2O emission was only of minor significance compared to the fertilizer loss through N2 evolution. Nitrous oxide fluxes from the control soil-water-columns averaged 9.4 g N ha-1 d-1. Addition of NO3-N to the columns increased N2O production 56% as compared to a 15% increase from the NH4-N addition. Results show that this wetland soil has a large capacity to process inorganic nitrogen entering the system as a result of agriculture run-off.

Rate of accumulation and emission of N2, N2O and CH4 from a flooded rice soil

In a field experiment using microplots, a flooded Crowley silt loam (Typic Albaqualfs) rice soil was fertilized with 15N labelled (60–74 atom %) urea and KNO3. Emission of N2, N2O and CH4 and accumulation in soil were measured for 21 d after fertilizer application.Emission of 15N2-N measured from the urea and KNO3 treated plots ranged from <15 to 570 and from 330 to 3,420 g ha−1 d−1, respectively. Entrapped 15N2-N in the urea treated microplots was significantly lower (<15 g to 2.1 kg ha−1) on all sampling dates compared to the 15N2-N gas accumulation in the KNO3 treated plots (6.4 to 31.5 kg ha−1). Emissions of N2O-N were low and did not exceed 4 g ha−1 d−1. Fluxes of CH4 from the fertilizer and control plots were low and never exceeded 33 g ha−1 d−1. Maximum accumulation of CH4 in the flooded soil measured 460 and 195 g ha−1 for the urea and KNO3 treatments, respectively.