Methane mitigation in flooded Louisiana rice fields

Summary A field experiment was conducted to determine whether selected nitrification inhibitors (encapsulated calcium carbide and dicyandiamide) and SO _inf4 ^sup-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 SO _inf4 ^sup-2 -containing compounds appear to be effective in reducing the CH₄ emitted from flooded rice fields.     

The interdependence of ammonia volatilization and denitrification as nitrogen loss processes in flooded rice fields in the Philippines

Summary The relative importance of ammonia volatilization and denitrification as loss processes following the application of urea to flooded rice by the traditional method was assessed at four sites with different characteristics in the Philippines. The effect of reducing ammonia loss on denitrification and total N loss was also studied. The total N loss was determined by a ¹⁵N-balance method and ammonia volatilization was assessed by a bulk aerodynamic method following the application of urea to small plots (4.8×5.2 m). As run-off was prevented and leaching losses were negligible, the denitrification loss was assessed as the difference between total N loss and ammonia loss. When urea was broadcast into the floodwater at transplanting, the ammonia loss varied from 10% to 56% of the applied N. Loss was smallest at Aguilar where wind speeds were low and the greatest at Mabitac where floodwater pH values and temperatures were high and the winds were strong. The ammonia loss was reduced at all sites by incorporating the urea into the soil by harrowing. However, the reduction achieved varied markedly between sites, with the largest reduction (from 56% to 7% loss of the applied N) being observed at Mabitac. The total N lost from the basal application into the floodwater ranged from 59% to 71% of the applied N. Incorporating the urea by harrowing reduced the total N loss at two sites, increased the total N loss at the third site, and had no effect at the fourth site. The denitrification losses ranged widely (from 3% to 50% of the applied N) when urea was broadcast into the floodwater at the four sites. The denitrification loss was low when the ammonia loss was high (Mabitac) and high when the ammonia loss was low (Aguilar). Reducing ammonia losses by incorporating the urea into the flooded soil resulted in increased denitrification losses at three of the sites and appeared to have no effect on denitrification at the fourth site. The results show that reducing the ammonia loss by incorporating urea into the soil does not necessarily result in reduced total N loss, and suggest that the efficiency of fertilizer N will be improved only when both N-loss processes are controlled simultaneously.     

Microbial degradation of penoxsulam in flooded rice field soils

The degradation of penoxsulam [2-(2,2-difluoroethoxy)-N-5,8-dimethoxy[1,2,4]triazolo[1,5-C]pyrimidin-2-yl-6-(trifluoromethyl)benzene-sulfonamide] was studied in flasks simulating flooded rice field conditions using four representative rice field soils from the Sacramento Valley. Degradation half-lives (t(1/2) values) ranged between 2 and 13 days. Increased degradation rates were observed in flask systems with steeper redox gradients between the flooded soil layer and the overlaying water. Two transient metabolites were identified that were temporarily formed in amounts exceeding 5% of the total initial mass of penoxsulam. The results of high-performance liquid chromatography/(14)C radiodetection studies indicate that the degradation of the triazolopyrimidine system and its substituents is the main pathway of microbial transformation processes. Microbial activity, as measured by dehydrogenase activity, was not affected by penoxsulam concentrations corresponding to the proposed maximum annual use rate of 40 g active ingredient/ha.     

Release of silicon from rice straw under flooded conditions

It is estimated that nearly 20 kg of SiO₂ is removed from the soil by rice plants for producing 100 kg brown rice (Takahashi 1987). Although there is a large amount of silicon in soil, little is available to the rice plant. To supply a sufficient amount of silicon to the rice plant for healthy growth, therefore, it is nccessary to supply various silicon materials to the soil. Rice straw application to the soil is one of the means.     

Soil properties and the macrofauna community in abandoned irrigated rice fields of northeastern Argentina

This study compared soil physical, chemical, and biological characteristics between natural grassland and recently abandoned rice fields in order to identify those variables that might explain the observed increase of Camponotus punctulatus anthills in abandoned rice paddy fields from Northern Argentina. Mainly due to a reduction of macropores and mesopores, overall porosity decreased by around 6% and bulk density was about 7% greater, in the 0- to 10- and 10- to 20-cm layers of the abandoned rice fields. Carbon and nitrogen content from organic matter increased (29% and 41% respectively for the 0- to 20-cm horizon) during cultivation but decreased (38% and 24%) 2 years after the last rice harvest. Forty percent of natural grassland-organic matter and 30% of abandoned rice-organic matter mineralized in less than 2 years. There was a different community structure between the abandoned rice fields and the undisturbed natural grassland and only a 20.6% (i.e. only 19 species from a total of 92) overlap in species composition. The abundance of macrofauna was greater in abandoned rice fields (2,208 individuals m^–2) in comparison to natural grasslands (288 ind m^–2) due to higher densities of small earthworms and Camponotus punctulatus ants; however, the Shannon index showed lower values in comparison to natural grasslands. Earthworms and C. punctulatus in the abandoned rice fields showed a change in their ¹³C signature indicating a switch in diet from natural grassland organic matter (C4) to organic matter from rice (C3). Our results indicate that the effects of rice cultivation practices did not seem to produce any physical or trophic limitations to recolonization by the macrofauna. It seems that changes in overall soil conditions have favored a change in the construction behavior of C. punctulatus which, in combination with population increases, could explain the explosion in number of anthills.     

Structural state of migrational-mycelial (typical) agrochernozems of the Kamennaya Steppe on plowed fields of different ages

Changes in the structural state of migrational-mycelial (typical) chernozems (Haplic Chernozems (Clayic, Aric, Pachic)) as dependent on the duration of their cultivation (from 20 to 120 years) are considered. Field studies were performed in 2013 on the fields of the Dokuchaev Research Institute of Agriculture in the Central Chernozemic Region of Russia (the Kamennaya Steppe area) used for growing cereals and row crops in rotation. The study showed that the most intensive degradation of the structure of chernozems takes place during the first two decades of their agricultural use. The maximum transformation of the soil structure is observed in the upper 10 cm, as this layer is subjected to the most frequent and intense mechanical impacts. The rate of structural degradation decreases with time until the equilibrium between disaggregation and aggregation processes is reached. The time required for this largely depends on the applied crop rotation systems and agrotechnologies. In this context, flexible assessment scales for the structural state of agrochernozems under conditions of different farming systems should be developed in order to perform monitoring of the physical properties of cultivated chernozems for their long-term efficient and ecologically sustainable use. Despite general disintegration and destruction of granular aggregates, the structural state of agrochernozems in the Kamennaya Steppe area remains sufficiently good even on the old-cultivated (120 yrs.) fields.     

Oxygen profiles and methane turnover in a flooded rice microcosm

Summary Dissolved O₂ was depleted within the top 3.5-mm surface layer of flooded rice soil microcosms without plants. In planted microcosms, however, O₂ was detectable down to at least 40 mm in depth. O₂ concentrations in the uppermost soil layers of microcosms with rice plants were higher in the light than in the dark, indicating O₂ production by photosynthesis. The CH₄ emission rates were nearly identical for illuminated and for darkened microcosms, demonstrating that the photosynthetically produced O₂ did not increase CH₄ oxidation in the rhizosphere. In contrast, CH₄ emission rates increased when the microcosms were incubated under an N₂ atmosphere, indicating that transport of O₂ from the atmosphere into the rhizosphere was important for CH₄ oxidation. CH₄ emission under air accounted for only 10%–20% of the cumulative CH₄ production determined in cores taken from the microcosms. Apparently, 80%–90% of the CH₄ produced was oxidized in the rhizosphere and thus was not emitted.     

Nitrification of ammonium in different components of a flooded rice soil system

Nitrification associated with the various components [subsurface soil from unplanted and planted (rhizosphere) fields, standing water and surface soil from planted and unplanted fields and leaf sheath suspensions] of submerged rice paddies was examined in incubation experiments with solutions inoculated with soil or water samples. Substantial nitrification occurred in all samples, standing water and surface soil samples in particular, during their 40-day incubation with NH ₄ ⁺ –N. Almost all the NH ₄ ⁺ –N, disappeared during incubation with standing water, was recovered as NO _inf3 ^sup- –N. This, compared to 70–80% from all soil samples and only 29% from leaf sheath suspensions. Significant loss of nitrogen, especially from leaf sheath suspensions, is probably due to nitrification-denitrification as evidenced by its complete recovery in the presence of N-Serve. Nitrification potential of the soil and water samples varied with the crop growth stage and was more pronounced at tillering and panicle inititation stages than at other stages. Nitrification potential of samples from green-manure-amended plots was distinctly less than that of samples from control and urea-amended plots. Most probable number (MPN) estimates of ammonium-oxidizing bacteria were always higher in surface soil in both planted and unplanted plots at all stages of crop growth.Dedicated to Professor J. C. G. Ottow on the occasion of his 60th birthday     

Thermal diffusivity of plowed leached meadow-chernozemic soils in the Adygeya Republic

Thermal diffusivity of the upper horizons of leached meadow-chernozemic soils varies in dependence on the soil water content within the following limits: 1.20–4.11 × 10⁻⁷ m²/s for the Ap horizon, 1.21–3.85 ×10⁻⁷ m²/s for the A1 horizon, and 1.35–3.73 × 10⁻⁷ m²/s for the A1B horizon. The relationships between the thermal diffusivity and the soil water content are described by S-shape curves with a long gently inclined segment within the range of water contents of <0.20 cm³/cm³, a distinct rise in thermal diffusivity within the water contents from 0.20 to 0.30–0.35 cm³/cm³, and a flattened or somewhat declining segment in the area with the high (>0.30–0.35 cm³/cm³) water contents. The thermal diffusivity of air-dried soil samples correlates with the physical clay (<0.01 mm) content. The Pearson correlation coefficient for these two variables equals −0.67 and is statistically significant at the significance level of 0.05. Regression equations allowing one to calculate the thermal diffusivity of the investigated soil horizons on the basis of data on the soil water content have been obtained.     

Potassium application reduces methane emission from a flooded field planted to rice

In a field study, potassium (K) applied as muriate of potash (MOP) significantly reduced methane (CH₄) emission from a flooded alluvial soil planted to rice. Cumulative emission was highest in control plots (125.34 kg CH₄ ha⁻¹), while the lowest emission was recorded in field plots receiving 30 kg K ha⁻¹ (63.81 kg CH₄ ha⁻¹), with a 49% reduction in CH₄ emission. Potassium application prevented a drop in the redox potential and reduced the contents of active reducing substances and Fe²⁺ content in the rhizosphere soil. Potassium amendment also inhibited methanogenic bacteria and stimulated methanotrophic bacterial population. Results suggest that, apart form producing higher plant biomass (both above- and underground) and grain yield, K amendment can effectively reduce CH₄ emission from flooded soil and could be developed into an effective mitigation option, especially in K-deficient soils.     

Leaching of hexachlorocyclohexane isomers in a flooded field unplanted or planted to rice

Leaching ofα-, β-, γ- andδ-isomers of hexachlorocyclohexane (HCH) in a commercial formulation, sprayed to a flooded field (unplanted or planted to rice) at 1.0 kg a.i. ha ^?1 onγ-isomer basis, was studied with the help of field-installed porous moisture extraction cups. Residues of HCH-isomers in the surface field water and leachates (at 15, 30 and 60 cm) were higher in planted field than in unplanted field, probably due to less volatilization of HCH-isomers under the crop cover. HCH-isomers, with the exception ofβ-isomer, migrated to 30 cm depth;β-isomer did not move beyond 15 cm depth possibly due to lower amount of this isomer available for leaching whileα-HCH was detected even at 60 cm depth.γ-Tetrachlorocyclohexene, a predicted metabolite ofγ-HCH in anaerobic environments, was detected in the the leachate even at 60 cm depth.     

Influence of the insecticide carbofuran on the production and oxidation of methane in a flooded rice soil

Applications of a commercial formulation of carbofuran, a carbamate insecticide, at rates of 2kg and 12kg active ingredient ha^–1 to flooded fields planted to rice led to significant inhibition of methane emission. Likewise, laboratory incubation studies showed that carbofuran applied at low rates (5 and 10μgg^–1soil) inhibited the net methane production relative to that of the control, but stimulated it when applied at a rate of 100μgg^–1soil. Interestingly, carbofuran increased the oxidation of methane when applied at low rates and inhibited it when applied at a rate of 100μgg^–1soil. Received: 5 May 1997     

The effect of phenyl phosphorodiamidate on urease activity and ammonia volatilization in flooded rice

Summary The behaviour of urease activity, ammoniacal N concentrations and pH in flood water and that of ammonia flux was investigated in a water-logged soil either in the presence or in the absence of rice and with three different treatments (control, urea and urea + phenyl phosphorodiamidate). In the presence of the phenyl phosphorodiamidate (PPD), that is a urease inhibitor, increases in ammoniacal N concentrations and in ammonia evolution were delayed but not eliminated. The degradation and/or the inactivation of PPD might have occurred, thus removing the inhibition of the enzyme activity.     

The fate of ammonium nitrogen applied to flooded rice as affected by zeolite addition

High rice (Oryza sativa L.) yields are closely related to plant absorption of a large amount of nitrogen (N). However, there is little information on the fate of N applied at the middle growth stages of rice. Labeled ¹⁵N ammonium sulfate was applied at the panicle formation stage in Experiment I, and 10 d after heading in Experiment II. Zeolite was also added at the concentration of 0, 0.01, and 0.1 kg kg^-1 to increase the cation exchange capacity (CEC) of the soil. The amount of ¹⁵N fertilizer in the soil surface water decreased exponentially and the fertilizer disappeared within 2 d after application. The soil that received zeolite at 0.1 kg kg^-1 exhibited significantly less ¹⁵NH₄ ⁺-N in the surface water and in the soil solution than the soil without the zeolite amendment. A significantly larger amount of exchangeable ¹⁵NH₄ ⁺-N was observed in the high zeolite-treatment of soil compared to the low zeolite-treatment of soil. The amount of exchangeable ¹⁵NH₄ ⁺-N increased initially, and thereafter decreased to traces 4 d after application in Experiment I, while 6 or 9 d after application in Experiment II. The disappearance of exchangeable ¹⁵NH₄ ⁺-N could be attributed mainly to the uptake by plants. The zeolite amendment or the time of N application did not significantly affect the amount of immobilized N. The rate of N adsorption was inhibited with increasing zeolite application. Moreover, zeolite application did not increase the recovery percentage of ammonium sulfate by rice plants. The total recovery of applied N ranged from 65 to 75%, irrespective of the zeolite treatments or the time of N application.     

Involvement of microaerophilic iron-oxidizing bacteria in the iron-oxidizing process at the surface layer of flooded paddy field soil

Journal of Soils and Sediments - To reveal whether microaerophilic Fe(II)-oxidizing bacteria (FeOB) participate in the Fe(II) oxidation at the oxic-anoxic interface in flooded paddy field soil,...     

Development of cyanobacterial blooms in Valencian rice fields

Seasonal variation of biomass, photosynthetic pigments and C and N contents of the cyanobacterial blooms developed during the crop cycles of 1998, 1999 and 2000 at two locations in Valencian rice fields (Spain) were studied to find their potential contribution to soil fertility. Blooms of Gloeotrichia sp., Gloeocapsa sp., Microchaete sp., and Nostoc sp. were small and dispersed and appeared only for a few weeks in the experimental fields of the Tancat de Malta location during the crop season of 1998. The biomass of these blooms ranged from 4.4 to 12.8 mg dry wt cm^–2. A bloom of Anabaena sp. was found in the same location during most of the crop cycles of 1998 and 1999, covering up to 80% of the experimental fields. The biomass of this bloom ranged from 2.7 to 11.4 mg dry wt cm^–2. In the moment of its maximal extension (July 1998) we estimate a total biomass of 2,100 kg dry wt for this bloom, equivalent to 420 kg dry wt ha^–1. In the Sueca location a bloom of Microchaete sp. was observed in August 1999 and during most of the crop cycle of 2000, when it covered a wide area (60–70%) of the experimental field. The biomass of this bloom ranged from 0.9 to 5.6 mg dry wt cm^–2. Carbon contents of the blooms ranged from 150 to 310 g mg^–1 dry wt and N contents ranged from 11 to 30.2 g mg^–1 dry wt. Taking into account their N content and their extension we estimate that the incorporation of cyanobacterial blooms could add 4–12 kg N ha^–1 to soil. From an agronomical point of view this means that, in spite of their impressive aspect, cyanobacterial blooms can only fulfill a small proportion of the N requirements of rice plants.     

Application of membrane inlet mass spectrometry to directly quantify denitrification in flooded rice paddy soil

Denitrification has long been considered a major mechanism of N loss when N fertilizer is applied to flooded rice paddies. However, the direct determination of denitrification in soils is almost impossible because of the high atmospheric background of dinitrogen (N₂). Dissolved N₂ in a small water sample can be rapidly and precisely measured through membrane inlet mass spectrometry (MIMS). This study is the first to directly measure N₂ flux through MIMS in flooded rice paddy plots that received different amounts of urea. Ammonia (NH₃) volatilization was measured simultaneously to verify whether NH₃ volatilization and denitrification are complementary loss mechanisms. The average cumulative N₂–N loss measured by MIMS 21 days after fertilization was 4.7?±?1.7 % of the applied N, which was within the range of the reported values obtained by cumulative recovery of (N₂ + N₂O)–¹⁵N and ¹⁵N-balance technique. Underestimation or overestimation of denitrification can be prevented in MIMS given that N₂ can be measured directly without ¹⁵N-labeled fertilizer. A good positive correlation was found between the dissolved in situ N₂ concentrations of floodwater and the denitrification rates of intact soil cores. Urea incorporation reduced NH₃ volatilization unlike surface broadcasting. However, urea incorporation significantly increased cumulative N₂–N loss during the 21 days after fertilization. Correlation analysis showed that nitrate (NO₃ ^?–N) concentration in floodwater could be the primary restricting factor for soil denitrification in the experimental field. Results suggest that MIMS is a promising technique for the measurement of denitrification in a flooded rice paddy.     

Placement effects of organic sources on nitrogenase activity and nitrogen-fixing bacteria in flooded rice soils

The placement effects of organic sources (cellulose and rice straw) at different depths on nitrogenase activity (acetylene reduction assay, ARA) associated with four tropical rice soils were investigated. Results showed that placement of organic sources in the top profile (1–2 cm) produced a higher nitrogenase activity; while placement in the 2–4 cm and 4–6cm profiles significantly decreased the activity irrespective of soil type. The effect of organic sources on nitrogenase varied depending on the soil type. Cellulose and rice straw caused differential stimulation in response to the placement. Evidence was provided for the creation of favourable redox potential supporting higher nitrogenase activity in series receiving organic amendments in the top profile. Higher nitrogenase activity in the top profile was associated with greater populations of nitrogen-fixing Azospirillum sp., anaerobic nitrogen fixers and Azotobacter sp. Moreover, the lower amounts of reducing sugars and higher carbon dioxide evolution gave evidence of higher microbial activity in the top profile. These results clearly indicate the positive relationship between nitrogenase activity, nitrogen-fixing populations and redox status in the top layers of flooded tropical rice soils. Received: 5 June 1996     

Bt-transgenic rice straw affects the culturable microbiota and dehydrogenase and phosphatase activities in a flooded paddy soil

There have been few investigations of the possible effects of genetically engineered plants on the microbiota and enzyme activities in flooded soil. We studied the influence of the transgenic rice KeMingDao (KMD) straw on the culturable microbiota and enzymatic activities in a flooded paddy soil under laboratory conditions. KMD contained a synthetic cry1Ab gene from Bacillus thuringiensis under the control of a maize ubiquitin promoter and linked in tandem with the gusA and hpt genes. The results showed that there were only some occasional significant differences (P<0.05) in the number of Colony forming units of aerobic bacteria, actinomycetes and fungi and in the number of anaerobic fermentative bacteria, denitrifying bacteria, hydrogen-producing acetogenic bacteria, and methanogenic bacteria between the paddy soil amended with Bt-transgenic rice straw and with the non-Bt parental rice straw during the early stages of incubation. From d14 to d84 there were significant increases (P<0.05) in soil dehydrogenase and soil neutral phosphatase activity in soils amended with rice straw compared to soil without added straw. The dehydrogenase activity was significantly greatly (almost 1.95-fold) in soil amended with Bt-transgenic straw from d7 to d14 but from d21 to d49 there was significantly greater activity (about 1.47-fold) in the soil amended with non-Bt-straw. There were no apparent differences between the activity of soil neutral phosphatase in the soils to which non-Bt-straw and Bt-straw had been added. However, both soils to which rice straws were added demonstrated significant differences in the number of microorganisms except for aerobic bacteria and enzymatic activities with respect to the control soil throughout the incubation. The above results indicated that the Bt-straw from KMD transgenic rice is not toxic to a variety of culturable microorganisms in the studied flooded paddy soil.     

Effect of organic residue amendment on mineralization of nitrogen in flooded rice soils under laboratory conditions

Abstract

This study was undertaken to assess the mineralization of nitrogen (N) in rice soils amended with organic residues under flooded condition. A lab incubation study with a 3x3 factorial design (two replications) was conducted with three rice soils (Joydebpur, Faridpur, and Thakurgaon) receiving the following treatments: 1) control, 2) rice straw (Oryza sativa L.), or 3) pea vine (Pisum sativum L.). The organic residue (25 mg straw g^‐1 soil) was mixed with soil and glass beads (1:1, soil to beads ratio), and transferred into a Pyrex leaching tube, flooded and then incubated at 35°C for up to 12 weeks. The soils in the leaching tubes were leached (while maintaining flooded condition) at 1,2,4, 8, and 12 weeks with deionized water for determination of NH₄‐N, NO₃‐N, pH, and Eh. Nitrogen mineralization in soils amended with rice straw was somewhat different than that of soils treated with pea vine. Soil treated with rice straw had a higher N mineralization rate than soils treated with pea vine, which was due to a lower carbon (C):N ratio for rice straw. The potentially mineralizable N pool (N_o) in soils amended with rice straw and pea vine under flooded conditions, estimated using a 1st order exponential equation, were 7 to 15 times, and 3 to 9 times greater for rice straw N_o values and pea vine, respectively, than the control. The K_N values for unamended soils ranged from 0.35 to 0.52 mg N kg^‐1 wk^‐1 and rice straw and pea vine treated soils were from 0.75 to 1.22 and 0.46 to 0.58 mgN kg^‐1 wk^‐1. The lower N_o and K_N values in pea vine treatments suggested there was greater immobilization of N than in rice straw treatments.