Kazuyuki Inubushi

Seasonal changes of CO2, CH4 and N2O fluxes in relation to land-use change in tropical peatlands located in coastal area of South Kalimantan

Tropical peatland could be a source of greenhouse gases emission because it contains large amounts of soil carbon and nitrogen. However these emissions are strongly influenced by soil moisture conditions. Tropical climate is characterized typically by wet and dry seasons. Seasonal changes in the emission of carbon dioxide (CO(2)), methane (CH(4)) and nitrous oxide (N(2)O) were investigated over a year at three sites (secondary forest, paddy field and upland field) in the tropical peatland in South Kalimantan, Indonesia. The amount of these gases emitted from the fields varied widely according to the seasonal pattern of precipitation, especially methane emission rates were positively correlated with precipitation. Converting from secondary forest peatland to paddy field tended to increase annual emissions of CO(2) and CH(4) to the atmosphere (from 1.2 to 1.5 kg CO(2)-C m(-2)y(-1) and from 1.2 to 1.9 g CH(4)-C m(-2)y(-1)), while changing land-use from secondary forest to upland tended to decrease these gases emissions (from 1.2 to 1.0 kg CO(2)-C m(-2)y(-1) and from 1.2 to 0.6 g CH(4)-C m(-2)y(-1)), but no clear trend was observed for N(2)O which kept negative value as annual rates at three sites.

Contribution of denitrification and autotrophic and heterotrophic nitrification to nitrous oxide production in andosols

To quantify the contribution of denitrification and autotrophic and heterotrophic nitrification to N2O production in Andosols with a relatively high organic matter content, we first examined the effect of C2H2 concentrations on N2O production and on changes in mineral N contents. The optimum C2H2 concentration for inhibiting autotrophic nitrification was 10 Pa. Secondly, and Andosol taken from an arable field was incubated for 32 days at 30°C at 60, 80, and 100% water-holding capacity with or without the addition of NH4+or NOinf3sup-(200 mg N kg-1), and subsamples collected every 4–8 days were further incubated for 24 h with or without C2H2 (10 Pa). At 60 and 80% water-holding capacity with NH4+added, 87–92% of N2O produced (200–250 μg N2O−N kg-1) was derived from autotrophic nitrification. In contrast, at 100% water-holding capacity with or without added NOinf3sup-, enormous amounts of N2O (29–90 mg N2O−N kg-1) were produced rapidly, mostly by denitrification (96–98% of total production). Thirdly, to examine N2O production by heterotrophic nitrification, the Andosol was amended with peptone or NH4+(both 1000 mg N kg-1)+citric acid (20 g C kg-1) and with or without dicyandiamide (200 mg N kg-1). Treatment with citric acid alone or with citric acid+dicyandiamide suppressed N2O production. In contrast, peptone increased N2O production (5.66 mg N2O−N kg-1) mainly by denitrification (80% of total production). However, dicyandiamide reduced N2O production to 1.1 mg N2O−N kg-1. These results indicate that autotrophic nitrification was the main process for N2O production except at 100% water-holding capacity where denitrification became dominant and that heterotrophic nitrification had a lesser importance in the soils examine.

Greenhouse gas emissions from tropical peatlands of Kalimantan,Indonesia

Greenhouse gas emissions were measured from tropical peatlands of Kalimantan, Indonesia. The effect of hydrological zone and land-use on the emission of N2O, CH4 and CO2 were examined. Temporal and annual N2O, CH4 and CO2 were then measured. The results showed that the emissions of these gases were strongly affected by land-use and hydrological zone. The emissions exhibited seasonal changes. Annual emission of N2O was the highest (nearly 1.4 g N m−2y−1) from site A-1 (secondary forest), while there was no signi.cant difference in annual N2O emission from site A-2 (paddy field) and site A-3 (rice-soybean rotation field). Multiplying the areas of forest and non-forest in Kalimantan with the emission of N2O from corresponding land-uses, the annual N2O emissions from peat forest and peat non-forest of Kalimantan were estimated as 0.046 and 0.004 Tg N y−1, respectively. The emissions of CH4 from paddy field and non-paddy field were estimated similarly as 0.14 and 0.21 Tg C y−1, respectively. Total annual CO2 emission was estimated to be 182 Tg C y−1. Peatlands of Kalimantan, Indonesia, contributed less than 0.3 of the total global N2O, CO2 or CH4 emission, indicating that the gaseous losses of soil N and C from the study area to the atmosphere were small.

Changes in mineral N, microbial biomass and enzyme activities in different soil depths after surface applications of dairy shed effluent and chemical fertilizer

A field experiment was conducted to determine the effects of surface applications of dairy shed effluent (DSE) (effluent collected from a dairy milking shed and consists of dung, urine and water) or chemical fertilizer (NH4Cl) on N dynamics, microbial biomass C and N and extracellular enzyme activities (protease, deaminase and urease) in different soil depths. The DSE and NH4Cl were applied to pasture soil at an equivalent rate of 200 kg N ha−1in May and November 1996, as autumn and late spring applications, respectively. Soil samples taken from different soil depths following the autumn application were analyzed for inorganic N, microbial biomass C and N and enzyme activities, while soil samples taken following the late spring application were analyzed for inorganic N only. The soil NH4+concentration, soluble organic C, protease, deaminase and urease activities, and microbial biomass C and N significantly increased in the 0–5 cm soil depth soon after the application of DSE. During the first 30 days, the soluble organic C, microbial C and N and protease activity also increased in the 10–20 cm, while there was no such increase in deaminase and urease activities below 10 cm soil depth. After day 30, the microbial and enzyme activities decreased in the surface as well as in the sub-surface layers possibly due to the exhaustion of the available carbon substrates but remained higher compared to the NH4Cl and control. The NH4Cl application, due to lack of organic substrates, had no effect on soluble organic C, protease or urease activities and biomass C. However, it did increase the deaminase activity and microbial biomass N. The NO3− concentration in lower soil depths of NH4Cl treated soils was significantly higher than those in the DSE and control. This indicates that possible NO3− leaching were more after NH4Cl addition than after DSE. N applied in autumn had higher potential for leaching than that applied in late spring because of increased drainage, lower pasture growth and N uptake during the winter period. Being a source of organic N, DSE showed better performance in maintaining higher pasture yield and N uptake than the NH4Cl and the control. Pasture yield and N uptake were always higher following the spring application than the autumn application because of the optimal environmental condition during summer. These results showed that soil treated with DSE had higher enzyme activities and microbial biomass than soil treated with chemical fertilizers and this may result in longer availability of N for plant uptake and reduce the risk of N leaching losses.

Response to Salinity in Rice: Comparative Effects of Osmotic and Ionic Stresses

Abstract The Effects Of The Osmotic Component Of Salt Stress On Rice Cultivar Ir64 Were Examined. Treatments Were Four Combinations Of Two Levels Of Osmotic Stress At Two Developmental Stages: Medium- And High-Level Stress Applied At The Vegetative And Reproductive Stages Using Salt (Nacl) And Polyethylene Glycol-6000 (Peg) As Sources Of Osmotic Stress. Both Peg And Nacl Reduced The Total Above Ground Biomass And Delayed Flowering And Maturity, With A Longer Delay Observed With The High-Level Stress. The Reduction In Number Of Filled Spikelets, 1,000-Grain Weight, And Hence Grain Yield Was Significantly Greater When They Were Applied During The Reproductive Stage Than During The Vegetative Stage. The Sodium Concentration In Plant Tissues Also Increased In Plants Treated With Nacl, Indicating That Besides Osmotic Stress, Plants Were Also Subjected To Ionic Stress. Treatment With Nacl Decreased The Potassium Concentration In Plant Tissues But Did Not Cause Significant Differences In Phenology, Biomass Accumulation, Yield Or N Uptake Compared With Peg. We Concluded That The Response Of Ir64 To Nacl Was Attributed To The Osmotic Component. These Findings May Be Specific To Ir64, Which Has A Medium Tolerance To Salinity Stress. Further Studies Are Needed With Longer Stress Durations To Achieve A Higher Na+ Concentration In Plant Tissues In Several Varieties With Contrasting Tolerance To Salt Stress To Further Establish The Relative Importance Of Osmotic Versus Ionic Components Of Salt Stress In Rice.

Effects of salts and moisture content on N2O emission and nitrogen dynamics in Yellow soil and Andosol in model experiments

Abstract The effects of salt type and its concentration on nitrification, N mineralization and N2O emission were examined under two levels of moisture content in Yellow soil and Andosol samples as simulated to agriculture under arid/semi-arid conditions and under heavy application of fertilizer in a glass-house, respectively. The salt mixtures were composed of chlorides (NaCl and NH4Cl) or sulphates [Na2SO4 and (NH4)2SO4] and were added at various concentrations (0, 0.1, 0.2, 0.4 and 0.6 M as in the soil solution). These salts were added to non-saline Yellow soil at different moisture contents (45 or 40 and 65% of maximum water-holding capacity; WHC) and their effects on the changes in mineral N (NH4+-N and NO3–-N) concentration as well as N2O emission were examined periodically during laboratory incubation. We also measured urease activities to know the effect of salts on N mineralization. Furthermore, Ca(NO3)2 solution was added at various concentrations (0, 0.1, 0.3, 0.5 and 0.8 M as in the soil solution) to a non-saline Andosol taken from the subsurface layer in a glass-house and incubated at different moisture contents (50% and 70% of WHC) to examine their effects on changes in mineral N. Nitrification was inhibited by high, but remained unaffected by low, salt concentrations. These phenomena were shown in both the model experiments. It was considered that the salinity level for inhibition of nitrification was an electric conductivity (1 : 5) of 1 dS m–1. This level was independent of the type of salts or soil, and was not affected by soil moisture content. The critical level of salts for urease activities was about 2 dS m–1. The emission rate of N2O was maximum at the beginning of the incubation period and stabilized at a low level after an initial peak. There was no significant difference in N2O emission among the treatments at different salt concentrations, while higher moisture level enhanced N2O emission remarkably.

Effect of land-use changes on nitrous oxide (N2O) emission from tropical peatlands

Tropical peatlands could be a potential source of nitrous oxide (N2O) which has a significant impact on global warming. To reduce N2O emission and develop best management practices for peatlands, the formation and emission rates of N2O as affected by land-use management (i.e., changing peatland into agricultural land) and the factors affecting the process must be understood. Therefore, one field and three laboratory incubation experiments were carried out during 1998–99 using peatland soils from 12 sites in South Kalimantan (Indonesia) and one site in Sarawak (Malaysia) to quantify the N2O emission and the factors affecting it. The results from the field experiment showed that land-use managements, changing water table and locations had a significant impact on N2O emission. Changing peatland into cultivated lands (cultivated upland and paddy field) enhanced the N2O emission. For example, cultivated upland Cassava crop resulted in the highest amounts of N2O emission (1.04 mg N m−2 h−1) compared to other treatments. The N2O emission during 1998 was higher than those during 1999 because of the changing water table and dry season in 1998. The laboratory experiments showed that the N2O emission was also strongly influenced by land-use management, soil moisture contents, addition of ammonium fertilizer or rice straw and soil depths. For example, the flooded conditions stimulated the N2O emission compared to that at 60% moisture contents. Similarly, the addition of ammonium fertilizer suppressed the N2O emission compared to control treatments because of the high ammonium contents that inhibit nitrification. Nevertheless, incorporation of rice straw to soil samples from 20 to 40 cm soil depth stimulated N2O emission.

Accumulation of Zinc and Copper in an Arable Field after Animal Manure Application

An experiment was conducted to examine the accumulation and mobility of heavy metals (Zn and Cu) at different depths in three types of arable soils (Brown Lowland soil, Andosol, and Brown Forest soil) amended with cattle and pig farmyard manures for 5 years. Nitric-perchloric acid digestion was performed for the determination of the total amounts of heavy metals, and 0.1 M hydrochloric acid extraction was performed for the determination of the amounts of soluble heavy metals. Results of the soil analysis indicated that pig farmyard manure application resulted in serious contamination of arable soils with Zn and potentially Cu. Especially, the Brown Forest soil displayed a high ability to accumulate heavy metals on the soil surface. Total-Zn concentration in surface soils was considerably affected by the holding capacity of soluble-Zn traction. Although the Andosol amended with pig farmyard manure showed higher concentrations of heavy metals related to the higher ability of retention on a weight basis, the soil did not contribute to high heavy metal accumulation because of its low bulk density. Heavy metals were easily leached in sandy soils such as Brown Lowland soil, and Cu was potentially stable compared with Zn. We suggest that long-term pig farmyard manure application to the Brown Lowland soil and Andosol with a light soil texture is associated with a higher risk of groundwater pollution than the application to the Brown Forest soil.

Effects of organic matter application on microbial biomass and available nutrients in various types of paddy soils

Abstract Twenty three kinds of paddy soils with different applications of fertilizer or organic matter in 6 experimental fields (Gley soil, Gray Lowland soil, and Brown Lowland soil) were collected before flooding. Changes in the contents of microbial biomass carbon (C) and nitrogen (N) measured by the chloroform fumigation-extraction method and adenosine triphosphate (ATP) content in soils were investigated with reference to soil properties, especially available nitrogen and phosphate. Values of E C, extractable soil organic C after fumigation determined by automated combustion oxidation, were affected by the soil types and manuring practices, ranging from 92 to 545 mg C kg−1. In contrast, the values of E N, extractable total N after fumigation, were markedly affected by manuring practices, ranging from 7.8 to 67.7 mg N kg1. The E C/E N ratios also varied with the soil types and manuring practices (range 5-19), and decreased to 5-11 by submerged incubation, suggesting the occurrence of changes in the mic...

Effectiveness of a subsurface drainage system in poorly drained paddy fields on reduction of methane emissions

Abstract Intensive field experiments were conducted from 1999 to 2001 to examine the effects of farmland improvement on methane (CH4) emission from two rice paddy fields in Niigata, Japan. Rice cultivation and field management were similar in both paddy fields; however, one field had a subsurface drainage system installed 0.6–0.8 m below the soil surface (drained paddy field) and the other had no such system (non-drained paddy field). Methane emissions from the drained paddy field during each rice-growing season were approximately 71% lower than those from the non-drained paddy field. The subsurface drainage system lowered the groundwater level and top of the gley soil layer to the drainage pipe level, enhanced soil permeability, and resulted in more oxidized soil conditions in the fallow season. The lower total and hot water extractable carbon in the plowed layer soil of the drained field versus the non-drained field strongly suggests that the organic substrate that gives rise to CH4 decomposed more quickly in the drained field. Ferrous iron concentrations in the fresh plowed layer soil, collected from before submergence up to mid-summer drainage, were also much lower in the drained field. This indicated that ferrous iron produced during the flooding seasons was quickly oxidized to ferric iron in the fallow season, which then acted as an electron accepter and inhibited CH4 production in the subsequent rice-growing season. In contrast, the continuous reductive conditions in the non-drained field (even in the fallow season) prevented most of the ferrous iron from being oxidized. Therefore, installing a subsurface drainage system greatly reduced CH4 emissions by improving aerobic conditions and reducing CH4 production potential. Methane emissions with a large inter-annual variation in the rice-growing season from the non-drained field were positively correlated with soil moisture in the plowed layer before submergence, which, in turn, greatly affected CH4 emission in the following rice-growing season.