Land use legacies and nitrogen fertilization affect methane emissions in the early years of rice field development

Methane (CH₄) emissions are critical to greenhouse gas (GHG) management in agriculture, especially in areas growing rice (Oryza sativa). However, studies on CH₄ emissions and the nitrogen (N) fertilization effect in new rice fields in subtropical regions are still scarce. In this study, we designed a split-plot field experiment in Jiangxi Province, southern China, to examine whether land-use legacies and N fertilization would influence CH₄ emissions. Using static chambers and gas chromatography, we measured CH₄ fluxes in a newly developed rice paddy and a 10-year-old rice paddy. We also measured climatic factors and soil chemical and physical properties to match the flux measurements. The results showed that annual CH₄ emissions in the new rice plots were significantly lower than in the old rice plots regardless of N fertilization. Annual CH₄ emissions increased with the land-use years of rice paddies, following the order of 1 year < 2 years < 3 years < 10 years. N fertilization significantly decreased CH₄ emissions by 36.9% in the first year after the new rice plots were developed, whereas it had no significant effects on CH₄ emissions in the old rice plots or the new rice plots in the second and third years. The results suggest that land-use legacies have significant effects on CH₄ emissions and may influence the N fertilization effect on CH₄ emissions in rice fields in subtropical regions. The findings suggest that land-use legacies should be considered in managing and estimating GHG emissions in rice-growing regions.     

Mitigating greenhouse gas and nitrogen loss with improved fertilizer management in rice: quantification and economic assessment

Several technologies have been developed to improve the recovery efficiency of N (RE_N) but their impacts on greenhouse gas (GHG) emission, N loss and economic implication are rarely analysed. A decision support system (DSS) has been developed to quantify inputs, outputs and balance of N in soil; GHG emission and RE_N with the prominent N management technologies in rice. This DSS, named InfoNitro (Information on Nitrogen Management Technologies in Rice), integrated analytical and expert knowledge with databases on bio-physical, agronomic and socio-economical features to establish input–output relationships related to N management in rice. Sixteen technologies, which differed in terms of water regime, method of N application, forms of N and tools of fertilizer recommendation were analysed for their RE_N, N losses, GHG emission and economic return in Haryana, a rice growing region in India. In the current farmers’ practice, RE_N was 32.7%, which increased up to 40.8% with various technologies except in mid-season drainage and alternate flooding technologies where it decreased up to 29.3%. Loss of N through leaching, volatilization and denitrification in the farmers’ practice (67.5 kg N ha⁻¹) decreased up to 40.5 kg N ha⁻¹ except in mid-season drainage and alternate flooding technologies where it increased. The technologies also reduced global warming potential (GWP) by 1 to 9%. However, the technologies except no tillage, mid-season drying and alternate flooding reduced the net income of the farmers. When the environmental cost (cost of N loss and GWP) was included net income with various technologies was either at par or more than the farmers’ practice. The marginal abatement cost of N loss was Rs. 8 to 134 kg⁻¹ N and for GWP was Rs. 766 to 4854 Mg⁻¹ CO₂ eq. Resource conserving technology was the most cost effective strategy to reduce N loss and GHG emission whereas integrated N management cost high for mitigating GHG emission.     

Integrating beef cattle on cropland affects net global warming potential

Recent interest in integrated crop-livestock (ICL) systems has prompted numerous investigations to quantify ecosystem service tradeoffs associated with management. However, few investigations have quantified ICL management effects on net global warming potential (GWP), particularly in semiarid regions. Therefore, we determined net GWP for grazed and ungrazed cropland in a long-term ICL study near Mandan, ND USA. Factors evaluated for their contribution to net GWP included carbon dioxide (CO₂) emissions associated with production inputs and field operations, methane (CH₄) emissions from enteric fermentation by beef cattle, change in soil carbon stocks, and soil-atmosphere CH₄ and nitrous oxide (N₂O) fluxes. Net GWP was significantly greater for grazed cropland (946 kg CO_2equiv. ha^-1 yr^-1) compared to ungrazed cropland (200 kg CO_2equiv. ha^-1 yr^-1) (P=0.0331). The difference in net GWP between treatments was largely driven by emissions from enteric fermentation (602 kg CO_2equiv. ha^-1 yr^-1). Among other contributing factors, CO₂ emissions associated with seed production and field operations were lower under ungrazed cropland (P?=?0.0015 and 0.0135, respectively), while soil CH₄ uptake was greater under grazed cropland (P?=?0.0102). Soil-atmosphere N₂O flux from each system negated nearly all the CO_2equiv. sink capacity accrued from soil carbon stock change. As both production systems resulted in net greenhouse gas (GHG) emissions to the atmosphere, novel practices that constrain GHG sources and boost GHG sinks under semiarid conditions are recommended.

     

Comparing a process-based agro-ecosystem model to the IPCC methodology for developing a national inventory of N2O emissions from arable lands in China

Nations are now obligated to assess their greenhouse gas emissions under the protocols of Article 4 of the United Nations Framework Convention on Climate Change. The IPCC has developed `spreadsheet-format' methodologies for countries to estimate national greenhouse gas emissions by economic sector. Each activity has a magnitude and emission rate and their product is summed over all included activities to generate a national total (IPCC, 1997). For N₂O emissions from cropland soils, field studies have shown that there are important factors that influence N₂O emissions at specific field sites that are not considered in the IPCC methodology. We used DNDC, a process-oriented agroecosystem model, to develop an unofficial national inventory of direct N₂O emissions from cropland in China. We assembled county-scale data on soil properties, daily weather, crop areas, N-fertilizer use, livestock populations (for manure inputs to cropland), and agricultural management for the 2500 counties in mainland China. Total 1990 cropland area was 0.95 million km². Total N-fertilizer use in China in 1990 was 16.6 Tg N. The average fertilization rate was 175 kg N ha⁻¹ cropland. One-year simulations with DNDC were run for each crop type in each county to generate estimates of direct N₂O emissions from soils. National totals were the sum of results for all crop simulations across all counties. Baseline simulations estimated that total N₂O emission from arable land in China in 1990 was 0.31 Tg N₂O-N yr⁻¹. We also ran simulations with zero N-fertilizer input; the difference between the zero-fertilizer and the baseline run is an estimate of fertilizer-induced N₂O emissions. The fertilizer-induced emission was 0.13 Tg N₂O-N yr⁻¹, about 0.8% of total N-fertilizer use (lower than the mean but within the IPCC range of 1.25±1.0%). We compared these results to our estimates of county-scale IPCC methodology emissions. Total emissions were similar but geographical patterns were quite different. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nutrients fixation by algae and limiting factors of algal growth in flooded rice fields under semi-arid Mediterranean conditions: case study in Thessaloniki plain in Greece

The aim of this study is to assess the fixation of the major nutrients C, N, P, Ca, Mg, K, Na by algal biomass produced in the rice fields of Thessaloniki plain in Greece under semi-arid Mediterranean conditions and to evaluate the limiting factors for their growth. Measurements were performed in experimental rice-field following the regional conventional practices (C–H treatment): (a) direct sowing, (b) continuous flooding with few intermissions, (c) use of nitrogen fertilizers at 176 kg N ha^?1, and (d) application of herbicides (active ingredients benzofenap and clomazone). Herbicides were not applied in a small part of the field isolated by bunds (C–NH treatment) in order to assess possible limiting effects of herbicides on algae growth. Climatic data, measurements of rice crop characteristics and water quality of the ponded water in the C–H part of the experimental field were also obtained in order to assess the limiting effects of light, temperature and nutrients based on a modelling approach. Green algae were found to be dominant in the specific system. Considering the two treatments, the results showed that herbicides did not affect algae growth probably due to the short period of exposure followed by the continuous flooding. Nutrients fixation by algae for C–H followed the order C (52.1 %) > Ca (5.6 %) > K (3.5 %) > N (2.4 %) > Mg (0.3 %) ≈ Na (0.3 %) > P (0.24 %) with a final dry biomass production at 1,118 kg ha^?1. Based on the measurements and model simulations the most limiting factors under the regional conventional practices of rice cultivation were the temperature at the initial and final stage of rice growing season, the light when the leaf area index of rice was >2 and phosphorus concentration in the ponded water. The mean algae growth rate during the flooding period was estimated at 8.2 kg ha^?1 day^?1, while the maximum rate was estimated at 15.9 kg ha^?1 day^?1 at the initial growth stages of rice before the beginning of intense light limitations from rice crop coverage.     

Urea briquette applicator for transplanted rice

A plunger-type, completely hand-operated applicator prototype, made of polyvinyl chloride (PVC), for deep placement of urea briquettes (UB), i.e., pillow-shaped urea supergranules with edges, in line transplanted rice has been developed for use by small-scale rice farmers. The field evaluation of the applicator was conducted in the Philippines during the 1989 dry season. The applicator consistently placed UB at proper depth (7 to 8 cm), which resulted in low concentrations of urea N (<7 ppm) in about 4 cm of floodwater 1 day after placement. These findings indicated that the prototype worked properly. Average work output of the applicator was 0.20 ha workday^–1 and may increase with practice. The yields of irrigated transplanted rice in the field trials show that agronomic efficiencies of hand-placed UB and applicator-placed UB were equal and were superior to those of split-applied prilled urea.     

Net ecosystem CO2 exchange and carbon cycling in tropical lowland flooded rice ecosystem

The seasonal fluxes of CO₂ and its characteristics with relation to environmental variables were investigated under tropical lowland flooded rice paddies employing the open path eddy covariance technique. The seasonal net ecosystem carbon budget was quantified by empirical modelling approach. The integrated net ecosystem exchange (NEE), gross primary production (GPP) and ecosystem respiration (RE) in the flooded rice field was ?448, 811 and 363 g C m^?2 in wet season. Diurnal variations of mean NEE values during the season varied from +3.99 to ?18.50 μmol CO₂ m^?2 s^?1. The daily average NEE over the cropping season varied from +2.73 to ?7.74 g C m^?2 day^?1. The net ecosystem CO₂ exchange reached its maximum in heading to flowering stage of rice with an average value of ?5.67 g C m^?2 day^?1. On daily basis the flooded rice field acted as a net sink for CO₂ during most of the times in growing season except few days at maturity when it became a net CO₂ source. The rate of CO₂ uptake by rice as observed from negative NEE values increased proportionally with air temperature up to 34 °C. The carbon distribution in different component of soil-plant system namely, soil organic carbon, dissolved organic carbon, methane emission, rhizodeposition, carbon in algal biomass, crop harvest and residues were quantified and carbon balance sheet was prepared for the wet season in tropical rice. Carbon balance sheet for tropical rice revealed 7.12 Mg C ha^?1 was cycled in the system in wet season.     

Morphology and mechanical properties of semi-interpenetrating polymer networks from polyurethane and benzyl konjac glucomannan

A series of semi-interpenetrating polymer network (semi-IPN) films coded as UB from castor oil-based polyurethane (PU) and benzyl konjac glucomannan (B-KGM) were prepared, and they have good or certain miscibility over entire composition range. Morphology, miscibility and properties of the UB films were investigated by using scanning electron microscopy (SEM), differential scanning calorimetry, dynamic mechanical analysis, ultraviolet spectrometer, wide-angle X-ray diffraction and tensile test. The results indicated that the UB films exhibited good miscibility when B-KGM content was lower than 15 wt%, resulting in relatively high light transmittance, breaking elongation and density. With an increase of the B-KGM content from 20 to 80 wt%, a certain degree of phase separation between PU and B-KGM occurred in the UB films. The tensile strength of the films UB increased from 7 to 45 MPa with an increase of B-KGM content from 0 to 80 wt%. By extracting the B-KGM with N, N-dimethylformamide from the semi-IPN, the morphology and phase domain size of the UB films were clearly observed by SEM. A continuous phase and dual-continuous phase model describing the semi-IPN were proposed to illustrate the morphology and its transition.     

Synergistic Enhancement and Separation of Zirconium(IV) and Hafnium(IV) with 3-Phenyl-4-Benzoyl-5-Isoxazolone in the Presence of Crown Ethers

Abstract

3-Phenyl-4-benzoyl-5-isoxazolone (HPBI) was synthesized and examined with regard to the synergistic solvent extraction behavior of zirconium(IV) and hafnium(IV) in the presence of various crown ethers (CEs), namely, 18-crown-6 (18C6), dicylohexano-18-crown-6 (DC18C6) and benzo-15-crown-5 (B15C5) from hydrochloric acid solutions. The results demonstrated that zirconium(IV) and hafnium(IV) were synergistically extracted into chloroform with mixtures of HPBI and CEs as ZrO(PBI)₂ · CE and HfO(PBI)₂ · CE, respectively. The complexation strength follows the order DC18C6 >18C6 > B15C5. The addition of CEs not only enhances the extraction efficiency of zirconium(IV) and hafnium(IV) but also significantly, especially in the presence of B15C5, improves the selectivity (Zr/Hf = 4.73) between these metal ions as compared to HPBI alone (Zr/Hf = 2.09). On the other hand, selectivity has been moderately decreased by the addition of 18C6 or DC18C6 to the metal-chelate system.     

Nitrogen loss and rice profits with matrix-based slow-release urea

Paddy fields account for a large proportion of cultivated land, with huge N consumption each year. Reducing N loss via application of low-cost slow-release fertilizers is beneficial for eco-friendly rice production. The current study aimed to investigate the effects of matrix-based urea on soil N availability, rice yield, agronomical efficiency (AE), and rice profits. A 2-year field experiment was conducted during 2015 and 2016 following a randomized block design. It included three treatments, i.e., control test (CK, without urea application), common urea (CU, 150 kg N ha^?1), and matrix-based urea (MU, 150 kg N ha^?1). Besides, three laboratory experiments were conducted to investigate the N leaching, ammonia volatilization, and slow-release mechanism. Results showed that application of MU increased rice yields by > 10%, biomass by > 6%, and AE by > 30% in both seasons. Greater yield, biomass, and AE in MU were largely attributed to higher soil available N, resulted from lower risk of N leaching and ammonia volatilization. Aggregate structure was partly responsible for lower N loss in MU. Greater soil available N in MU increased rice height, leaf area, root area, leaf total chlorophyll, and activity of nitrate reductase and glutamine synthetase in flag leaves, and thus favored rice growth. Compared with CU, MU increased fertilizer cost by about 23 USD ha^?1, but increased rice profits by > 230 USD ha^?1 due to greater yield. Overall, matrix-based urea is suitable for application in field rice production, due to its low risk of N loss and acceptable profitability.     

Effect of digested sewage sludge on the efficiency of N-fertilizer applied to barley

Enhanced microbial activity following sewage sludge land application may affect soil N cycling and, therefore, plant available N. We studied the effect of anaerobically treated sewage sludge on N-fertilizer efficiency and on some aspects of the soil N cycling. Field plots (3 m × 9 m) sown with barley (Hordeum vulgare L.) in November were amended with a) sludge (80 mg ha-¹) and ammonium nitrate (150 kg N ha-¹), b) ammonium nitrate (150 kg ha-¹) only, c) or left unamended. Monthly soil samples were taken from 0 to 20-and 20 to 50-cm depths to determine soil inorganic N (NH₄ ⁺, NO₃-). Denitrification in the upper 20-cm horizon was estimated by measuring N₂O+N₂ emission from undisturbed soil samples by the acetylene-inhibition technique. Crop yield parameters were analysed before harvesting, and grain production was recorded. With respect to the control, the yield increase for the N-fertilizer treatment was 85% and 45% for the sludge + N-fertilizer treatment. The decrease of N-fertilizer efficiency in sludge amended plots was presumably due to a decrease in spring plant available N. Presumably, microbial immobilisation and denitrification in organic amended treatments were responsible for the decrease in N-fertilizer efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and properties of shape memory polyurethanes generated from schiff-base chain extender containing benzoyl and pyridyl rings

In this study, 4,4′-diphenylmethane diisocyanate and polytetramethylene glycol were used to prepare a prepolymer; N,N′-bis(4-hydroxybenzylidene)-2,6-diaminopyridine (BHBP) was used as a chain extender; and these elements were combined to prepare a novel polyurethane, BHBP/PU. Gel permeation chromatography revealed that the molecular weight of the BHBP/PU samples increased as the BHBP content was increased. Fourier transform infrared spectroscopy demonstrated that high BHBP content facilitated strong hydrogen bonding in the samples. Differential thermogravimetry indicated that the initial decomposition temperature of BHBP/PU-3 was approximately 10 °C higher than that of BHBP/PU-1. Differential scanning calorimetry and dynamic mechanical analysis revealed that increasing the BHBP content substantially increased both the glass transition and dynamic glass transition temperatures of the BHBP/PU samples. The tensile strengths of BHBP/PU-1, BHBP/PU-2, and BHBP/PU-3 were 7.7, 10.9, and 21.6 MPa, respectively, with corresponding Young’s moduli of 0.7, 1.9, and 3.3 MPa. These results demonstrated that both the tensile strength and Young’s modulus of the BHBP/PU samples increased as the BHBP content was increased. Moreover, the BHBP/PU samples exhibited excellent shape recovery of >90%.     

Effects of NCO/OH molar ratio on miscibility and properties of semiinterpenetrating polymer networks from polyurethane and benzyl konjac glucomannan

Semi‐interpenetrating polymer network (semi‐IPN) films with different NCO/OH molar ratios of the urethane prepolymer, coded as UB, were prepared from polyurethane (PU) and benzyl konjac glucomannan (B‐KGM) by a casting method. The effect of the NCO/OH molar ratio of the urethane prepolymer on the miscibility and properties of the UB films was investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, thermogravimetric analysis, and swelling and tensile tests. The results indicated that, with an increase of the NCO/OH ratio, the crosslink density of the UB films increased, resulting in improved miscibility between PU and B‐KGM and a relatively high light transmittance of the UB films. However, the thermal stability of the UB films decreased with increase of the NCO/OH ratio of the urethane prepolymer, due to the depolymerization of the urethane bonds of the PU networks. When the NCO/OH ratio increased from 2 to 4, the tensile strength of the UB films increased from 15 to 27 MPa, while the breaking elongation decreased from 72 to 16%, resulting from the chemical and physical crosslinks, namely, the enhancement of the covalent bonds and hydrogen‐bonding networks. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1304–1310, 2003     

Micro-computerized tomography analysis of cement voids and pull-out strength of glass fiber posts luted with self-adhesive and glass-ionomer cements in the root canal

This study evaluated the pull-out strength of different glass fiber posts and measured volume of cement and voids in the cement in the root canal utilizing micro-computerized tomography (micro-CT) analysis after they were cemented with two different luting cements. Canine teeth (N = 40) were endodontically treated and randomly divided into four groups depending on the fiber post and the cement type (n = 10 per group) as follows: Group RU: (RelyX + RelyX U200), Group PU: (PINpost + RelyX U200), Group RF: (RelyX + FujiCEM 2), Group PF: (PINpost + FujiCEM 2). Each tooth was scanned using micro-CT and the percentage of cement and void volume at the coronal, middle, and apical levels was calculated. Pull-out tests were performed by applying tensile load parallel to the long axis of the posts (0.5 mm/min). Data were analyzed using, ANOVA, Kruskal–Wallis, and Mann–Whitney U tests (α = 0.05). Regardless of cement type, the percentage (%) of cement volume in the RelyX post groups (RU:31–36; RF:29–40) was significantly higher than that in the PINpost groups (PU:19–23; PF:18–22) (p < 0.05). The percentage of void volume at the PINpost groups (PU:6–11; PF:8–13) was significantly lower than that in the RelyX groups (RU:2; RF:3) (p < 0.05). No significant differences were observed in pull-out strength (N) between the four experimental groups (RU:358.8 ± 56.2; RF:299 ± 64.8; PU:311.9 ± 61.3; PF:293.1 ± 91.3) (p > 0.05). The micro-CT analysis demonstrated that the percentage of cement and void volumes vary depending on the type of fiber post and cement used. No correlation between cement, void volume, and pull-out strength was observed.     

Greenhouse gas intensity and net annual global warming potential of cotton cropping systems in an extremely arid region

A long-term fertilizer experiment investigating cotton-based cropping systems established in 1990 in central Asia was used to quantify the emissions of CO₂, CH₄ and N₂O from April 2012 to April 2013 to better understand greenhouse gas (GHG) emissions and net global warming potential (GWP) in extremely arid croplands. The study involved five treatments: no fertilizer application as a control (CK), balanced fertilizer NPK (NPK), fertilizer NPK plus straw (NPKS), fertilizer NPK plus organic manure (NPKM), and high rates of fertilizer NPK and organic manure (NPKM+). The net ecosystem carbon balance was estimated by the changes in topsoil (0–20 cm) organic carbon (SOC) density over the 22-year period 1990–2012. Manure and fertilizer combination treatments (NPKM and NPKM+) significantly increased CO₂ and slightly increased N₂O emissions during and outside the cotton growing seasons. Neither NPK nor NPKS treatment increased SOC in spite of relatively low CO₂, CH₄ and N₂O fluxes. Treatments involving manure application showed the lowest net annual GWP and GHG intensity (GHGI). However, overuse of manure and fertilizers (NPKM+) did not significantly increase cotton yield (5.3 t ha^?1) but the net annual GWP (?4,535 kg CO₂_eqv. ha^?1) and GHGI (?0.86 kg CO₂_eqv. kg^?1 grain yield of cotton) were significantly lower than in NPKM. NPKS and NPK slightly increased the net annual GWP compared with the control plots. Our study shows that a suitable rate of fertilizer NPK plus manure may be the optimum choice to increase soil carbon sequestration, maintain crop yields, and restrict net annual GWP and GHGI to relatively low levels in extremely arid regions.     

Study of bimetallic corrosion related to Cu interconnects using micropattern corrosion screening method and Tafel plots

On-chip microscopic corrosion, originating from contact of dissimilar metals, can cause serious reliability issues for integrated circuits and microelectromechanical devices. A new micropattern corrosion screening method combined with Tafel plots were employed to study Cu bimetallic corrosion in acid and base solutions relevant to the chemical–mechanical planarization process. The results demonstrated that Cu corrosion on Ru is much more severe compared to Cu corrosion on Ta substrates. Tafel plots confirm the nobility trend of Ru > Cu > Ta. The micropattern corrosion study shows the Cu bimetallic corrosion depends on specific chemicals and bimetallic contacts. Strong complexing ligands like NH₃ combined with energetically favorable Cu/Ru bimetallic contact promote faster Cu corrosion under alkaline conditions (9 ≤ pH ≤ 11.4). Micropattern corrosion screening was shown to be useful in identifying the metastable surface layer during Cu corrosion and determining the optimal benzotriazole concentration for Cu corrosion inhibition.     

Soil aggregates response to tillage and residue management in a double paddy rice soil of the Southern China

Soil aggregate stability is a key indicator of soil quality and environmental sustainability of agroecosystems. The protection of organic material within aggregates against microbial decomposition is regarded as an important process in soil organic carbon stabilization but detailed knowledge about this process is still lacking. The objective of our study was to examine the multiple year effects of plow tillage with residue removed (PT0), plow tillage with residue incorporation (PT), rotary tillage with residue retention (RT), and no-till with residue retention (NT) on soil water stable aggregates (WSA) under a double rice (Oryza sativa L.) cropping system in the Southern China. Results showed that the NT system increased the proportion of >2 mm aggregate fraction, and reduced the proportion of <0.053 mm aggregates at 0–5 cm depth in 2011. Compared with PT0 and PT, significantly higher large macroaggregate (>2 mm) associated-C contributions to TOC were observed in the surface layer (0–10 cm depth) under RT and NT. A significant positive correlation between TOC and macroaggregate (>2 and 2–0.25 mm) associated-C was observed at 0–20 cm soil depth in the paddy rice ecosystem. Therefore, conversion to NT, could enhance the formation of stable macroaggregate, macroaggregates associated-C, and total C contents in paddy soil of Southern China.     

Deep placement of urea supergranules in transplanted rice: Principles and practices

Rice is the most important food crop in the developing countries of Asia, where population densities are very high and overall dietary levels are not adequate. In south and southeast Asia, rainfed and irrigated transplanted rice occupies nearly two–thirds of the rice-growing area and produces more than 80% of the paddy rice. In these areas, prilled urea (PU) conventionally applied by farmers is very inefficiently used by transplanted rice largely because of serious losses (up to 60% of applied N) via NH₃ volatilization, denitrification, leaching, and/or runoff. In order to minimize N loss, especially loss due to denitrification, historically the Japanese have used different ways of deep placing fertilizer N. In 1975, IFDC proposed use of supergranules of urea (USG) in place of mudballs containing urea fertilizer to achieve the same agronomic benefits as achieved through the Japanese concept of deeppoint placement of fertilizer N in transplanted rice. USG can be prepared by melt-type processes (pan granulation, falling curtain, and fluid bed) and briquetting (a special type of compaction). The latter process seems to be the most cost-effective viable alternative. Small-scale briquetting machines have been developed to produce urea bgriquettes (UB) at village level at a rate of 200–250 kg h^?1. Basically, USG are large, discrete particles of ordinary urea [(NH₂)₂CO] containing 46% N as NH₂ (amide form); their weights may vary from 1 to 2 g per particle. USG from melt granulation process are nearly spherical with a relatively smooth surface, while UB from briquetting will be pillow-shaped with broken edges. Placement of USG can be done efficiently by handafter conventional line transplanting (e.g., researcher's method or IFDC transplanting guide method) orduring line transplanting (e.g., IFDC dispenser method) at the rate of one USG near the center of each four rice hills to a 7–10 cm soil depth. The IFDC methods have been developed mainly for economically disadvantaged small rice farmers of developing countries, especially those who transplant rice at random in rainfed areas. Other alternative manual methods such as incorporation of broadcast USG, random deep placement of USG by hand before line transplanting, or the deep placement by foot before or after transplanting may be less labor intensive; however, their agronomic efficiency has been low and highly variable, and they therefore cannot be recommended to farmers. Various continuous operation-type applicators (prototypes) have been developed in the Philippines, India, and China for mechanical deep placement of USG in line-transplanted rice. A few prototypes have been found to be labor saving and agronomically efficient when tested on research farms. However, several design-related problems associated with their metering mechanisms, placement depths, closing of furrows at the placement sites, output per workday, and/or operators' comfort, etc., need to be solved. In short, continuous operation-type applicators that are affordable and still efficient for deep placement of UB are not yet available for use on farmers' fields where floodwater and soil conditions vary substantially. The noncontinuous operation-type UB applicator prototype developed by IFDC is not as labor saving as the continuous operation-type applicators. However, its proper use with adequate practice can help to minimize the drudgery and to save up to 40% of the labor required for the hand placement method. This completely manual UB applicator, made of polyvinyl chloride (PVC) is simple to use, lightweight, and affordable as well as agronomically efficient on farmers' fields. As a result of diffusive transport and cation exchange, typically steep concentration gradients (or spatial distribution patterns) of ammonium exist at the placement sites and eventually control the rate and duration of availability of USG-N to the rice plants. USGper se is not a slow-release nitrogen fertilizer but behaves like a slowly available nitrogen fertilizer. Because the deep-placed USG-N is well protected from various N loss mechanisms (except leaching) at the placement sites in soils and the spatial ammonium concentration gradients help to improve its plant availability, (1) uptake of N by rice plants (recovery) is significantly increased, (2) relatively smaller amounts of USG-N as nonexchangeable ammonium and/or immobilized organic N stay in soil, and (3) eventually N losses (gaseous and runoff) are markedly decreased. Thus, this practice is agronomically efficient as well as environmentally safe. However, this practice should not be used in permeable soil with coarse texture and low cation exchange capacity (CEC) because the high loss of USG-N via leaching will significantly decrease N uptake by the rice plants and eventually grain yield too. Several hundred field trials conducted by national and international institutions in south and southeast Asia since 1975 have demonstrated the agronomic superiority of the deep placement of USG vis-a-vis split applications of PU in transplanted rice. In general, paddy yield responses to deep-placed USG tend to be more curvilinear than do those to split-applied PU, thus resulting in higher agronomic efficiency for deep-placed USG in the lower range of N rates (30–80 kg N ha^?1) than in the higher range of N rates (> 90 kg N ha^?1). Depending on agroclimate and N rates used, in general deep-placed USG can help to provide a saving of urea fertilizer of up to 65% with an average of 33% and can help to increase grain yields up to 50% with an average of 15% to 20% over that with the same amount of split-applied N as PU, especially in the lower range of N rates. USGper se is not an efficient nitrogen fertilizer, but the proper deep placement of USG in transplanted rice makes it agronomically efficient. In using USG, consideration of the following factors should help to ensure agronomic efficiency of deep-placed USG and increase the chances of obtaining additional yield.

1. Soil factors: Only use in soils having a low water percolation rate and a CEC ? 10 meq 100 g^?1 soil.
2. Plant factors: Give preference to short- to medium-duration dwarf rice varieties. For the longduration variety, basal deep-placed USG with a suitable topdressing of N as PU at panicle initiation stage would be helpful.
3. Management factors: Apply basally 30 to 60 kg USG-N ha^?1 using only USG of the right weight (1–2 g urea granule^?1). Place one supergranule for each four hills at 7–10 cm soil depth using the right plant population and modified spacing. Use modified 20 cm × 15 cm or 20 cm × 20 cm spacing to facilitate efficient placement of USG by hand or machine. Workers should always use the so-called traffic lane of the modified spacing for performing all post-transplanting field operations. When deep placement of USG is delayed after transplanting, extra care is necessary to close the holes left at the placement sites. When puddling is inadequate or improper and deep placement is done during transplanting, some care may be required to close the holes.

A scheme of small-scale production of UB at village level, using briquetting machines and locally available PU as a feedstock, looks promising for developing countries. The estimated production cost of UB is likely to be up to 10% higher than that of PU. In general, the estimated incremental benefit/cost ratios of hand deep-placed USG in line-transplanted rice are quite attractive, usually ?5 for small rice farmers of developing Asia. Technological and agroeconomic considerations suggest that the practice of hand deep placement of USGduring or after line transplanting appears to be a right agrotechnology for the resource-scarce small rice farmers of developing countries for efficiently using affordable doses of nitrogen (30–60 kg UB-N ha^?1) to significantly increase grain yields of transplanted rice. For other rice farmers who are not economically handicapped, who have access to irrigation, and who transplant rice in line and can afford to use high rates of N (> 90 kg N ha^?1), it can be an attractive practice, if appropriate machines for deep placement of USG have been developed. Therefore, research and development work is needed to develop affordable, labor-saving, and agronomically efficient continuous operation-type applicators for mechanical deep placement of UB. The use of USG as a source of N for transplanted rice has potential in developing countries. What is now required is to first develop practical stepwise and region-specific agrotechnologies consisting of appropriate UB supply schemes and rice farming systems based on hand or machine deep placement of UB in line-transplanted rice for different regions in a given country. Then it will be necessary to adopt an appropriate diffusion strategy for transfer of the region-specific agrotechnologies to the rice farmers. In this extension activity, long-term commitment and integrated efforts are required by national government organizations as well as by nongovernment organizations and the fertilizer industry.     

Agronomic performance of urea briquette applicator in transplanted rice

Field trials were conducted in the Philippines and India during 1989 and 1990 seasons to study comparative yield responses of transplanted rice (Oryza sativa L.) to pillow-shaped urea briquettes (UB) deep placed by an applicator (prototype developed by IFDC) and by hand immediately after transplanting. The applicator-placed UB consistently increased grain yields over the split-applied prilled urea, and the additional yields ranged from 0.23 to 1.48t ha^–1 (5 to 83%) for 25 to 63 kg N ha^–1. Agronomic responses of transplanted rice to the UB placed by the applicator and by hand were statistically equal. Modified rice hill spacing may be considered as a requirement for efficient use of the applicator. The results demonstrate that with the UB applicator it is possible to deep place UB mechanically and achieve the agronomic efficiency that is achieved by hand deep placement of the UB.     

Nitrate percolation and discharge in cropped Andosols and Gray lowland soils of Japan

Contamination of groundwater with nitrate (NO₃) derived from agricultural activity is serious problem in many countries worldwide. We investigated the annual (growing and non-growing seasons) behavior of NO₃–N in the soil pore water of cropped Andosols and Gray lowland soils under eight crop groups (Type A: paddy rice, Type B: winter crops, Type C: vegetables 1, Type D: vegetables 2, Type E: vegetables and forages, Type F: legume crops, Type G: orchard, and Type H: grass). In the vegetable group (Type C) and the orchard group (Type G), which required large amounts of fertilizer and frequent top-dressing, NO₃–N concentrations in the soil pore water were extremely high. In these agricultural lands, it was clear that the inorganic nitrogen produced by nitrification in surface soil was dominantly discharged from a depth of 90 cm in July to September. The descending order of the amount of discharge of NO₃–N (N-discharge) was Type C > G > D > E > F > B > H > A for the Andosol, and Type G > C > F > D > E > B > H > A for the Gray lowland soil. If fertilization of the vegetables and orchard was performed based on the standard application amount, the annual average NO₃–N concentration at a depth of 90 cm exceeds 10 mg L^?1. To reduce the risk of groundwater contamination by NO₃–N, we calculated the annual cumulative water flux density and annual cumulative NO₃–N flux density. We examined the calculated fertilizer amount and proposed reduced fertilizer application amounts so that the annual average concentration of NO₃–N in soil pore water would not exceed 10 mg L^?1. The standard application amount of nitrogen fertilizer for vegetables should be reduced by 65.8 and 30.8 kg ha^?1 in the Andosol and the Gray lowland soil, respectively. We also proposed that the standard application amount of nitrogen fertilizer be reduced by 59.9 and 40.7 kg ha^?1 in Andosol orchards and Gray lowland soil orchards, respectively.