Agnes Padre

• PhD
• Consultant at International Rice Research Institute

This study comprises field experiments on methane emissions from rice fields conducted with an Eddy-Covariance (EC) system as well as test runs for a modified closed chamber approach based on measurements at nighttime. The EC data set covers 4 cropping seasons with highly resolved emission rates (raw data in 10 Hz frequency have been aggregated to...

This study comprises a set of methane emission measurements in rice fields located in the four agro-ecological zones of the Mekong River Delta (MRD), namely the zones with (i) alluvial soils, (ii) salinity intrusion, (iii) deep flood, and (iv) acid sulfate soils. These zones have very distinct bio-physical conditions and cropping cycles that will a...

This study aimed to assess the relative influence of key soil parameters on methane and nitrous oxide emissions from rice fields under continuous flooding and alternate wetting and drying (AWD) in four countries in southeast Asia with distinct soil properties.

This study comprises a comprehensive assessment, integration, and synthesis of data gathered from a 3-year field experiment conducted at four sites in Southeast Asia, namely Hue, Vietnam; Jakenan, Indonesia; Prachin Buri, Thailand; and Muñoz, Philippines, to assess the site-specific feasibility of alternate wetting and drying (AWD) as a greenhouse...

Vietnam is the world’s fifth largest rice producing country. Since methane (CH4), a potent greenhouse gas (GHG), emission from the rice cultivation accounts for 14.6% of the national anthropogenic GHG emission, developing and disseminating mitigation options are the urgent need. Alternate wetting and drying (AWD) is the irrigation technique, in whi...

Alternate wetting and drying (AWD) is a water-saving irrigation technique in a paddy field that can reduce the emission of methane, a potent greenhouse gas (GHG). It is being adopted to Asian countries, but different results are reported in literatures on methane, nitrous oxide emission, and rice productivity under AWD. Therefore, the local feasibi...

This study comprises greenhouse gas (GHG) emission measurements on rice fields in the Vu Gia/Thu Bon Basin in Central Vietnam , as part of an interdisciplinary research project. The experiments were conducted in the delta lowland (DL) and hilly midland (HM), over three seasons (summer–autumn in 2011 and 2012; winter–spring season in 2012) with two...

Purpose The objective of this study was to determine the changes in the main soil chemical properties including pH, electrical conductivity (EC), available phosphorus (P), soil organic carbon (SOC) and total nitrogen (TN) stocks after long-term (31 years) additions of two types of organic matters—rice straw and rice straw compost, combined with NPK...

A long-term experiment on combined inorganic fertilizers and organic matter in paddy rice (Oryza sativa L.) cultivation began in May 1982 in Yamagata, northeastern Japan. In 2012, after the 31st harvest, soil samples were collected from five fertilizer treatments [(1) PK, (2) NPK, (3) NPK + 6 Mg ha−1 rice straw (RS), (4) NPK + 10 Mg ha−1 rice straw...

Industrially produced N-fertilizer is essential to the production of cereals that supports current and projected human populations. We constructed a top-down global N budget for maize, rice, and wheat for a 50-year period (1961 to 2010). Cereals harvested a total of 1551 Tg of N, of which 48% was supplied through fertilizer-N and 4% came from net s...

South Asian countries will have to double their food production by 2050 while using resources more efficiently and minimizing environmental problems. Transformative management approaches and technology solutions will be required in the major grain-producing areas that provide the basis for future food and nutrition security. This study was conducte...

Methane (CH4) emissions from rice paddies often show significant diurnal variations, most likely driven by diurnal changes of radiation and temperature in air, floodwater, and soil. Field measurements, however, are often scheduled at a fixed time of a given measuring day, thereby neglecting sub-daily variations of CH4 emissions. Here we evaluated d...

Rice fields are considered as one of the major sources of methane (CH4), and they also emit nitrous oxide (N2O). A field experiment was conducted at the International Rice Research Institute, Philippines, in 2010–2011 using a temperature free-air controlled enhancement (T-FACE) system. Our objectives were to assess (i) the suitability of the T-FACE...

Rapid, precise, and globally comparable methods for monitoring greenhouse gas (GHG) fluxes are required for accurate GHG inventories from different cropping systems and management practices. Manual gas sampling followed by gas chromatography (GC) is widely used for measuring GHG fluxes in agricultural fields, but is laborious and time-consuming. Th...

Rapid, precise, and globally comparable methods for monitoring greenhouse gas (GHG) fluxes are required for accurate GHG inventories from different cropping systems and management practices. Manual gas sampling followed by gas chromatography (GC) is widely used for measuring GHG fluxes in agricultural fields, but is laborious and time-consuming. Th...

New cropping systems and good management practices for different environments were evaluated to maximize crop and input productivity and explore opportunities for greenhouse gas mitigation. In a field trial (clay with 1.27% total C and 0.075% total N) in South India, we compared crop productivity and greenhouse gas (GHG) emissions of a conventional...

Seasonal rainfall in the Philippines is known to be modulated by ENSO phenomenon, with El Niño frequently contributing to reduced rainfall and drought while La Niña resulting in excessive rainfalls, floods and more intense typhoons. The alterations in rainfall patterns can have considerable feedback on solar radiation, air temperature, and soil moi...

An assessment of spatial and temporal variations in methane (CH4) emission was conducted in three experimental fields (UQ, UY and UE) of the International Rice Research Institute Experimental Farm in Bay, Laguna, Philippines during the 2009 dry season. Aside from CH4 fluxes, the following parameters were also determined: hot water-extractable C (HW...

Soil organic matter (SOM) is essential for sustaining food production and maintaining ecosystem services and is a vital resource base for storing C and N. The impact of long-term use of synthetic fertilizer N on SOM, however, has been questioned recently. Here we tested the hypothesis that long-term application of N results in a decrease in SOM. We...

The seasonal and annual variability of sensible heat flux (H), latent heat flux (LE), evapotranspiration (ET), crop coefficient (Kc) and crop water productivity (WPET) were investigated under two different rice environments, flooded and aerobic soil conditions, using the eddy covariance (EC) technique during 2008–2009 cropping periods. Since we had...

The seasonal fluxes of heat, moisture and CO2 were investigated under two different rice environments: flooded and aerobic soil conditions, using the eddy covariance technique during 2008 dry season. The fluxes were correlated with the microclimate prevalent in each location. This study was intended to monitor the environmental impact, in terms of...

Water and nutrient availability are two major constraints in most rice-based rainfed shallow lowland systems of Asia. Both stresses interact and contribute to the low productivity and widespread poverty in this environment. The objective of this study was to improve the understanding of interaction between the two factors and to identify varietal c...

Conventional tillage and crop establishment methods such as puddled transplanting in the rice–wheat (Oryza sativa L.–Triticum aestivum L.) system in the Indo-Gangetic Plains (IGP) require a large amount of water and labor, both of which are increasingly becoming scarce and expensive. We attempted to evaluate alternatives that would require smaller...

The impacts of continuous applications of an organic manure (farmyard manure [FYM], green manure [GM], and wheat straw [WS]) combined with inorganic fertilizers (N, P, and K) on soil parameters and productivity of rice (Oryza sativa L.)–wheat (Triticum aestivum L.) systems were investigated in two long-term experiments under conventional tillage in...

Long-term trends of crop yields have been used as a means to evaluate the sustainability of intensive agriculture. Previous studies have measured yield trends from long-term rice–rice and rice–wheat experiments in different sites from the slopes of individual site regressions of yield over time. The statistical significance of each site regression...

A long-term experiment (LTE) on a rice-wheat system was initiated in 1963 at the Kyushu National Agricultural Experiment Station, in Fukuoka, Japan, to determine the effects of continuous application of rye grass/wheat straw, rice straw and rice straw compost, alone or in combination with inorganic N on crop yields. Increase in rice yields and enha...

tions at specified growth stages is the most common practice followed by the farmers (PhilRice, 1991; Pillai Low N use efficiency (NUE) continues to be a problem in the rice and Kundu, 1993).This does not consider the dynamic (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system. The leaf color chart (LCC)-based real-time N management can...

Soil C oxidized by neutral KMnO4, or permanganate-oxidizable C (POC), has been used as an index of labile C by several workers, although the nature of organic C (OC) oxidized has not been well elucidated. This study aimed to determine the reactivity of diverse organic compounds found in the soil with KMnO4 to judge the reliability of POC as an inde...

Imbalanced and inadequate use of chemical fertilizers is responsible for low rice- (Oryza sativa L.) wheat (Triticum aestivum L.) productivity in many resource-poor farmers' fields. Wheat yields in post-rice soils are also constrained due to soil conditions created by puddling in rice, especially in fine to medium textured soils. Organic amendments...

The rice–wheat cropping system, occupying 24 million hectares of the productive area in South Asia and China, is important for food security. Monitoring long-term changes in crop yields and identifying the factors associated with such changes are essential to maintain and/or improve crop productivity. Long-term experiments (LTE) provide these oppor...

Three 15N labelling strategies for estimating below-ground N in Sesbania rostrata grown in pots under flooded conditions were examined. The estimated proportions of total plant N resident below-ground were 13% (stem injection), 42% (leaf immersion) and 56% (adventitious root feeding). The average estimate based on leaf and root immersion (49%) was...

Major improvements in the productivity of rice (Oryza sativa L.) and wheat (Triticum aestivum L.) have occurred in South Asia since 1965-1966 when the Green Revolution began. However, after the 1980s, yield stagnated or declined. We analyzed grain yield trends, soil C, N, P, and K status, and P and K balances in a 14-yr rice-wheat experiment conduc...

A long-term field experiment was conducted to determine the effects of indigo (Indigofera tinctoria) on the productivity of rainfed lowland rice-based cropping systems: rice–tomato, rice–tobacco or soyabean, rice–maize, and rice–garlic. Indigo was grown as an intercrop during the dry season and incorporated as green manure for wet season rice. Dry...

A long-term field trial was conducted to determine yield trends in relation to nutrient uptake and efficiency in different rice-based cropping systems. The cropping systems had a significant effect on wet season rice yield when residues were not recycled but had no effect otherwise. Rice yield decreased after the first year of crop residue incorpor...

A field experiment was conducted in the dry season at Los Banos, Philippines, to assess the differences in grain yield and N utilization of 10 medium-duration (119�4 days after seeding [DAS]) genotypes and 10 long-duration (130�4 DAS) ones with varying acquisition and usage of soil and fertilizer N. Signi®cant differences among genotypes were obser...

Plant N uptake and grain yield are important components of N use efficiency. Grain yield is easily measured, but plant N analysis is time consuming and requires hazardous chemicals or expensive equipment. A nondestructive method involving the least equipment and skill, to detrmine N uptake, is needed in agronomic and plant breeding experiments. A n...

Field screening trials were conducted in two dry seasons to assess variability in grain yield, N uptake and N utilization for 180 rice genotypes, mostly lowland indica improved varieties or elite breeding lines of different growth durations [60 each of early (100-110 days), medium (111-119 days) and late (120-135 days)], without the addition of N f...

Rice is the most important food crop of the developing world: staple food for over two billion people in Asia and for hundreds of millions in Africa and Latin America. To feed the ever-increasing population of these regions, the world’s annual rice production must increase from the present 460 million tons to 560 m tons by the year 2000 and to 760...

Root and stem nodulation, nitrogen fixation (acetylene-reducing activity), growth and N accumulation by Sesbania rostrata as affected by season and inoculation were studied in a pot experiment. The effects of S. rostrata as a green manure on succeeding wet-season and dry-season rice yields and total N balance were also studied. S. rostrata grown du...

International Rice Research Institute. Saturday Seminars. Feb. 11 1989. 55pages

A plant sampling procedure for measuring ability to stimulate N2 fixation using a modified acetylene reduction (AR) assay for 3 consecutive days at heading stage is described. The method is suitable for detecting rice varietal differences in ability to stimulate N, fixation. The effects of environmental and plant-related factors on ARA (acetylene r...

The effects of incorporation and surface application of straw to a wetland rice field on nitrogen fixation (C2H2 reduction), bacterial population and rice plant growth were studied. Rice straw (5 t ha-1) was chopped (10- to 15-cm pieces) and applied to the field 2 weeks before transplanting IR42, a long-duration variety, and IR50, a short-duration...

Nitrogen fixation associated with 16 rice (Oryza saliva) varieties or lines of short and long durations, grown in a flooded field, during the 1984 wet season and 1985 dry season was measured by a simple and rapid acetylene reduction assay. Assaying the plants at heading stage for 3 consecutive days was found suitable for determining varietal differ...

The effects of incorporation and surface application of straw to a wetland rice field on nitrogen fixation (C2H 2 reduction), bacterial population and rice plant growth were studied. Rice straw (5 t ha-1) was chopped (10- to 15-cm pieces) and applied to the field 2 weeks before transplanting IR42, a longduration variety, and IR50, a short-duration...

Laboratory cultures, soil cultures, and natural samples of N2-fixing blue-green algae (BGA) from rice fields were analyzed for dry matter, ash, N, C, P, and a few other constituents. Results show a very large variability of the composition. Dry matter contents ranged from 0.28% to 13.6% (average 3.3%). Ash contents ranged from 15.6% to 71.3%. Nitro...

Five rice (Oryza sativa L.) varieties with different growth durations were grown in a flooded field with and without straw amendment in the dry and wet seasons of 1984. Plant growth components, plant-associated acetylene-reducing activity (ARA). bacterial enumeration, and soil ARA were measured throughout the rice growth cycle. Plant-associated ARA...

A short-term laboratory acetylene reduction assay using cut plant-soil samples incubated in the dark was developed for measuring relative N2-fixing activities associated with field-grown rice plants. The assay sample consists of rhizosphere soil, root, and cut stem and leaf sheath. The cut plant-soil assay is relatively simple, rapid, and convenien...

The total N content of soils from long-term fertility plots in two sites in the Philippines was measured by Kjeldahl analysis. One site had grown 24 and the other 17 crops of irrigated rice (Oryza sativa L.). It appears that the total soil N at each site did not decrease during the cropping period. There was little evidence that N, P, or K fertiliz...

Uptake of N from a blue-green alga (Nostoc sp.) by rice (Oryza sativa) was studied in pot and field experiments. Availability of UN from blue-green algae incorporated into the soil ranged between 23 and 28% for the first crop and between 27 and 36% for the first and second crops. Surface application of the algal material reduced N availability to 1...

The effect of different methods of nitrogen fertilizer application on the algal flora and biological nitrogen fixation (Acetylene-reducing activity) in a wetland rice soil was studied in pot and field experiments. Broadcast application of urea inhibited nitrogen fixation and favored the growth of green algae. In contrast, deep placement of urea sup...

A long-term field trial, from 1991 to 2000, was conducted in an isohyperthermic udic eutropept clay loam to determine the effect of intensified cropping and fertilizer application on the nutrient status of the soil and crop yield, and to find out the influence of crop residue addition on the yield of rice. There were 5 levels of N applied to rice (...