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Dry direct seeding of rice (DDSR) is being increasingly used in water-scarce areas across Asia. When drought occurs, deep sowing may enable germinating seeds to utilize the residual moisture below the surface. Our objective was to examine the effects of different sowing depths on DDSR crop growth. Two yield experiments, one in the Philippines and the other in Japan, were established in rainfed lowlands, but drought did not occur. Across the experiments, sowing at a depth of 6 to 7 cm reduced the percentage of emergence compared with sowing at a depth of 1 to 2 cm (25% vs. 73%), which resulted in lower yield (3.5 vs. 4.4 t ha−1). The relative yield (deep-sowing/shallow-sowing) was positively correlated with the percentage emergence under deep sowing. Cultivars with no significant yield reduction under deep sowing maintained high emergence (>30%) under deep sowing. Seedling's ability to emerge after deep sowing greatly differed among cultivars: the percentage emergence ranging from 0% to 18% from a depth of 8 to 10 cm, and from 11% to 44% from a depth of 6 to 7 cm. An ancillary field experiment was conducted under drought during the dry season in the Philippines: deep sowing increased the percentage emergence compared with shallow sowing (41% vs. 5%), when the soil surface was severely dry. Our results suggest that choosing cultivars that can tolerate deep sowing is a prerequisite for using deep sowing in DDSR, and that future breeding of DDSR should focus on this tolerance. [ABSTRACT FROM AUTHOR]

The use of herbicides in combination with hand weeding has been shown to be effective against a variety of weeds in irrigated and rainfed wet direct-seeded rice in the Philippines. In the case of dry direct-seeded-drip-irrigated rice; however, these aspects are not known. A study was conducted to determine the influence of two weed control techniques on weeds, yield, and economics of dry direct-seeded-drip-irrigated rice under Philippine conditions. Four treatments -- [T1] unweeded; [T2] application of pre-emergence herbicide using pretilachlor, followed by two times hand weeding; [T3] application of post-emergence herbicide using bispyribac-sodium, followed by two times hand weeding; and [T4] weed-free using the sequential application of pre- and post-emergence herbicides followed by six times hand weeding -- were tested and arranged in RCBD with three repetitions. T1 has the highest weed density and biomass with lower grain yield (901.8 kg ha-1) but no net income. T2 and T3 had lower weed biomass than T1 but could not be compared with T4, where no weed density and biomass were recorded at 15, 30, and 45 DAS (days after seeding) in both dry and wet seasons. Grain yields at T2 (3,794.4 kg ha-1) were not significantly different from T3 (4,341.3 kg ha-1) except when compared with T4 (5,7245 kg ha-1). Net income in T2 was higher by PHP 20,575.1 over T1 and T3 by PHP 9,831.4 over T2. T4 had the highest grain yield among all treatments and achieved an advantage of PHP 45,272.1, 24,697.0, and 14,865.7 over T1, T2, and T3, respectively, in terms of net income. Herbicide application followed by hand weeding reduced weed growth and improved rice yield and net income. The combination of preand post-emergence herbicides followed by six times hand weeding was much more effective at suppressing weeds and achieving higher grain yield and net income. [ABSTRACT FROM AUTHOR]

Worldwide, rice production contributes about 10% of total greenhouse gas (GHG) emissions from the agricultural sector, mainly due to CH4 emissions from continuously flooded fields. Alternate Wetting and Drying (AWD) is a promising crop technology for mitigating CH4 emissions and reducing the irrigation water currently being applied in many of the world's top rice‐producing countries. However, decreased emissions of CH4 may be partially counterbalanced by increased N2O emissions. In this case study for the Philippines, the national mitigation potential of AWD is explored using the process‐based biogeochemical model LandscapeDNDC. Simulated mean annual CH4 emissions under conventional rice production for the time period 2000–2011 are estimated as 1,180 ± 163 Gg CH4 yr−1. During the cropping season, this is about +16% higher than a former estimate using emission factors. Scenario simulations of nationwide introduction of AWD in irrigated landscapes suggest a considerable decrease in CH4 emissions by −23%, while N2O emissions are only increased by +8%. Irrespective of field management, at national scale, the radiative forcing of irrigated rice production is always dominated by CH4 (>95%). The reduction potential of GHG emissions depends on, for example, number of crops per year, residue management, amount of applied irrigation water, and sand content. Seasonal weather conditions also play an important role since the mitigation potential of AWD is almost double as high in dry as compared to wet seasons. Furthermore, this study demonstrates the importance of temporal continuity, considering off‐season emissions and the long‐term development of GHG emissions across multiple years. Plain Language Summary: Worldwide, rice production contributes to about 10% of total greenhouse gas emissions of the agricultural sector mainly due to CH4 emissions from fields that are continuously flooded. Alternate Wetting and Drying (AWD) is an alternative cropping practice where fields are irrigated a few days after the disappearance of the ponded water. This study explores the mitigation potential of nationwide introduction of AWD in the Philippines. Results from the application of a process‐based model suggest a considerable decrease in CH4 emissions by −23%. Compared to N2O, CH4 is responsible for more than 95% of the total radiative forcing under conventional or AWD field management. Key Points: Nationwide, Alternate Wetting and Drying (AWD) reduces CH4 emissions by −23%N2O emissions contribute to less than 5% to the total radiative forcing under conventional or AWD field managementMitigation of AWD depends on, for example, seasonal weather conditions, cropping intensity, irrigation, residue management, and soil texture [ABSTRACT FROM AUTHOR]

Small-scale farmers in developing Asian countries have minimal agricultural mechanisms available to them. In the Philippines, postharvest losses in rice production can reach about 36% in the drying process alone. Thus, the inflatable solar dryer (ISD) was developed through the collaboration of the University of Hohenheim, the International Rice Research Institute, and GrainPro Philippines Inc. Although the ISD was successfully tested with different agricultural products, further characterization of the ISD design is required for predicting the drying performance. To this end, the airflow behavior in the ISD was simulated using computational fluid dynamics (CFD) via ANSYS Fluent. Moreover, a thermal model was developed in MATLAB/Simulink by taking into account heat transfer in the heating area and coupled heat and mass transfer within the drying area. Three batches of drying experiments were performed and airflow measurements were taken inside the dryer to validate the models. The MATLAB/Simulink model was further used to predict the drying performance under various weather conditions spanning 10 years. The simulated temperatures and moisture content in the ISD showed high accuracy (mean absolute percentage error (MAPE) < 10%) with the experimental data. The proposed dynamic model provides an efficient computational tool that can be applied to predict the drying performance and to optimize the ISD design. [ABSTRACT FROM AUTHOR]

The sun drying of agricultural products is a complicated process involving heat transfer, mass transfer, and variable weather conditions. Surface reflection (albedo), a crop's radiative property, plays an essential role in energy balance, and understanding its contribution can improve the thermal analysis. In this study, field experiments were conducted in the Philippines to explore the influence of surface albedo on the sun drying of paddy rice. First, we implemented energy and mass balance equations in a transient model with the surroundings using a graphical programming language in Matlab/Simulink®. Second, we identified the influence of albedo on the sun drying model by using a sensitivity analysis. Third, we investigated the relationship of paddy rice albedo and the solar zenith angle. Lastly, we integrated the albedo function into the sun drying model. The simulation outputs were validated with field experiments. A better estimation of the measured exit temperature and instantaneous mass were obtained when a variable albedo was applied. This study makes clear that introducing a variable albedo has a positive impact on model improvement. This information is important for application in solar drying technologies, so that the drying process can be better assessed. [ABSTRACT FROM AUTHOR]

The Philippines is experiencing extreme weather events (typhoons and floods) which often result to significant rice postharvest losses, among other things. In this study, a new and mechanized postharvest system that integrates field handling and drying of the paddy grains is proposed to speed up the operation and help ensure a good quality harvest even when affected by typhoons or floods. The system makes use of eight 500 kg capacity specially-designed bags that function both as grain containers during transport and as drying bins. The drying operation is accomplished using these bags while mounted on the floor inside a typhoon-resistant shelter. [ABSTRACT FROM AUTHOR]

Meloidogyne graminicola is one of the most important plant-parasitic nematodes in rice. Breeding for natural resistance and tolerance is considered one of the most economical and sustainable approaches to control this damaging pathogen. Quantitative trait loci (QTL) mapping was carried out in a recombinant inbred line (RIL) population derived from a cross between the Asian rice genotypes IR78877-208-B-1-2 and Dinorado. IR78877-208-B-1-2 is an aerobic rice genotype that is resistant and tolerant to M. graminicola. Dinorado is a traditional upland rice genotype from the Philippines that is characterized by its aroma and prized for its cooking quality. The host response of 300 F4 lines derived from this cross was evaluated in both nematode infested and non-infested concrete beds in the dry seasons of 2013 and 2014. Five genotypes were found consistently resistant while 13 genotypes were consistently partially resistant to M. graminicola. QTL mapping for M. graminicola resistance/tolerance, yield-contributing traits, and yield revealed four main effect QTLs (qJ2RS2.1, qJ2GRT2.1, qJ2RS3.1, and qJ2GRT3.1) associated with reduced nematode reproduction on chromosomes 2 and 3 and two QTLs (qGR3.1 and qGR5.1) associated with reduced root galling on chromosomes 3 and 5. Twenty main effect QTLs associated with yield-contributing traits and yield were also found. Our study further identified co-locating QTLs associated with nematode resistance, yield-contributing traits, and yield on chromosomes 3 and 5. QTLs harboring candidate genes, such as OsBAK1, OsDST, OsIPT4, and DUF26, for higher grain yield and tolerance to abiotic and biotic stress, were identified. These QTLs and the RILs that are consistently resistant and tolerant to M. graminicola, and which are high-yielding in nematode-infested fields, can be utilized in breeding programs to improve the resistance and tolerance of Asian rice to this important pathogen. [ABSTRACT FROM AUTHOR]

This paper examines genetic erosion in rice landraces thriving in traditional smallholder agricultural systems in the Sarangani uplands, Philippines. In these marginal areas, the crop is closely interwoven with tribal culture and is vital in ensuring food security among upland households. Field visits unveiled high varietal diversity for upland rice and a rich tapestry of indigenous knowledge associated with its cultivation and use. Study results, however, revealed the tapering of the crop's genetic base due to farmers' changing priorities, pest infestation, weakening seed supply systems, shift to cash crops, natural calamities, environmental degradation, government programmes and peace and order problems. Consequently, these pressures undermined traditional agricultural systems in Sarangani upland communities causing food and water scarcity, hunger and suffering on a catastrophic scale. Interdisciplinary strategies aimed at simultaneously averting further varietal losses and environmental degradation while improving human well-being are therefore warranted. Furthermore, making traditional rice farming a lucrative endeavour will induce the younger generation to remain in the uplands and choose farming as a profession. This way, biocultural restoration of agriculture will be attained and the continued presence of the tribal groups in the Sarangani uplands will be ensured for a very long time. [ABSTRACT FROM AUTHOR]

Production of irrigated rice (Oryza sativa L.) without conventional soil submergence may increase water use efficiency but risk a decline in rice yield. Spatial variability in rice yield and relationships among yield and soil properties were examined across a 3.3-ha experimental site after uniform crop management. The site was initially consolidated from small, previously puddled parcels of land into eight laser-leveled plots across a 2.1-m elevation gradient in the Philippines. Six crops of rice in rotation with three crops of mungbean (Vigna radiata (L.) R. Wilczek) were then grown from January 2012 to March 2015. The four rice crops in the dry season (crops 1, 2, 4, and 6) were irrigated using an overhead sprinkler system to maintain soil water potential greater than −10 kPa without soil submergence. Soil was puddled and flooded with irrigation for only rice crop 5 grown in the wet season. Mean rice yield with full fertilization was 6.1 Mg ha−1 for crop 2 but only 3.6 Mg ha−1 for crop 6. Yield for rice crop 6 ranged from 1.6 to 5.4 Mg ha−1 across 36 locations in the 3.3-ha site. Rice yield for crop 6 was inversely related to soil bulk density (r = −0.72 and −0.80, P < 0.001), log 10 saturated hydraulic conductivity (K sat) (r = −0.71, P < 0.001), and sand content (r = −0.63, P < 0.001). Yield was directly related to water-filled pore space of soil (r = 0.61, P < 0.001). Field locations with large downward water movement and the correspondingly most aerobic soil conditions were most prone to low rice yields and large yield decline. Rice yield was directly related to anaerobic N mineralization (r = 0.72, P < 0.001) and soil ammonium-N (r = 0.54, P < 0.001) at 16 days after transplanting and to indigenous N supply (r = 0.83, P < 0.001), as determined from rice yield without application of fertilizer N. These relationships suggested lower net N mineralization at locations with the most aerobic soil conditions, as determined by water-filled pore space. Rice yield was, however, not limited by insufficient fertilizer N. Anaerobic N mineralization and indigenous N supply were unrelated to optimum fertilizer N rate calculated from yield gain with fertilizer N, which was determined at 36 locations using paired plots with and without added N. The long rainy season and clayey soil at the site limited triple-cropping systems to two rice crops and only one non-rice crop per year. In such environments where crop rotation is not an option to prevent yield decline for rice grown without soil submergence, periodic soil submergence to increase anaerobic soil conditions would be required to sustain rice yield. Our study suggested that soil bulk density and K sat , which can increase for successive rice crops grown without puddling and soil submergence, could serve as indicators of field locations prone to yield decline from factors other than water-deficit stress and requiring a period of soil submergence to sustain large rice yields. • Rice yield without soil submergence ranged from 1.6 to 5.4 Mg ha−1 across 3.3-ha site • Yield was inversely related to soil bulk density and saturated hydraulic conductivity • Rice yield was directly related to soil water-filled pore space and N mineralization • Low yield of N-fertilized aerobic rice was due to factors other than insufficient N • High bulk density and downward water flow may indicate need for soil submergence [ABSTRACT FROM AUTHOR]

Dry direct-seeded rice (DDSR) is an adaptive practice used in rainfed lowlands of tropical Asia where insufficient rainfall at the onset of the wet season makes it difficult to successfully transplant rice seedlings. However, basic guidelines for nutrient management to support DDSR are lacking. Here, we evaluated crop growth and yield in DDSR with different N fertilizers (ammonium sulfate, urea, and coated compound fertilizer) applied at different timings. The total N rate was fixed at 100 kg ha−1. On-station trials were conducted at the International Rice Research Institute, in the Philippines, during the wet seasons of 2017 and 2018, and 17 on-farm trials were conducted in nine provinces in 2018 and 2019. In the on-station trials, ammonium sulfate did not increase yield compared with urea and coated compound fertilizer in either year. Application of N fertilizers at sowing promoted plant N uptake and early shoot growth, but the effect of the timing of N application on yield was not significant. The on-farm trials showed that a uniform N management recommendation is unlikely to be effective in DDSR. Yield increased significantly with coated compound fertilizer relative to the uncoated fertilizers in clay and silty clay soils, but not in other soil types. In general, flexible timing of the first application of N, ranging from 0 to 30 days after sowing, had no significant effect on yield, but the omission of N application at sowing reduced yield by 13–25% in two trials on sandy soils with a low nutrient-holding capacity. • Three N fertilizers were applied in three regimes for dry direct-seeded rice. • Ammonium sulfate didn't give higher yield than urea and coated fertilizer. • Coated fertilizer gave highest yield on clayey soils but not on other soils. • First N application could be delayed by 30 days except on highly sandy soils. [ABSTRACT FROM AUTHOR]

In the Philippines most of the dryland rice pests are distinct from those of wetland culture. Partitioned-growth-stage yield loss studies revealed the highest losses in dryland rice were due to sown-seed and seedling pests (ants, field crickets, mole crickets, and termites) as well as root feeders (white grubs and root aphids) and early seedling pests (seedling maggot and flea beetle) more than the common foliar wetland pests. Losses (5-71%) were highest in the sites with the smallest rice area in which pests were concentrated and the poorest soils (which constrain yield compensation) along a continuum of dryland rice habitats. Crop management practices such as overseeding and fertility management can mitigate potential losses to a large degree. Therefore integrated crop management plays a central role in integrated pest management in dryland rice cultivation where the use of insecticides should be minimized for economic and environmental reasons. [ABSTRACT FROM AUTHOR]

Abstract: Genotype by environment (G×E) interactions were investigated in Vandana and a subset of 13 BC2 and BC3 lines of an improved indica upland rice cultivar, Vandana, backcrossed with a drought-tolerant traditional japonica cultivar, Moroberekan, which has a thick and extensive root system, in response to eight hydrological field environments conducted at Los Baños, in the Philippines, between 2001 and 2003. The G×E interaction accounted for 13% of the total sum of squares with environment and genotype responsible for 84 and 3%, respectively. Cluster analysis identified four environment and six genotype groups, which accounted for 70% of the G×E sums of squares. Of this, AX1, AX2 and AX3 accounted for 27, 22 and 21% of the G×E-SS, respectively. AX1 represented yield potential; AX2 was related to soil conditions, aerobic status and possibly VPD; and AX3 to change in phenology (days to flowering) with stress. The four environment groups were considered as broadly representative of contrasting rice production environments, including lowland-type, upland-wet season and upland-aerobic environments that experienced vegetative- or anthesis-stage drought stress. Genotype groups differed in adaptation to these diverse environments. For genotype groups G1–G6, G3 (VM150) had stable yields across environments; G1 (VM134) had the greatest grain yield in lowland-type environments (E2); G5 (VM135) in wet season environments (E3); G6 (VM168) in anthesis-stage drought (E4); G2 (Vandana and VM26) in vegetative- and anthesis-stage drought (E1 and E4); G4 had average yields across environments. Implications for breeding of rice adapted to contrasting hydrological environments are discussed, with the caution that adaptation to more than one environment type is desirable, because, as is demonstrated in this paper, an untimely climatic event can transform one environment type into another. Our results suggest that selection in one environment type may not give benefit in other environment types, so testing in more than one environment type is essential. [Copyright &y& Elsevier]

Meloidogyne graminicola, the rice root-knot nematode, has become a constraint on Asian rice production due to rice cropping intensification and increasing scarcity of water. This work relates to the assessment of crop rotation, fallow and nematicide treatments in naturally infested fields to manage M. graminicola populations and prevent yield losses. One or two consecutive crops of cowpea or seasons of fallow before a rice crop lowered nematode populations and improved rice yield by 30-80%. Methyl bromide was used to determine yield potential and almost eradicated the nematode, trebling rice yield. Carbofuran improved yield of the first rice crop but did not affect the second rice crop. Due to its short life cycle, M. graminicola populations were similar after only a single rice crop and after three consecutive crops. It is recommended that, to ensure higher rice yields, M. graminicola populations should be maintained at low density by non-host crop rotations or fallows, ideally for two seasons before planting rice. [ABSTRACT FROM AUTHOR]

Rice seedling maggot Atherigona oryzae Malloch is a minor pest of upland rice Oryza sativa L. and maize Zea mays L. in the Philippines. Two cultural control methods, early planting and overseeding, were evaluated separately on upland rice in an eroded, high rainfall area in Northern Mindanao. Farmers plant maize ahead of upland rice in separate fields with the onset of the rainy season. Regression analysis from data over six seasons showed on average the first 50% of farmers who planted ahead of their neighbours suffered damage significantly below the 5% deadheart action threshold. When early rice planting relative to one's neighbours was combined with earliness with regard to sowing maize, damage was further reduced. Useful methods for forecasting deadhead incidence 1-2 months ahead of rice planting were developed. The deadheart incidence rate was highly correlated with the amount of rain that fell in February and March as well as with the number of adults collected from bait traps in March or April. Six seeding rates were compared in 20-kg increments from 50 to 150 kg/ha with and without insecticide seed treatment. There was no significant yield response over the seeding rates tested when protected by insecticide, but when untreated, the highest yield occurred at 120 kg seed/ha and the greatest return at 90 kg/ha. Yields declined above the 120 kg/ha level from interplant competition Rice seedling maggot egg density decreased but the deadheart incidence rate increased with increasing plant densities, both linearly. Perhaps higher plant densities led to greater larval survival and dispersal. Planting rice early is dependent on early maize planting. Planting maize early and following maize within the generation period of rice seedling maggot with rice sown from 90 to 120 kg/ha would be particularly beneficial in years when the rice seedling maggot is predicted to be a high risk. [ABSTRACT FROM AUTHOR]

Using eight morphological parameters with six cluster analysis methods, a set of 21 traditional and four improved Philippine upland rice cultivars (cvs) could be separated into five groups: (1) improved semi-dwarf plant type, (2) improved or ‘moderately modified’ (short) Indica plant type, (3) traditional tall Indica plant type, (4) traditional tall Japonica plant type and (5) traditional short Japonica plant type. The results emphasized the importance of the separation into Indica and Japonica plant types, but the cultivars could be classified more accurately using growth characteristics such as tillering ability, followed by plant height and leaf area parameters. The clusters containing Indica cvs consistently showed a higher tiller number per plant, a higher growth stage (DC classification) and narrower leaves than clusters with Japonica cvs. The parameters culm length, plant height, leaf area, leaf length and width were represented in subgroups with both long and short expression of the respective characteristic. Use of the existing variability of morphological traits within the group of traditional upland rice cvs should be beneficial in recommendation, breeding, selection and development of upland rice cvs for the different rice ecosystems as well as for the upland rice/rice blast pathosystem. [ABSTRACT FROM AUTHOR]

Alternate Wetting and Drying (AWD) is a well-known low-cost water-saving and climate change adaptation and mitigation technique for irrigated rice. However, its adoption rate has been low despite the decade of dissemination in Asia, especially in the Philippines. Using cross-sectional farm-level survey data, this study empirically explored factors shaping AWD adoption in a gravity surface irrigation system. We used regression-based approaches to examine the factors influencing farmers' adoption of AWD and its impact on yield. Results showed that the majority of the AWD adopters were farmers who practiced enforced rotational irrigation (RI) scheduling within their irrigators' association (IA). With the current irrigation management system, the probability of AWD implementation increases when farmers do not interfere with the irrigation schedule (otherwise they opt to go with flooding). Interestingly, the awareness factor did not play a significant role in the farmers' adoption due to the RI setup. However, the perception of water management as an effective weed control method was positively significant, suggesting that farmers are likely to adopt AWD if weeds are not a major issue in their field. Furthermore, the impact on grain yields did not differ with AWD. Thus, given the RI scheduling already in place within the IA, we recommend fine-tuning this setup following the recommended safe AWD at the IA scale. [ABSTRACT FROM AUTHOR]