Three near-isogenic lines (NILs) of <i>Oryza sativa</i> subsp. <i>indica</i&... more Three near-isogenic lines (NILs) of <i>Oryza sativa</i> subsp. <i>indica</i> cv. IR64 (Dro1-NIL, Sta1-NIL, Dro1+Sta1-NIL) with <i>DEEPER ROOTING 1</i> (<i>DRO1</i>), a novel gene for steeper root growth angle, and/or with <i>Stele Transversal Area 1</i> (<i>Sta1</i>), a QTL for wider stele area, were tested under flooded lowland (FL), alternate wetting and drying lowland (AWD), and rainfed upland (UP) conditions in 2013 and 2014 to compare the effects of <i>DRO1</i> and <i>Sta1</i> on yield across different water management regimes. Genotypic variation and water management effects were significant for grain yield, aboveground biomass, and harvest index, as well as their interactions with year, but no significant genotype × water interaction was detected. Dro1-NIL had 14% higher yield than that of IR64 across the three water conditions due to higher harvest index, aboveground biomass, leaf...
This study was carried out to identify the vulnerability of rice production to salinity intrusion... more This study was carried out to identify the vulnerability of rice production to salinity intrusion arising from climate change in Giao Thuy, a coastal district of Nam Dinh Province, located in Red River Delta in Vietnam. From the analysis of historical climate data at Nam Dinh city, both mean maximum and minimum temperatures increased by about 0.3 and 0.1 °C per decade, respectively, during the period of 1961–2010. Salt concentration of the river water was higher at the irrigation gate closer to river mouth (Con Nhat) than at the upstream gate (Ha Mieu), which generally increased from 2003 to 2012, with the average maximum concentration up to 2.13 % at Con Nhat gate in 2010. The salt water concentration in the riverside field outside the dyke reached 3.6 %, while among the fields within dyke the salinity was only 0.7 % at maximum in January 2013, and the values were higher in paddy fields close to the dyke than far from the dyke. Average yield among the selected 27 fields from 2011 summer to 2013 spring rice was higher in spring rice (748 g m−2) but lower in summer rice (417 g m−2) mainly due to unfavorable weather such as cold spell at flowering and flood at harvesting time. Rice yield was lowest in general in the most downstream commune Giao Thien, and was significantly lower in field located close to the dyke than those far from the dyke. This spatial variability of rice yield may not be directly attributable to salinity, but to the other factors such as shift of irrigation intake gate to further upstream and/or different management such as less input of N fertilizer and use of traditional local variety.
Weed infestations are a major cause of yield reduction in rice (Oryza sativa) cultivation, partic... more Weed infestations are a major cause of yield reduction in rice (Oryza sativa) cultivation, particularly with direct‐seeding methods, but the relationship between weed dynamics and water availability in Cambodian paddy fields has not been documented previously. We surveyed the weed abundance and weed seed banks in the soil of paddy fields with inferred differences in their water regime in 22 farm fields in three provinces of Cambodia in the 2005 and 2006 rainy seasons. We studied rain‐fed lowland fields in upslope and downslope topographic positions and fields at different distances from the irrigation water source inside an irrigation rehabilitation area. The weed seed banks were estimated by seedling emergence in small containers and weed abundance and vigor were estimated by a simple scoring system. The estimated weed seed bank in the top 5 cm of soil ranged from 52.1 to 167 × 103 seeds m−2 (overall mean of 8.5 × 103 seeds m−2) and contained a high proportion (86%) of sedge specie...
Abstract The farmers’ management practices and grain yield were examined in the consecutive 4 cro... more Abstract The farmers’ management practices and grain yield were examined in the consecutive 4 cropping seasons from wet season rice (WSR) in 2008 to dry season rice (DSR) in 2010 across upstream, midstream and downstream fields, along two secondary drainage canals (located either upstream or downstream side along the main canal) in the Kamping Puoy Irrigation Rehabilitation area (KPIR). In WSR, standing water depth was much deeper in downstream fields where medium and late maturing varieties were planted from May than in upstream fields where early and early medium maturing varieties were planted later (mostly in July and August). In DSR there was less difference in water conditions between upstream and downstream fields and variation in planting and harvesting time was small. As the area percentage of fields where DSR was introduced increased from 2008 (54%) to 2010 (100%), planting time in WSR was later (e.g., from May to July) with declining proportion of dry seeding method and mid-season tillage. Grain yield was low in DSR, particularly in 2010 (287 and 247 g m-2 in 2009 and 2010 on average, respectively), due to insufficient weed control and small amount of fertilizer, and the yield was lowest in fields which practiced DSR for the first time. Grain yield in WSR (286 and 291 g m-2 in 2008 and 2009 respectively) increased by transplanting, use of high yielding Raing Chey variety, and application of a larger amount of N chemical fertilizer. These findings indicated that the agriculture extension support to farmers, particularly in DSR, is a key important factor for rice yield improvement in KPIR.
Abstract: The crop management in direct-seeded rice to promote growth during the reproductive sta... more Abstract: The crop management in direct-seeded rice to promote growth during the reproductive stage was evaluated in weed-controlled toposequentially intermediate fields in a small watershed in Northeast Thailand. In 2004, the effectiveness of topdressing with 21 kg ha-1 of nitrogen at the panicle initiation stage were examined using two genotypes, KDML105 and IR57514-PMI-5-B-1-2 (IR57514) seeded at the rates of 500, 250 and 125 seeds m-2. In 2005 and 2006, the effectiveness of a new management (seeding rate of 125 seeds m-2 and nitrogen application of 90-101 kg ha-1; CM2) was compared with that of conventional management (seeding rate of 500 seeds m-2 and nitrogen application of 50 kg ha-1; CM1) using 3 genotypes (KDML105, IR57514 and HY71) seeded in May and June. In 2004, the number of spikelets on the tertiary pedicel at a low seeding rate in KDML105 was greatly increased by topdressing. In 2005 and 2006, CM2 had higher grain yield than CM1 (346 vs. 235 g m-2), owing to its larger spikelet number per panicle, heavier shoot dry weight and greater nitrogen uptake. May-seeding resulted in longer non-flooded period in the seedling to tillering stage, lower SPAD reading value around heading and less shoot dry weight increase from heading to maturity, and had lower grain yield than June-seeding (253 vs. 328 g m-2). This reduction in grain yield was larger for late-heading KDML105 than in early heading IR57514. These results indicated the effectiveness of the new crop management (CM2) for direct-seeded rice in toposequentially intermediate fields with less weed infestation or weed-controlled conditions.
Abstract To characterize the annual and spatial variation in grain yield of deepwater rice on the... more Abstract To characterize the annual and spatial variation in grain yield of deepwater rice on the floodplains of Tonle Sap Lake, Cambodia, from 2008 to 2011 we collected information on water availability, farming practices, and rice yield through intensive field monitoring, farmer interviews and yield sampling along a transect line of a water depth gradient. A total of 86 fields covering 91.5 ha were divided into 3 zones: an upper zone where only lowland rice (LR) was grown (referred to as ULR), a middle zone where both LR and floating rice (FR) were grown (MLR and MFR, respectively), and a lower zone closest to the lake where only FR was grown (LFR). The inundation from Tonle Sap Lake was within the normal range in 2008 and 2009, but it was extremely large and caused a complete crop failure in the study area in 2011. Conversely, no inundation occurred in 2010. Continuous standing of water started earlier (i.e., early September) in the lower zone and reached maximum depth in mid-October; water receded earlier (i.e., mid- to late November) in the upper zone than in the lower zone. FR was broadcast earlier (April) and harvested later (January) than LR (May and late November to December, respectively). A total of 6 LR varieties and 4 FR varieties with different heading times were planted during the study period. Maximum and average yields of LR were higher than those of FR, and from 2008 to 2011 the proportion of the LR variety Raing Chey planted steadily increased, whereas that of the late-maturing floating rice variety Veal Veng decreased. Grain yield in the middle zone was the lowest of the three zones. Maintenance of standing water after heading, larger input of N fertilizer, and appropriate weed management were found to contribute to higher yields for both LR and FR. These results should help farmers to cope with unpredictable flooding in areas where deepwater rice is cultivated.
Three near-isogenic lines (NILs) of <i>Oryza sativa</i> subsp. <i>indica</i&... more Three near-isogenic lines (NILs) of <i>Oryza sativa</i> subsp. <i>indica</i> cv. IR64 (Dro1-NIL, Sta1-NIL, Dro1+Sta1-NIL) with <i>DEEPER ROOTING 1</i> (<i>DRO1</i>), a novel gene for steeper root growth angle, and/or with <i>Stele Transversal Area 1</i> (<i>Sta1</i>), a QTL for wider stele area, were tested under flooded lowland (FL), alternate wetting and drying lowland (AWD), and rainfed upland (UP) conditions in 2013 and 2014 to compare the effects of <i>DRO1</i> and <i>Sta1</i> on yield across different water management regimes. Genotypic variation and water management effects were significant for grain yield, aboveground biomass, and harvest index, as well as their interactions with year, but no significant genotype × water interaction was detected. Dro1-NIL had 14% higher yield than that of IR64 across the three water conditions due to higher harvest index, aboveground biomass, leaf...
This study was carried out to identify the vulnerability of rice production to salinity intrusion... more This study was carried out to identify the vulnerability of rice production to salinity intrusion arising from climate change in Giao Thuy, a coastal district of Nam Dinh Province, located in Red River Delta in Vietnam. From the analysis of historical climate data at Nam Dinh city, both mean maximum and minimum temperatures increased by about 0.3 and 0.1 °C per decade, respectively, during the period of 1961–2010. Salt concentration of the river water was higher at the irrigation gate closer to river mouth (Con Nhat) than at the upstream gate (Ha Mieu), which generally increased from 2003 to 2012, with the average maximum concentration up to 2.13 % at Con Nhat gate in 2010. The salt water concentration in the riverside field outside the dyke reached 3.6 %, while among the fields within dyke the salinity was only 0.7 % at maximum in January 2013, and the values were higher in paddy fields close to the dyke than far from the dyke. Average yield among the selected 27 fields from 2011 summer to 2013 spring rice was higher in spring rice (748 g m−2) but lower in summer rice (417 g m−2) mainly due to unfavorable weather such as cold spell at flowering and flood at harvesting time. Rice yield was lowest in general in the most downstream commune Giao Thien, and was significantly lower in field located close to the dyke than those far from the dyke. This spatial variability of rice yield may not be directly attributable to salinity, but to the other factors such as shift of irrigation intake gate to further upstream and/or different management such as less input of N fertilizer and use of traditional local variety.
Weed infestations are a major cause of yield reduction in rice (Oryza sativa) cultivation, partic... more Weed infestations are a major cause of yield reduction in rice (Oryza sativa) cultivation, particularly with direct‐seeding methods, but the relationship between weed dynamics and water availability in Cambodian paddy fields has not been documented previously. We surveyed the weed abundance and weed seed banks in the soil of paddy fields with inferred differences in their water regime in 22 farm fields in three provinces of Cambodia in the 2005 and 2006 rainy seasons. We studied rain‐fed lowland fields in upslope and downslope topographic positions and fields at different distances from the irrigation water source inside an irrigation rehabilitation area. The weed seed banks were estimated by seedling emergence in small containers and weed abundance and vigor were estimated by a simple scoring system. The estimated weed seed bank in the top 5 cm of soil ranged from 52.1 to 167 × 103 seeds m−2 (overall mean of 8.5 × 103 seeds m−2) and contained a high proportion (86%) of sedge specie...
Abstract The farmers’ management practices and grain yield were examined in the consecutive 4 cro... more Abstract The farmers’ management practices and grain yield were examined in the consecutive 4 cropping seasons from wet season rice (WSR) in 2008 to dry season rice (DSR) in 2010 across upstream, midstream and downstream fields, along two secondary drainage canals (located either upstream or downstream side along the main canal) in the Kamping Puoy Irrigation Rehabilitation area (KPIR). In WSR, standing water depth was much deeper in downstream fields where medium and late maturing varieties were planted from May than in upstream fields where early and early medium maturing varieties were planted later (mostly in July and August). In DSR there was less difference in water conditions between upstream and downstream fields and variation in planting and harvesting time was small. As the area percentage of fields where DSR was introduced increased from 2008 (54%) to 2010 (100%), planting time in WSR was later (e.g., from May to July) with declining proportion of dry seeding method and mid-season tillage. Grain yield was low in DSR, particularly in 2010 (287 and 247 g m-2 in 2009 and 2010 on average, respectively), due to insufficient weed control and small amount of fertilizer, and the yield was lowest in fields which practiced DSR for the first time. Grain yield in WSR (286 and 291 g m-2 in 2008 and 2009 respectively) increased by transplanting, use of high yielding Raing Chey variety, and application of a larger amount of N chemical fertilizer. These findings indicated that the agriculture extension support to farmers, particularly in DSR, is a key important factor for rice yield improvement in KPIR.
Abstract: The crop management in direct-seeded rice to promote growth during the reproductive sta... more Abstract: The crop management in direct-seeded rice to promote growth during the reproductive stage was evaluated in weed-controlled toposequentially intermediate fields in a small watershed in Northeast Thailand. In 2004, the effectiveness of topdressing with 21 kg ha-1 of nitrogen at the panicle initiation stage were examined using two genotypes, KDML105 and IR57514-PMI-5-B-1-2 (IR57514) seeded at the rates of 500, 250 and 125 seeds m-2. In 2005 and 2006, the effectiveness of a new management (seeding rate of 125 seeds m-2 and nitrogen application of 90-101 kg ha-1; CM2) was compared with that of conventional management (seeding rate of 500 seeds m-2 and nitrogen application of 50 kg ha-1; CM1) using 3 genotypes (KDML105, IR57514 and HY71) seeded in May and June. In 2004, the number of spikelets on the tertiary pedicel at a low seeding rate in KDML105 was greatly increased by topdressing. In 2005 and 2006, CM2 had higher grain yield than CM1 (346 vs. 235 g m-2), owing to its larger spikelet number per panicle, heavier shoot dry weight and greater nitrogen uptake. May-seeding resulted in longer non-flooded period in the seedling to tillering stage, lower SPAD reading value around heading and less shoot dry weight increase from heading to maturity, and had lower grain yield than June-seeding (253 vs. 328 g m-2). This reduction in grain yield was larger for late-heading KDML105 than in early heading IR57514. These results indicated the effectiveness of the new crop management (CM2) for direct-seeded rice in toposequentially intermediate fields with less weed infestation or weed-controlled conditions.
Abstract To characterize the annual and spatial variation in grain yield of deepwater rice on the... more Abstract To characterize the annual and spatial variation in grain yield of deepwater rice on the floodplains of Tonle Sap Lake, Cambodia, from 2008 to 2011 we collected information on water availability, farming practices, and rice yield through intensive field monitoring, farmer interviews and yield sampling along a transect line of a water depth gradient. A total of 86 fields covering 91.5 ha were divided into 3 zones: an upper zone where only lowland rice (LR) was grown (referred to as ULR), a middle zone where both LR and floating rice (FR) were grown (MLR and MFR, respectively), and a lower zone closest to the lake where only FR was grown (LFR). The inundation from Tonle Sap Lake was within the normal range in 2008 and 2009, but it was extremely large and caused a complete crop failure in the study area in 2011. Conversely, no inundation occurred in 2010. Continuous standing of water started earlier (i.e., early September) in the lower zone and reached maximum depth in mid-October; water receded earlier (i.e., mid- to late November) in the upper zone than in the lower zone. FR was broadcast earlier (April) and harvested later (January) than LR (May and late November to December, respectively). A total of 6 LR varieties and 4 FR varieties with different heading times were planted during the study period. Maximum and average yields of LR were higher than those of FR, and from 2008 to 2011 the proportion of the LR variety Raing Chey planted steadily increased, whereas that of the late-maturing floating rice variety Veal Veng decreased. Grain yield in the middle zone was the lowest of the three zones. Maintenance of standing water after heading, larger input of N fertilizer, and appropriate weed management were found to contribute to higher yields for both LR and FR. These results should help farmers to cope with unpredictable flooding in areas where deepwater rice is cultivated.
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