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Direct seeding: research strategies and opportunitiesProceedings of a Workshop,
Book is
available S. Pandey and L. Velasco Direct seeding for rice establishment is spreading rapidly in Asia. This paper provides an overview of the patterns of adoption of direct-seeding methods in Asia. The rising wage rate, increasing availability of chemical weed control methods, and the need to intensify rice production systems were considered to be the major driving forces. The potential advantages and problems with direct seeding are discussed and the likely future patterns of changes are indicated. Finally, research priorities for improving the productivity of direct-seeding systems are presented. Direct seeding of rice in Asia: emerging issues and strategic research needs for the 21st century V. Balasubramanian and J.E. Hill The area under direct-seeded rice has been increasing as farmers in Asia seek higher productivity and profitability to offset increasing costs and scarcity of farm labor. This paper reviews the direct-seeding technology for rice crop establishment, assesses the development of crop management techniques in relation to constraints posed by direct seeding, and suggests research areas for further improving the technology. Rice is direct-seeded by essentially two methods (dry and wet seeding) based on the physical condition of the seedbed and seed (pregerminated or dry). Dry seeding is practiced in rainfed lowland, upland, and flood-prone areas. Wet seeding is a common practice in irrigated areas, and it is further subdivided into aerobic wet seeding, anaerobic wet seeding, and water seeding, based on the level of oxygen in the vicinity of the germinating seed or the depth of floodwater at seeding. Seeds may be broadcast or sown in rows on dry/moist/puddled soil, whereas only broadcasting is used for seeding on water. Direct seeding offers such advantages as faster and easier planting, reduced labor and less drudgery, earlier crop maturity by 7-10 d, more efficient water use and higher tolerance of water deficit, less methane emission, and often higher profit in areas with an assured water supply. Although labor and its associated costs may be reduced for crop establishment, other technologies are essential to overcome constraints imposed by direct seeding. For example, we should enhance the interaction of crop stand establishment, water management, and weed control in relation to crop lodging in both dry- and wet-seeded rice. Technology for land preparation, precision leveling, and prevention of crop lodging must be improved in wet direct-seeded rice. Similarly, management practices and control strategies are currently lacking for several pests (rats, snails, birds, etc.) that damage surface-sown seeds and for problem weeds that compete with rice seedlings. Greater understanding is required on the effect of planting or tiller density on weed pressure, pest damage, grain yield, grain quality, harvest index, and crop lodging at maturity to develop management strategies for high-density direct-sown rice in the tropics. Higher resistance to lodging is essential in rice varieties selected for intensive direct seeding to achieve high yields (> 8 t ha-1). Furthermore, varieties must be improved for early seedling vigor, weed competitiveness, tolerance of low oxygen level or submergence, and resistance to drought. We must find practical solutions to alleviate these constraints and to ensure optimum conditions for seeding. Only then will direct seeding become an attractive and sustainable alternative to traditional transplanting of rice. Gogorancah rice in Indonesia: a traditional method in the modern era A.M. Fagi and S. Kartaatmadja Indonesia's successful increase in rice production has been attributed to the use of improved varieties, application of adequate fertilizers, and intensive pest and weed control. Considerable development and rehabilitation of the irrigation infrastructure have made it possible to expand area planted to rice and implement modern crop management. This paper reviews the origin of the gogorancah system of rice production, its successful adoption, and research to further improve that technology. Traditional techniques of land preparation, seedling establishment, and water management from rainfed systems were combined with cultivar choice and nutrient and weed management used for modern, high-yielding rice varieties to increase rice productivity and cropping intensity and to sustain rice production in rainfed systems. A successful trade-off between the traditional and modern rice cultivation systems in rainfed rice areas resulted in great success through a massive campaign by the government. The gogorancah technique has been practiced successfully by farmers in flooded rice, where the crop can be submerged at maturity. With this technique, mature panicles could be harvested before deepwater submergence occurred. The subsequent expansion of gogorancah in nonpuddled, bunded fields has become a national agenda in the rice intensification program. Results demonstrate that the gogorancah technique is a scientifically sound method of rice cultivation from the agronomic and physiological points of view. The beushening system of rice crop establishment in eastern India V.S. Tomar In India, of 42.2 million ha planted to rice, the rainfed lowland ecosystem occupies about 35%. Rice yields from this ecosystem range from 0.5 to 1.5 t ha-1 compared with irrigated rice yields of 3-4 t ha-1. Low yields in the rainfed lowland ecosystem, specifically in eastern India, are due to drought and flood experienced in the same season, the slow spread of high-yielding varieties, poor plant populations, severe infestation of weeds including wild rice, low fertilizer-use efficiency, infertile soils, and incidence of insect pests and diseases. Beushening is a traditional cultural practice of cross-plowing the dry-seeded (broadcast) standing crop of rice 25-35 d after seeding when 15-20 cm of rain water gets impounded in rice fields, followed by laddering and seedling redistribution. It is commonly practiced in shallow to medium submerged lowlands in eastern India. This practice loosens the soil, controls weeds, improves water-use efficiency, improves tillering and nutrient uptake, reduces insect pests, and helps redistribute seedlings. Resource-poor farmers in these areas therefore achieve moderately good production with limited inputs and less intensive labor use under conditions of uncertain rainwater and infertile soils. An analysis of available information on different aspects of beushening shows that conceptually it should not be considered as a crop establishment technique only, but as a system of rainfed lowland rice cultivation. The specific biophysical and socioeconomic characteristics of eastern India and changing trends in irrigated and transplanted rice cultivation indicate that the beushening rice system is going to stay. Moreover, many opportunities exist to improve its productivity. The major constraints to improving rice yields under beushening have been analyzed. Little information is available on different aspects of the system. In this paper, priority research issues are discussed, such as the efficient use of rainwater, the development of suitable high-yielding rice varieties, integrated plant nutrient management including green manuring, improving plant stand, supplemental weed control measures, and improved tillage/interculture implements that will help in understanding and improving rice yields. Nguyen Duy Can and Vo-Tong Xuan Direct seeding, a common traditional cultural practice for floating rice used by Mekong Delta farmers for hundreds of years, became more widespread after the introduction of modern rice varieties IR5 and IR8 in 1968. The area under direct seeding of modern rice in the Mekong Delta has increased markedly during the last three decades because of crop intensification as well as labor shortage and other economic factors. Farmers direct-seed their rice in both irrigated and rainfed ecosystems and under diverse environmental conditions. Four typical direct-seeding techniques of rice were observed: zero-tillage seeding, water seeding, dry seeding, and wet seeding. The productivity of each type of direct-seeding method and the corresponding farmer income are discussed. Most common modern rice varieties with short growth duration (90-105 d) can be used successfully in the four seeding methods. Farmers can enhance rice land productivity and labor efficiency by selecting an appropriate direct-seeding method considering soil and hydrologic conditions of their field, availability of appropriate land preparation equipment, and irrigation-drainage systems in the locality. Impact of direct seeding on rice cultivation: lessons from the Muda area of Malaysia Nai-Kin Ho and Z. Romli Direct seeding has emerged as a viable alternative to transplanting in Malaysia. In the Muda area, direct seeding comprises four basic techniques: wet seeding, dry seeding, water seeding, and volunteer seeding. Wet and dry seeding have had a significant impact on rice cultivation practices in the Muda area since their introduction in the 1970s. Improvements in farm management, especially the refinement of land preparation and land leveling, the availability of pre- and postemergence herbicides with wide application windows, and the use of water pumps to solve localized irrigation and drainage problems by farmers themselves, all contribute to the yield-enhancing nature of direct seeding. Ninety-two percent of the Muda farmers reported that the yield of direct-seeded rice crops is superior to that of transplanted crops. General yield trends are in this order: wet seeding > dry seeding > volunteer seeding. Studies conducted in the Muda area indicate that the technological possibilities of raising rice yield potential would come from direct-seeded rice. In the face of water scarcity, dry seeding enables relatively earlier crop establishment compared with wet seeding and transplanting. Dry seeding also contributes significantly to maintaining high cropping intensity where irrigation supply is limited. Innovative farmers who practice dry seeding obtain an additional harvest from ratoon crops. A direct-seeded crop required only 34% of the total labor requirement of the transplanted crop. Farmers could rely substantially on their own family labor and their control over the timing of farming activities is enhanced. Dry seeding and wet seeding have also resulted in a significant cost reduction. On average, direct seeding has enabled Muda farmers to save 29% of the total cost of a transplanted crop. Among the various direct-seeding methods, production cost was in this order: volunteer seeding < dry seeding < wet seeding. However, continuous herbicide application in direct seeding has led to a weed shift and the development of herbicide-resistant biotypes. Lessons from the Muda area reveal that strengthening research and extension linkages and active participation of farmers in field studies are needed to achieve sustainable rice production under direct-seeded conditions. G. Trébuil and S. Thungwa For many decades, dry seeding was the dominant farmers' practice for establishing rainfed lowland rice (RLR) in the drought- and submergence-prone areas bordering the Songkhla lagoon along the eastern coast of southern Thailand. Because of the highly constraining soil-water complex, RLR growers have been combining an array of dry-seeding and transplanting practices adapted to varying soil and climatic conditions to be able to grow rice in their fields every year, although with a relatively low but rather stable crop productivity. During the past decades, RLR dry-seeding techniques dominated the three main types of household-based farming systems, while paddy fields most infested by weeds, particularly wild rice, were transplanted. Land preparation and crop establishment on heavy-textured soils, water depth control, and weed infestation, especially by wild rice, were found to be major interrelated problems that can be addressed by strategic and applied research to stabilize yields and increase labor productivity of local dry-seeded rice systems. Labor productivity in dry-seeded paddies is often very low because of the tedious and highly time-consuming hand-weeding and thinning-transplanting practice. At least 50 d ha-1 are needed to achieve an RLR yield of more than 2.2 t ha-1 and 150 d ha-1 in wild rice-infested fields for effective control by using the integrated approach designed over time by farmers. Agronomic and economic results of on-farm experiments on land preparation and row seeding demonstrate the potential of this technique in high weed-infestation situations. Recently, a limited crop diversification scheme based on integrated systems of small-scale crop-fish rearing led to an improvement in the capture of water and supplementary irrigation. During the 1987-96 decade of high economic growth, the scarcity of farm labor increased because off-farm employment opportunities were more attractive and readily available. As a consequence, in association with adopting new early maturing cultivars and combined with mechanizing the RLR harvest, an important increase in wet-seeded rice has been observed since 1996. Development trends and farmers' benefits in the adoption of wet-seeded rice in Thailand S. Isvilanonda Rice is an important crop in Thailand. A large area and a relatively low production cost have contributed to the country's comparative advantage in the world rice market. Significant investments in agricultural infrastructure, particularly irrigation systems and a marketing network, and in agricultural research and extension over the past few decades are the major factors that have stimulated productivity increases. The widespread adoption of modern varieties and high intensity of rice cropping, especially under favorable production environments, coupled with rapid growth in the nonagricultural sector raised rural wage rates. As a result, opportunities for saving labor in rice production were increasingly sought. This economic necessity led to a shift from the traditional transplanting method of rice establishment to direct seeding using pregerminated seeds. This method is now widely used in the Central Plain of Thailand. This paper analyzes the factors contributing to a successful transition in crop establishment methods and the impact of this transition on factor use and rice profitability on irrigated rice farms. F. Molle and C. Chompadist The rice systems of the Central Plain of Thailand have undergone drastic changes in the last 30 years. Technical change has been driven by a combination of factors including demographic changes, land development and water control, and mechanization. The recent spread of wet direct seeding is put in its historical context and the complementarity between dry and wet seeding, the two currently dominant techniques, is shown to be related to different socioeconomic and hydrologic situations. Some prospects for further technical change are addressed. Economics of direct seeding in northeast Thailand S. Pandey, L. Velasco, and N. Suphanchaimat In Thailand, the rice establishment method has shifted from transplanting to direct seeding in response to labor scarcity. Using survey data from Khon Kaen, this paper examines patterns of the shift in crop establishment methods, factors influencing the choice of crop establishment method, and the impact of such a shift on rice production and productivity. Results show that biophysical factors such as weed incidence, rainfall pattern, sufficiency of water supply, field elevation, and hydrology are the major determinants of farmers' choice of crop establishment method. In addition, wage rates, availability of family labor, and power for land preparation were found to be the major economic factors influencing the choice of crop establishment method. Although rice yields were similar for wet seeding and transplanting, dry seeding resulted in a significantly lower yield. As dry seeding is practiced mainly in upper fields with lower productive capacity, rice production in these fields would not have been economically viable had farmers not used this labor-saving method. A lower technical efficiency associated with dry seeding relative to other methods indicates that potential exists for improving the dry-seeding method through better technology. Implications for developing technologies for land preparation, weed management, developing new varieties, and other aspects of rice production are derived. Status of dry-seeding technologies for rice in Korea M.-H. Lee, J.K. Kim, S.S. Kim, and S.T. Park In 1991, direct-seeding technology in Korea was adopted and disseminated gradually to farmers. Farmers now practice two methods of direct seeding, dry and wet seeding. Dry seeding (seeding under dry conditions) has several advantages over wet seeding (seeding under flooded conditions), such as good seedling stand, lodging resistance, and less incidence of bird and fungi damage. In addition, less labor is required for tillage, seeding, and field management. Dry seeding is a method that uses a drill seeder attached to a tractor to plant 40 kg of dry seed ha-1 right after final land preparation. There are two different types of dry seeding-flat drill seeding for well-drained soils and high-ridged drill seeding for poorly drained soils. Six direct-seeding varieties that are highly lodging-resistant and have good germination under low-temperature conditions had been developed and released to farmers by 1998. The ideal seeding time in Korea is from 20 April to 10 May when the daily mean air temperature is higher than 13 °C. Optimum seedling stand is 90-150 seedlings m-2. The level of optimum nitrogen fertilizer is 150-180 kg ha-1, which is 40-70 kg ha-1 higher than that for transplanting and wet seeding. However, phosphate and potassium are applied at the same rate of about 70 and 80 kg ha-1 as for transplanted and wet-seeded rice, respectively. An important technology for the success of dry seeding is effective weed control because the weed emergence period is longer than that of transplanting or wet seeding. Three systematic herbicide application methods are recommended during the dry period: either before or after rice seedling emergence and during flooding. Once the seedling stand is established, the rice crop needs to be irrigated at the third-leaf stage, 25-30 d after seeding, requiring two or three mid-summer drainages to increase lodging resistance. During the full cropping season, the labor requirement for dry seeding is 30% lower than that for machine-transplanted rice using semiadult seedlings. Overall, rice production costs using direct seeding are about 20% lower than those of machine-transplanted rice. Seedling broadcasting in China: an overview Tang Sheng-xiang In recent years, China has developed an effective technique for rice plant establishment: seedling broadcasting. In 1995, the technique was applied to 98,700 ha. Because of its significant advantages of saving labor, reducing time between harvesting the previous crop and establishing a new rice crop, higher yield, and increasing farmers' total income, the area applied to this technique expanded rapidly to 6.7 million ha in 2000. This represents 21.8% of the total rice-growing area in China. Four basic practical forms of seedling broadcasting are used: hand broadcasting seedlings produced by a wet bed, hand broadcasting seedlings produced by a dry bed, hand broadcasting seedlings produced by a dry bed with soft polyvinyl chloride (PVC) trays, and machine broadcasting seedlings produced by a dry bed with soft PVC trays. The third is the most popular method adopted by farmers in China. The area under seedling broadcasting increased fast in rice regions due to a higher labor cost, labor shortage, and short turnaround time in rice-rice and wheat-rice cropping systems, as well as in high-income rural areas. The key requirements for seedling broadcasting are good land preparation, good varieties, vigorous seedlings, suitable seedling density, and good water and weed management. This paper discusses the research areas for facilitating the development of this technique. M.A. Mazid, S.I. Bhuiyan, M.A. Mannan, and L.J. Wade In most rainfed drought-prone environments, water shortages constrain farm productivity toward the end of the season for the wet-season rice crop and/or for a second crop after rice. Dry seeding, instead of transplanting rice, may help solve this problem. Dry-seeded rice can be established and harvested earlier, with a reduced risk of drought to the crop and, at the same time, leave a longer favorable period for growing a postrice crop. Recent research has established the prospects of dry-seeded rice-based farming systems in drought-prone environments of various countries, including the Philippines and Bangladesh. This paper summarizes some of that research conducted within the auspices of the Rainfed Lowland Rice Research Consortium (RLRRC), a regional research network coordinated by IRRI. Some common issues that deserve further investigation are discussed. P.R. Hobbs, Y. Singh, G.S. Giri, J.G. Lauren, and J.M. Duxbury With the introduction of new, improved shorter duration wheat and rice varieties in South Asia in the mid-1960s, double cropping of these two cereals became possible. Rice is grown in the wet, monsoon summer months and wheat follows in the dry, cool winter in one calendar year. More than 12 million ha are grown to rice and wheat in Bangladesh, India, Nepal, and Pakistan. Another 10 million ha are grown in China. This rice-wheat system is one of the most important cropping systems for cereal production and food security in the region. Most of the rice in this system is managed by transplanting rice seedlings into puddled soils. This age-old method of planting is used to reduce water percolation. It also helps control weeds. But puddling also degrades the soil physical condition with resulting difficulties in establishing and growing succeeding upland crops such as wheat. Much of the research in the region looks at the possibility of establishing rice without puddling. Major perceived hurdles include the inability to economically control weeds and increased water use. However, there are situations when water tables are high or soils are fine-textured where puddling is not needed to slow water infiltration and where dry-seeding technology may work. Less research has been done on evaluating this technology on a systems basis. This paper presents data from experiments conducted at Pantnagar University in India and at the Nepal Agricultural Research Council (NARC) Bhairahawa Wheat Research Center in the tarai region. Experiments looked at the effects of various tillage and crop establishment practices on the productivity of both rice and wheat. At both sites, rice yield was not adversely affected by direct seeding without puddling and, in Nepal, it was not affected by deep tillage before establishment. Direct seeding led to greater weed pressure at Pantnagar but not at Bhairahawa. Crop damage from brown planthopper was higher in direct-seeded plots in one year at Pantnagar. Rice yield attributes were altered by direct seeding, indicating a need to optimize plant density and spacing parameters for this practice. At Pantnagar, soil bulk densities were lowered and infiltration rates increased without puddling. This led to a different water management regime for direct-seeded rice and provided a better soil physical condition for the succeeding wheat crop. Wheat yields were affected by various tillage options whether applied in the rice season or in the wheat season. Wheat yields were significantly higher when rice soils were not puddled. At Pantnagar, zero tillage did not do as well as conventional tillage but this may have been because of insufficient moisture for good root development in zero-till plots. At Bhairahawa, the reverse was true, especially in 1997-98, when wet conditions caused a delay in planting in the treatment with tillage. Here, significant interactions were also observed between rice and wheat tillage and establishment practices. The best wheat yield was obtained when soil was deep-tilled and unpuddled for rice and not tilled for wheat (surface-seeded). The lowest yield was obtained when surface-seeded wheat followed conventional tillage and puddling for rice. Although rice yields were higher than wheat yields, differences in the latter were most important for overall system productivity. This paper suggests that direct-seeded rice on unpuddled soils is feasible and that zero-till wheat following unpuddled rice soils is cost-effective, conserves resources, and does not reduce yield. Mechanization issues in tillage and crop establishment for dry direct-seeded rice R.R. Bakker, M.A. Bell, and J.F. Rickman As labor is being drawn away from agriculture, rice farmers in Asia increasingly adopt various labor-saving technologies. Traditional methods of tillage and crop establishment are being replaced, and the use of mechanization in farming operations is increasing. This paper addresses how mechanization can help alleviate some of the constraints to achieving higher productivity in dry direct-seeded rice by highlighting examples from recent research. Mechanization can lead to more timely crop establishment, reduce weeding cost, reduce variability in emergence, and lead to better control of water movement in the field. Some common constraints to the successful adoption of mechanization by rice farmers are reviewed as well. On-farm seed priming to improve crop establishment and yield in dry direct-seeded rice D. Harris, R.S. Tripathi, and A. Joshi Seed priming differs from pregermination in direct-seeded rice. Primed seed-seeds soaked overnight in water and then surface-dried and immediately sown-will only germinate in moist soil. Pregerminated seed, on the other hand, has a protruding plumule and radicle, typically broadcast onto puddled soil, and is susceptible to damage during sowing. It will continue to germinate, even when sown under inappropriate soil conditions. Moreover, if broadcast on a free water surface, primed seeds sink quickly, whereas pregerminated seeds float and risk being redistributed by the wind, resulting in patchy stands. Work with farmers on upland rice in South Asia has demonstrated that priming seed with water before direct sowing has many advantages. Primed seed germinates and emerges faster (1-3 d) and more uniformly and seedlings grow more vigorously, leading to a wide range of phenological and yield-related benefits. Glasshouse experiments showed that a delay in emergence of rows of rice by 1 to 3 d reduced seedling vigor by 20% to 45%. In addition, primed crops often flower and mature earlier and give higher yields. In 2 years of on-station experiments in Rajasthan, India, priming seed of 10 upland rice cultivars resulted in statistically significant mean yield increases in 1997 (1.7 t ha-1 vs 2.0 t ha-1, or an increase of 18%) and in 1999 (0.6 t ha-1 vs 0.84 t ha-1, an increase of 40%). In 1997, priming resulted in better emergence (91% vs 61%), earlier flowering (71 d vs 74.7 d), taller plants (108 cm vs 94 cm), longer panicles (22.4 cm vs 20.3 cm), and more panicles plant-1 (5.7 vs 4.9). Very early capture of resources appears to be important in determining some of the benefits associated with seed priming and a hypothesis to explain this response in upland rice is discussed. Recently published data on resource partitioning in young rice seedlings showed that the superior early growth vigor of Oryza glaberrima in relation to O. sativa was due to the early onset of autotrophic growth, a high degree of resource partitioning to leaves, and a large specific leaf area. These data are reinterpreted here to show that faster emergence following seed priming could result in better resource capture that might contribute to growth and yield advantages associated with priming. L.V. Du and T.P. Tuong Poor crop establishment and high weed infestation are among the main constraints to the adoption of dry-seeded rice. Field experiments were conducted in the 1998 and 1999 rainy seasons in Binh Chanh, Vietnam, to test the hypothesis that seed priming, seeding rate, and appropriate timing of seeding can improve crop establishment and enhance weed suppression in dry-seeded rice. The experiments were carried out with rice cultivar OMCS94 in a split-plot design, with seeding dates in the main plots, seeding rates (in 1999) or timing of weed control (in 1998) in subplots, and seed priming treatments in sub-subplots. When rice is seeded in very dry soil (near wilting point), priming, especially with 14% KCl solution and saturated CaHPO4 solution, increased established plant density, final tiller number, and grain yields compared with the unprimed treatments. When soil moisture content at seeding was at or near saturation, seed priming decreased established plant density and slightly reduced grain yields compared with the unprimed treatment. Late seeding reduced weed infestation because secondary tillage eliminated weeds that emerged after primary tillage. Using a higher seeding rate to get an adequate stand reduced weed dry weight and increased rice yield, but offered little benefit when the established plant density was already high. Findings suggest that in drought-prone areas, seed priming can reduce the need for using a high seeding rate, but priming can be detrimental if seeding takes place when soil is at or near saturation. Rice cultivar requirements for direct seeding in rainfed lowlands S. Fukai This paper reviews the performance of rice genotypes established from direct seeding in rainfed lowlands. It attempts to determine plant types that are suitable for this rice cropping system. The paper first describes growth and yield of crops established from transplanting and direct seeding. Direct seeding, particularly broadcasting, often enables seeding early in the season with high established plant density and consequently higher yield compared with transplanting. However, establishment from direct seeding may be affected by adverse conditions such as submergence and drought, particularly in the rainfed lowland ecosystem where water control is limited. Problems with weeds and lodging are common in direct-seeded fields and yields can be greatly affected. As a result, yield variation tends to be larger under direct seeding. The next section describes cultivar requirements for rainfed lowland rice under direct seeding. Crop establishment is important particularly for direct-seeded rice, and the ability to germinate and emerge under a wide range of moisture conditions is required. There are notable genotypic differences in seedling vigor and submergence tolerance. Semidwarf genotypes do not commonly have strong vigor, but some genotypes are vigorous and appear to be promising as they also have high yield potential. Photoperiod-insensitive cultivars with high yield potential appear to be suitable for direct-seeded rice under diverse growing conditions. Short-duration rice cultivars seem to be more affected by weeds because of poor competitiveness or the inability to recover from the adverse effect of weeds. Traditional, tall, long-duration cultivars could compete against weeds better. However, they are unsuitable for direct seeding if they are prone to lodging under high density and shallow planting conditions. The ideal plant type that can strongly compete against weeds has shoots that spread and cover the ground rapidly during the vegetative stage, but, with the onset of panicle initiation, these shoots will not dominate reproductive organ development. In addition to these specific requirements for direct seeding, there are also more general genotypic requirements for rainfed lowland rice. The key point is adaptation to adverse water conditions, either drought or submergence. There is a trade-off between high potential yield under favorable conditions and adaptation to adverse water conditions. Therefore, the ideal cultivar type for direct-seeded rainfed lowland rice is largely determined by target environmental conditions; therefore, identification of environmental conditions is required. H. Kyu, S.T. Amarante, A.A. Gomez, H.P. Samonte, R.P. Robles, and L.J. Wade In rainfed lowland rice, the shortage of labor for transplanting and the need to increase cropping intensity have resulted in a greater adoption of wet seeding. But the shift to wet seeding may reduce the reliability of stand establishment and increase competition from weeds. For improved performance of wet-seeded rice, a reliable and vigorous crop stand is needed to obtain stable yield and suppress weed growth. A better understanding of variation in seed and seedling vigor and the implications for yield stability is needed, especially for rainfed systems. This paper examines seed vigor in four lines by considering variation caused by environment, cultivar, and seed lot in the germination cabinet. The implications of variation in seed and seedling vigor were then examined in the greenhouse and the field. Seedling vigor had potential benefits for subsequent growth that may be carried through to yield. But, with severe late stress, adverse consequences may accrue if inputs were used to compensate for poor early vigor. Results demonstrated that plants could compensate for poor early vigor under suitable conditions. Possessing inherent seedling vigor was an advantage under unpredictable rainfed situations, since attempts to compensate for low seedling vigor by N application may be detrimental if water stress occurred late in the season. Further research is needed to better understand the dynamics of compensatory responses and to determine whether selection of cultivars with greater seed and seedling vigor can harness the benefits of adding inputs under all conditions, without the risk of getting lower yields if subsequent conditions are less favorable. The dry-seeding technique for saving water in irrigated rice production systems D.F. Tabbal, S.I. Bhuiyan, and E.B. Sibayan The dry-seeding technique, as an alternative to the transplanting method of rice crop establishment, was evaluated for its usefulness and farmers' adoption potentials for three consecutive wet seasons from 1995 to 1997 in the Upper Pampanga River Integrated Irrigation System (UPRIIS) service area, Philippines. The effects of two water regimes (continuous standing water and continuous saturated soil condition) and two methods of weed control (recommended herbicide weed control only and recommended herbicide plus hand weeding on dry-seeded rice) were evaluated in field experiments. The feasibility of dry seeding was also assessed by comparing its yield performance with yields of transplanted rice from neighboring farmers' fields. Results showed that when weed growth was not a major problem, which was the case in the last two years, the average yield of dry-seeded rice was similar to that obtained in transplanted or wet-seeded rice on neighboring farms. In dry-seeded rice, yield from plots with continuous standing water was statistically the same as that from plots with continuous saturated soil water. But when weed growth was high, yield from the combined treatment of herbicide and hand weeding was significantly higher than that from the herbicide treatment alone. The use of the dry-seeding technique eliminated the need for irrigation water during land preparation. Fields were plowed, harrowed, leveled, and seeded in dry or moist soil. This allowed rainfall to be more effectively used to support seed germination and crop growth than transplanted rice. About 32% and 22% of the total water used was from the irrigation source applied to supplement rainfall for maintaining continuous standing water and continuous saturated soil regimes, respectively, in the experimental field. Most of the 21 randomly selected farmers who were interviewed in 1997 said that dry seeding was a good alternative to transplanting because rainfall and irrigation water were used more productively. They emphasized that the dry-seeding technique was appropriate, especially when irrigation water was scarce, because it was possible to prepare and broadcast seeds even in dry or moist soil conditions. A few farmers, however, were concerned that dry seeding may be difficult to adopt in areas with clayey soils because of tilling problems under dry conditions. During the 1998 wet season, a serious water shortage was experienced in the UPRIIS service area. Three farmer-collaborators during the field experiment and one additional farmer adopted the dry-seeding technique and obtained yields of 3.0-3.7 t ha-1. Moreover, the 17 neighboring farmers who similarly adopted dry seeding got average yields of 3.4-4.0 t ha-1. About 50% of these farmers obtained significantly lower yields in the 1998 wet season than in the 1997 wet season. Despite the low yields in 1998, farmers who adopted dry seeding expressed satisfaction with the method because they were able to grow a rice crop despite the serious water shortage. They also did not need to spend money to control golden snails (a problem in transplanted rice) or to pay for extra labor for transplanting. R.J. Cabangon, T.P. Tuong, E.B. Tiak, and N. bin Abdullah To ensure food security in Asia, it is imperative to identify rice production systems that require less irrigation water input than the conventional transplanted rice (TPR). This study investigated the effect of the large-scale adoption of wet-seeded rice (WSR) and dry-seeded rice (DSR) on irrigation input and water productivity based on kilograms of rice produced per unit volume of water input. Water balance components, crop establishment method, progress in farming activities, and rice yield of individual farmers were monitored in three irrigation service units (ISU) from 1988 to 1994 in the Muda Irrigation System of Malaysia. Yields did not differ statistically at the 5% level. Land preparation duration was significantly reduced in DSR and WSR compared with TPR. This led to a significant reduction in irrigation and total water input (rainfall and irrigation) during the land preparation period. However, TPR-ISU had a significantly shorter crop growth duration and lower irrigation and total water input than DSR-ISU and WSR-ISU. Over the whole crop season, water productivity of irrigation (WPI) of DSR-ISU was significantly higher than WSR-ISU and TPR-ISU. Reduced irrigation input and higher WPI in DSR-ISU were attributed to its ability to make use of early rainfall for early crop establishment. WSR-ISU had lower irrigation water than TPR-ISU because the water savings during the land preparation period outweighed the higher water input during the crop growth period. Since this may not be true in other conditions, site-specific management of WSR versus TPR has to be considered when assessing the relative advantage in water productivity. Nutrient management of direct-seeded rice in different ecosystems of eastern India H.C. Bhattacharyya, V.P. Singh, and K. Borkakati Direct seeding of rice is practiced in all rice-growing environments. It is the only crop establishment technique used in the uplands, is very common in deep and very deepwater areas, and is becoming increasingly popular in traditionally transplanted rainfed and irrigated lowlands. Seeds are broadcast, drilled, or dibbled into dry soil in the uplands and into dry, wet, or puddled soil in the lowlands. Because the crop is established directly from seeds as opposed to transplanting, early growth and root development of direct-seeded rice encounter different soil conditions from those of transplanted rice. Direct-seeded rice is subject to diverse and heterogeneous soil environments as opposed to the more uniform conditions encountered by transplanted rice, for which flooding and puddling ensure a more uniform seedbed. Differences also exist among different ecosystems (upland, rainfed lowland, irrigated lowland, deepwater) in soil type, land preparation, and method of direct seeding. Thus, nutrient management options developed for traditional transplanted rice are unlikely to be suitable for direct-seeded rice. A major difference is in N fertilizer management. In aerobic soils, nitrate is the dominant form of N for plant uptake, unlike in anaerobic soils, where the ammonium form of N is dominant. When sown and grown in an aerated soil environment, rice roots and root hairs develop unhindered, the rhizosphere is acidified by root exudates, and, thus, the young rice plants can efficiently extract P and use soil nitrate, which is mineralized during land preparation. Thus, the recovery of soil N is higher in early growth of direct-seeded rice. Phosphate studies show that P applied at seeding or soon after (but not later than the active tillering stage) and absorbed during tillering is most efficiently used for grain production. Thus, the better ability to extract P at the early growth stage of direct-seeded rice should improve grain production. Direct-seeded rice is also reported to be efficient in using applied as well as residual K. A major factor that influences nutrient use in direct-seeded rice is soil moisture. In rainfed environments, a direct-seeded crop is often subject to periods of drought. Thus, the timing (split dressing) and form (controlled release) of fertilizer application are major issues in direct-seeded rice, especially in the lowlands. Developing a direct-seeding technology package for rainfed lowland rice in Lao PDR Sipaseuth, P. Sihavong, V. Sihathep, P. Inthapanya, M. Chanphengsay, and S. Fukai Direct seeding could be a useful alternative to transplanting in rainfed areas where labor is scarce at crop establishment and early rains are insufficient to puddle the soil for timely transplanting. The status of direct-seeding technology that is applicable to rainfed lowland rice in Lao PDR is described and the research areas that require further work to develop a sound technology, particularly for central and southern Lao PDR, are highlighted. Findings from our recent work under the Australian Centre for International Agricultural Research (ACIAR)-funded project on "Plant breeding strategies for rainfed lowland rice in northeast Thailand and Lao PDR" are the basis of this paper. The experimental program examined the following areas of direct seeding: land preparation, time of sowing, seed rate and method of sowing, cultivars required, weed control measures, and labor resource requirement. In several cases, comparisons were made with the transplanting system. The main conclusions point to the importance of the choice of correct seeding time when soil moisture conditions are adequate, using a high sowing rate, particularly in the row arrangement, and using cultivars that are high-yielding and do not lodge easily. A technology package for direct seeding developed for Lao PDR is described. Research areas that require further work to develop sound technology packages include sowing method, particularly the development of a simple planting implement, weed control measures, identification of areas suitable for direct seeding, and a new double-cropping system based on direct-seeded rice. Influences of changing from transplanting to direct seeding on the status of some pest species T. Wada Changes in farming practices from transplanting to direct-sown rice affect pest status. The main factors that influence pests are longer exposure of young seedlings, longer plant duration in the field, and high plant density. One of the most important economic pests in direct-sown rice is the apple snail, Pomacea canaliculata. The apple snail feeds avidly on young seedlings. Germinating seedlings are more than 200 times more susceptible to damage by the snail than transplanted seedlings. Sometimes, no rice plants are established in water-seeded fields because of heavy snail contamination. Drainage after sowing greatly reduces rice damage since it immobilizes the snails. Approximately 90% of plants were established when fields were drained for 2 wk after sowing compared with fields without snails. Three weeks of drainage can almost prevent damage by snails when the plant is at the 5-leaf stage. Increasing the drainage period, however, exacerbates weed problems. Fortunately, because of recent developments in herbicides, it has become possible to keep rice fields drained for 2 wk or so. But simply adopting drainage does not always solve the problem. If the drainage of residual water is insufficient, snail infestations can spread rapidly. Making ditches or ridging can enhance drainage, but neither seems to be fully successful. Brown planthopper (BPH) Nilaparvata lugens and whitebacked planthopper (WBPH) Sogatella furcifera are threats to direct-sown rice if paddies are poorly managed, for example, by abusing the use of nonselective insecticides. According to studies of planthopper populations conducted in direct-sown rice in the Muda area of West Malaysia, population growth patterns were basically similar to those in transplanted fields. Planthoppers produce two consecutive generations and a third optional generation, depending on interactions between planthoppers and their natural enemies. But, two planthopper species displayed different preferences for certain rice stages during their migration. WBPH macropters invaded fields of germinating rice, resulting in a population buildup. Thus, WBPH sometimes increased tremendously in fields with very young plants. WBPH caused hopperburn, although it is very rare, in direct-sown fields in Malaysia, which has never happened in other South Asian countries where a majority of fields are transplanted. On the other hand, the BPH invasion always peaks 30-50 d after sowing, which seems to suggest that a longer plant duration has no influence on direct-sown rice. Various types of direct sowing are being studied in Japan. Among them, seed sowing on submerged rice fields is the most promising for stable production. In this method, seeds are coated with an oxygen provider and, sometimes, pesticides for plant protection. This new method will be presented in this paper. Weed management in direct-seeded rice in South Vietnam D.V. Chin and M. Mortimer The Mekong River Delta in South Vietnam is a major rice production area in which four types of direct-seeding methods are practiced: wet seeding, dry seeding, zero-tillage seeding, and water seeding. Traditional wet direct seeding remains the most popular form of cultivation, accounting for up to 60% of the area sown. Yield losses as high as 46% caused by weeds have been reported; consequently, farmer adoption of herbicides has increased rapidly in the last decade together with the wider use of alternative crop establishment methods. This paper summarizes current crop establishment and weed management practices in direct-seeded rice. The role of various land preparation practices and straw burning in reducing the weed seed bank in the long term is compared, and the impact of no-tillage systems for weed control was evaluated for both wet- and dry-seeded rice. Weed species shifts in response to serial herbicide application in wet-seeded rice in Malaysia Azmi Man and M. Mortimer A long-term field study began at the MARDI Research Station, Seberang Perai, Malaysia, in 1996 to investigate changes in weed communities of wet-seeded rice in response to repeated applications of eight herbicides (2,4-D, bensulfuron, pretilachlor, quinclorac, propanil, fenoxaprop-P-ethyl, molinate + propanil, and benthiocarb + propanil) in common farm use. Rice yields and weed species abundance 60 days after seeding were assessed in eight consecutive seasons of a planned 10-season study. Rice yields declined over the initial course of the study, but on average were the highest (3.4 t ha-1) in benthiocarb + propanil and bensulfuron-treated plots and the lowest (<2 t ha-1) in fenoxaprop-treated plots. However, differences in yield gain arising from the use of alternative herbicides were often small in most seasons. Plots were usually dominated (> 50% proportional abundance) by a single weed species, reflecting differential responses to selective herbicides, with Echinochloa crus-galli being the most abundant in 2,4-D-treated plots, Scirpus grossus under bensulfuron, and Monochoria vaginalis in the remaining plots. Changes in rankings of subdominant weed species depended on season and did not indicate strong successional processes. Managing direct seeding for rainfed lowland rice with particular attention to weed control P. Romyen, S. Khunthasuvon, and S. Fukai This paper describes briefly the recent work on direct seeding in rainfed lowland rice in northeast Thailand funded by the Australian Centre for International Agricultural Research. Seven experiments were conducted in 1996-98 to establish a basis for developing technology for direct-seeded rice, particularly in relation to weed control. We investigated (1) seeding time for good establishment, (2) seeding rate for competition against weeds, and (3) the use of cultivars with high yield potential and vigorous growth. When the crop was planted early in the season, quick-maturing cultivars flowered too early in the wet season and yield decreased. In one experiment in which the weed population was high and no weed control was conducted throughout crop growth, a high seeding rate of 200 kg ha-1 was required to minimize the adverse effect of weeds. On the other hand, when weeds were controlled, a seeding rate of 100 kg ha-1 produced the highest yield. Cultivars with low established plant density competed poorly with weeds. Canopy structure and maturity also affected competitive ability against weeds. Quick-maturing cultivars were more affected by weeds and had greatly reduced yields. This study highlighted the overall importance of weeds in determining the yield of direct-seeded rice in the rainfed lowlands. |
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Economics of direct seeding in Asia: patterns of adoption and research priorities Direct seeding of rice in Asia: emerging issues and strategic research needs for the 21st century Gogorancah rice in Indonesia: a traditional method in the modern era The beushening system of rice crop establishment in eastern India Impact of direct seeding on rice cultivation: lessons from the Muda area of Malaysia Development trends and farmers’ benefits in the adoption of wet-seeded rice in Thailand Economics of direct seeding in northeast Thailand Status of dry-seeding technologies for rice in Korea Seedling broadcasting in China: an overview Mechanization issues in tillage and crop establishment for dry direct-seeded rice On-farm seed priming to improve crop establishment and yield in dry direct-seeded rice Rice cultivar requirements for direct seeding in rainfed lowlands The dry-seeding technique for saving water in irrigated rice production systems Nutrient management of direct-seeded rice in different ecosystems of eastern India Developing a direct-seeding technology package for rainfed lowland rice in Lao PDR Influences of changing from transplanting to direct seeding on the status of some pest species Weed management in direct-seeded rice in South Vietnam Weed species shifts in response to serial herbicide application in wet-seeded rice in Malaysia Managing direct seeding for rainfed lowland rice with particular attention to weed control |
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