Flood vulnerability assessment in the light of rice cultivation characteristics in Mekong River flood plain in Cambodia

More than 2 million hectares of the lower Mekong River flood plain (Cambodian Plain), which extends from southern Cambodia to the border with Vietnam, is cultivated with rice; and more than 60 % of the population in the flood plain are farmers involved in rice cultivation. Rice production in this area is seriously affected by floods almost every year; on the other hand, the farmers need floodwater for their crop fields. Therefore, the farming in this area is about coping with floods, and flood countermeasures should be carefully planned based on good understanding of the livelihood of the farmers. Thus, this study aimed to identify flood-vulnerable rice-growing communities in the Mekong River flood plain in Cambodia. In this research, we proposed a useful methodology to make flood inundation maps by conducting a simple analysis by combining satellite-based digital elevation model (DEM) and river water level data based on the flood characteristics in this area. Then, rice-crop vulnerability maps were derived from previous maps and results from other past researches using the geographical information system (GIS). Comparison among those maps was also conducted to find out the relationship between DEM and people’s lifestyles in this area. This simple, inexpensive methodology was proven useful to understand major crop damage and vulnerability in relation to floods in this area, based on flood characteristics in the Cambodian flood plain. Because the method is a GIS-based approach, it can deliver more accurate results when provided with more accurate data.

     

Flood vulnerability assessment in the light of rice cultivation characteristics in Mekong River flood plain in Cambodia

Demographic changes, such as aging and depopulation in rural areas, are major reasons for the recent abandonment of the terraced paddy fields in Japan. In addition, the low productivity of terraced paddy fields, due to their small area and the difficulty of using machinery on the plots, further abet this trend. Recent research has shown a growing interest in multifunctional conservation and maintenance of the ecosystem and traditional agro-culture of terraced paddy fields. This paper aims to elaborate on the conservation activities of endangered terraced paddy fields in Japan, by using the case of Shiroyone Senmaida to discuss conservation experience and lessons, and recommend future strategies for adaptive management of the rice terraces under the GIAHS framework, as well as the next necessary steps for research. As an outstanding cultural landscape and tourist attraction in Noto Peninsula, the conservation scheme combining financial support from governmental subsidy, the “owner system” of interaction with urban dwellers, and labor support by conservationist volunteers has contributed to the conservation of traditional farming on Senmaida’s terraced paddy fields. Still, as is the case in other parts of Japan, lack of financial support and an aging farming population threaten conservation of terraced paddy fields in Noto Peninsula.     

Field level damage of deepwater rice by the 2011 Southeast Asian Flood in a flood plain of Tonle Sap Lake,Northwest Cambodia

The 2011 flood damaged about 11 % of planting area in Cambodia, but the damaged proportion reached 30 % in Sangke district, Battambang province, located in the flood plains of Tonle Sap Lake. The aim of this study was to characterize completely damaged deepwater rice production due to the flood along the transect from the town-side shallower fields to the lake-side deeper fields. The flooding water from Tonle Sap Lake rose with 7 cm/day in September and October in the deeper fields where floating rice was grown and 8–10 cm/day in October in the shallower fields where lowland rice was grown. The maximum water was recorded on 16 October with 3.2 and 2.0 m at the deepest and shallowest edge fields. The area was characterized as flatness with only 1.2 m elevation differences in 4.3 km distance along the transect. The flooding water took 13.7 h for approaching 100 m distance. Complete recession of flood water was end of November at the shallow edge and at late December in the deep edge in 2011. The flooding duration deeper than 50 cm was 2.5 month and nearly 3 months in the middle zone and deeper floating rice area, respectively. The complete submergence started first in some fields in the middle zone on 12 September, followed by the shallower lowland rice area, and finally in the deep floating rice area by 1 October. Countermeasures to improve rice production in deepwater rice area in the floodplain of Tonle Sap Lake were proposed.     

The role of paddy rice in recharging urban groundwater in the Shira River Basin

Agricultural fields in the middle Shira River basin play an important role as a source of groundwater recharge; however, the water balance between the agricultural water and river water is unclear. This study was conducted to investigate the water balance in the fields by measuring the stream flow of agricultural water channels, which draw water from the Shira River. The flow rate of water channels was found to increase in the beginning of May, which corresponded to the cultivation of paddy rice fields. During summer, the total agricultural intake was comparable to the river flow observed in the middle Shira River Basin. Determination of the water budget for the targeted area revealed that most of the recharged water was dependent on agricultural irrigation from the river. The annual recharge of the overall target area was estimated to be as high as 15,300 mm. In addition, the infiltration rate was as high as 170 mm/day in the paddy fields during summer, and as high as 30 mm/day in the upland fields during winter. In order to recover the groundwater recharge in this region, it is necessary to extend the submerged period to include periods in which the stream water in the Shira River is not subject to heavy rainfall as well.     

Assessing the acceptance of the system of rice intensification among farmers in rainfed lowland rice region of Cambodia

We conducted interview survey with rainfed rice farmers at a commune in southern Cambodia to identify the determinants of their adoption or rejection of the system of rice intensification (SRI) for the wet season of 2014. SRI was first introduced to the commune in 2003 and spread among the farmers, but the number of farmers discontinuing the practice has increased since 2011. We classified the farmers into four categories: those who practice SRI in all their fields (OA), farmers who practice SRI in some of their fields (PA), farmers who had practiced SRI but discontinued it (DA), and farmers who have never practiced SRI (CR). Farmers in different categories of SRI adoption differed in their access to water sources. The majority of OA and PA farmers had supplementary water sources, which was, however, available to less than 50% of DA farmers and only 15% of CR farmers. Both PA and DA farmers mentioned water shortage as the reason for not practicing SRI in some (PA) or any (DA) of their fields, but they differed in the number of rice fields. All the PA farmers had more than one field, whereas a majority of DA farmers had only one field. Labor shortage and difficulty of planting in a regular grid pattern were also mentioned as the reason for not practicing SRI by the farmers, particularly by DA farmers. Water constraint and difficulties in transplanting were thus identified as two major determinants of SRI adoption/rejection at the study site.     

基于“两河流域”棉区变迁分析的棉花生产发展研究

相比粮食作物,目前我国棉花生产机械化发展不平衡、质量效益不充分。笔者以黄河流域棉区、长江流域棉区为例,深入剖析其棉花生产变迁成因,提出我国棉花产业发展思路。     

Labor requirements of system of rice intensification (SRI) in Cambodia

Local governments, NGOs, system of rice intensification (SRI) adopters, and researchers in Cambodia have extensively discussed the SRI. Agreement on the benefits, however, remains elusive. Some claim SRI increases rice yields at lower costs; others state that the evidence is still inconclusive. The adoption and impact of innovations influenced by the most practical SRI principles, which adopters can and do implement, as well as other SRI labor requirement have yet to be comprehensively investigated. This study aimed at elucidating and comparing distinct aspects of SRI labor requirements and conventional practices that can lead to more intensive SRI adoption. A household survey and field observations were conducted in three rain-fed villages in the southern part of Cambodia: two in Kampot Province and one in Kampong Speu Province. Findings showed little or no difference between SRI labor requirements and conventional practices. Laborers are in high demand when preparing land and nurseries, transplanting seedlings, and harvesting. Rice farmers alone or hired laborers have generally proved sufficient to date. Hired labor costs depend on the supply of farmer-family labor and the efficacy of the “Sharing-hand” system, not on farming techniques per se. This system helps alleviate hired labor costs, one of the highest cost factors. The findings also indicated that the degree of SRI adoption shows no correlation between the home-to-plot distance and availability of farmer-family labor or hired labor. The key factors for improving the degree of SRI adoption are farmer zeal and careful attention rather than the home-to-plot distance and availability of labor.     

Effects of crop establishment techniques on weeds and rice yield

Field and pot studies were conducted to evaluate the effects of seven rice establishment techniques {puddling transplanting (PT), no tillage transplanting (NTT), puddling drum wet seeding (PDWS), no tillage drum wet seeding (NTDWS), conventional tillage dry drilling (CTDD), furrow irrigated raised beds system dry drilling (FIRBSDD), and no-tillage dry-drilling (NTDD)} and water submergence stress on weeds and rice yield. The highest yield and least weed abundance were in the PT treatment. The direct seeded rice (DSR), both dry and wet exhibited severe weed infestation, and compared to transplanting showed reduced yield both in the presence and absence of weeds. The yield losses due to weeds in the DSR treatments ranged from 91.4 to 99.0%, compared to 16.0 and 42.0% in the transplanting treatments (PT and NTT). Weeds, including Cyperus rotundus L., Dactyloctenium aegyptium (L.) Willd., Digera arvensis Forsk., Phyllanthus niruri L., and Trianthema portulacastrum L. which were found in the un-puddled DSR treatments were absent in the puddled plots, particularly the PT treatments. In pot studies, continuous water-submergence (2.5 cm) for 20 days reduced the emergence of C. rotundus, D. aegyptium, T. portulacastrum, and Echinochloa crus-galli (L.) Beauv. by 99.4, 100, 100, and 24.4%, respectively, compared to alternate wetting–drying. In farmer's field studies, when compared to the PT treatments, the DSR treatments exhibited lower yields (15.8%) with coarse varieties (HKR-47 & IR-64), but fine cultivars (Sharbati & PB-1) exhibited similar yields under both systems. In view of the shortage of labour for manual transplanting, there is a need to develop suitable cultivars for aerobic system conditions (unpuddled DSR and NT machine-transplanting).     

Modeling the dependence of the crop calendar for rain-fed rice on precipitation in Northeast Thailand

Rain-fed lowlands are major agricultural ecosystems used for rice production in Northeast Thailand. Developing a tool to assess the effects of variable water conditions on the regional scale yield is also important to predict the effects of climate change on food supply. To estimate regional yields, we need a simple but accurate measure of the crop calendar (i.e., the distribution of planting dates), which has a strong influence on grain yield. In this article, we modeled the dependence of the crop calendar on rainfall patterns based on a survey of the region’s farmers as a part of an effort to provide a stronger basis for regional yield estimates. Our survey, conducted in 11 provinces for 2 years, confirmed the existence of large windows for sowing and transplanting versus narrow windows for heading and harvesting for rain-fed lowland rice culture in all the provinces. Variable water, soil, and toposequential conditions in the paddy fields were responsible for the large sowing and transplanting windows, whereas the use of photoperiod-sensitive varieties explained the narrow windows for heading and harvesting. The crop calendar was well expressed as a function of cumulative precipitation from June onward. When the crop calendar model was combined with a simple phenology-based model that uses growing degree-days adjusted by a day-length factor, we could estimate the rice crop calendar under rain-fed lowland conditions with acceptable accuracy. The model described in this article will be combined with a crop growth model to improve regional yield estimates for rain-fed lowland rice.     

Effect of fertilization on crop responses and solute transport for rice crop in a sub-humid and sub-tropical region

In order to increase the efficacy of water and control the losses of fertilizer, it is necessary to assess the influence of level of fertilization on crop responses, movement and balance of water and solutes from fertilizers in the root zone. With this goal, the reported study was undertaken to determine the effect of fertilization on crop responses and fertilizer solute transport in rice crop field in a sub-humid and sub-tropical region. Field experiment was conducted on rice crop (cultivar IR 36) during the years 2003, 2004, and 2005. The experiment included four fertilizer treatments comprising different levels of fertilizer application. The fertilizer treatments during the experiment were: F₁ = control with N:P₂O₅:K₂O as 0:0:0 kg ha^?1; F₂ = fertilizer application of N:P₂O₅:K₂O as 80:40:40 kg ha^?1; F₃ = fertilizer application of N:P₂O₅:K₂O as 120:60:60 kg ha^?1 and F₄ = fertilizer application of N:P₂O₅:K₂O as 160:80:80 kg ha^?1. The results of the investigation revealed that the magnitudes of crop parameters such as grain yield, straw yield, and maximum leaf area index increased with increase in fertilizer application rate. The levels of fertilization had very little effect on water loss via deep percolation and water use by the crop. The levels of fertilization had considerable effect on N leaching loss and uptake of N whereas it had no significant impact on leaching loss of water-soluble phosphorus. This indicated that PO₄-P leaching loss was very low in the soil solution as compared to nitrogen due to fixation of phosphorus in soils. The results also revealed that increase in level of fertilization increased water use efficiency considerably by increased crop yield. From the observed data of nutrient use efficiency, crop yield and environmental pollution, the fertilization rate of N:P₂O₅:K₂O as 80:40:40 kg ha^?1 (F₂) was the most suitable fertilizer treatment for rice crop among studied treatments.     

Relations of rice seeding rates to crop and weed growth in aerobic rice

Aerobic rice describes a management adaptation to reduced irrigation water supplies but, due to reduced intervals of flooding in this system, this requires revised weed management approaches to reduce costs and provide effective weed control. One approach is to make the crop more competitive and reduce the effects of weeds on the crop by using higher rice seeding rates. A study was conducted in the Philippines and India in 2008 and 2009 to assess the relations of seeding rates (15-125 kg ha⁻¹) of hybrid and inbred varieties to crop and weed growth in aerobic rice. Plant densities, tillers, and biomass of rice increased linearly with increased in seeding rates under both weedy and weed free environments. Weed biomass decreased linearly with increasing seeding rates from 15 to 125 kg ha⁻¹. Panicles and grain yields of rice in competition with weeds increased in a quadratic relation with increased seeding rates at both locations; however, the response was flat in the weed free plots. A quadratic model predicted that seeding rates of 48-80 kg ha⁻¹ for the inbred varieties and 47-67 kg ha⁻¹ for the hybrid varieties were needed to achieve maximum grain yield when grown in the absence of weeds, while rates of 95-125 kg seed ha⁻¹ for the inbred varieties and 83-92 kg seed ha⁻¹ for the hybrid varieties were needed to achieve maximum yields in competition with weeds. On the basis of these results, seeding rates greater than 80 kg ha⁻¹ are advisable where there are risks of severe weed competition. Such high seeding rates may be prohibitive when using expensive seed, and maximum yields are not the only consideration for developing recommendations for optimizing economic returns for farmers. Results of the present study do suggest however that increasing seeding rates of aerobic rice does suppress weed growth and reduce grain yield losses from weed competition. This information could be incorporated in integrated crop management packages to manage weeds more effectively.     

Impact of crop and nutrient management on crop growth and yield,nutrient uptake and content in rice

Paddy and Water Environment - System of rice intensification (SRI) together with appropriate nutrient management holds promise in increasing rice productivity with micronutrient enriched grains....     

Yield formation and tillering dynamics of direct-seeded rice in flooded and nonflooded soils in the Huai River Basin of China

Water shortage in the Huai River Basin prompts farmers to adopt water-saving technologies such as direct-seeded nonflooded or aerobic rice. Different cultivation practices impact on tiller growth and development. Improved insight into tiller dynamics is needed to increase yield in these production systems. We conducted field experiments with four direct-seeded rice varieties under flooded and nonflooded conditions in Mengcheng county, Anhui province, in 2005–2006. The soil water content in the nonflooded treatment varied between saturation and field capacity. Yields in nonflooded soil ranged from 3.6 to 4.7 t ha⁻¹, and did not differ significantly from yields in flooded soil that ranged from 3.6 to 5.1 t ha⁻¹. Variety had a significant effect on biomass, yield, panicle number, spikelet number, grain weight, and grain filling percentage. Panicle number was the main factor limiting yield, resulting from a low tiller emergence frequency and a low fraction of productive tillers in both the flooded and the nonflooded soils. On average, the panicle number was 159–232 m⁻², including 34–167 productive tillers per m² for all the varieties under the two water regimes. The contribution of productive tillers to yield varied between 7% and 47%. There were two peaks of tillers that contributed to yield, one at the low (4th or 5th) and one at the high (10th or 11th) phytomer orders. Frequencies of tiller emergence at most phytomer orders were higher in the flooded soil than in the nonflooded soil. There were no significant differences in frequencies of productive tiller emergence and contributions to yield from tillers between the soil water regimes for three of the four tested varieties. To increase yield in direct-seeded nonflooded rice production systems, both the tiller emergence frequency and the fraction of productive tillers should increase through breeding, improved crop management, or a combination.     

Impacts of water cycle changes on the rice market in Cambodia: stochastic supply and demand model analysis

A supply and demand model for rice in Cambodia, which includes among other factors evapotranspiration as a water supply variable impacting regional yields and planted areas, is developed to aid in the design of agricultural policies and planning. Impacts are determined stochastically by drawing on water cycle distributions and evaluating the resulting variation in production and price bands for local rice markets. The results of the baseline analyses indicate that production of wet and dry season rice steadily increases and the consumption per capita slightly decreases due to the negative income elasticity. Results of a partial stochastic analyses show that the production of rice in regions where elevations are high and the land vulnerable to flooding are the most sensitive to increased fluctuations in water supply. The changes also affect the rice market through equilibrium price changes. The upper price band, which is the width between average and 90th percentile, is larger than the lower band, which is the width between average and tenth percentile, suggesting that the situation of low income consumers could grow worse under an unstable environment with relatively larger upward price spikes. The results imply that development of irrigation facilities and water management systems maybe required for Cambodian provinces which rely heavily on agriculture, particularly rice production, under increasing climatic variation.     

Assessment of management of direct seeded rice production under different water conditions in Cambodia

In order to assess direct seeding of rice technology to cope with future agricultural labor shortage in Cambodia, agronomic experiments were conducted in 2005 and 2006 to compare direct seeding with transplanting under three water conditions (non-flooded, shallow flooded, and deep flooded conditions) with/without weed control by herbicides (bentazone and cyhalofop-butyl) for two Cambodian rice varieties (shorter stature and early maturity Sen Pidao, taller stature and longer maturity Phka Rumduol). Average rice yield in 2 years was lower in direct seeding (341 g m⁻²) than transplanting (404 g m⁻²), but interaction components with year, varieties, water conditions, and weed management were significant, and the attained maximum yield of direct seeding (510 and 464 g m⁻² for Phka Rumduol variety in shallow flooded condition with weeding in 2005 and 2006, respectively) was similar to that of transplanting. Plant length and dry weight of rice were reduced in non-flooded and deep flooded conditions compared with shallow flooded condition, and grain yield was the highest in shallow flooded condition. Yield advantage of Phka Rumduol over Sen Pidao increased under direct seeding, particularly under non-flooded conditions in 2005 because weed infestation was more suppressed in Phka Rumduol even without weeding. Increase in 100 g m⁻² of weed infestation prior to heading (dry weight basis) reduced about 20% of attainable yield with weed control. This study identified importance of stature and growth duration of rice varieties and presence of standing water as well as the weed control, in order to develop and extend direct seeding in the Cambodia.     

浅谈水稻冷害指标的调整

针对吉林省辽河农垦管理区水稻田与旱田小气候不同特点,以观测的事实为依据,提出水稻田冷害指标的调整建议:水稻移栽始期日均气温稳定通过11.2℃;6月10日以前,水稻秧苗受冷害温度下调为<15℃;而7月份冷害温度应上调为<17.7℃;8月份上调为<18.4℃;9月份为<19.0℃。并指明,夜间是水田预防低温冷害的重点时间。     

长江中下游地区主要优质稻品种简介

由于从200O年起南方早税稻品种将退出保护价收购范围,优质水稻品种在长江中下游地区得到了较大推广。各地确定的优质稻品种,湖南高档的为湘晚舢2号、3号、5号、9号、10号、11号、中香五号,中档的为中化早5号、中化早81、中鉴IOO、香两代68、培两优288;江西早稻为嘉育948、金优4O2、优14O2、嘉早935、赣早舢37号、香两代68、安两代早25、中鉴IOO,晚稻为中香1号、赣晚讪19号、赣晚税923、江西丝苗、鹰代晚、赣晚舢14号、65002、金优桂99、博优752;湖北优质的有扬稻6号、嘉育948、舟903、金优桂99、常化63、荆优928、金优158、香两优…     

两优培九单晚种植的高产特点及栽培技术

两优培九是由江苏省农科院和国家杂交水稻工程技术研究中心合作育成的两系杂交籼稻组合。2000年引入江山市试种 ,2002年全市种植面积0.3万hm2,占单晚面积的44.98 % ,预计2003年将进一步扩大种植 ,成为江山市单晚的当家品种。据两年的调查显示 ,两优培九在江山市常规栽培单产仅为550kg/667m2 ,相当于示范片中低产田产量。这说明当地多数农民并未真正掌握两优培九组合的高产特点和栽培技术 ,有必要作进一步的探讨。一、两优培九的生育期及适应性经江山市2年的试验观察认为 ,两优培九感温性强、感光性不及协优9308组合 ,早播早成熟 ,全生育期14…     

Impacts of climate change on rice market and production capacity in the Lower Mekong Basin

The supply of water is affected by climate changes. In addition, high economic growth in the lower Mekong River countries including two large rice exporters is expected to reduce the per capita consumption of rice as incomes grow. Consequently, the need exist to investigate changes in supply and demand using econometric models of rice markets in the countries, where water supplies are expected to change. The objective of this research is to clarify impacts of water supply changes on rice producers and consumers using supply and demand models of rice considering changes in the water supply to aid in producing agricultural policies and plans. The following two simulations were conducted in this assessment: (a) baseline and (b) CC_B2. The simulation of the baseline includes the assumption that the evapotranspiration (ET) of each province after 2000 is the average quantity of ET from 1995 to 1999. The simulation of the CC_B2 includes the assumptions that ET of each province after 2010 accords with the IPCC socioeconomic scenario B2. The simulation results suggest that climate change will depress wet season rice production in Cambodia and Mekong River Delta (MRD) region in Vietnam, and that of dry season rice in the MRD region in Vietnam and northeastern region (Isan) Thailand. The simulation results also indicate that climate change will increase farm prices of rice in Cambodia, Vietnam, and Thailand. The results suggest that climate changes will weigh on the livelihood of rice consumers, especially those of poor rural populations.