Uptake efficiency of 15N-urea in flooded and aerobic rice fields under semi-arid conditions

Paddy and Water Environment - The sustainability of traditional rice (Oryza sativa L.) cultivation in many Asian countries is being questioned due to severe water shortage conditions, envisaging...     

Analysis by numerical experiments of desalinization of a salt-affected paddy field using a rice husk underdrainage system

Paddy and Water Environment - In a monsoon climate, salt accumulates not only in drylands, but also in paddy fields during the dry season. Because natural desalinization by gravitational drainage...     

Root growth dynamics and stomatal behaviour of rice (Oryza sativa L.) grown under aerobic and flooded conditions

Aerobic rice culture is a new technology designed to reduce water use, but the vulnerability of rice to aerobic condition has limited its development. The objective of this study was to characterize the root growth and stomatal behaviour of four rice cultivars grown in flooded and aerobic culture for 2 years. In aerobic culture, where the soil water potential at 20-cm depth averaged between −15 and −30 kPa, total root biomass was significantly lower than in flooded culture for the whole growth period, owing to a reduction in root biomass in the surface layer. Dry-matter partitioning to roots decreased, but the ratio of deep root biomass to total root biomass tended to be higher in aerobic culture than in flooded culture. The low root-to-shoot ratio and poor root growth in the surface layer in aerobic culture are attributable to the considerable reduction in adventitious root number. As a result, the varietal difference in total root biomass was due largely to individual root growth in aerobic culture. Stomatal closure was distinct at the vegetative stage in aerobic culture, even when the soil water potential was near field capacity, partly because of the poor rooting vigour. When the soil water potential at 20-cm depth was below −50 kPa, the stomatal behaviour reflected the root growth in the subsurface layer. These results suggest the role of vigorous root growth in soil water uptake and hence, in maintaining transpiration in aerobic rice culture.     

直播单季晚稻田杂草发生特点与防治对策

直播稻作为轻型栽培技术 ,具有省工、节本、高产、高效优势 ,深受广大农户特别是种粮大户的欢迎 ,已成为浙江省水稻栽培的重要方式。２０００年全省直播稻面积达２１．６万ｈｍ２,占全省水稻播种面积的１３．５ % ,其中直播单季晚稻１４．０万ｈｍ２。由于直播稻播种量少 ,水稻苗期空间大 ,干湿交替时间长 ,田间杂草种子多 ,繁殖快 ,常常因发生草害而减产 ,甚至因草荒而绝收。大面积生产实践表明 ,直播稻田的草害问题一直是影响直播稻普及推广的主要障碍因子之一。一、杂草发生特点１ .杂草种类据海宁市新仓镇调查观测 ,直播单季晚稻田杂草…     

IT field monitoring in a Japanese system of rice intensification (J-SRI)

A demonstration study on Information Technology (IT) field monitoring was conducted in a rice field under the System of Rice Intensification (SRI) environment in Shinshiro City, Aichi Prefecture, Japan. The IT system used in this study consisted of an intelligent sensor node web-server that is equipped with in situ camera and sensor networks for agrometeorological, soil, and plant growth monitoring. Dynamic changes in soil moisture, water level, agrometeorological, and environmental conditions were measured and monitored. With this precision farming set-up, understanding and easy assessment of the salient field conditions and phenomena such as cyclic soil wetting and drying as well as critical crop growth stages were made possible. Based on the findings of the demonstration experiment, the system was effective, reliable, and efficient in monitoring soil moisture parameters and agrometeorological information in remote rice field environment. The actual field conditions were captured well by a combination of images, numerical, and graphical data sets. With this precise information, the frequency of irrigation was found to be every 7 days. The rice field was irrigated up to a moisture level of 0.592 m³/m³ (~600 mV) and allowed to be depleted to a moisture level of 0.417 m³/m³ (~400 mV). With this alternate drying and wetting method (AWD), a 25.71% of irrigation water was saved. In this study, rice production was made more scientific and more reliable. Hence, the use of IT field monitoring system represented a viable medium for the realization of better rice productivity which leads to the ethic of sustainable agriculture.     

Parameterization of canopy resistance for modeling the energy partitioning of a paddy rice field

Paddy and Water Environment - Models for predicting hourly canopy resistance (r c) and latent heat flux (LET) based on the Penman–Monteith (PM) and bulk transfer methods are presented. The...     

寒地水稻调节肥施用效果分析

通过对调节肥施入的不同时期、不同施入量的田间试验研究,结果表明,调节肥施入量增加到31%,于8.1～8.5叶时施入,能提高叶面积指数,增加光合能力,提高水稻产量。     

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.     

寒地水稻病害生物防治技术研究

针对近年水稻田间生态环境变化而产生的一些新病害问题,利用生物防治手段,研究优质水稻生产中病害防治技术。结果表明,应用8%好米得颗粒剂防治稻瘟病、叶鞘腐败病等水稻病害,成本虽较高,15～20元/667m2,但防效在80%～100%,经济效益达147.52元/667m2,效果居参试药剂第一位。2%加收米与多菌灵混合喷施,防病效果也较好,成本较8%好米得减少4.5～9.0元/667m2。     

Prediction of grain weight,brown rice weight and amylose content in single rice grains using near-infrared reflectance spectroscopy

The potential of near-infrared reflectance spectroscopy (NIRS) for simultaneous analysis of grain weight (mg), brown rice weight (mg) and milled rice amylose content (AC, %) in single rice grains was studied. Calibration equations were developed using 474 single grain samples, scanned as both rice grain and brown rice. An independent set containing 90 F₂ generation grains was used to validate the equations. In general, equations developed using the first derivative resulted in superior calibration and validation statistics compared with the second derivative and those developed using brown rice were superior to those developed from the rice grain. Fitting equations were developed and monitored with an external validation set. The standard error of prediction (corrected for bias) SEP(C) for AC, brown rice weight and rice grain weight for equations developed using brown rice were 2.82, 1.09 and 1.30, with corresponding coefficient of determinations (r²) of 0.85, 0.71 and 0.67, and SEP(C)/S.D. of 0.39, 0.57 and 0.59, respectively. It was demonstrated that NIRS provides a convenient way to screen single intact grains. This will be advantageous in early generation selection in rice breeding programs.     

Development of control release urea fertilizer model for water and nitrogen movement in flooded rice

Paddy and Water Environment - Application of control release fertilizer in rice cultivation is a smart way to reduce the environmental nitrogen contamination and enhance the nitrogen use...     

Biotic and abiotic causes of yield failure in tropical aerobic rice

Aerobic rice is a new production system for water-short environments. Adapted varieties are usually direct dry seeded and the crop grown under aerobic soil conditions with supplementary irrigation as necessary. Occasionally, yield failures occur which may be related to soil health problems. In the dry season of 2006 and 2007, we conducted a field experiment in the Philippines, to identify the major causes of such yield failure. Four treatments were implemented: (i) Control of direct dry-seeded rice (improved upland variety Apo), (ii) Biocide application, (iii) transplanting into aerobic soil, and (iv) 1 year fallow. Yield in the Biocide treatment was 2 t ha⁻¹ in both years. In all other treatments, yield was 0–0.3 t ha⁻¹. Plants grown in the Biocide treatment showed a reduced degree of galling of roots caused by root-knot nematodes (RKN) and better general root health than the Control treatment. Potentially pathogenic fungi were isolated from root samples (Pythium sp., Fusarium sp., and a Rhizoctonia-like species). Abiotic effects of the Biocide treatment were an increase in KCl-extractable N (initial season 2007) and a decrease in initial soil pH. In the Control treatment, soil pH increased from 6.5 to 8.0 over the two seasons. In 2007, plant tissue analysis indicated Mn deficiency in the Control treatment. Plants that were subjected to foliar micronutrient sprays reacted positively to Fe and Mn sprays in the Control treatment, and Mn spray in the Biocide treatment. We concluded that the Biocide application led to favorable soil conditions by reducing biotic stresses such as RKN and improving nutrient availability. In the other treatments, an interaction of RKN and micronutrient deficiencies with increasing soil pH led to yield failure.     

Gene targeting using the Agrobacterium tumefaciens-mediated CRISPR-Cas system in rice

Background

The type II clustered, regularly interspaced, short palindromic repeat (CRISPR)/ CRISPR-associated protein 9 (Cas9) system is a novel molecular tool for site-specific genome modification. The CRISPR-Cas9 system was recently introduced into plants by transient or stable transformation.

Findings

Here, we report gene targeting in rice via the Agrobacterium tumefaciens-mediated CRISPR-Cas9 system. Three 20-nt CRISPR RNAs were designed to pair with diverse sites followed by the protospacer adjacent motif (PAM) of the rice herbicide resistance gene BEL. After integrating the single-guide RNA (sgRNA) and Cas9 cassette in a single binary vector, transgenic rice plants harboring sgRNA:Cas9 were generated by A. tumefaciens-mediated stable transformation. By analyzing the targeting site on the genome of corresponding transgenic plants, the mutations were determined. The mutagenesis efficiency was varied from ~2% to ~16%. Furthermore, phenotypic analysis revealed that the biallelic mutated transgenic plant was sensitive to bentazon.

Conclusions

Our results indicate that the agricultural trait could be purposely modified by sgRNA:Cas9-induced gene targeting. CRISPR-Cas9 system could be exploited as a powerful tool for trait improvements in crop breeding.     

Effects of planting date and variety on flooded rice production in the deepwater area of Thailand

Crop management plays an important role in the transition from a deepwater rice to a flooded rice production system but information about optimum management strategies are currently lacking. The goal of this study was to determine the effect of planting date and variety on flooded rice production in the deepwater area of Thailand. Two experiments were conducted at the Bang Taen His Majesty Private Development Project in 2009 and 2010 to represent conditions prior to flooding (early rainy season) and after flooding (dry season). The early rainy season crop covered the period from May to October 2009, while the dry season crop covered the period from November 2009 to April 2010. The experimental design was a split plot with four main plots and three sub plots replicated four times. The treatments for the main plot were various planting dates, while the treatments for the sub plots were rice varieties. The dates of the critical developmental phases of rice were recorded and biomass was sampled during the growing period. The collected data were statistically analyzed using ANOVA and treatment means were compared to identify the appropriate plating date and the best variety for the area. The highest average yield was obtained for variety PSL2 across transplanting dates from June 19 to July 23, with an average yield of 3898 kg ha⁻¹. The dry season crop showed that both biomass and yield were affected by the interaction between planting date and variety. The highest yield was obtained for variety PTT1 transplanted on November 9. The research showed that the variety PSL2 is the most suitable variety for early rainy season production with a transplanting date ranging from June 19 to July 23, while the variety PTT1 planted on November 9 was the best management practice for the dry season crop. However, a high yielding flooded rice variety that has a short growth duration is still needed for this area.     

Economic assessment of water-saving irrigation management techniques and continuous flooded irrigation in different rice production systems

Paddy and Water Environment - Globally, increasing water scarcity and higher production costs are the challenges in the cultivation of conventional transplanted rice (TPR). Under such conditions,...     

Self-made microlysimeters to measure soil evaporation: a test on aerobic rice in northern Italy

Soil water balance researches aimed at improving crop water use efficiency often require the determination of soil evaporation. In this technical note, the performance of simple and cheap self-made microlysimeters for the measurement of soil evaporation was tested in an aerobic rice field managed by intermittent irrigation. Six microlysimeters obtained by cutting commercial PVC pipes and closing the bottom ends with caps were positioned in appropriate PVC outer casings installed into the soil. Three measurement campaigns (for a total of 11 measurement periods) were carried out in different vegetation cover conditions (rice development, rice maturity and after the crop harvest). Evaporation amounts were analysed with respect to climatic data, vegetation cover and soil water status and, finally, compared with the simulated results of a FAO Penman–Monteith “dual crop coefficient” model implemented with site-specific data. Evaporation rates in the three campaigns were closely dependent on the evaporative demand of the atmosphere ETo (R ² = 0.96, 0.98, 0.96), while the slope of the linear regression curve was strongly related to the vegetation cover (b = 0.29, 0.12, 0.94); soil water content, always rather high during the experiments, did not affect the evaporation rate. Measured and simulated evaporation amounts showed a close agreement: the linear regression was characterized by slope and R ² of 0.98 and 0.95, while RMSE and NSE indices were 0.15 and 0.94. From the tests conducted, we can conclude that the self-made microlysimeters presented in this note are affordable instruments for measuring soil evaporation, at least in temperate climate conditions.     

Predicting water surface evaporation in the paddy field by solving energy balance equation beneath the rice canopy

The energy flux on the ground surface depends not only on climatological and biophysical controls in the vegetative canopy, but also on the available energy and energy partitioning beneath the canopy. Quantifying the evaporation and energy partitioning beneath the canopy is very important for improving water and energy utilization, especially in arid areas. In this study, we measured meteorological data, the net radiation and latent heat flux beneath the rice canopy, and then applied the radiation and energy balance equations to get the water surface temperature beneath the rice canopy. To apply the equations, we constructed shortwave and longwave radiation beneath the canopy sub-models and a bulk transfer coefficient sub-model. A plant inclination factor was parameterized with plant area index for the shortwave and longwave radiation sub-models. Bulk transfer coefficient was parameterized by plant area index and soil heat flux was predicted by the force restore model. With calculated water surface temperature and constructed sub-models, we reproduced net radiation and latent heat flux beneath the rice canopy. As a result, the reproduced water surface temperature, net radiation, and latent heat flux beneath the rice canopy were very close to the measured values and no significant differences were found according to 2-tail t test statistical analysis. Therefore, we conclude that these constructed sub-models could successfully represent water surface temperature, net radiation, and latent heat flux beneath the rice canopy.     

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.