Rice Cultivation Systems Research Articles

Rice sheath blight disease control by native endophytic Bacillus subtilis from Kuttanad, a Globally Important Agricultural Heritage System

ABSTRACT Kuttanad in India is known as ‘the rice bowl of Kerala’ and renowned for its unique rice cultivation system that is below sea level. However, rice production in this wetland ecosystem is seriously threatened by sheath blight disease caused by the fungus Rhizoctonia solani, which has resulted in a significant decline in grain quality and a 50% loss in yield. In the present study, we isolated two endophytic Bacillus subtilis strains, NIIST B616 and NIIST B627, from the roots of rice plants growing in the Kuttanad region and tested their efficacy in controlling sheath blight disease. We found that rice plants inoculated with a combination of both Bacillus strains and R. solani had a 64.71% lower disease incidence and a 31.02% higher harvest index than plants treated with R. solani alone. An analysis of defence-related enzymes and chemicals revealed that treatment with both isolates together greatly enhanced levels of l-phenylalanine ammonia-lyase (PAL; 2.8 fold), peroxidase (POX; 7.4 fold), polyphenol oxidase (PPO; 4.5 fold), and total phenol (8.5 fold) compared with plants treated solely with R. solani, indicating that these isolates significantly increased plant defence responses through induced systemic resistance (ISR), and this finding was validated through a split-root experiment. More detailed analysis using gas chromatography–tandem mass spectrometry (GC-MS/MS) and liquid chromatography–tandem mass spectrometry (LC-MS/MS) techniques revealed that cyclo-(Pro-Leu) and cyclo-(Pro-Phe) were the major components responsible for the antifungal properties of the two isolates and their capacity to trigger ISR in plants. Thus, the Bacillus strains and their metabolites may be deemed viable alternatives for controlling the prevalence of sheath blight disease in rice plants and augmenting rice production at unique locations such as Kuttanad.

Effects and mechanisms of chlormequat on horizontal transfer of antibiotic resistance genes through plasmid-mediated conjugation in agro-ecosystems

Chlormequat (CCC) is widely used in agricultural production to increase the crop yield. However, the effects of CCC on transfer of ARGs in agricultural system are still unclear. In this study, using E.coli DH5α (carrying RP4 plasmid with AmpR, TetR, KanR) as the donor bacterium, E.coli HB101, endophytic Pseudomonas sp. Ph6 or rhizosphere Pseudomonas putida KT2440 as the recipient strain, three conjugative systems were designed to investigate the effects of CCC on ARG transfer. Meanwhile, hydroponics experiments were designed to study the ARG spread in the rice-nutrient solution system after CCC application. The results showed that CCC significantly promoted the RP4 conjugation by expanding cell membrane permeability and improving the relative transcription levels of trfAp, trbBp, traA and traL genes in RP4. Furthermore, the conjugation frequency between E. coli and Pseudomonas was much higher than that between E. coli cells. Compared with spraying foliage with 2500 mg·L−1 of CCC, soaking seeds with 250 mg·L−1 of CCC was more beneficial to the colonization of ARB in rice, and also increased the abundance of ARGs in rice cultivation system. These results remind that the use of CCC in agricultural production might promote the ARG transmission in agro-ecosystems; however, foliage spraying with 2500 mg·L−1 of CCC could control its spread.

Biochar from paddy field - A solution to reduce PFAS pollution in the environment

Generally, activated carbons demonstrated a notable ability to capture long-chain PFAS, but exhibited relatively lower effectiveness for short-chain PFAS. Thirteen commercially available activated carbons in Japan underwent testing for their adsorption capacity of PFAS in water. The activated carbon derived from rice husk, Triporous™-PFAS, exhibited the highest adsorption capacity (over 95%) for PFAS from ultrashort-chain (perfluorocarbon chain: C1 for perfluorocarboxylic acid (PFCA) and C2 for perfluoroalkane sulfonic acid (PFSA)) to long-chain PFAS (C13 for PFCA and C10 for PFSA). An earlier lysimeter study highlighted Andosol, representative soil in Japan, as a potential medium for removing PFAS from irrigation water. Considering cultivating rice on Andosol fields and producing biochar from rice husks and rice straw, a new rice cultivation system is proposed. This system aims to facilitate continuous removal of PFAS from the environment in Asia. Japanese rice cultivation system produces not only rice but also biochar to remove PFAS from water circulation system. The total fluorine content in the tested activated carbon materials ranged from 0.18 to 38 μg g−1 F. Based on the results from background F blank and adsorption capacity, TriporousTM-PFAS-F was shown to be an option to lower the method detection limit for a proposed international standard method for measuring total PFAS.

Respons Agronomi dan Fisiologi Genotipe Padi (Oryza sativa L.) pada Budi Daya Berkelanjutan

Efforts to maintain rice production in the future face many challenges, including the availability of increasingly narrow land, attacks by plant pest organisms, and declining land fertility due to improper cultivation systems. More than 70% of rice fields are in a disturbed ecological status due to cultivation technology that could be more environmentally friendly, which can interfere with the sustainability of rice self-sufficiency. An environmentally friendly rice cultivation system needs to be developed. This study aims to measure the agronomic and physiological responses of 3 rice genotypes in sustainable cultivation systems. The experiment used a Group Random Design on 3 rice genotypes (black, red, and white) in both conventional and sustainable cultivation systems. The research was carried out in the experimental garden of Polinela Organic Farm, Lampung State Polytechnic, from September 2020 to September 2021. The results showed that the plant, leaf greenery, number of tillers, number of panicles, grain weight per panicle, and biomass weight were not significantly different between conventional and sustainable cultivation. At the same time, the harvest and production indices per hectare were significantly different. The physiological responses to the photosynthesis and transpiration rates differed markedly in conventional and continuous cultivation. In contrast, the conductance of stomata did not differ significantly in both cultivation systems. The red rice genotype is the best, and it has a broader adaptation to conventional and sustainable cultivation systems. Keywords: agronomy, conventional sysem, physiology, rice genotype, sustainable system

Water saving rice cultivation using sheet-pipe subsurface irrigation

Water saving in rice cultivation has assumed paramount importance, especially in the context of climate change. The introduction of sheet-pipe technology in Indonesia heralded as an innovative subsurface irrigation and drainage system, is poised to revolutionize how to manage this vital resource. Our study was designed with two primary objectives: first, to investigate how rice plants respond when water levels are deliberately reduced using the sheet-pipe technology; and second, to comprehensively analyze water productivity and water use efficiency in comparison to conventional flooded rice cultivation systems. We conducted two distinct experiments: one employing sheet-pipe subsurface irrigation (SSI) and the other utilizing conventional flooded irrigation (CFI). In the SSI setup, the water level was maintained at a depth of 5–10 cm below the soil surface 20 days after transplanting to harvesting. With this setting, the soil moisture was maintained at around 85–95 degrees of saturation. On the other hand, the CFI approach involved water flowing directly over the soil surface, with the water level consistently maintained at a mere 2–3 cm above it. Interestingly, while the SSI method did lead to a reduction in yield, it has significant benefits. Our results showed that a reduction in yield was observed for the SSI 15.5–18.6 % lower compared to the conventional method (CFI). However, the SSI is environmentally benefit compared to the conventional method by reducing 37.5–50.5 % in water irrigation, increasing water use efficiency (WUE) up to 70.8 %, and improving 3.2–10.4 % in water productivity. Our findings reveal that optimizing water conservation may have a disadvantageous effect on rice yield, indicating the importance of optimal water level. Future research to find the optimal water level that balances yield production and environment is required, especially to adapt to dry and warming climate change in the future.

Spatio-temporal changes of rice cropping system in Anhui Province from 2010 to 2020

Monitoring changes in rice production is of significant importance for addressing food security concerns in China. However, obtaining long-term, high-resolution rice planting maps is challenging due to the influence of cloud cover and temporal resolution limitations. This study, conducted on the Google Earth Engine (GEE) platform, utilizes Landsat and Sentinel data and employs the difference in normalized difference vegetation index method (dNDVI) to extract the distribution in rice cultivation systems in Anhui Province over the past decade. The results indicate that, between 2010 and 2020, the area of single cropping rice cultivation in Anhui Province increased by 12513.612 km², while the area of double cropping rice cultivation decreased by 13527.892 km². The rice replanting index declined by 31%. With a notable shift observed in 2015, where a substantial area of double cropping rice was replaced by single cropping rice cultivation. Consequently, over the past decade, there has been a gradual decrease in the rice cultivation area in Anhui Province, accompanied by a significant shift from double to single cropping cultivation, and a continuous decline in the replanting index. This research provides vital clues for a deeper understanding of the rice planting pattern, offering scientific support for the sustainability of food production.

Mechanisms of chloride to promote the uptake and accumulation of cadmium in rice (Oryza sativa L.)

Cadmium (Cd) contamination in rice ecosystems posed a critical challenge to global food security and environmental health. This study aimed to unveil the key mechanisms trough hydroponic experiments by which chloride (Cl−) promoted the absorption and accumulation of cadmium (Cd) in rice plants. The findings elucidated that the addition of Cl− increased Cd uptake by rice roots (5.1 % ∼ 61 %), acting both directly by enhancing root morphology and indirectly through regulating of the main transporter genes of Cd. The study unveiled that Cl− addition significantly improves Cd bioavailability in roots, which was discernible through the augmentation of Cd concentration and proportion in subcellular fractions, coupled with elevated energy values in key cellular components. Moreover, Cl− addition further augmented the intricate process of Cd transport from roots to shoots (16.1– 86.7 %), which was mainly attributed to the underexpression of OsHMA3 and the decrease in the formation of sulfuhydryl substances. This research provides a comprehensive understanding of the complex mechanisms governing Cd dynamics in rice plants in the presence of Cl−. By elucidating these processes, our findings not only contribute to fundamental knowledge in plant metal uptake but also hold promising implications for mitigating Cd contamination in rice cultivation systems.

Plant Physiological Performances, Plant Growth, Grain Yield and Methane Emission of Rice (Oryza Sativa L.) in Response to Water Management as Adaptation Strategy for Climate Change

Continuously flooded rice systems are a major contributor to the greenhouse gases (GHG) emissions in the agriculture sector in Malaysia. Intermittent irrigation has been recommended to replace conventional rice water management to save water and reduce GHG emissions without compromising rice yields. This study was conducted in two growing seasons at Malaysia’s largest rice granary area to determine the effectiveness of different water management practices on conserving water, mitigating GHG and maintaining rice grain yields. Three water management treatments were continuous flooding (CF), saturated and wet conditions from transplanting to heading and flooding until maturity (S-F) and continuous saturated and wet conditions (CS). The results showed that S-F and CS reduced water inputs between 15.0-16.8% and 32.0-34.0% as compared to CF, respectively. Water-saving treatments mostly did not significantly affect the plant's physiological performance, plant growth parameters, growth rate, grain yield and yield parameters. The results indicated that soil saturated and wet conditions provided adequate soil moisture content for the plant’s requirement similar to flooding conditions. Maintaining soil at saturated and wet conditions during the vegetative stage reduced 24.18-39.76% of methane emissions. However, maintaining soil at saturated and wet conditions throughout the growing season reduced 34.52-55.08% of methane emissions. In conclusion, intermittent irrigation could be an effective adaptation technique for simultaneously saving water and mitigating GHG while maintaining high rice grain yields in rice cultivation systems.

Assistance to Farmers in Increasing Rice Production Through Direct Seed Planting System in Langsat Permai Village, Bungaraya District

The increase in agricultural yields of food crops and horticulture in Langsat Permai Village, Bungaraya District was initiated by the construction of canal blocking in the activities of the Partner Village Service Program by DIKTI in the 2017-2019 implementation year which will continue until 2023. However, the harvest index (HI) of rice has not reached 300 due to the transplanting system, so that it takes quite a long time from the transplanting period to finally harvesting and replanting. Therefore, the rice cultivation system with the direct seed planting system can be a solution that can help farmers increase the harvest index (HI) and rice crop production. The activity partners who were the targets of the activity were farmers and members of the Langsat Permai Village youth group. Assistance is carried out by providing knowledge about rice cultivation using the direct seed planting system starting from the understanding of the direct seed planting system, its tool, the advantages and disadvantages of rice cultivation using the direct seed planting system, as well as the stages of the direct seed planting system cultivation from land preparation, seed preparation, planting to fertilization. Based on the results of the mentoring carried out, the knowledge of farmers and youth groups in Langsat Permai Village about rice cultivation using the direct seed planting system has increased compared to before the mentoring activities were carried out.

The Effect of Irrigation Techniques on Sustainable Water Management for Rice Cultivation System - A Review

Rice serves as a fundamental sustenance for approximately half of the global population, particularly in Asia. Nevertheless, the cultivation of rice demands a substantial water supply, and the challenges associated with water deficits have been exacerbated by irregular rainfall patterns induced by global warming. Consequently, there is a critical need to reassess irrigation techniques to effectively tackle these issues. In this comprehensive review, the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) method was employed to systematically explore literature on irrigation techniques aimed at fostering sustainable water management in rice cultivation systems. The primary components of the framework encompass water consumption and water-related characteristics, soil-related characteristics, and plant-related characteristics, encompassing relevant components and indicators. Two alternative irrigation methods, namely alternate wetting and drying (AWD) and saturated soil irrigation (SSI), have been proposed to enhance water use efficiency (WUE) in rice cultivation compared to traditional continuous flooding (CF). These alternative irrigation methods do not adversely affect rice yield, both quantitatively and qualitatively. Furthermore, these alternative irrigation approaches have the potential to mitigate greenhouse gas (GHG) emissions, particularly methane emissions, in rice production. This review underscores the significance of data on alternate irrigation systems, providing valuable insights for researchers and policymakers in formulating strategies that align at every level for practical implementation. This is crucial as it is relevant to multiple organizations and stakeholders. Moreover, in the face of inclement weather conditions resulting from climate change, the study's findings indicate that research on farmers' adaptation, plant stress, and resilience within the rice cultivation system is still in its nascent stages. This highlights the pressing need for further exploration and advancement in these areas to develop effective strategies for coping with the challenges posed by climate change.

Late Neolithic to Bronze Age water management and upland rice cultivation in the mountainous areas of Southeastern China Coast

The southeast coast of China is a crucial area for the spread of agriculture from mainland Asia to Taiwan and the islands of Southeast Asia. However, whether prehistoric rice cultivation in this region was lowland or upland remains unclear. This study used a detailed phytolith analysis to evaluate temporal changes in structure at three coastal sites of varying altitudes in the Fujian Province of China, Longgang, Zhengjiashan, and Gehongshan. Samples were collected from two cultural phases, the Neolithic Huangguashan and Bronze Age Huangtulun cultures. Additionally, a new physical index, the sensitive-to-fixed phytolith ratio, was used to identify the environmental conditions in which crops were cultivated. Using this method, the number of sensitive types can be less or greater than that of fixed types, corresponding to drought or paddy field rice cultivation systems, respectively. The results showed an interplay of rice and millet farming at these sites. The crop phytolith ratio revealed that rice was dominant in the crop structure. However, notable differences existed in the proportion of different crops and phytolith assemblages across the various sites. The sensitive-to-fixed phytolith ratios, indicative of wet-dry environmental changes, were 1.56 and 1.07 at the low-altitude Longgang and water-rich Zhengjiashan sites, respectively, suggesting lowland rice cultivation. In contrast, the sensitive-to-fixed ratio at the high-altitude Gehongshan site was only 0.8, implying upland rice cultivation. The phytolith assemblage variation among the different sites also revealed an increase in dryland crops from low to high altitudes, indicating that the inhabitants of the southeastern coastal mountainous area modified their crop structure and rice cultivation methods during the Neolithic–Bronze Age transition to overcome environmental limitations. In summary, this study presents phytolith evidence for prehistoric upland rice cultivation on the southeast coast of China, offering valuable insights into the development of the prehistoric subsistence economy in the region.

Comparative Study of Musculoskeletal Disorders and Quality of Life between Traditional and Semi-modern Paddy Farmers of Gilan

Background and Objectives: Musculoskeletal disorders and low quality of life are the most common problems among paddy farmers in the world. Paddy farmers are exposed to inappropriate postures, long working hours and stressful environmental conditions. The aim of this study was to compare different farming methods of rice cultivation (traditional and semi-modern) on the prevalence of musculoskeletal disorders and life quality of paddy farmers.
 Methods: This descriptive-analytical study was conducted in rice fields with 150 paddy farmers as a sample group (100 traditional paddy farmers and 50 semi-modern paddy farmers). Musculoskeletal disorders and quality of life were assessed using the Nordic questionnaire and the Lancashire Quality of Life Profile, respectively.
 Results: The prevalence of musculoskeletal disorders in the neck, lower back and shoulders is higher in traditional paddy farmers compared to farmers who work in semi-modern rice cultivation system. Present results demonstrated that there was no significant difference between various rice cultivation methods and musculoskeletal disorders on life quality. Furthermore, different farming methods of paddy cultivation have no significant effect on paddy farmers' life quality.
 Conclusion: The prevalence of lower back musculoskeletal disorders among paddy farmers portrays the consequence from long-term exposure to inappropriate posture from strenous activity.

Economic and Operational Evaluation of the Use of Two Manual Rotary and Cono Weeders in an Intensive Rice Cultivation System (SRI) in the Central Zone of Burkina Faso

Rice, the Burkina Faso's fourth most important cereal in terms of surface area, production and annual per capita consumption, is a staple food. The high demand for rice is far from being met by national production. Several constraints, including weeds, are causing huge yield losses. The aim of this study is to assess the economic impact of innovative mechanical weed management technologies, with a view to increasing the productivity of irrigated rice in Burkina Faso. The Boulbi irrigated paddy field was used for experimentation. The evaluation was carried out on the farm using a completely randomized Fisher block design in a 4-repeat SRI. The performance of three weeders, two designed (rotary (T2) and cono (T3)), was evaluated with the Africa Rice model (T1), compared with weeding with a hand hoe (T0). Data were collected on performance and yield parameters. They were recorded with XLSTAT Version 2016.02.27444 and subjected to descriptive analyses. Results showed that weeding with weeders reduced labor time for the three weeding operations by 55% with T1, 65% with T2 and 70% with T3 compared with T0. The yield increase was 37.20% with T3, 32% with T2 and 22% with T1 compared with T0. The operating account results show additional gains of 386,250 FCFA with T3, 319,417.8 FCFA with T2 and 223,583.9 FCFA with T1 compared to T0.

Synergistic Effects of N Fertilization and Irrigation on Soil Bacterial Community in Super Rice Paddies

Nitrogen reduction, in association with increased planting density and irrigation management, has been widely adopted in super rice cultivation systems to pursue higher yield with lower input. Here, soil microbial community structures under accurate N and water management were investigated after four years of experiments. Plot experiments were conducted with three treatments, including conventional farming practice (CF), reduced nitrogen with increased plant density (RNID), and reduced nitrogen with increased plant density and precise irrigation (RNIDPI). The results showed that RNID treatment increased soil bacterial diversity, enriched biomarker bacterial taxa, and altered bacterial community structure, with pH as the influential factor. The phylum Chloroflexi was enriched in the treatment of N reduction, while a higher ratio of Firmicutes was present in CF treatments. RNID treatment witnessed a low proportion of bacterial functional groups involved in nitrification and nitrate reduction. N fertilizer reduction with irrigation management increased rice yield (up to 22%) without changing the major soil fertility properties except for the increased pH and decreased ammonium N. The results suggest that N reduction, in association with increased plant density and accurate irrigation, is beneficial for super rice production.

Multi-environment evaluation of rice genotypes: impact of weather and culm biochemical parameters against sheath blight infection.

Sheath blight caused by Rhizoctonia solani is one of the major diseases of rice, causing widespread crop losses. The use of semi-dwarf rice varieties in the ongoing nutrient-intensive rice cultivation system has further accentuated the incidence of the disease. An ideal solution to this problem would be identifying a stable sheath blight-tolerant genotype. A multi-environment evaluation of 32 rice genotypes against sheath blight infection was conducted over six seasons across two locations (Agricultural Research Farm, Institute of Agricultural Sciences, Banaras Hindu University (28.18° N, 38.03° E, and 75.5 masl), for four years during the wet seasons (kharif) from 2015 to 2018 and two seasons at the National Rice Research Institute (20°27'09" N, 85°55'57" E, 26 masl), Cuttack, Odisha, during the dry season (rabi) of 2019 and the kharif of 2019, including susceptible and resistant check. Percent disease index data were collected over 4 weeks (on the 7th, 14th, 21st, and 28th day after infection), along with data on other morphological and physiological traits. The resistant genotypes across seasons were the ones with a higher hemicellulose content (13.93-14.64) and lower nitrogen content (1.10- 1.31) compared with the susceptible check Tapaswini (G32) (hemicellulose 12.96, nitrogen 1.38), which might explain the resistant reaction. Three different stability models-additive main effect and multiplicative interaction (AMMI), genotype + genotype x environment (GGE) biplot, and multi-trait stability index (MTSI)-were then used to identify the stable resistant genotypes across six seasons. The results obtained with all three models had common genotypes highlighted as stable and having a low area under the disease progress curve (AUDPC) values. The ideal stable genotypes with low disease incidence were IC 283139 (G19), Tetep (G28), IC 260917 (G4), and IC 277274 (G10), with AUDPC values of 658.91, 607.46, 479.69, and 547.94, respectively. Weather parameters such as temperature, rainfall, sunshine hours, and relative humidity were also noted daily. Relative humidity was positively correlated with the percent disease index.

REVITALIZING INDIGENOUS AGRICULTURAL KNOWLEDGE AND PRACTICES: MANUGAL AS AN ENVIRONMENTALLY SUSTAINABLE FARMING METHOD IN DAYAK NGAJU, INDONESIA

For thousands of years, the Dayak Ngaju people in Central Kalimantan have practiced a traditional rice cultivation system called Manugal, which involves planting rice directly on the ground without artificial fertilizers or pesticides. This method relies on rainwater and natural materials, and it is guided by the teachings of the Kaharingan belief system, recognizing rice as a divine manifestation, and adhering to the traditional calendar. However, the Green Revolution and the globalization of modern food production, initiated in the late 1960s, introduced intensive agriculture, chemical inputs, and high-yielding crop varieties. This modernization marginalized local traditions, including Manugal, in Central Kalimantan. This qualitative descriptive case study examines the background of the Green Revolution and its impact on Manugal, the ecological consequences of agricultural modernization, and the comparison between Manugal and modern monoculture farming systems. The study aims to propose strategies for maintaining the Manugal tradition and achieving ecological sustainability.

Identification of a Seed Vigor–Related QTL Cluster Associated with Weed Competitive Ability in Direct–Seeded Rice (Oryza Sativa L.)

Direct seeding of rice (Oryza sativa L.) is a low-labor and sustainable cultivation method that is used worldwide. Seed vigor and early vigor are important traits associated with seedling stand density (SSD) and weed competitive ability (WCA), which are key factors in direct-seeded rice (DSR) cultivation systems. Here, we developed a set of chromosome segment substitution lines with Xiushui134 as receptor parent and Yangdao6 as donor parent and used these lines as a mapping population to identify quantitative trait loci (QTLs) for seed vigor, which we evaluated based on germinability–related indicators (germination percentage (GP), germination energy (GE), and germination index (GI)) and seedling vigor–related indicators (root number (RN), root length (RL), and shoot length (SL) at 14 days after imbibition) under controlled conditions in an incubator. Ten QTLs were detected across four chromosomes, of which a cluster of QTLs (qGP11, qGE11, qGI11, and qRL11) co-localized on Chr. 11 with high LOD values (12.03, 8.13, 7.14, and 8.75, respectively). Fine mapping narrowed down the QTL cluster to a 0.7-Mb interval between RM26797 and RM6680. Further analysis showed that the QTL cluster has a significant effect (p < 0.01) on early vigor under hydroponic culture (root length, total dry weight) and direct seeding conditions (tiller number, aboveground dry weight). Thus, our combined analysis revealed that the QTL cluster influenced both seed vigor and early vigor. Identifying favorable alleles at this QTL cluster could facilitate the improvement of SSD and WCA, thereby addressing both major factors in DSR cultivation systems.

Assessment of the Suitability of Extractants for Predicting Plant Available Arsenic in Some Tropical Rice Growing Inceptisols of Eastern India

ABSTRACT The complex behavior of arsenic (As) in soil in conjunction to crop mediated transfer through the food chain necessitates a thorough evaluation of its phyto-availability. In this pretext, the present experiment has been conducted to determine the best chemical extractant for plant available As under the As-prone, rice-dominant agro-ecosystems of Gangetic West Bengal, India. Based on the tube-well arsenic data (JPOA, UNICEF), surface soil samples from high, medium, low and uncontaminated As sites have been collected. A pot study with rice cv. IR-36, exposed to varying levels of As (0, 0.1, 0.2, 0.3 and 0.4 mg L−1) was conducted. Ten chemical extractants were used in this study. The As extraction pattern followed the pattern of (HCl+H2SO4)>; (NH4-oxalate+Ascorbic acid)>; (Malic+Citric)> NaOH> KH2PO4> NaHCO3>; (H2O2+HNO3)> NH4F> NH4Cl> NH4OAc. On the 85th day after sowing, the rice plants were harvested keeping in mind that the maximum uptakes of heavy metals like As occurs during the peak vegetative growth (panicle initiation) stage. The soil As correlated with rice dry matter As accumulation as: NH4-oxalate+ascorbic acid (r = 0.729**)> NH4Cl (r = 0.698**)> H2O2+HNO3 (r = 0.697**)> NH4F (r = 0.693**)>Malic+Citric (r = 0.666**)> KH2PO4 (r = 0.615**)> HCl+H2SO4 (r = 0.608**)> NaOH (r = 0.589**)> NaHCO3 (r = 0.571**)> NH4OAc (r = 0.533*). Statistical analyses through correlation sum and stepwise multiple regression modeling revealed that NH4-oxalate+ascorbic acid had the best relationship with all other extractants, As fractions and soil physicochemical characters and therefore emerged as the best suited extractant of As for the wide-scale experimental locations under rice cultivation system.

High-Resolution Ratoon Rice Monitoring under Cloudy Conditions with Fused Time-Series Optical Dataset and Threshold Model

Ratoon rice, an effective rice cultivation system, allows paddy rice to be harvested twice from the same stubble, playing an important role in ensuring food security and adapting to climate change with its unique growth characteristics. However, there is an absence of research related to remote-sensing monitoring of ratoon rice, and the presence of other rice cropping systems (e.g., double-season rice) with similar characteristics poses a hindrance to the accurate identification of ratoon rice. Furthermore, cloudy and rainy regions have limited available remote-sensing images, meaning that remote-sensing monitoring is limited. To address this issue, taking Yongchuan District, a typical cloud-prone region in Chongqing, China, as an example, this study proposed the construction of a time-series optical dataset using the Modified Neighborhood Similar Pixel Interpolator (MNSPI) method for cloud-removal interpolation and the Flexible Spatiotemporal DAta Fusion (FSDAF) model for fusing multi-source optical remote-sensing data, in combination with vegetation index features and phenological information to build a threshold model to map ratoon rice at high-resolution (10 m). The mapping performance of ratoon rice was evaluated using independent field samples to obtain the overall accuracy and kappa coefficient. The findings indicate that the combination of the MNSPI method and FSDAF model had a stable and effective performance, characterized by high correlation coefficient (r) values and low root mean square error (RMSE) values between the restored/predicted images and the true images. Notably, it was possible to effectively capture the distinct characteristics of ratoon rice in cloudy and rainy regions using the proposed threshold model. Specifically, the identified area of ratoon rice in the study region was 194.17 km2, which was close to the official data (158–180 km2), and the overall accuracy and kappa coefficient of ratoon rice identification result were 90.73% and 0.81, respectively. These results demonstrate that our proposed threshold model can effectively distinguish ratoon rice during vital phenological stages from other crop types, enrich the technical system of rice remote-sensing monitoring, and provide a reference for agricultural remote-sensing applications in cloudy and rainy regions.

Fertilization as the most critical factor affecting yield response and agronomic efficiency of phosphorus in Chinese rice production: evidence from multi-location field trials.

Efficient utilization of phosphorus (P) has been a major challenge for sustainable agriculture. However, the responses of fertilizer rate, region, soil properties, cropping systems and genotypes to P have not been investigated comprehensively and systematically. A comprehensive analysis of 9863 fertilizer-P experiments on rice cultivation in China showed that rice yield increased first and then fell down with the addition of P fertilizer, and the highest yield of 7963 kg ha-1 was observed under 100% P treatment. Under 100% P treatment, the yield response of applied P (YRP ) and agronomic efficiency of applied P (AEP ) were 12.8% and 30.1 kg ha-1 , respectively. Lower soil pH (< 5.5) and organic matter (< 30.0 g kg-1 ) were associated with lower YRP and AEP . By contrast, soil available P < 25.0 mg kg-1 resulted in decreased YRP (15.3 to 11.4%) and AEP (32.3 kg kg-1 to 26.2 kg kg-1 ), whereas soil available P > 25.0 mg kg-1 maintained the relatively stable YRP and AEP . Also, the YRP and AEP were significantly higher for single-cropping rice compared to other cropping systems. Moreover, the rice genotypes such as 'Longdun', 'Kendao' and 'Jigeng' had higher YRP and AEP than the average value. Overall, the fertilizer-P rate was the primary factor affecting YRP and AEP , and the recommended P fertilizer rate can be reduced by 9-21 kg P ha-1 compared to existing expert recommendations. The present study highlights the role of fertilizer-P rate in maximizing the YRP and AEP , thereby providing a strong basis for future fertilizer management in rice cultivation systems. © 2023 Society of Chemical Industry.