Rice single cropping or ratooning agro-system: which one is more environment-friendly?

Mechanism harvesting of main crops straw returning effects on ratooning fragrant rice yield and 2-acetyl-1-pyrroline and their drivers to soil microbial communities

Straw return to the field is an important measure for increasing soil fertility to increase production. Recent studies have shown that straw return to fields can increase rice yield, but the effect of straw return to fields on ratooning rice is limited. To address this problem, this paper investigated the effect of straw return on a ratooning rice system by harvesting at different heights during the first season. A two-year field experiment was conducted by using a fragrant rice variety (Meixiangzhan 2) as the material. Three experimental treatments including i) the CK treatment: manual harvesting and straw harvested at a height of 20 cm was not returned to the field; ii) the MT1 treatment: mechanical harvesting and straw was returned to the field at a harvest height of 10 cm; iii) the MT2 treatment: mechanical harvesting and straw at a harvest height of 20 cm was returned to the field. The investigated parameters in the rice cropping system in this study were the agronomic traits, yield formation, soil properties, and root soil microorganisms. We found that compared with those in the CK treatment, the yield and 2AP content in the MT treatment significantly increased, the yields of MT1 and MT2 increased by 18.17-32.64% and 12.19-20.42%, respectively. The contents of available potassium, available phosphorus, ammonium nitrogen and active organic carbon in the soil were significantly increased by straw return to the field. The soil capacity increased, and rice production increased. In addition, the straw returned to the field produced a large amount of cellulose and anaerobic environment, which provided an explanation for the increase in some anaerobic bacteria, such as pseudxanthomonas, Rhodobacteriaceae and desulphurides in the MT treatment group. Specifically, straw return provides a large amount of organic material for rice cultivation systems and improves soil fertility under the action of microorganisms to increase production. Overall, the interaction between straw return and harvest height had different effects on yield and 2AP content, and the MT2 treatment was the most beneficial for harvesting ratooning fragrant rice.

Recognition and localization of ratoon rice rolled stubble rows based on monocular vision and model fusion

Introduction

Ratoon rice, as a high-efficiency rice cultivation mode, is widely applied around the world. Mechanical righting of rolled rice stubble can significantly improve yield in regeneration season, but lack of automation has become an important factor restricting its further promotion.

Methods

In order to realize automatic navigation of the righting machine, a method of fusing an instance segmentation model and a monocular depth prediction model was used to realize monocular localization of the rolled rice stubble rows in this study.

Results

To achieve monocular depth prediction, a depth estimation model was trained on training set we made, and absolute relative error of trained model on validation set was only 7.2%. To address the problem of degradation of model's performance when migrated to other monocular cameras, based on the law of the input image's influence on model's output results, two optimization methods of adjusting inputs and outputs were used that decreased the absolute relative error from 91.9% to 8.8%. After that, we carried out model fusion experiments, which showed that CD (chamfer distance) between predicted 3D coordinates of navigation points obtained by fusing the results of the two models and labels was only 0.0990. The CD between predicted point cloud of rolled rice stubble rows and label was only 0.0174.

A synthesis of the evidence regarding the efficacy of alternative field management practices in rice cultivation using life cycle assessment

Field management practices are an important factor in mitigating climate change and increasing agricultural production. However, no study has synthesized the evidence on the efficacy of alternative field management practices and reviewed life cycle assessments that consider all emissions over the entire or part of the life cycle of rice production. Thus, 68 papers were reviewed and grouped into 13 field management categories. The management practices were evaluated in terms of yield, area-scaled greenhouse gas (GHG) emissions, and yield-scaled GHG emissions against base management practices. The yield increase of these field management practices was between -6 % and 12 %, with some exceptions. It was only nonpuddling that simultaneously increased the yield and reduced both the area-scaled GHG and yield-scaled GHG emissions with respect to the base category. Water management, including alternate wetting and drying or single and multiple drainage and no-tillage, performed well in reducing the average area-scaled GHG and yield-scaled GHG emissions, although the average yield was reduced slightly. For the remaining many management practices, the increase in area-scaled GHG emissions was larger than the change in yield, so the yield change had little impact on yield-scaled GHG emissions. The higher increase in area-scaled GHG emissions than the change in yield requires innovative and new approaches, such as implementing alternative management together with water management, of which the effect was observed in some of the papers reviewed in this study. Therefore, this study recommends selecting nonpuddling, water management or no-tillage as climate mitigation management options. The evaluation of field management will be more robust if more impact categories are considered, including missing aspects (i.e., soil fertility).

Ratoon Rice System of Production: A Rapid Growth Pattern of Multiple Cropping in China: A Review

In this review, the significance of ratoon rice was introduced, and the research status and development trends of ratoon rice were also summarized. It is pointed out that mechanically harvested ratoon rice is the developing direction of future ratoon rice. On this basis, we analyzed the relationship between the yield of ratoon rice and many factors, such as variety characteristics, sowing date, water control, fertilizer, and many others. It is important to construct a comprehensive and practical evaluation system for rice regeneration that can provide a basis for high-yield cultivation of machine-harvested ratoon rice. At the same time, it is suggested that combining high-yield cultivation with the green ecological efficiency of rice can achieve better production and improve the quality of rice. Finally, some problems with ratoon rice development were put forward. An in-depth study on the rhizosphere biology and regulation techniques of ratoon rice and the effective ecological compensation mechanism increased the capacity and quality of ratoon rice. Further, the functioning of such research can enhance the planting area for ratoon rice and improve food security.

Shifts in the diversity of root endophytic microorganisms across the life cycle of the ratooning rice Jiafuzhan

The diversity of root endophytic microorganisms, which is closely related to plant life activities, is known to vary with the plant growth stage. This study on the ratooning rice Jiafuzhan explored the diversity of the root endophytic bacteria and fungi and their dynamics during the plant life cycle. By sequencing the 16S ribosomal ribonucleic acid (16S rRNA) and internal transcribed spacer (ITS) genes, 12,154 operational taxonomic units (OTUs) and 497 amplicon sequence variants (ASVs) were obtained, respectively. The root endophytic microorganisms of rice in the seedling, tillering, jointing, heading, and mature stages of the first crop and at 13, 25, and 60 days after regeneration (at the heading, full heading, and mature stages of the second crop, respectively) were analyzed using diversity and correlation analyses. There were significant differences in the α-diversity and β-diversity of root endophytic bacteria and fungi in the growth stage. Additionally, linear discriminant analysis (LDA) effect size (LEfSe) analysis revealed biomarker bacteria for each growth stage, but biomarker fungi did not exist in every stage. Moreover, the correlation analysis showed that the bacterial and fungal biomarkers interacted with each other. Furthermore, the nitrogen-fixing genus Bradyrhizobium existed in all growth stages. These findings indicate the pattern of root endophytic microorganisms of ratooning rice at different growth stages, and they provide new insights into the high yield of the second crop of ratooning rice (in light of the abundance of various bacteria and fungi).

Physiological and transcriptomic analysis reveal the regulatory mechanism underlying grain quality improvement induced by rice ratooning

BACKGROUND

Ratoon rice cropping has been introduced for increased rice production in southern China and, as a result, has been becoming increasingly popular. However, only a few studies have addressed the regulatory mechanism underlying grain quality improvement induced by rice ratooning.

RESULTS

In this study, parameters of rice quality, including head rice yield, chalky grain percentage, grain chalkiness degree, hardness and taste value, were shown to be much improved in the ratooning season rice as compared to its counterparts main and late cropping season rice, indicating that such an improvement was irrespective of seasonal effects. In addition, the nutritional components of grains varied greatly between main-cropping season rice, ratooning season rice and late-cropping season rice and displayed a significant correlation with rice quality. Finally, the regulatory mechanism underlying rice quality improvement revealed that gibberellin-dominated regulation and plant hormone signal transduction jointly contributed to a decrease in formation of chalky grains.

CONCLUSION

This work improves our knowledge on rice quality improvement under rice ratooning, particularly on the regulatory mechanism of plant hormones. © 2022 Society of Chemical Industry.

GF14f gene is negatively associated with yield and grain chalkiness under rice ratooning

BACKGROUND

Ratoon rice cropping has been shown to provide new insights into overcoming the current challenges of rice production in southern China. However, the potential mechanisms impacting yield and grain quality under rice ratooning remain unclear.

METHODS

In this study, changes in yield performance and distinct improvements in grain chalkiness in ratoon rice were thoroughly investigated, using physiological, molecular and transcriptomic analysis.

RESULTS

Rice ratooning induced an extensive carbon reserve remobilization in combination with an impact on grain filling, starch biosynthesis, and ultimately, an optimization in starch composition and structure in the endosperm. Furthermore, these variations were shown to be associated with a protein-coding gene: GF14f (encoding GF14f isoform of 14-3-3 proteins) and such gene negatively impacts oxidative and environmental resistance in ratoon rice.

CONCLUSION

Our findings suggested that this genetic regulation by GF14f gene was the main cause leading to changes in rice yield and grain chalkiness improvement of ratoon rice, irrespective of seasonal or environmental effects. A further significance was to see how yield performance and grain quality of ratoon rice were able to be achieved at higher levels via suppression of GF14f.

Contamination, ecological, and health risk assessment of heavy metals and organophosphorus pesticides in single, double, and ratoon cropping of rice: a case study in Mazandaran, North of Iran

This study investigated the contamination and health risk assessment of heavy metals and organophosphorus pesticides in single, double, and ratoon cropping of rice in Mazandaran province, north of Iran. A total of 17 sampling locations in rice farms were selected and soil and rice samples were collected from farms in 5 counties of Mazandaran. Soil and rice samples were then transferred to the lab for further analysis. The concentration of pesticides and heavy metals was then analyzed using gas chromatography-mass spectrometry (GC-MS) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. Mercury was analyzed using a Leco mercury analyzer. Target hazard quotient (THQ), total target hazard quotient (TTHQ), carcinogenic risk (CR), and total carcinogenic risk (TCR) in children and adults were used. Potential ecological risk also was used to test the possible hazards of heavy metals to the environment. Heavy metals concentration in rice and soil samples in different farming steps revealed different levels. THQ showed no considerable risk in consuming contaminated rice to adults and children considered, while TTHQ revealed potential non-carcinogenic risks. Ni had the most carcinogenic risks to target human groups, and TCR showed carcinogenicity for carcinogenic heavy metals in all stations. Findings showed no ecological risks of metals to the environment. In conclusion, rice farmers in Mazandaran use the lands multiple times during the year to increase the performance, function, quality, and quantity of rice, but the possible toxic effects of heavy metals and pesticides on consumers and the environment should not be overlooked.

Genetic Dissection of Rice Ratooning Ability Using an Introgression Line Population and Substitution Mapping of a Pleiotropic Quantitative Trait Locus qRA5

Ratooning ability is a key factor that influences ratoon rice yield, in the area where light and temperature are not enough for second season rice. In the present study, an introgression line population derived from Minghui 63 as the recipient parent and 02428 as the donor parent was developed, and a high-density bin map containing 4568 bins was constructed. Nine ratooning-ability-related traits were measured, including maximum tiller number, panicle number, and grain yield per plant in the first season and ratoon season, as well as three secondary traits, maximum tiller number ratio, panicle number ratio, and grain yield ratio. A total of 22 main-effect QTLs were identified and explained for 3.26–18.63% of the phenotypic variations in the introgression line population. Three genomic regions, including 14.12–14.65 Mb on chromosome 5, 4.64–5.76 Mb on chromosome 8, and 10.64–15.52 Mb on chromosome 11, were identified to simultaneously control different ratooning-ability-related traits. Among them, qRA5 in the region of 14.12–14.65 Mb on chromosome 5 was validated for its pleiotropic effects on maximum tiller number and panicle number in the first season, as well as its maximum tiller number ratio, panicle number ratio, and grain yield ratio. Moreover, qRA5 was independent of genetic background and delimited into a 311.16 kb region by a substitution mapping approach. These results will help us better understand the genetic basis of rice ratooning ability and provide a valuable gene resource for breeding high-yield ratoon rice varieties.

Comparisons between main and ratoon crops in resource use efficiencies, environmental impacts, and economic profits of rice ratooning system in central China

Rice production in China is constrained by excessive water consumption, labor shortage, large environmental footprint, and low economic profit. Rice ratooning is a promising practice to increase famers' profit with higher resource use efficiency and less environmental impact compared with other rice cropping systems. However, there is limited information on the differences in energy use efficiency, water and labor productivity, environmental footprint, and economic return between main crop (MC) and ratoon crop (RC) in this cropping system. This study was conducted to compare the system performance between the two crops of ratoon rice using on-farm survey data. Average grain yield was 8.40 and 4.55 t ha^-1 for MC and RC, respectively. Although RC produced 45.9% lower grain yield, it had 57.3% less total energy input and 71.0% lower total production cost than MC, which resulted in a significantly higher energy use efficiency, net energy ratio, net economic return and benefit-to-cost ratio. Lower total energy input and production cost of RC was mainly attributed to the reduction in fertilizer application and labor input, respectively compared with MC. In addition, both labor and water productivity of RC was significantly higher than those of MC. Furthermore, the global warming potential (GWP) and yield-scaled GWP of RC was 59.3% and 23.4% lower than those of MC, respectively, due to lower agronomic inputs and GHGs emissions. Overall, our results suggested that RC had higher resource use efficiency, better economic performance, and less environment impact compared with MC.

Systematic approach to source-sink apportionment of copper in paddy fields: Experimental observation, dynamic modeling and prevention strategy

The accumulation of heavy metals in paddy rice severely impacts the health of consumers and plants. In this study, a systematic approach to source-sink apportionment of copper in paddy fields was developed by considering all bioenvironmental interfaces. Experimental data from two experimental fields (namely Field A and Field B) in the first harvest period was collected. Then, mass-balance-based models with dynamic critical loads were established to evaluate the year of excess for copper. The results indicated that irrigation water contributed the highest portion (96.2-98.8%) of total copper inputs. Under the business-as-usual scenario, the soil copper concentration of Field A and Field B might exceed the Taiwanese national standard within 66 and 24 years, respectively. In addition, alternate wet-dry irrigation was found to be one of the total solutions to reducing copper accumulation in soils by 17-48%. It could also provide a significant reduction of water usage in paddy fields by ~25%, thereby increasing the resilience to extreme climate change events. Lastly, based on the field observations, three improvement strategies on sustaining soil quality towards better agricultural environment were proposed. The connection of copper accumulation in soils with dietary and ecological risks was also briefly illustrated.

Exergy flow of rice production system in Italy: Comparison among nine different varieties

Exergy analysis is receiving considerable attention as an approach to be applied for making decisions toward moving to a sustainable and energy-efficient food supply chain. This study focuses on how the selection of variety affects the exergy flow of a paddy rice production system. In this regard, nine varieties of rice in Italy, the largest rice producer in Europe, were evaluated using the cumulative exergy analysis approach. Sensitivity analysis of inputs consumption and the exergy management scenarios of the most sensitive inputs are also provided in this study. The results indicated that the cumulative exergy consumption value of the investigated rice varieties ranges from 16.09 GJha^-1 to 25.80 GJ ha^-1. Fossil fuels and chemical fertilizer consumption were the most significant contributors to the total energy consumption in all investigated varieties. Luna variety, with the cumulative degree of perfection value of 7.96 and renewability indicator of 0.88, was identified as the most exergy-efficient variety of rice in Italy.

Ratoon rice production in central China: Environmental sustainability and food production

Rice is an important strategic food crop for China concerning food security and environmental sustainability. Ratoon rice (RR) is proposed as a promising rice system to increase grain yield via improving multiple crop index. It is increasingly attractive for farmers due to its high resource efficiency and low labor requirement. Nevertheless, little information is known about the environmental profile of RR production. A comprehensive assessment regarding productivity and sustainability is of urgent importance. This paper aims to investigate the productivity and environmental impact of RR production and to identify its environmental hotspots through life cycle assessment (LCA) methodology. The analysis was conducted based on land-based and yield-based function units (FUs) using on-farm data from 561 RR producers in Hubei Province, China. The results, which were calculated using the land-based FU, showed that the yields for RR production were an average of 25.3% higher than the yields for traditional single rice production. However, the environmental impacts of RR production disproportionally increased, leading to 23.5% to 35.1% higher pollutant emissions. Opposite results were obtained from the comparisons based on the yield-based FU. The worse environmental results per hectare were canceled out because of its higher yields in RR production, leading to lower environmental impacts per ton of rice. If 18% of the current area that should be planted with traditional double rice shifted into RR instead of traditional single rice, a considerable increase in total rice production would be achieved with minimal environmental impacts. The major contributors to pollutions were methane emissions produced from flooded fields, emissions related to fertilizer and pesticide application, and diesel fuel for machinery. Increased environmental burdens in RR compared to the traditional single rice production were mainly attributed to the additional fertilizers and longer growing period. The study's results indicate that RR can be a viable alternative option to increase productivity with minimal environmental impact in rice production.

Manipulating osa-MIR156f Expression by D18 Promoter to Regulate Plant Architecture and Yield Traits both in Seasonal and Ratooning Rice

Background

Rice (Oryza sativa L.) feeds more than half of the world's population. Ratooning rice is an economical alternative to the second seasonal rice, thus increasing the yield of ratooning rice is highly important.

Results

Here we report an applicable transgenic line constructed through the manipulation of osa-MIR156f expression in rice shoot using the OsGA3ox2 (D18) promoter. In seasonal rice, the D18-11 transgenic line showed moderate height and more effective tillers with normal panicle. In ratooning rice, axillary buds outgrew from the basal node of the D18-11 transgenic line before the harvest of seasonal rice. More effective tillers produced by the outgrowth of axillary buds contributed to the plant architecture improvement and yield increase. Additionally, it was found that osa-miR156f down-regulated the expression of tillering regulators, such as TEOSINTE BRANCHED1 (TB1) and LAX PANICLE 1 (LAX1). The expression of DWARF10, DWARF27 and DWARF53, three genes being involved in the biosynthesis and signaling of strigolactone (SL), decreased in the stem of the D18-11 transgenic line.

Conclusion

Our results indicated that the manipulation of osa-MIR156f expression may have application significance in rice genetic breeding. This study developed a novel strategy to regulate plant architecture and grain yield potential both in the seasonal and ratooning rice.