Integrated emergy and economic evaluation of the dominant organic rice production systems in Jiangsu province, China.

Changing from conventional to organic farming might have fewer negative environmental impacts because of the avoidance of synthetic fertilizer and chemical pesticides. In this study, the economic viability and environmental and sustainability performance of the four dominant organic (rice-green manure rotation (RG), rice-duck co-culture (RD), rice-crayfish co-culture (RCF) and rice monoculture (RM)) and one conventional (rice monoculture (CRM)) rice production modes were evaluated in Jiangsu Province, China. Compared with the CRM mode, organic rice production increased economic benefits density and improved the economic benefit of crop land and irrigation water use. With the lowest total emergy input and the highest rice yield, the CRM mode showed the highest ecological efficiency in converting resources to total available energy content and nutrition density unit among the five rice production modes. However, the RCM mode showed higher environmental pressure and lower sustainability than the four organic modes due to the larger proportion of nonrenewable emergy input. The RM mode was the most uneconomic organic rice production mode with the highest cost input and the lowest product output but had relatively higher sustainability due to the higher proportion of renewable resources to total emergy inputs. Compared with the RM mode, the value-to-cost ratio, economic benefit density and benefit-cost ratio were increased in the RG, RD and RCF modes. Although the RD and RCF modes had higher efficiency in converting resources to total nutrition density units and monetary value, they imposed higher environmental pressure with a lower renewable fraction and emergy sustainability index than those in the RM mode. The RG mode had higher emergy utilization efficiency and the highest renewable fraction and emergy sustainability index among the four organic rice production modes. Considering the ecological and economic effects, the RG mode was conducive to improving the economic viability and sustainability of organic rice production.

Transforming agrifood systems in a win-win for health and environment: evidence from organic rice-duck coculture.

BACKGROUND: Rice-duck coculture is an ecological agricultural mode; however, the nutritional and environmental benefits of transforming from conventional rice monoculture to rice-duck coculture are unknown. Based on survey data and the life-cycle assessment approach, this study conducted a carbon footprint evaluation of conventional rice monoculture (CR), organic rice monoculture (OR), and organic rice-duck coculture (ORD) using different functional units. RESULTS: The carbon footprint per hectare of ORD (7842 ± 284 kg CO2 eq ha-1 ) was slightly lower than that of CR (7905 ± 412 kg CO2 eq ha-1 ), while higher than that of OR (7786 ± 235 kg CO2 eq ha-1 ). Although the rice yield of ORD was slightly lower than that of CR, its nutrient density unit (NDU) did not decrease significantly due to the additional duck yield. Thus, the carbon footprint per NDU of ORD was significantly lower than that of OR by 24.3% (P < 0.05) and was 5.8% higher than that of CR, but this was not statistically significant. Due to the higher economic profits of ORD, its unit of carbon footprint per economic profit was significantly reduced (by 47.1-75.7%) compared with the other two farming modes, while the net ecosystem economic budget was significantly increased by 98.5-341.9% (P < 0.05). CONCLUSION: Transforming from a rice monoculture to a coculture system will contribute to a win-win situation for human health and environmental sustainability. This study highlighted the abundant nutritional output function of the rice-duck coculture and analyzed the urgency and necessity of transitioning from traditional agriculture to ecological agriculture from the production and consumption perspectives. © 2022 Society of Chemical Industry.

Influence of organic rice production mode on weed composition in the soil seed bank of paddy fields.

Introduction: It is of great significance to determine the composition of the soil weed seed bank under different organic rice production modes to provide decision making support for rational integrated weed management in organic rice production. Methods: The soil weed seed bank of the four dominant organic production modes, namely, rice-green manure rotation (RG), rice monoculture (RM), rice-crayfish coculture (RC) and rice-duck coculture (RD), with different numbers of consecutive planting years (3 to 10 years) in different sites in Jiangsu Province were investigated to determine the influence of organic rice production mode on weed composition. Results and Discussion: There were significant differences in the weed composition in the soil seed bank among the four organic rice production modes. The most dominant weed group was broadleaf weeds in the soil seed bank under the RG and RM modes; however, under the RM mode, the most dominant weed species were sedge and grass weeds. Sedge and grass weeds dominated the soil seed bank of the RC and RD modes, respectively. Therefore, specific weed management strategies could be formulated based on the differences in weed composition under different organic rice production modes. The application of organic fertilizer and irrigation were identified as primary factors associated with the differences in weed composition in the soil seed banks, which had higher effects on the weed composition than hand weeding. Consequently, fertilization and irrigation strategies that alter weed composition could be used as improved weed management program components in organic rice production systems. Long-term organic rice planting is beneficial for increasing weed diversity in paddy fields. Our results indicated that weed species diversity increased and weed community evenness and dominance decreased with the increase in the number of consecutive planting years under all four organic rice production modes.

Intra- and cross-field dispersal of Beckmannia syzigachne seed by a combine harvester.

BACKGROUND: Beckmannia syzigachne (Steud.) Fernald has become a dominant weed that has evolved resistance to major herbicides used in the wheat fields of rice-wheat double cropping areas of the middle and lower reaches of the Yangtze River, China. Seed dispersal occurs over long distances via irrigation water. As mechanical harvesting services popularize, there is concern that combine harvesters could play an increasing role in B. syzigachne seed dispersal. RESULTS: Random sampling of 30 combine harvesters at wheat harvest determined that an average of 8000 B. syzigachne seeds remain in the combine after wheat harvesting, predominantly on the metal plate. These seeds could potentially be transported into adjacent fields. A double exponential model predicted that seeds remaining on the metal plate could be dispersed over 7885 m2 into the next field. Within a field, the number of fallen seeds and their dispersal distance were positively correlated to panicle density. Combines spread seeds away from the source potentially creating new weed patches. During irrigation and rotary tillage ploughing, 70% of B. syzigachne seeds scattered in the field floated on the water surface and were moved away by the wind. CONCLUSION: Both wheat combine harvesters and water flow effectively spread B. syzigachne seeds. Areas with high B. syzigachne population density should be carefully harvested separately, and the metal plate should be carefully cleaned to prevent spreading the weed across fields and region. Floating B. syzigachne seeds displaced to field edges by water can be physically removed with nets to prevent further distribution by water.

Weed seed bank dynamics responses to long-term chemical control in a rice-wheat cropping system.

BACKGROUND: It remains an open question if the long-term application of single chemical herbicides would inevitably lead to increased weed populations and result in out-of-control weeds. The annual dynamics of weed seed bank responses to different weeding measures (chemical herbicide, hand weeding and no weeding) in rice-wheat cropping systems were compared to observe the succession of weed communities under different weed selection pressures for 17 years. RESULTS: In unweeded rice-wheat cropping plots, the initially dominant broadleaf weeds were overtaken by grasses and eventually by sedges, while in plots subjected to chemical herbicide or hand weeding, broadleaf weeds remained dominant followed by grasses. The rice-wheat cropping system favoured the spread of paddy weed species; weeding had little effect on the composition of the dominant rice weeds but greatly influenced that of wheat weeds. Total seed density tended to decrease in both weeded and unweeded plots, but the species density and composition of the seed banks differed among plots treated differently. Weeding slightly increased weed species diversity and decreased weed community evenness and dominance in the first several years, but this scenario could have negative consequences in the long term; however, without weeding, stronger interspecific competition led to a decrease in weed species diversity whereas weed community evenness and dominance increased. CONCLUSION: Long-term and repeated application of pre-emergence chemical herbicides and hand weeding had similar effects on the weed community dynamics, indicating that exclusive application of pre-emergence herbicide could maintain the weed community at a durable relatively low infestation level. © 2019 Society of Chemical Industry.