| The rice-rapeseed system is one of the major rice-based cropping systems in the Yangtze River Valley.It is very important to clarify the production status and main limiting factors of rice-rapeseed system to achieve annual high yield and ensure the safety of food and oil in China.Previous studies mostly analyzed the production status and yield from the perspective of single-season crops,and few studies on the comprehensive analysis from the perspective of multi-cropping system.Therefore,we first collected and analyzed national statistical data and identified the production status of middle rice（and single-season late rice）and rapeseed in the eight major rice-rapeseed system provinces of the Yangtze River Valley（YRV）,including the upper reaches（Sichuan,Chongqing,Guizhou）,middle reaches（Hunan,Hubei,Jiangxi）and lower reaches（Anhui,Jiangsu）,and intended to explore the theoretical production level of rice-rapeseed system in the YRV.Furthermore,a field survey was conducted in Wuxue City,Hubei Province,to explore the production status,yield-limiting factors and possible ways to improve the yield of rice-rapeseed systems at the farm level.This study aimed to provide theoretical guidance for improving the annual yield and promoting the sustainable development of rice-rapeseed systems.The results of this study were as follows:（1）In this study,the smaller area of middle rice（and single-season late rice）and rapeseed in each province in the statistical data was used as the theoretical rice-rapeseed system area,and the sum of middle rice（and single-season late rice）and rapeseed equivalent yield was used as the theoretical yield of rice-rape system.Through analysis:The total theoretical planting area of the rice-rapeseed system in the YRV was 5.21×106ha,accounting for 17%and 78%of the national rice and rapeseed area,respectively.Among the eight major planting provinces,Hunan,Sichuan and Hubei have the largest planting area,accounting for 65%of the total rice-rapeseed system area in the YRV.The theoretical annual yield of the rice-rapeseed system（rice yield+rapeseed equivalent yield）in the YRV was 11.84 t ha-1,in which middle rice（and single-season late rice）and rapeseed were 8.34 and 2.06 t ha-1,respectively.The yield was highest in the lower reaches of the YRV at the regional level and was highest in Jiangsu at the provincial level.The theoretical production of the rice-rapeseed system in the YRV is 5.32×107t,in which the highest production was in Sichuan,followed by Hunan and Hubei,accounting for 23%,22%and 20%of the theoretical total production of the YRV,respectively.（2）For fertilizer application analysis,the total annual chemical fertilizer input in the rice-rapeseed system among different provinces in the YRV ranged from 226 to463 kg ha-1,and the nitrogen fertilizer rate ranged from 180 to 353 kg N ha-1,which was highest in Jiangsu in the lower reaches of the YRV.In addition,the partial factor productivity of nitrogen（PFP-N）of the rice,rapeseed and rice-rapeseed systems was highest in the middle reaches of the YRV.At the provincial level,rapeseed PFP-N was the highest in Jiangxi,and rice and rice-rapeseed systems were the highest in Hubei.For economic benefit analysis,the rice-rapeseed system in the upper reaches of the YRV had the highest net income and benefit-to-cost ratio（excluding household labor costs）,which were 35%and 88%higher than those in the middle reaches and 22%and 77%higher than those in the lower reaches.This was mainly due to the lower mechanization level in the upper reaches of the YRV,resulting in lower cash costs.Compared with other provinces,as one of the top three provinces with the highest total production of the rice-rapeseed system,Hubei Province had the highest cash cost and mechanization level in the rapeseed season compared to other provinces,and its production and PFP-N were also at a relatively high level.（3）The results of a sample survey of farmers in Wuxue City,Hubei Province,showed that the average yields of rice,rapeseed（equivalent yield）and rice-rapeseed systems in Wuxue were 8.11,3.10 and 11.21 t ha-1,respectively,which were lower than those in both Hubei Province and the YRV.By further classification of the farmers’yields into high,medium and low yield levels,the proportions of high,medium and low yield levels in rice were 11%,77%,13%,and in rapeseed were 12%,71%,17%,respectively,while the proportion with high yields in both rice and rapeseed was only approximately 3%.By combining yield and nitrogen fertilizer application,the proportion of farmers with high yield and high efficiency in rice,rapeseed and rice-rapeseed systems were only 3%.The proportion of farmers with high-yield and medium-efficiency in the rice-rapeseed system was 16%higher than that in the rice or rapeseed season.In addition,the annual net income and benefit-to-cost ratio of the rice-rapeseed system in Wuxue were 17355 CNY ha-1and 1.26,respectively.Cash cost was mainly attributed to the costs of leasing operation cost and fertilizer,accounting for 65%of the total cash cost.（4）The yield-limiting factor analysis indicated that the rice yield of the rice-rapeseed system in Wuxue was mainly affected by field size,topsoil depth,variety,disease,insect and weed management,and fertilizer management.The rapeseed yield was mainly affected by soil type,variety,and mechanical harvesting.By increasing the topsoil depth of and timely prevention and control of diseases,pests and weeds in rice season,improving soil quality and reducing mechanical harvest loss in rapeseed season,and optimizing fertilizer application strategies and variety selection of rice-rapeseed system,it is beneficial to further improve the yield of rice-rapeseed system.In summary,this study explores the current theoretical production status of rice-rapeseed system in China,and through the investigation of farmers in Wuxue,Hubei Province,the yield limiting factors in the rice-rapeseed system of farmers in this area are preliminarily explored,which provides a theoretical basis for realizing the annual high yield and high efficiency of rice-rapeseed system and promoting the sustainable development of the system. |
