Agronomic Performance And Economic Analysis Of Zero-tillage And UAV-seeding Rapeseed-Ratoon Rice Rotation System

Rice-rapeseed rotation is the main rotation system in central China.However,the planting area of rice-rapeseed rotation system in Yangtze River has decreased rapidly in recent years,mainly because the traditional system has a large labor demand and high arable land use intensity,which does not conform to the trend of light simplification and sustainable development of agriculture.Ratoon rice is an important cultivation system to adapt to the transformation period of rice in China,which is of great significance to improve the total grain yield in China.In addition to the oil function,rapeseed can also be used as high-quality green manure and silage.At the same time,it is multifunctional,such as vegetable,honey and sightseeing.Zero-tillage and UAV-seeding rapeseed—ratoon rice rotation system is a simplified planting system instead of the traditional rice-rapeseed rotation.However,little knowledge of the annual yield and economic benefits under this system.In addition,the effect of returning rapeseed to the field as green manure at full flowering stage on rice yield of subsequent ratoon rice system remain limited.Therefore,the investigation and field experiments were conducted simultaneously from 2020-2021.The investigation was conducted in villages where rice was grown in large areas of rapeseed-ratoon rice rotation in different sites of Jiupu Village,Qichun County;Zhongling Village,Xiantao City;Siwumen Village,Honghu City;Maolaoyuan Village,Jianli City,Hubei Province.The green manure and silage yield in the flowering stage of rapeseed and the annual yield of ratoon rice were measured,and the economic benefit was calculated and analyzed;The field experiment was conducted in Jiupu Village,Qichun County,Hubei Province.Field experiment was arranged in a spit plot design with rapeseed returning in main season as main plot（S:rapeseed returning;CK:rapeseed not returning）,N rate in main season as subplot(N₀:0 kg N ha^-1;N₈₀:80 kg N ha^-1;N₁₂₀:120 kg N ha^-1;N₁₈₀:180 kg N ha^-1)with four replications.Yield and yield components were measured and calculated,the objective of this study was to explore the effects of rapeseed returning and nitrogen management on the yield of ratoon rice.The main results are as follows:（1）Plant height,leaf width,and seedling number at the seedling stage of rapeseed between different sites in the investigation were in the range of 14.9-23.3 cm、4.2-8.3cm and 2.27-2.67×10⁵ plants ha^-1,respectively.The growth of rapeseed in Qichun was the best,mainly because its sowing date was the earliest,while the growth of rapeseed in other places was poor with the delay of sowing date.The yield of silage（fresh weight）,green manure（fresh weight）and dry matter（oven drying weight）during flowering stage of rapeseed at different sites were in the range of 23.3-31.7、31.5-46.2 and 8.40-15.2 t ha^-1,respectively.Overall,the growth potential of Qichun was better than that of the other sites before rapeseed return,which was consistent with its seedling stage performance.In addition,the yield of silage,green manure,and dry matter during the flowering stage of rapeseed in the field experiment was 41.2,52.1,and 15.6 t ha^-1,respectively.（2）The investigation results showed that there were differences in the yield of ratoon rice among different sites.The main and ratoon crop yields were in the range of 8.25-10.5 t ha^-1 and 3.75-4.50 t ha^-1,respectively,and the annual yield reached 12.0-15.0 t ha^-1.Among them,the yield during both the main and ratoon crop of ratoon rice was highest in Xiantao,while it was lowest at the Jianli.In field experiment,main crop and ratoon crop produced grain yield,ranging of 8.09-9.57 t ha^-1and 4.28-5.24 t ha^-1,respectively.The total grain yield of ratoon rice was in 12.37-14.81 t ha^-1.However,rapeseed return had no significant effect on yield and yield related traits in both seasons of ratoon rice,which might be due to several factors including the time of rapeseed return,the way of rapeseed return,and soil fertility;applying nitrogen fertilizer in main season significantly increased the yield in both the main and ratoon seasons,but there were no significant differences between the fertilization treatments,which may have been influenced by the relatively high soil fertility,and the lodging under the high nitrogen treatments.（3）The results of the investigation showed the high economic efficiency of zero-tillage and UAV-seeding rapeseed—ratoon rice rotation system.The productive inputs during the growing season of rapeseed were in range of 3600-4215￥ha^-1among sites,and the main difference came from the mechanical inputs when rapeseed was returned to field;ratoon rice produced inputs between 13650-14850￥ha^-1 in the growing season,and the main differences were related to fertilizers,pesticides,and harvested inputs.The most dominant input in the zero-tillage and UAV-seeding rapeseed—ratoon rice rotation system was mechanical input,which accounted for34.2%on average;the second were fertilizer and manual inputs,which accounted for24.9%and 18.6%on average,respectively;while seeds and pesticides had the lowest inputs.The economic income of rapeseed as silage among sites was in the range of5580-7590￥ha^-1;while the income of ratoon rice was in the range of 31500-36150￥ha^-1,with the difference mainly coming from the main season.On average,the net income and return on investment under the zero-tillage and UAV-seeding rapeseed—ratoon rice rotation system reached 21135￥ha^-1 and 215.9%,respectively,with considerable economic benefits.In conclusion,the high yields of silage,green manure,and ratoon rice were produced by adopting the zero-tillage and UAV-seeding rapeseed—ratoon rice rotation system indicated that this system had considerable economic benefits and showed great development prospects.However,under the condition of field experiment,it is found that the rapeseed returning and fertilization treatments in main season had no significant effects on the yield of ratoon rice,which may be affected by many factors.At the same time,the effect of rapeseed returning may take years to manifest.Therefore,the effect of rapeseed as a green manure return field on soil fertility needs to be further tested.