| Jiangsu is one of the major provinces producing japonica rice in China.Due to the abundant temperature,light,and high nitrogen fertilizer application,the total production and yield of japonica rice in Jiangsu ranked in the forefront of maj or japonica rice producing provinces.Since the implementation of agricultural supply side reform in 2015,the goals of rice production in Jiangsu has shifted from the high yield to the coordinated improvement of yield,quality,and benefit.To survey the application of main japonica rice varieties in Jiangsu after 2015 and investigate their response of yield,quality,and benefit to nitrogen fertilizer,this study investigated the planting situation of japonica rice varieties and nitrogen fertilizer application in japonica rice production from 2016 to 2020.On this basis,in 2020 and 2021,the two main late-maturing medium-japonica rice varieties,including Nanjing 9108 and Huaidao 5 with the largest planting area in Jiangsu Province,were used as experimental materials to investigate the response of yield quality and nitrogen use efficiency to nitrogen application at the Shatou Base in Yangzhou City,Jiangsu Province.Four nitrogen fertilizer levels including NO(0kg·hm-2),N1(180kg·hm-2),N2(270kg·hm-2),and N3(360kg·hm2)were set up.Rice yield and its composition factors,rice quality,nitrogen absorption and utilization of the main japonica rice varieties were systematically studied under the condition of rice were mechanical transplanted.A comprehensive evaluation and costbenefit analysis were also conducted on the yield,quality,and nitrogen utilization efficiency of japonica rice under different nitrogen fertilizer level.The nitrogen fertilizer level for the synergistic improvement of yield,quality,and benefit of Jiangsu japonica rice was identified,and relevant countermeasures and suggestions were proposed for Jiangsu japonica rice production,in order to provide reference for the high-quality development of Jiangsu japonica rice.1.Main results of research:(1)Changes in main japonica rice varieties and their yield and quality characteristics in Jiangsu from 2016 to 2020:The main cultivated japonica rice varieties in Jiangsu were divided into three growth types:medium-ripening medium-japonica,late-maturing medium-japonica,and earlymaturing late-japonica.A comparative study was conducted on the top 10 japonica rice varieties with an average planting area from 2016 to 2020 among the three types.It was found that the top 10 japonica rice varieties had an area of 451.01 thousand hectares,716.89 thousand hectares,and 301.90 thousand hectares,respectively.Among them,the non soft rice and soft rice varieties with the largest planting area of medium-ripening medium-japonica are Huajing 5 and Xudao 9,respectively,accounting for 22.67%and 6.26%of the planting area of medium-ripening mediumjaponica;The non soft rice and soft rice varieties with the largest planting area of late-maturing medium-japonica are Huaidao 5 and Nanjing 9108,respectively,accounting for 32.71%and 44.87%of the planting area of late-maturing medium-japonica;The non soft rice and soft rice varieties with the largest planting area of early-maturing late-j aponica are Wuyunjing 31 and Nanjing 5055,respectively,accounting for 11.79%and 47.31%of the planting area of early-maturing latejaponica.Compared with 2016,the proportion of total planting area of top 10 japonica non-soft rice varieties in Jiangsu rice planting area decreased by 5.03-6.91%in 2020,while the proportion of total planting area of top 10 japonica soft rice varieties in Jiangsu rice planting area increased by 0.72-4.62%.Taking soft rice(Xudao 9,Nanjing 9108 and Nanjing 5055)and non-soft rice(Huajing 5,Huaidao 5 and Wuyunjing 31)with the largest planting area among medium-ripening medium-j aponica,late-maturing medium-japonica and early-maturing late-j aponica)and non-soft rice(Huajing 5,Huaidao 5 and Wuyunjing 31)as materials,the yield and quality performance of these varieties in different regions under the same cultivation conditions were investigated.The results showed that compared with non soft rice varieties,there were no significant differences in the brown rice rate,milled rice rate,head milled rice rate,and protein content of soft rice varieties.However,the chalkiness area,taste value,peak viscosity,and breakdown of soft rice varieties were significantly higher,while the amylose content,trough viscosity,final viscosity,setback,and consistence were significantly lower.After 2015,under the conditions of agricultural supply side reform in Jiangsu,the planting area of soft rice japonica rice was increased.Compared with non soft rice japonica rice,although the appearance of soft rice japonica rice was slightly cloudy,the yield was equivalent and the taste quality was improved.(2)Nitrogen fertilizer application status in Jiangsu japonica rice production from 2016 to 2020:From 2016 to 2020,the total nitrogen fertilizer application used in the production of japonica rice in Jiangsu showed a gradual downward trend,with a first decrease and then an increase in the amount of nitrogen fertilizer applied per hectare.Compared with 2016,in 2020,the total nitrogen fertilizer application used for japonica rice in Jiangsu decreased by 108700 tons,a decrease of 14.71%;The nitrogen fertilizer application rate per hectare of Jiangsu japonica rice decreased by 16.80kg,a decrease of 4.64%.From 2016 to 2020,the nitrogen utilization efficiency of Jiangsu japonica rice showed a trend of first increasing and then decreasing.Compared with 2016,the nitrogen utilization efficiency of Jiangsu japonica rice in 2020 increased by 1.38 kg·kg-1,an increase of 5.53%.Compared with the production of japonica rice in Liaoning,Jilin,and Northeast Heilongjiang provinces,there is still a situation of high total nitrogen fertilizer application and low nitrogen utilization efficiency in the production of japonica rice in Jiangsu.(3)Response of yield,quality,and benefit of major japonica rice varieties in Jiangsu to nitrogen fertilizer:To clarify the reasonable nitrogen fertilizer input for the synergistic improvement of yield,quality,and benefit of Jiangsu japonica rice,four nitrogen fertilizer levels were set up to study the response of yield,quality,and benefits to nitrogen fertilizer,using the two late maturing medium japonica rice varieties(Nanjing 9108 and Huaidao 5)with the largest planting area in Jiangsu.The results showed that the yield of Nanjing 9108 and Huaidao 5 showed an increasing and then decreasing trend with the increase of nitrogen fertilizer application,with the highest under N2 nitrogen fertilizer application conditions.The appropriate nitrogen fertilizer application promoted tillering,ensured sufficient panicles,increased panicle formation rate,and increased leaf area index at heading stage to above 7.0,in order to enhance the dry matter accumulation and proportion of rice population after heading.Secondly,under N2 conditions,it can also promote the rational accumulation and distribution of nitrogen within rice plants,improve the nitrogen transport amount,transport rate,and contribution rate of plants after heading,and relatively improve the physiological utilization rate of nitrogen in rice.Once again,with the increase of nitrogen fertilizer application,the processing quality of Nanjing 9108 and Huaidao 5 improved,while the chalkiness rice rate and chalkiness area in appearance quality showed a trend of first decreasing and then increasing,reaching the optimal level under N2 nitrogen fertilizer.With the increase of nitrogen fertilizer application,the protein content in grains increases,and the taste quality of rice decreases.A comprehensive evaluation of rice yield,quality,and nitrogen efficiency under different nitrogen fertilizer application showed that with the increase of nitrogen fertilizer application,the comprehensive evaluation of yield,quality,and nitrogen utilization efficiency of Nanjing 9108 and Huaidao 5 showed a trend of first increasing and then decreasing.At the N2 nitrogen fertilizer level,the comprehensive evaluation of yield,quality,and nitrogen utilization efficiency of Nanjing 9108 and Huaidao 5 are the highest,reaching 97.14 and 91.98 points respectively,which can achieve a synergistic improvement of rice yield,quality,and nitrogen efficiency.Further calculation of the cost and profit of Jiangsu’s japonica rice production showed that production value,profit,and cost profit margin of japonica rice showed a trend of first increasing and then decreasing with the increase of nitrogen fertilizer application,all reaching their maximum at the N2 level.At the N2 level,the production value of Nanjing 9108 and Huaidao 5 reached 31039.53 yuan·hm-2 and 29057.95 yuan·hm-2,respectively;The profits reached 8586.64 yuan · hm-2 and 6605.06 yuan · hm-2 respectively;The cost profit margin reached 38.24%and 29.42%respectively.At the level of N2 nitrogen fertilizer,the maximum production efficiency of japonica rice was achieved.2.Relevant countermeasures and suggestions:(1)Strengthen the synergy between yield,quality and benefit to enhance the cultivation and promotion of japonica rice varieties:Since 2015,since the supply side reform of agriculture in Jiangsu,rice production has begun to shift from the original pursuit of high yield to the coordinated improvement of yield,quality,and benefit.However,in this transformation process,there is still a lack of j aponica rice varieties that synergistically improve yield,quality,and nitrogen efficiency.Although soft rice has the characteristics of high yield and good taste quality compared to non soft rice,there is still great room for improvement in its appearance quality.Therefore,it is necessary to strengthen the improvement of appearance quality of Jiangsu soft rice japonica rice in a targeted manner.At the same time,in response to the planting system of two crops per year in Jiangsu Province,which requires a large amount of nitrogen fertilizer application and the characteristics of japonica rice fertilizer tolerance,japonica rice varieties also need to be screened for varieties that can efficiently utilize nitrogen fertilizer for high yield and quality under appropriate nitrogen fertilizer levels,in order to achieve the synergistic improvement of Jiangsu’s japonica rice production yield,quality,and nitrogen efficiency,and promote the high-quality development of the rice industry.(2)Promote the rational application of nitrogen fertilizer for Jiangsu japonica rice:The high yield of japonica rice production in Jiangsu comes at the cost of high nitrogen fertilizer application.High nitrogen fertilizer application not only reduces fertilizer utilization efficiency,but also pollutes the environment.This study indicates that under the premise of appropriately reducing nitrogen fertilizer application,the high yield of japonica rice can be ensured.Therefore,the production of japonica rice in Jiangsu should take into account the synergistic improvement of rice yield,quality,and nitrogen efficiency through rational nitrogen fertilizer application,including research and development of nitrogen fertilizer application,application ratio,and appropriate ratios of nitrogen,phosphorus,potassium,including medium and trace fertilizers,to meet the growth needs of synergistic improvement of rice yield,quality,and nitrogen efficiency.Secondly,we need to accelerate the development of new fertilizers.Microbial fertilizers that can control the release rate of fertilizer nutrients,reduce fertilizer loss,improve soil environment and nutrient conditions,accelerate organic matter decomposition,and enhance soil fertility.On this basis,it is necessary to accelerate the promotion and application of precise and efficient fertilization techniques such as mechanical sounding fertilization,in order to reduce the amount of nitrogen fertilizer application in Jiangsu japonica rice production and improve nitrogen fertilizer utilization efficiency. |
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