Research On The Application Of Rootstock Grafting In Cucumber Nitrogen Fertilizer Reduction

Cucumber plays a major role in the protected cultivation of vegetable crops in China.At present,in the process of facility cucumber production,farmers apply a large amount of nitrogen fertilizer in pursuit of high yield,resulting in waste of nitrogen fertilizer resources,low nitrogen utilization rate and serious inhibition of cucumber growth and development.Therefore,this study first evaluated the nitrogen efficiency of 14 pumpkin rootstocks suitable for cucumber grafting in order to screen nitrogen efficient rootstocks;Then the rootstock was grafted with cucumber,and the appropriate nitrogen reduction level was determined according to the growth and nitrogen absorption and utilization efficiency of grafted cucumber seedlings through different concentrations of nitrogen treatment;Then,the effect of rootstock grafting on nitrogen absorption and utilization of cucumber seedlings under nitrogen reduction was studied to explore the effect of nitrogen efficient rootstock grafting on improving nitrogen use efficiency of cucumber seedlings;Finally,the effects of nitrogen efficient rootstock grafting on the yield and quality of cucumber under the condition of nitrogen reduction were studied by reducing the application of nitrogen fertilizer before and after flowering.The results of this study will not only provide ideas for revealing the nutritional and physiological mechanism of grafting yield increase,but also provide scientific and technological support for using grafting to improve nitrogen use efficiency in production and realize the production of reducing nitrogen application and increasing efficiency of protected cucumber.The main results are as follows:1.Selection of cucumber rootstocks suitable for nitrogen fertilizer reduction.14cucumber rootstock varieties were treated with standard nitrogen（7 m M）and nitrogen reduction（4 m M）,and the differences of root and shoot fresh weights,plant height,stem diameter,root length and dry matter accumulation were compared.The results showed that the changes of 14 rootstock varieties under nitrogen treatment were quite different.Among them,the growth indexes of‘Ribenjingtiantaimu（R5）rootstock increased significantly under nitrogen reduction treatment,showing better growth than that under normal nitrogen level;After the evaluation of nitrogen use efficiency by cluster analysis,the‘Ribenjingtiantaimu（R5）rootstock was finally selected as a nitrogen efficient rootstock suitable for cucumber grafting.2.The nitrogen reduction concentration suitable for the growth and nitrogen absorption and utilization of grafted cucumber was determined.The plants of self-grafted（‘Jinchun No.4’cucumber grafted onto‘Jinchun No.4’）seedlings and rootstock-grafted seedlings（‘Jinchun No.4’cucumber grafted onto‘Ribenjingtiantaimu’pumpkin）were treated with nutrient solutions at five different nitrogen levels（14 m M,7m M,4 m M,2 m M and 0.5 m M）.The differences of plant growth,root morphology,photosynthetic characteristics and nitrogen use efficiency were analyzed,and the comprehensive growth evaluation of plants was carried out by TOPSIS.The results showed that the best comprehensive growth of self-grafted seedlings was showed at 7 m M nitrogen level,while for the rootstock-grafted cucumber seedlings was best performanced at 4 m M nitrogen level.Moreover,the growth indexes of rootstock-grafted cucumber seedlings under different nitrogen concentrations were all better than those of self-grafted seedlings.The results showed that excessive and insufficient application of nitrogen fertilizer will inhibited the growth of the plant,while rootstock grafting could effectively promote the growth and nitrogen efficient absorption and utilization of cucumber seedlings,and the performance was better under 4 m M nitrogen reduction treatment.Therefore,it was determined that 4 m M nitrogen concentration was a suitable nitrogen reduction concentration for rootstock grafting,which can maintain the normal growth of cucumber seedlings and improve nitrogen utilization efficiency.3.Study on the mechanism of improving nitrogen absorption and utilization of cucumber Seedlings by rootstock grafting under nitrogen fertilizer reduction.The plants of self-grafted（‘Jinchun No.4’cucumber grafted onto‘Jinchun No.4’）seedlings and rootstock-grafted seedlings（‘Jinchun No.4’cucumber grafted onto‘Figleaf Gourd’and‘Ribenjingtiantaimu’pumpkin）were treated with by standard nitrogen（7 m M）and nitrogen reduction（4 m M）treatment.The differences of plant growth,root morphology,nitrogen absorption and utilization efficiency,nitrogen metabolism related enzyme activity and product content were analyzed.The results showed that nitrogen reduction（4 m M）treatment inhibited the growth,root morphological characteristics and nitrogen absorption and assimilation efficiency of self-grafted plants（J/J）,but the inhibition was alleviated in rootstock-grafted plants（J/F and J/R）,and the growth,root morphological characteristics,NO₃^-absorption and assimilation efficiency and nitrogen metabolic enzyme activity in J/R plants were the best.The results showed that nitrogen efficient rootstock grafting could make plants make better use of the strong nitrogen absorption capacity of their roots and enhance the potential of aboveground nitrogen metabolism,so as to improve the plant growth and nitrogen use efficiency（NUE）of cucumber seedlings.4.The effects of rootstock grafting on the yield and quality of cucumber under nitrogen fertilizer reduction.The plants of self-grafted（‘Jinchun No.4’cucumber grafted onto‘Jinchun No.4’）seedlings and rootstock-grafted seedlings（‘Jinchun No.4’cucumber grafted onto‘Ribenjingtiantaimu’pumpkin）were treated with nitrogen reduction before and after flowering,respectively:T1:7 m M（before flowering）+7 m M（after flowering）;T2:4m M（before flowering）+7 m M（after flowering）;T3:4 m M（before flowering）+4 m M（after flowering）.The changes of plant growth,photosynthetic characteristics,yield and quality were analyzed.The results showed that the growth and photosynthesis of self-grafted cucumber plants were inhibited under the condition of reduced nitrogen application,which resulting in a significant reduction in yield and fruit quality.However,nitrogen efficient rootstock grafting significantly enhanced the photosynthesis,yield and fruit quality of cucumber plants under all nitrogen treatments.Although the yield and quality of rootstock-grafted plants under T3（nitrogen reduction before and after flowering）treatment decreased compared with the normal nitrogen level（T1）,it was equivalent to or even better than that of self-grafted plants under T1 treatment.The results implied that nitrogen efficient rootstock grafting could effectively improve the yield and fruit quality of cucumber,and the application of 4 m M nitrogen fertilizer during the whole growth period of cucumber can not only ensure that the yield and quality of cucumber are not affected,but also improve the nitrogen use efficiency and greatly save fertilizer resources.Therefore,it is the appropriate concentration of nitrogen fertilizer reduction for the production of cost-saving and efficiency enhancing grafting cultivation of cucumber in protected areas,which can be used as a reference value for production.