Effects Of Nitrogen Application And Mixed Seeding Ratio On Interspecific Relationship And Forage Quality Of Vicia Sativa L. And Sorghum Sudanense

In recent years,China’s livestock industry has been increasing its demand for high-quality forage production,however,the grassland in the western northeast of China is seriously degraded due to overload grazing and soil salinization,resulting in insufficient forage supply and causing pressure on the development of livestock production;on the other hand,the unreasonable use of nitrogen fertilizer leads to a decrease in fertilizer utilization rate,reducing the yield of forage and also polluting the soil environment,causing soil to be caked and acidified.Sorghum sudanense,as a high quality forage preferred by livestock,is rich in digestible substances and has a well-developed root system,which needs to absorb a lot of nitrogen fertilizer from the soil during its growth and development,so monoculture planting of Sorghum sudanense will increase the amount of nitrogen fertilizer input and raise farmers’planting cost.In the artificial grass planting mode,mixing Sorghum sudanense with leguminous forage grass is a superior planting method,which can reduce the use of nitrogen fertilizer and improve the forage yield and farmers’economic benefits.In order to solve the problems of insufficient forage supply,decreasing agricultural fertilizer utilization rate and serious soil ecological pollution in China,this experiment was conducted with Vicia sativa L.and Sorghum sudanense,and three treatments of nitrogen application were set,namely N0(0kg N/hm^-2),N90（90 kg N/hm-²）and N180(180 kg N/hm^-2);five mixed rate treatments,A1（100%Vicia sativa L.）,A2（75%Vicia sativa L.+25%Sorghum sudanense）,A3（50%Vicia sativa L.+50%Sorghum sudanense）,A4（25%Vicia sativa L.+75%Sorghum sudanense）and A5（100%Sorghum sudanense）.The agronomic traits,canopy structure,interspecific competition ability and nutritional quality of Vicia sativa L.and Sorghum sudanense were analyzed to investigate the interspecific interactions between Vicia sativa L.and Sorghum sudanense in the mixed system of bean and grass forage.The interspecific interactions between Vicia sativa L.and Sorghum sudanense in the mixed system of bean and grass forage and their influence mechanisms were investigated to provide a theoretical and scientific basis for the large-scale promotion of high-yielding and high-quality mixed forage planting methods and the sustainable and efficient utilization of grass.The main conclusions of this experiment are as follows.（1）Nitrogen application increased the plant height,stem thickness,stem to leaf ratio and fresh to dry ratio of Vicia sativa L./Sorghum sudanense,and higher forage yield was harvested,and the plant height and stem thickness of both forage grasses tended to increase with the increase of nitrogen application.The highest total forage yield of 9.57 t/ha^-1was achieved when the proportion of mixed sowing was A4,while the yield of single sowing Vicia sativa L.was 2.24 t/ha^-1and that of single sowing Sorghum sudanense was 5.93 t/ha^-1.The total forage yield of mixed sowing was significantly improved compared with that of single sowing.In the mixed sowing system,Vicia sativa L.could play a role in promoting the growth and development of Sorghum sudanense,and improve the total forage yield as well as the individual plant yield of Sorghum sudanense by increasing the agronomic traits such as plant height and stem thickness.（2）Nitrogen application could improve the light energy interception rate of plant community canopy structure,mainly by improving the plant leaf area index,increasing the normalized difference vegetation index and reducing the visible light transmittance,and the regulation effect on plant community canopy structure was better under N90 and N180treatments than N0 treatment.The highest normalized difference vegetation index and leaf area index and the lowest visible light transmittance of forage grass were achieved with nitrogen application of N180.Nitrogen application and mixed sowing increased the chlorophyll content of forage grasses,and the highest chlorophyll content of both Vicia sativa L.and Sorghum sudanense was achieved at the N180 treatment and the mixed sowing rate of A2.The lowest chlorophyll content was found in Vicia sativa L.at the rate of A4 and Sorghum sudanense at the rate of A5.The increase of Sorghum sudanense sowing reduced the chlorophyll content of Vicia sativa L.,while the increase of Vicia sativa L.sowing increased the chlorophyll content of Sorghum sudanense,improved the nitrogen utilization status of Sorghum sudanense,and delayed leaf senescence.（3）The land equivalent ratio of Vicia sativa L.and Sorghum sudanense was greater than1,and the highest land equivalent ratio was reached when the nitrogen application rate was N180 and the proportion of mixed sowing was A2,which could better play the role of land advantage and improve land utilization.In the process of forage growth,the interspecific competition rate of forage was less than 1 when the mixed sowing ratio was A4,and the interspecific competition ability of Sorghum sudanense was strong under this mixed sowing treatment,which had a hindering effect on the growth and development of Vicia sativa L.and occupied a dominant position in the mixed sowing system.In the mixed sowing ratio A3,the relative total yield of forage grass was greater than 1.The interspecific competition between the two species could be converted into interspecific complementation,and the growth resources were used together to achieve the effect of mutual benefit and symbiosis.The relative total yield of forage grass was less than 1 under the mixed seeding ratio of A2 and A4,and the Vicia sativa L.and Sorghum sudanense showed interspecific competition with each other.（4）With the increase of nitrogen application,the acidic detergent fiber and neutral detergent fiber contents of Vicia sativa L.and Sorghum sudanense decreased and the crude protein content increased,and the nutritional value of forage could be effectively improved under the treatment of N180.The mixture of sowing ratio A2 promoted the quality and yield of Sorghum sudanense,mainly by reducing the content of acidic detergent fiber and neutral detergent fiber and increasing the crude protein content of forage.When Sorghum sudanense was sown with A5,the acidic detergent fiber and neutral detergent fiber content were the highest,the crude protein content was the lowest,and the nutritional quality was poor.The advantages of mixed seeding of Vicia sativa L./Sorghum sudanense are reflected in the mutual benefits and competitive relationship between the species.In particular,a reasonable proportion of mixed planting can improve the plant height,stem thickness,stem to leaf ratio and fresh to dry ratio of Sorghum sudanense,optimize the canopy structure of the plant population of Vicia sativa L./Sorghum sudanense mixed grass,improve the interspecific competition relationship,enable the two species to make full use of nutrients,light and water resources,bring into play the complementary effect between forage grasses,reduce the acidic detergent fiber and neutral detergent fiber content of Sorghum sudanense.This experiment shows that by establishing a reasonable amount of nitrogen application and sowing ratio for planting Vicia sativa L./Sorghum sudanense mixed grass,we can improve forage yield,nitrogen fertilizer utilization efficiency and forage quality,providing a theoretical basis for the promotion of artificial grass planting and vigorous development of animal husbandry in northeast China,and ensuring the sustainable and healthy development of animal husbandry industrialization.