Effects Of Planting Density And Nitrogen Application Rate On Growth,Physiology,Yield And Quality Of Alfalfa In Coastal Saline-Alkali Land

Soil salinization has become a major abiotic stress limiting agricultural production worldwide.The area of saline-alkali land in my country is about 3.46×107 hm2,of which the salinization of agricultural arable land is about 7.6×106 hm2,accounting for about 1/5 of the cultivated land area in my country.Jiangsu coastal development strategy has been approved by the State Council and upgraded to a national strategy.Therefore,the development and utilization of Jiangsu coastal saline-alkali land plays an important role.Alfalfa has high nutritional value,is resistant to cold and drought,and its root nodules have strong nitrogen fixation.It is the largest grass species in my country.my country is also relatively backward in terms of alfalfa planting methods,cultivation management,etc.,so that the yield and quality of alfalfa have always been at a low level.Therefore,in this experiment,alfalfa(Medicago sativa L.)WL919 was used as the material,and 3 seeding rates of 15.0 kg·hm-2(D1),30.0 kg·hm-2(D2),and 45.0 kg·hm-2(D3)were set,150.0 kg·hm-2(N1),225.0 kg·hm-2(N2),and 300.0 kg·hm-2(N3)nitrogen application rates to explore the effects of different planting densities and nitrogen application rates on the growth of alfalfa in coastal saline-alkali land,physiology,yield and quality,in order to provide a theoretical basis for high-yield cultivation of alfalfa in coastal saline-alkali land.1.Effects of Planting Density and Nitrogen Application on Growth Characteristics and Yield of Alfalfa in Saline-Alkaline LandWith the growth and development of alfalfa,the plant height,fresh grass yield and hay yield of alfalfa increased first and then decreased with the increase of planting density,and reached the highest at medium density(D2),and increased with the increase of nitrogen application rate.At 150 d after seeding,the plant height was higher under the D2N1 and D2N2 treatments;the fresh weight and dry weight yields both reached the highest under the D2N2 treatment.When the nitrogen application rate was the same,the leaf area of alfalfa generally increased with the increase of density,indicating that increasing the nitrogen application rate was beneficial to increase the leaf area of alfalfa.Under the interaction conditions of planting density and nitrogen application rate,D3N2 and D3N3 treatments could significantly increase the leaf area of alfalfa during the whole growth period of alfalfa.2.Effects of Planting Density and Nitrogen Application on Physiological Characteristics of Alfalfa in Saline-Alkaline LandThe content of MDA was the lowest at 60 d after seeding,when nitrogen application rate had no significant effect on MDA content(P>0.05),and at 120 d after seeding,the content of MDA was the lowest under the D3N2 combination.With the increase of planting density and nitrogen application rate,the content of proline first increased and then decreased.The content of soluble sugar increased with the increase of nitrogen application rate,firstly increased and then decreased with the increase of planting density.Overall,the superoxide dismutase activity increased with the increase of planting density and nitrogen application,and the activity reached the maximum value under D2N2 treatment;The peroxidase activity was the highest;the catalase activity was the highest under the treatment of D2N2 and D3N2.Appropriately increasing nitrogen application rate is beneficial to the increase of chlorophyll a content in alfalfa slices.In general,increasing planting density is beneficial to the increase of chlorophyll a content.Appropriate increase of nitrogen application rate was beneficial to the increase of chlorophyll b content,and the combination of medium density and high nitrogen application rate(D2N3)under mixed cropping conditions was most beneficial to the increase of chlorophyll b content.The contents of N,P and K all increased with the increase of nitrogen application rate,the contents of N and K increased with the increase of planting density,while the content of P increased first and then decreased with the increase of planting density,that is,the density Too high is not conducive to the increase of P content in alfalfa plants.3.Effects of Interaction between Planting Density and Nitrogen Application Rate on The Quality of Alfalfa Forage in Saline-Alkali LandThe content of crude protein in alfalfa plants could be significantly increased by increasing nitrogen application rate,and the crude protein content was the highest under D1N1 and D1N2 treatments.Under the density of D1,increasing the nitrogen application rate can increase the crude fat content of plants;under the nitrogen application rate of N2,increasing the planting density can increase the crude fat content,and the D3N2 treatment is most beneficial to the increase of the crude fat content.The crude ash content first increased and then decreased with the increase of nitrogen application rate;under N2 and N3 nitrogen application rates,increasing nitrogen application rate and planting density were beneficial to the reduction of crude ash content in alfalfa plants.In general,the content of acid detergent fiber increased first and then decreased with the increase of planting density and nitrogen application;the content of acid detergent fiber was the lowest in D1N1 and D3N3 treatments.Under the seeding rate of D3,increasing nitrogen fertilizer can reduce the content of neutral detergent fiber in plants;under N3 condition,increasing the planting density can reduce the content of neutral detergent fiber in plants.The relative forage value increased with the increase of nitrogen application rate;under N1 condition,the relative forage value increased with the increase of planting density;the relative forage value of D2N2 and D3N3 treatments was the highest,which was 118%.