Effects Of Different Planting Methods On The Yield And Germination Characteristics Of Medicago Sativa L. Seeds In The West Of Northeast China

Alfalfa(Medicago sativa L.),as a high-quality perennial legume forage,plays an important role in animal husbandry.Alfalfa has the advantages of high yield,high grass quality and strong drought resistance and currently widely planted in China.The climate in the western part of Northeast China has brought obstacles to overwintering of alfalfa,and planting risks such as seeds falling off after maturity due to raining.In the Songnen Plain,alfalfa normally is planted in low-yield farmland,degraded grassland or saline-alkali land with high planting density and flat strip sowing,which resulting in a serious risk of low yield of alfalfa seeds.The western part of Northeast China is one of the advantageous production areas for alfalfa planting.The low yield of seeds during the harvest period and the high purchase price have become the main limiting factors for the large-scale promotion and cultivation of alfalfa in this area.The grain yield of alfalfa is closely related to ecological factors such as planting row spacing and cultivation practises.Rainfall during the flowering period of alfalfa was the main reason for the significant difference in grain yield.This study selected the local alfalfa variety "Dongmu No.1" as the research object.During the alfalfa growth period,agronomic characters,canopy structure,overwintering rate and seed germination index,the effects of different planting row spacing,cultivation mode and mowing time on the yield and quality of alfalfa seeds were discussed.The purpose of this work is to stabilize and increase the yield of alfalfa seeds in western Northeast China.The research results have important practical significance for guiding the production of alfalfa seeds in western of Northeast China.The main conclusions obtained are as follows:(1)The analysis of the botanical traits of alfalfa under five different row spacings in windy sandy land showed that alfalfa positively affected by grain yield through density and NDVI.The grain yield and germination rate showed a trend of increasing with row distance and then decreasing.The yield of alfalfa seeds was the highest under the row spacing of 50 cm,which were 647.33 kg/ha and 685.86 kg/ha,respectively,in the tow years.The seed germination rate of the row spacing of 70 cm was the highest,which were 93.30 % and 94.17 %,respectively in tow years.When alfalfa planting row spacing is moderate,there is less competition among and within alfalfa plants,which is conducive to the formation and growth of seeds.In the case the row spacing is too small or too large,it will affect the utilization of environmental resources,resulting in a decrease in germanation rate.Under the condition of moderate row spacing,alfalfa showed increased trends in podding rate and number of grains,which was conducive to the formation of yield.(2)The botanical characteristics of alfalfa under five different row spacings in saline-alkali land indicated that with the increase of planting row spacing,the yield of alfalfa seeds increased first and then decreased.Under different row spacing,alfalfa grain yield was determited the number of inter-nodes,and inversely affected by plant height,LAI and VLT.During the growth and development of alfalfa seeds,with the increase of plant yield,there were significant differences in the resource allocation of the population.In the case the row spacing is too small,each individual plant will be allocated less growth space;by contrary,the row spacing is too large,the more individual resources will be concentrated to the stem and leaf organs of alfalfa.This experiment showed that under mild saline-alkali conditions,the yield of alfalfa seeds under 60 cm row spacing was significantly higher than that of other row spacings,with a yield of 348.02 kg/ha;the germination rate of alfalfa seeds under 75 cm row spacing was significantly lower than that under other row spacings.The seed germination rate was 76.01%.Properly increasing the row spacing is conducive to achieving stable grain yield.(3)The analysis of the botanical characteristics of alfalfa under different cultivation modes of saline-alkali land showed that there were significant differences in the grain yield of alfalfa under the conditions of flat cropping,ridge platform,ridge gang and furrow planting.But the four planting modes had no significant effect on the germination rate of alfalfa seeds.The yield of alfalfa seeds sown in flat cropping was significantly higher than that of other planting modes.Under flat cropping,alfalfa can improve grain yield through the positive regulation of stem diameter,rhizome density and NDVI.The vegetative organs of alfalfa with significantly higher density and NDVI are well developed and the photosynthetic utilization efficiency is higher,which can further provide nutrition for reproductive organs such as seeds,and better maintain the growth and development of alfalfa seeds.(4)The analysis of botanical characteristics of alfalfa after early harvesting in saline-alkali land showed that early harvesting had a significant effect on alfalfa grain yield,but had no significant effect on seed germination rate.After early mowing in late May and early June,the parameters of alfalfa plant height,stem diameter,number of branches and single branch weight were all higher than those of alfalfa after mowing in mid-June.Alfalfa showed tall plants,thick stems,many branches,loose distribution,and strong lodging resistance in alfalfa populations.Cutting alfalfa in advance can effectively delay the time of seed maturation and provide the possibility to avoid the yield reduction caused by the rain and heat in the same season.Considering different soil conditions and planting methods,the production of alfalfa seeds should be adapted to local conditions,and different cultivation and management methods should be implemented in combination with different soil conditions.In the western part of Northeast China,the suitable row spacing for alfalfa in sandy land is 50 cm,and the suitable row spacing for alfalfa in saline-alkali land is 60 cm.For alfalfa in saline-alkali land,the suitable seedbed construction mode is flat cropping and ridge top sowing.Mowing alfalfa in late May or early June in saline-alkali land is the best time to save seeds,which can increase grain yield.