Comparison Test on Adaptability of Six Medicago sativa (Alfalfa) Varieties in Guangxi

Jinhua QIU Yilong HUANG Fanquan ZENG Jinyi WEI Na YAO

Abstract In order to screen the Medicago sativa （alfalfa） varieties suitable for planting in Guangxi， six domestic and foreign heat-resistant alfalfa varieties， namely WL903， WL712， WL525HQ， 59N59，Elite 9 and Longwei 6010， were selected and tested for growth performance， nutritional value and over-summer rate by the random block method. The results showed that the alfalfa varieties with better plant height and fresh grass yield were 59N59 and WL903， which showed the plant heights reaching 62.01 and 62.53 cm， respectively， and the fresh grass yields up to 40.93 and 38.38 t/hm2， respectively， exhibiting extremely significant differences from the poorly performing Longwei 6010 （P<0.01）. The nutritional value of each tested variety was good， and the crude protein content was more than 20%. Among them，Elite 9 had a crude protein content as high as 28. 43%. The over-summer rates of the six alfalfa varieties were all higher than 75%. It showed that the alfalfa varieties with fast growth， high yield， high nutritional value and high over-summer rate in this experimental area were 59N59 and WL903， which are suitable as the first varieties for planting in Guangxi.

Key words Medicago sativa; Variety comparison; Production performance; Nutritional value; Over-summer rate

Medicago sativa （alfalfa） is an excellent perennial legume forage. Because of its high yield， rich nutrition， good palatability， wide adaptability and strong resistance， it is called "king of forage" and "feed Queen[1]. Also， because of its good effect of fertilization and soil improvement， it is also an important green manure crop and has an irreplaceable role in promoting the sustainable and healthy development of animal husbandry and grassland[2]. Because alfalfa is generally poor in heat resistance， it is difficult to get over summer. Currently， it is mainly planted in the north， less planted in the south， and is mainly planted in winter. Different alfalfa varieties and alfalfa in different regions have different over-summer rates. To solve the over-summer problem of alfalfa in the south， some studies have been carried out. Qin et al.[3] shaded alfalfa during the over-summer period， and found that mild shading reduced the stress of high temperature and strong light on the growth of alfalfa， and increased its over-summer rate. Liu et al.[4] conducted a study on the effects of high temperature stress in summer on the photosynthetic physiological mechanism of alfalfa， and believed that Sardi， Alfaking and CUF were varieties strongly resistant to heat. Zhang et al.[5] studied the physiological and biochemical reactions of 22 alfalfa varieties during the over-summer period， among which Sitel， Derby and Huangguan are heat-resistant varieties. At present， few studies have been conducted on the breeding of heat-resistant alfalfa varieties for Guangxi climate and geographical conditions. In recent years， Guangxi has vigorously developed healthy ecological farming， and the demand for fine pastures， especially high-quality legumes， has surged. In this study， six heat-resistant M. sativa varieties were tested for their adaptability in Guangxi， and their growth performance， nutritional quality and over-summer rate were investigated， aiming to select suitable alfalfa varieties for Guangxi and provide theoretical basis and technical support for solving the problem of lack of high-quality feed in southern animal husbandry and the popularization and application of alfalfa in the south.

General Situation of Experimental Field

The experimental site is located in the scientific research base of the Animal Husbandry Research Institute of Guangxi Zhuang Autonomous Region in the suburb of Nanning， Guangxi. The experimental area has a tropical monsoon climate， with plenty of sunshine， abundant rainfall， little frost and no snow， and long summer and short winter. The annual average temperature is around 21.6 ℃， the average temperature of the coldest January in winter is 12.8 ℃， and the average temperature of the hottest July and August in summer is 28.2 ℃. The average annual rainfall is 1 304.2 mm and the average relative humidity is 79%. The soil pH of the experimental site is 6.8， and the nutrient contents are as follows： organic matter 23.8 g/kg， total nitrogen 0.165%， total phosphorus 0.056%， total potassium 1.07%， hydrolyzable nitrogen 109 mg/kg， available phosphorus 16.8 mg/kg， and rapidly available potassium 101 mg/kg.

Materials and Methods

Tested Medicago sativa

A total of six varieties： WL903， WL712， WL525HQ， 59N59，Elite 9 and Longwei 6010， were purchased from Beijing Zhengdao Ecological Technology Co.， Ltd. and Guangxi Grassland Supervision Center， as shown in Table 1.

Experimental design

The experiment was carried out in 2015-2018， using a random block test design， with three repetitions. Each plot had an area of 15 m2 （3 m×5 m）. After plowing and leveling the experimental field， ridges were formed for rowing and seeding， with a row spacing of 30 cm. Each plots included 10 rows， and the seeding rate was 30 g/plot. The seeding time was November 10， 2015. Organic manure fertilizer was applied at 10 000 kg/hm2 as the base fertilizer before sowing， and the sown seeds were covered with soil 1-2 cm. At the seedling stage and after each mowing， weeding and irrigation with the topdressing were performed once， and the fertilizing amount was 30 kg/hm2 each time. The forage was moved with sickles manually at the initial flowering stage. In 2016， 2017 and 2018， the forage was mowed 4 times every year averagely， on January 22， March 13， April 28， and May 26， respectively.

Indicator determination and methods

Plant height

Before each time of yield determination， 10 plants were randomly selected from each plot to measure the absolute height of the plants and obtain the average value. The measurement was performed before four times of cutting within a year， and the average value of the four times was calculated as the average plant height of the year.

Grass yield

When measuring the yield， the first and last rows in each plot were mowed first， and then， 50 cm on each side of the remaining rows was mowed. The remaining part was mowed to measure the yield， and the fresh grass yield was calculated based on this area. Finally， the hay yield was calculated according to dry weight/fresh weight ratio.

Determination of nutritional components

Samples were sent to the Guangxi Analysis and Testing Center for analysis and determination at the first mowing each year. The determined indexes were crude protein， crude fiber， crude fat， neutral detergent fiber， and acid detergent fiber.

Over-summer rate

Three representative sample segments were selected from each plot， and each sample segment was 1 m long. Before summer and after the high temperature summer season， the total number of plants in each sample segment was counted to calculate the over-summer rate in the segment （Over-summer rate = Total number of plants before summer/Total number of plants after summer×100%）.

Statistical analysis of data

The excel software was used to establish the original test database. The DPS13.5 software was used to analyze the significance of the test data. The LSD method was used for multiple comparisons. The test results were expressed as "mean±standard error".

Results and Analysis

Plant height

The plant height measurement results of the six alfalfa varieties are shown in Table 2.

From Table 2， it could be seen that the annual plant heights of the WL series of M. sativa were generally higher， while the annual plant heights of Elite 9 and Longwei 6010 were lower. In 2016 and 2017， there were no significant differences in plant height between the WL series and the M. sativa variety 59N59 （P>0.05）， while in 2018， the WL series and 59N59 showed extremely significant differences from Longwei 6010 （P<0.01）. The three-year average plant heights ranked from high to low as WL712>WL903>59N59>WL525HQ>Longwei 6010>Elite 9. The differences in plant height between the WL series and 59N59 were not significant （P>0.05）， and they had extremely significant differences from Elite 9 and Longwei 6010 （P<0.01）. Through calculation， WL712 was 20.76% high than Longwei 6010， and 21.41% higher than Elite 9.

Grass yield

The comparative analysis of fresh grass and hay yields of the six alfalfa varieties is shown in Table 3 and Table 4.

It could be seen from Table 3 that when comparing the fresh grass yield among the 3 years， the fresh grass yields of alfalfa varieties in 2017 were the highest except WL903， followed by 2018， and the lowest in 2016. The three-year average plant heights ranked from high to low as 59N59>WL712>WL903>WL525HQ>Elite 9 >Longwei 6010. 59N59 was not significantly different from WL712 and WL903 （P>0.05）， but had a significant difference from WL525HQ （P<0.05） and extremely significant differences from Elite 9 and Longwei 6010 （P<0.01）. The three-year average yield of 59N59 reached 40.93 t/hm2. It was higher than the average yield of Longwei 6010 which was the lowest by 30.06%.

It could be seen from Table 4 that the hay yields of the various alfalfa varieties was highest in 2018， followed by 2017， and lowest in 2016. During the experiment， the hay yield of 59N59 was always the highest， which was significantly different from Longwei 6010 and Elite 9 in 2016 （P<0.05）， and significantly different from Longwei 6010 in 2017 （P<0.05）， while the differences between various varieties were not significant in 2018 （P>0.05）. The three-year average hay yields from high to low were in order of 59N59>WL712>WL903>WL525HQ>Elite 9>Longwei 6010. Consistent with the fresh grass yield sequence， 59N59 was not significant from WL712 and WL903 （P>0.05）， but had a significant difference from WL525HQ （P<0.05） and extremely significant differences from Longwei 6010 and Elite 9 （P<0.01）.

Nutritional value evaluation

The nutritional contents of the first crops of the six alfalfa varieties from 2016 to 2018 are shown in Table 5.

It could be seen from Table 5 that the crude protein contents of various tested alfalfa varieties were all higher than 20%， and Elite 9 had the highest crude protein content， which was not significantly different from Longwei 6010 （P>0.05）， but significantly higher than other four varieties （P<0.05）.Elite 9 and Longwei 6010 had higher crude fat contents， and lower crude fiber， neutral detergent fiber and acid detergent fiber contents， which meant that they were better in nutritional components than other four varieties.

Over-summer rate

The statistical results of the three-year over-summer rates of the six alfalfa varieties are shown in Fig. 1. The over-summer rate is a key indicator reflecting the heat resistance of alfalfa. It could be seen from Fig. 1 that the six alfalfa varieties tested had better heat resistance， and the three-year average over-summer rates were all higher than 75%. Among them，Elite 9 showed an over-summer rate was as high as 95%. The over-summer rates of the six alfalfa varieties from high to low ranked as Elite 9>Longwei 6010>WL903>59N59>WL712>WL525HQ.

Discussion

Comparison of production performance among different alfalfa varieties in Guangxi

Plant height and grass yield are important indicators for evaluating alfalfa productivity[6-7]. The plant heights and grass yields of the three alfalfa varieties WL712， WL903 and 59N59 were relatively high， and the plant height were positively correlated with the grass yield， which is basically consistent with the research results of Kang et al.[8]， Zhang et al.[9] and Gao et al. [10].

Comparison of nutritional components among different alfalfa varieties

Crude protein content and crude fiber content are the main measures of alfalfa quality[11-12]. In the actual production of M. sativa， the best period of harvest is when the yield and quality indicators reach the best comprehensive balance point， which is the initial flowering period of M. sativa[13]. In this study， the tested alfalfa varieties were sampled at the initial flowering stage， and their nutritional components were analyzed and determined. The crude protein contents of the six alfalfa varieties were all higher than 20% and the crude fiber contents were lower than 30%. It shows that the tested alfalfa varieties are all high-quality varieties. The results of this study showed that Elite 9 had the best nutritional quality， followed by Longwei 6010， again with 59N59 and WL903， and WL712 showed the worst nutritional quality.

Comparison of climate adaptability among different alfalfa varieties

In the introduction of alfalfa in the northern region， the overwintering rate is an important factor to be considered. However， the experimental area selected in this study is warmer in winter， so the introduced alfalfa can safely overwinter， and the over-summer rate is more important. The six alfalfa varieties underwent three years of over-summer rate statistics， and all showed an over-summer rate higher than 75%， and the heat resistance was thus relatively good， indicating that they have good growth adaptability in Guangxi. In this study， only a simple statistics of over-summer rate was made， and the physiological and biochemical determination in the over-summer period and the heat tolerance mechanism were not investigated， and need further study.

Conclusions

To sum up， the six alfalfa varieties tested could adapt to the climatic conditions of Guangxi， and could safely survive summer. Under the climatic conditions in Guangxi， the first alfalfa varieties with high grass yield and better nutritional quality are 59N59 and WL903， which could be grown to raise animals while solving the problem of lacking green grass in the winter season. They are high-quality forage varieties that improve natural pastures and build artificial grasslands.

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