Adaptability Comparison of Chinese Milk Vetch（Astragalus sinicus）Varieties for Double-rice Cropping System in Hunan

Yanhong LU, Yulin LIAO, Xing ZHOU, Saijun TU, Jun NIE , Jian XIE, Zengping YANG, Weidong CAO

1. Soil and Fertilizer Institute of Hunan Province, Hunan Academy of Agricultural Sciences, Changsha 410125, China;

2. Scientific Observing and Experimental Station of Arable Land Conservation(Hunan), Ministry of Agriculture, Changsha 410125, China;

3. College of Resources and Environment, Hunan Agricultural University, Changsha 410128, China;

4. Station of Soil and Fertilizer, Agricultural Bureau of Nanxian County, Nanxian 413200, China;

5. Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing 100081, China

Hunan Province is a typical agricultural province, one of the important grain production bases in China, and always a main grain supply province. Rice is the staple food crop in Hunan Province, its yield and cultivated area both rank the first in China[1]. With the development of social economy and the fast promotion of urbanization in China, the nonagriculturalization trend of cultivated land is irreversible[2], the decrease of cultivated land area day by day affects the safety of grain production in Hunan Province to a large extent. Chinese milk vetch (Astragalus sinicus), as a green manure with a long history,plays an important role in effectively fertilizing the soil, improving the environment, increasing crop yield and quality and reducing fertilizer input[3].Rice rice green manure used to be the most important farming mode of paddy field in Hunan Province. The largest cultivated area of green manure ever reached 2×106hm2in Hunan Province,which accounted for 58%of agricultural acreage[4]. However, in recent 30 a, the transfer of economic barycenter affects the input composition and quantity of organic material of paddy field, the rice production in Hunan Province almost all relies on fertilizer input at present, the organic manureand farmyard manure input into paddy field are low,and the cultivated area of green manure also declines sharply.In addition, the multiple crop index and the yield of double cropping rice are high, and the nutrient consumption is great, causing the decline of rice soil fertility, the shallowing of arable layer,the accumulation of soil nutrient in topsoil, the aggravation of secondary gleization, the enlargement of medium- and low-yield field area and the continuous declination of soil overall quality[5-6].Therefore,developing green manure crop production and utilization is of significant practical significance for cultivating and promoting the farmland productivity of double cropping rice field and guaranteeing food security in Hunan Province.

Rice rice winter fallow is the main cropping pattern in Hunan Province at present.By statistics,the double cropping area of rice rice in the whole province paddy field is 1 635 000 hm2,and the area of rice rice green manure is about 300 000 hm2[7]. There has always been green manure planting and production in Hunan Province, Chinese milk vetch is the main green manure variety in Hunan paddy growing area.For a long time, the planting and utilization of Chinese milk vetch has played an important role in improving the soil of medium- and low-yield field,soil fertility and ecological environment[8]. Soil fertilizer workers of Hunan Province bred the Chinese milk vetch varieties suitable for double cropping rice production in 1970s, such as Xiangfei 1, Xiangfei 2 and Xiangfei 3,etc. For the atrophy of cultivated area and the stagnation of the research work,the seeds of those suitable Chinese milk vetch varieties are almost no sale in the market, and the characters of those varieties have gradually degraded. At the same time, the farming season of double cropping rice production has already changed greatly at present, some farming measures like the ploughing and transplanting improved sharply compared with 1970s and 1980s,the flowering phases of the existing Chinese milk vetch varieties can not meet the requirements of modern double cropping rice farming system.Lacking the new Chinese milk vetch varieties is the main bottleneck limiting the restoration and development of green manure in double cropping rice region of Hunan Province,especially the new early-blossoming and mid-yield variety suitable for modern double cropping rice.To resume green manure production and screen out new Chinese milk vetch varieties adapting to modern southern double cropping rice farming system, Soil and Fertilizer Institute of Hunan Province has taken early blossoming, appropriate yield and high nutrient content as the breeding objectives of new Chinese milk vetch variety since 2008,moreover, Xiangzi 2 was successfully bred.To verify the suitability of Xiangzi 2 in modern double cropping rice production,the field trial in Gaoqiao Town,Changsha County, Changsha City was carried out during 2010 -2014,hoping to make the variety serve double cropping rice production as soon as possible.

Materials and Methods

Experimental varieties

There were five experimental varieties of Chinese milk vetch, such as Xiangzi 2, Xiangfei 2, Xiangfei 3, Yujiangdaye and Xinyang Chinese milk vetch. Thereinto, Xiangfei 2 and Xinyang variety are early blossoming varieties, Xiangfei 3 and Yujiangdaye are middle blossoming varieties, Xiangzi 2 is a new variety with wild Chinese milk vetch variety in Wangcheng District of Changsha City as the parents bred by Soil and Fertilizer Institute of Hunan Province, it belongs to an early blossoming variety.

Experimental design

The experiment was conducted in Fanlin Village, Gaoqiao Town,Changsha City during 2010-2014.The soil was alluvial sandy soil with medium fertility developed from river sediment,the preceding crop was late rice with uniform growth, the experimental field had not been planted Chinese milk vetch for more than 30 a.After the harvesting of late rice, removing the straw and trenching for the field were done. The experiment adopted random arrangement with three repetitions, the plot area was 66.7 m2, the drainage ditches with 30 cm width and 15 cm depth were digged around each plot, so as to ensure the expedite drainage, and guard row with 1.5 m was set outside the plot. The experiment must be carried out in different plots each year.

Sowing methods and management

2-3 d after the harvesting of late rice, Chinese milk vetch was sown.Before sowing, seed dressing with rhizobium was carried out, then sowing after airing, the seeding method was sowing in drill with the width of 10 cm, then watering once after planting,so as to accelerate seed germination.Ditch cleaning and draining away the water were done in winter and spring.During the test duration, hydrops can not be in the field, drought resisting before winter was done once and ditch cleaning in the early spring was also done once.

Observation projects and data processing

In the experiment, field observation was often done,and the agronomic traits of plants at the seedling stage,wintering period, full-bloom stage and mature period were measured, at the same time, the growth rate of plants was observed.

Half of each variety in each plot in the full-blossom period was mowed and the yield of fresh grass was measured, and nitrogen, phosphorus and potassium contents in each plant were tested. For the other half, they were mowed at the mature period to test the yield of seeds, and the seeds of each plot were knocked and dried in the sun separately,then the yield of seeds was measured.

Conventional method[9]was adopted to measure the nutrients of nitrogen, phosphorus and potassium in each plant.

All data were processed by Excel 2003 software.

Results and Analyses

Comparison on the growth period

The growth period of Chinese milk vetch, especially full-blossom period,plays an important role to timely production of southern modern double cropping rice. The tillage of southern rice field starts from the end of March to the beginning of April, so the fullblossom period of Chinese milk vetch must be during the end of March and the beginning of April.From Table 1,itwas seen that the time from sowing to full-bloom stage of Xiangzi 2 was relatively close to that of Xinyang variety,namely 166 and 167 d, respectively, it had not significant difference; the fullbloom stage of Xiangzi 2 was respectively earlier than Xiangfei 2,Xiangfei 3 and Yujiangdaye by 4, 7 and 8 d, thus Xiangzi 2 had extremely significant differences with the three varieties(P＜0.01);the average whole growth stage(from sowing to mature period) of Xiangzi 2 and Xinyang variety was both 202 d, which was extremely shorter than that of the other three varieties.Xiangzi 2 showed the characters of early blossoming and early mature.

Comparison on the quality of plants before winter

The quality of Chinese milk vetch plants before winter plays a decisive role to the yield of the variety at the full-bloom stage. The survey on the plant quality of each variety was carried out before the winter (before the end of December) during 2010-2013;from Table 2,it can be drawn that from the quality of each Chinese milk vetch variety before winter, Xinyang variety showed weaker growth vigor in plant height, branch number and root length, while the other varieties had not obvious differences, the plant height and branch number of Xiangzi 2 were slightly higher than those of the other varieties. The difference of root nodule was obvious within the year,but the interannual difference was not obvious.

Comparison on the nutrient content at full-bloom stage

The contents of nitrogen, phosphorus and potassium in Chinese milk vetch at the full-bloom stage directly affect the fertilizing soil for Chinese milk vetch planting and the effect providing nutrient for crops. The nutrient content at the full-bloom stage (based on dry basis) was in Table 3. Total N contents of Xiangzi 2, Xiangfei 2, Xiangfei 3, Yujiangdaye and Xinyang Chinese milk vetch were 3.00% ,2.96%,2.85%,2.96%and 2.87%, respectively.Total N content of Xiangzi 2 was significantly higher than that of the other varieties.But the contents of total P, total K and plant moisture of each variety had not obvious differences.

Comparison on the quality of plants at the full-bloom stage

The main function of Chinese milk vetch is used as green manure in spring, and the quality of Chinese milk vetch plants at the full-bloom stage is a key indicator measuring the variety.The characters of each variety at the full-bloom stage were surveyed in Table 4, the height of Xiangzi 2 was 114.8 cm, which was slightly lower than that of Xiangfei 2, Xiangfei 3 and Yujiangdaye; the weight per plant of Xiangzi 2 was 115.9 g,which was lower than that of Xiangfei 2, Xiangfei 3 and Yujiangdaye; however, the height and the weight per plant of Xiangzi 2 were obviously higher than those of Xinyang variety, thus showed the character of moderate yield;the differences on stem diameter of each variety were not obvious.

Table 1 The growth periods of different Chinese milk vetch varieties during 2010－2014 d

Table 2 The quality of different Chinese milk vetch varieties before winter

Comparison on fresh grass yield at the full-bloom stage and seed yield at the mature period

The optimal overturning stage of Chinese milk vetch is full-bloom stage,the fresh grass yield at the full-bloom stage directly affects the contents of nitrogen, phosphorus, potassium and organic matter in the soil[10].If the overturning quantity of Chinese milk vetch is too low, its nutrient and organic content will also be lower, thereby causing the non-ideal fertilizing effect,however,excessive overturning quantity of Chinese milk vetch will cause the increase of overturning difficulty,and even cause the poisoning phenomenon due to insufficient decomposition time[11],therefore,the overturning quantity is really not the more the better. Some researches showed that the optimal overturning quantity of Chinese milk vetch in paddy field under modern farming system was about 22 500 kg/hm2[12].As shown in Table 5,it can be seen that the average yield of fresh grass of Xiangzi 2 at the fullbloom stage was 23 843 kg/hm2,which was lower than fresh grass yield of Xiangfei 2, Xiangfei 3 and Yujiangdaye,but higher than that of Xinyang variety.It was generally believed that the optimal overturning quantity of Chinese milk vetch was about 22 500 kg/hm2,and the yield of Xiangzi 2 was in the suitable range of returning to the field,thus it was beneficial to the improvement of soil fertility and the increase of rice crop.

The seed yield of Chinese milk vetch directly affects the benefit of seed reservation.As seen in Table 5,it can be shown that the seed yield ofXiangzi 2 was obviously higher than that of the other varieties.The average seed yield of Xiangzi 2 in 4 a was 645 kg/hm2, which was respectively higher than that of Xiangfei 2,Xiangfei 3,Yujiangdaye and Xinyang variety by 26.8%,70.4%,31.6%and 59.1%.

Table 3 The nutrient content in different Chinese milk vetch varieties at the full-bloom stage %

Conclusions and Discussions

Through variety observation and comparison, it can be found that Xiangzi 2 has its unique varietal characteristics,and it is more aligned with the requirements of winter green manure in double-rice cropping region than the other four Chinese milk vetch varieties.

(1)The growth period of Xiangzi 2 is short, thus it is suitable to grow in double-rice cropping region. Its suitable sowing date is from the end of October to the beginning of November after the harvesting of late rice, and it also can be interplanted under the late rice in the early and middle of October,the full-blossom period is from the midto-end of March to early April, and the mature period is in early May, the whole growth period is about 202 d,the full-bloom stage is obviously earlier than that of Xiangfei 2, Xiangfei 3 and Yujiangdaye, and is similar to that of Xinyang variety. The transplanting time of early season rice in double-rice cropping region of Hunan Province is from late April to early May, Chinese milk vetch generally needs to overturn 5-15 d in advance, thus early-flowering variety Xiangzi 2 and Xinyang variety suit for the double-rice cropping system and will not affect the farm operation of early season rice.

(2)The fresh grass yield of Xiangzi 2 is moderate,and the nutrient content is high. It also has the advantages of vigorous growth, strong growth vigor,strong cold resistance, drought resistance and disease resistance at the seedling stage. Lots of studies have demonstrated that the optimal overturning quantity of Chinese milk vetch in paddy field at the full-bloom stage under modern farming system was about 22 500 kg/hm2[13-14].In the experiment,it was shown that Xinyang Chinese milk vetch is an early-blossoming variety, but its fresh grass yield is too low(it is only 61.5%of Xiangzi 2),thus it can not reach the ideal effect of fertilizing the soil.Xiangfei 2 also can meet the seasonal requirement of doublerice cropping system, but its fresh grass yield at the full-bloom stage is higher than the optimal overturning quantity by 39.9%, if overturning entirely, the operative difficulty index of overturning will be increased and runt early season rice may be caused, if removing parts of them,it will take time and a lot of work.The average yield of extremely early-blossoming Xiangzi 2 at the full-bloom stage is 23 842.5 kg/hm2, which is close to the optimum overturning quantity of Chinese milk vetch, and total N content in fresh grass of Xiangzi 2 at the full-bloom stage is higher than that of all the other varieties, thus the variety shows a good fertility property and is suitable for planting and using in double-rice cropping region.

(3)The low seed yield of Chinese milk vetch in southern paddy field is always the main bottleneck limiting the development of southern Chinese milk vetch seed industry. The seed reservation yield of Chinese milk vetch in southern paddy field is generally about 300-450 kg/hm2, the low seed yield directly affects the seed reservation benefit of Chinese milk vetch.The fullbloom stage of Xiangzi 2 is earlier than that of the other common varieties by 3-10 d,which can effectively avoid the effect of southern rainfall on pollination, in addition, it has strong reproductive capacity, and the seed yield is high, thus it can be popularized quickly, thereby providing the needs for agricultural production.

Table 5 The fresh grass yield at the full-bloom stage and seed yield at the mature period of different Chinese milk vetch varieties kg/hm2

As a green manure crop,Chinese milk vetch not only has the functions of raising soil fertility and improving ecological environment, etc., but also canprovide the nutrition for other crops after overturning for its own nutrient elements like nitrogen, phosphorus and potassium, etc.[15]. The area of double cropping rice in Hunan Province reaches 1 600 000 hm2,these fields of double cropping rice are suitable for Chinese milk vetch planting. In the experiment, the results showed that Xiangzi 2 is an extremely early-blossoming and early-maturing Chinese milk vetch variety with moderate fresh grass yield, high nutrient contents,stable characters and wide adaptability.So, it is suitable for planting in double-rice cropping region in Hunan Province and other same latitude regions which have similar ecological conditions.

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