Method for improving productivity of alfalfa grassland in semi-arid region

Abstract

The application discloses a method for improving productivity of alfalfa grassland in semi-arid area, which comprises the following steps: sowing in the same period strip sowing mode of planting one row of alfalfa every two rows of feed oat; harvesting mixed forage of alfalfa and feed oat only once in the first year, and not ploughing the land after mowing; in the second year, sowing two rows of feed oat in the alfalfa row without ploughing from late April to early May after the alfalfa turns green; harvesting mixed forage of alfalfa and feed oat in the first harvest in the second year; harvesting alfalfa grass in the second and third harvests; in the third year and the following years, sowing two rows of feed oat in the alfalfa row without ploughing after the alfalfa turns green from late April to early May; in the third year and the following years, harvesting mixed forage of alfalfa and feed oat in the first harvest at the initial flowering period of alfalfa in late June; and harvesting alfalfa grass in the second and third harvests. The application has high utilization rate of natural precipitation, does not need irrigation, has high yield, and can effectively improve the productivity of alfalfa grassland in semi-arid area.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of crop cultivation method, and particularly relates to a method for improving productivity of alfalfa grassland in semi-arid region. BACKGROUND

[0002] In China, dry land is mainly distributed in the north of the Huaihe River, the Qinling Mountains and the Kunlun Mountains. Dry land agricultural production accounts for 58% of the country's grain and more than 75% of beef and mutton, and also covers more than 70% of the ecologically fragile areas. Therefore, in the semi-arid region with relatively less rainfall, promoting the development of agriculture and animal husbandry is of great significance to ensure national food security and ecological security.

[0003] In recent years, with the rapid development of China's animal husbandry, the planting area of alfalfa (Medicago sativa L. Medicago sativa L. , hereinafter referred to as "alfalfa") has been increasing, and alfalfa has become the most important perennial legume forage grass in the vast northern dry land areas of Northwest China, North China and Northeast China. However, in order to obtain high yield, the traditional planting method of dry land alfalfa monoculture or mixed planting with perennial gramineous forage grasses requires multiple irrigation every year, resulting in a large consumption of underground water, which not only increases the production cost of planting enterprises, but also aggravates the ecological pressure in the northern dry land area.

[0004] Therefore, there is an urgent need in the prior art for a mixed planting method for improving the productivity of alfalfa grassland in semi-arid region, which has high utilization rate of natural precipitation, does not require irrigation, and has high yield. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art and provide a method for improving the productivity of alfalfa grassland in semi-arid region, which has high utilization rate of natural precipitation, does not require irrigation, and has high yield.

[0006] The purpose of the present application is achieved by the following technical solution: a method for improving the productivity of alfalfa grassland in semi-arid region, comprising the following steps:

[0007] 1) Selection of suitable region

[0008] Selecting uncultivated land or low-yield land in the farming-pastoral ecotone of the northern semi-arid region without irrigation;

[0009] 2) Pre-sowing preparation

[0010] In the fall of the year before sowing, ploughing, removing the residues of the previous crop, and fertilizing are carried out;

[0011] 3) Sowing in the first year

[0012] Select alfalfa and forage oat varieties suitable for planting in the semi-arid region of northern China, and sow the seeds on the same day after treatment; under dry farming conditions, choose the middle to late May when the rainy season arrives to sow seeds; according to the same period strip sowing method of planting one row of forage oats every two rows of alfalfa;

[0013] 4) First year field management

[0014] Weed control, fertilization, pest control;

[0015] 5) First year harvest and storage

[0016] Only one harvest of mixed forage grass of alfalfa and forage oats is made in the first year before the first frost to ensure the safe overwintering of alfalfa; mowing is carried out in clear weather, and the stubble height is 6-8 cm; after mowing, the land is not plowed, which facilitates the accumulation and conversion of more organic matter by alfalfa and forage oat root systems in the winter;

[0017] 6) Second year sowing

[0018] In the second year, after the alfalfa turns green, 2 rows of forage oats are sown in the alfalfa row without tillage in late April to early May when it rains;

[0019] 7) Second year field management

[0020] From the second year, the perennial alfalfa has been successfully planted, and other weeds in the field grow very weakly, so no weed control is performed; fertilization, pest control;

[0021] 8) Second year harvest and storage

[0022] 2-3 harvests are made in the north dry land; the first harvest of mixed forage grass of alfalfa and forage oats: mowing is carried out in clear weather in late June when alfalfa is in the early flowering stage, and the stubble height is 6-8 cm; the second and third harvests of alfalfa grass: mowing is carried out in clear weather in late July and late August when alfalfa is in the early flowering stage, and the stubble height is 6-8 cm.

[0023] 2. A method for improving the productivity of dryland alfalfa grassland in a semi-arid region, further comprising the following steps:

[0024] 9) Third year and subsequent sowing

[0025] In the third year and subsequent years, after the alfalfa turns green, 2 rows of forage oats are sown in the alfalfa row without tillage in late April to early May when it rains, and no seed fertilizer is applied from the third year;

[0026] 10) Third year and subsequent field management

[0027] In the third year and later, perennial alfalfa has been successfully planted, and other weeds in the field grow very weakly, and no weed control is needed in the third year and later, fertilization, pest control;

[0028] 11) Storage in the third year and later

[0029] In the third year and later, 2-3 cuts of forage grass are harvested annually in the dry land of the north; the first cut of alfalfa and oat mixed forage is harvested: in late June when alfalfa is in the initial flowering stage, mowing is carried out on sunny days, and the stubble height is 6-8 cm; the second and third cuts of alfalfa grass are harvested: in late July and late August, respectively, when alfalfa is in the initial flowering stage, mowing is carried out on sunny days, and the stubble height is 6-8 cm.

[0030] In the step 9), the oat forage is sown at a rate of 10-15 kg / acre, and the sowing depth is 4-5 cm. After sowing, shallow covering and timely pressing are performed.

[0031] In the step 10), fertilization: when alfalfa is in the branching stage, 150 kg of urea per hectare is applied by scattering with rainfall; pest control: according to the occurrence condition, unmanned aerial vehicle is used for spraying insecticide, and pesticide is stopped 10 days before harvesting.

[0032] In the step 2), the plowing depth of abandoned land or low-yield land is 30 cm, and after plowing, the land is leveled with a harrow; 15 days before sowing, herbicides are used to remove weeds and remove the remnants of the previous crop; organic fertilizer is applied before sowing, and the fertilization amount is 10000-15000 kg / hm2.

[0033] In the step 3), alfalfa selects varieties with autumn dormancy level ≤4 and cold resistance index ≤2, and oat forage selects varieties with medium-late maturity, strong stress resistance, and high yield and quality; the purity of the selected seeds is above 98%, and the germination rate is above 85%; seed treatment: commercial alfalfa nodule bacteria agent is prepared into a bacterial solution according to the usage instruction, sprayed on alfalfa seeds, and fully stirred uniformly, or directly used for seed dressing with dry powder; precision seeding machine is used for sowing, the row spacing is 20 cm, the alfalfa sowing amount is 2-2.5 kg / acre, the sowing depth is 1-2 cm, the oat forage sowing amount is 10-15 kg / acre, the sowing depth is 4-5 cm, and 15 kg / acre of compound seed fertilizer is applied integrally in strips during sowing, and shallow covering and timely pressing are performed after sowing.

[0034] In the step 4), weed control: when the alfalfa seedling height is 10-15 cm, intertillage is performed once; fertilization: when alfalfa is in the branching stage, 150 kg of urea per hectare is applied by scattering with rainfall; pest control: prevention is given priority to, and according to the occurrence condition, unmanned aerial vehicle is used for spraying insecticide, and pesticide is stopped 10 days before harvesting; other measures: during the growth of forage grass, livestock and poultry are prevented from entering the grassland to feed;

[0035] In the step 6), the forage oat is sowed at 10-15 kg / acre, and sowed at 4-5 cm deep, and the compound seed fertilizer is sowed at 15 kg / acre at the same time, and then shallowly covered and timely pressed.

[0036] In the step 7), fertilization: when the alfalfa is in the branching period, 150 kg of urea per hectare is applied by spraying along with the rainfall; pest control: the pest control is mainly prevention, and the unmanned aerial vehicle is used to spray the pesticide according to the occurrence condition, and the pesticide is stopped 10 days before the harvest.

[0037] The beneficial effects of the present application are: 1. The present application selects the mixed sowing of alfalfa and annual high-quality drought-resistant forage oat, in the first year of growth, fully utilizes the characteristics of high utilization rate of natural rainfall and rapid growth of the annual forage oat, effectively inhibits other weeds, reduces the invasion of weeds on the alfalfa in the planting year, and thus reduces the production cost required for weed control.

[0038] 2. The present application selects the mixed sowing of alfalfa and annual forage oat, and from the second year, on the basis of the successful planting of the perennial alfalfa, the growth of other weeds is weak, the forage oat is sowed again in the row, the water evaporation in the field is reduced, the utilization efficiency of the forage grass on the natural rainfall under the drought condition is improved, and the technical problem of large water consumption of the alfalfa grassland under the drought condition in the semi-arid area is effectively solved.

[0039] 3. Through the mixed sowing method of 1 row of alfalfa and 2 rows of forage oat, not only the biological nitrogen fixation effect of the legume forage alfalfa is fully utilized, the nitrogen in the atmosphere is transferred to the soil, and the forage oat of the gramineous forage is utilized, but also the utilization rate of the light and heat resources on the ground is effectively improved, so that the purpose of significantly increasing the yield and quality of the forage is achieved, and the technical problem of low yield of the alfalfa single sowing under the drought condition in the semi-arid area is effectively solved. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a column chart of the influence of single sowing and different mixed sowing modes on the yield of forage grass;

[0041] Figure 2 is a column chart of the influence of single sowing and different mixed sowing modes on the forage oat height in the planting year;

[0042] Figure 3 is a column chart of the influence of single sowing and different mixed sowing modes on the stem-leaf ratio of forage oat in the planting year;

[0043] Figure 4 is a column chart of the influence of single sowing and different mixed sowing modes on the tillering number of forage oat in the planting year. DETAILED DESCRIPTION

[0044] The present application will be described in detail below in combination with the drawings. EMBODIMENT

[0045] 1 Materials and methods

[0046] 1.1 Test site

[0047] The test site was located in Ma Dianjian Gou village, Xingyang Town, Zhengyan Banner, Xilingol League, Inner Mongolia (42°05′N, 114°05′E, average altitude 1200 m). The region belongs to the climate of the middle temperate continental arid, large diurnal temperature difference, sufficient light, and rainy and hot season. The precipitation is less and concentrated, the annual average precipitation is 351 mm, the annual average temperature is 1.9℃, the average temperature of the coldest month is-19.1℃, and the average temperature of the hottest month is 17.6℃. The frost-free period is about 120 days, the effective accumulated temperature of ≥10℃ is 2000℃-2350℃, the sunshine hours of the pasture growing period (May-September) is about 1350 hours, and the soil is mainly chestnut soil.

[0048] 1.2 Test materials

[0049] The test selected forage oat of Gramineae and alfalfa, forage soybean and arrow pea of Leguminosae as research materials. The oat variety for the test was “Qingshuihe Oat” from the Seedling Station of Qingshuihe County, Hohhot City, Inner Mongolia Autonomous Region; the alfalfa variety for the test was “Zhongcao No. 13” from the Grassland Institute of Chinese Academy of Agricultural Sciences; the forage soybean variety for the test was “Guixia No. 3” from the Guangxi Zhuang Autonomous Region Academy of Agricultural Sciences; and the arrow pea variety for the test was “Qingshuihe Arrow Pea” from the Seedling Station of Qingshuihe County, Hohhot City, Inner Mongolia Autonomous Region.

[0050] 1.3 Test design and field management

[0051] The test adopted a completely randomized block design, and 9 treatments were set, including 5 mixed planting (intercropping) treatments: forage oat / forage soybean 2:1 (2 rows of forage oat + 1 row of forage soybean), forage oat / alfalfa 2:1 (2 rows of forage oat + 1 row of alfalfa), forage oat / alfalfa 3:1 (3 rows of forage oat + 1 row of alfalfa), forage oat / arrow pea 2:1 (2 rows of forage oat + 1 row of arrow pea), and forage oat / arrow pea 3:1 (3 rows of forage oat + 1 row of arrow pea). There were 4 single planting treatments, including single planting forage oat, single planting forage soybean, single planting alfalfa, and single planting arrow pea. Each treatment was set with 3 replicates. The plot area was 20 m 2(4 m × 5 m), and a 50-cm isolation strip was set between plots. On June 1, 2022, the seeding rate of forage oat, forage soybean, alfalfa, and arrow pea was 225, 60, 22.5, and 90 kg / hm2, respectively. The seeding rate of mixed planting (intercropping) was calculated according to the percentage of single planting. The row spacing was 20 cm. The seeding depth of forage oat, forage soybean, and arrow pea was 4-5 cm, and that of alfalfa was 1-2 cm. During the seedling stage, the plots were manually weeded and irrigated in a timely manner. When the forage oat was at the jointing stage, urea was applied to all plots at a rate of 150 kg / hm2. At the end of August 2022, all plots were harvested for forage, and the stubble height of alfalfa was 5-7 cm. The land was not plowed after harvesting.

[0052] In mid-April 2023, two rows of forage oat were sown in the inter-row of the 2:1 mixed planting plot of forage oat / alfalfa after the alfalfa turned green. The seeding rate of forage oat was 12 kg / acre, and the seeding depth was 5 cm. Compound fertilizer was applied at a rate of 15 kg / acre during sowing. After sowing, the soil was lightly covered and timely pressed. Since the alfalfa had been successfully planted the following year, the growth of other weeds in the field was very weak, and weed control was not necessary. When the alfalfa was at the branching stage, 150 kg of urea per hectare was applied with rainfall by spraying. Pest control was mainly preventive, and pesticides were sprayed by unmanned aerial vehicles according to the occurrence. Ten days before harvesting, pesticides were stopped. Under the experimental conditions, three crops of forage were harvested each year. The first crop of mixed grass of alfalfa / forage oat was harvested in late June during the initial flowering period of alfalfa. The weather was sunny, and the stubble height was 8 cm. Drying, baling, and storage were completed within 7 days after mowing. The second and third crops of alfalfa grass were harvested in late July and late August, respectively, during the initial flowering period of alfalfa. The weather was sunny, and the stubble height was 6-8 cm. Drying, baling, and storage were completed within 7 days after mowing.

[0053] In mid-April 2023, two rows of forage oat were sown in the inter-row of the 2:1 mixed planting plot of forage oat / alfalfa after the alfalfa turned green. The seeding rate of forage oat was 12 kg / acre, and the seeding depth was 5 cm. Compound fertilizer was applied at a rate of 15 kg / acre during sowing. After sowing, the soil was lightly covered and timely pressed. Since the alfalfa had been successfully planted the following year, the growth of other weeds in the field was very weak, and weed control was not necessary. When the alfalfa was at the branching stage, 150 kg of urea per hectare was applied with rainfall by spraying. Pest control was mainly preventive, and pesticides were sprayed by unmanned aerial vehicles according to the occurrence. Ten days before harvesting, pesticides were stopped. Under the experimental conditions, three crops of forage were harvested each year. The first crop of mixed grass of alfalfa / forage oat was harvested in late June during the initial flowering period of alfalfa. The weather was sunny, and the stubble height was 8 cm. Drying, baling, and storage were completed within 7 days after mowing. The second and third crops of alfalfa grass were harvested in late July and late August, respectively, during the initial flowering period of alfalfa. The weather was sunny, and the stubble height was 6-8 cm. Drying, baling, and storage were completed within 7 days after mowing.

[0054] 1.4 Index determination and method

[0055] The test was conducted in mid-August 2022 and 2023.

[0056] 1.4.1 Plant height

[0057] In the plot, 10 plants with uniform growth were randomly selected, and the absolute height from the base to the top of the plant was measured with a tape measure as the plant height.

[0058] 1.4.2 Number of branches / tillers

[0059] In the plot, 10 plants with uniform growth vigor were randomly selected for each species, and the number of tillers was counted for grasses and the number of branches was counted for legumes.

[0060] 1.4.3 Forage yield

[0061] In the center of the plot, a 1 m × 1 m quadrat was selected, and all forages in the quadrat were cut to a stubble height of 5 cm. The forages were then separated and packaged in envelopes, labeled, and brought back to the laboratory. They were then killed in a 105℃ oven for 30 minutes and dried at 65℃ for 48 hours until constant weight. The dry forage yield of each forage was calculated.

[0062] 1.4.4 Stem-leaf ratio

[0063] In the plot, 10 plants were randomly selected for each species, and the stems and leaves were separated. They were then killed in a 105℃ oven for 30 minutes and dried at 65℃ for 48 hours until constant weight. The dry weight of the stems and leaves was then measured. The stem-leaf ratio was calculated using the following formula:

[0064]

[0065] 1.5 Data processing

[0066] Data was processed using Excel 2010 software, analyzed using IBM SPSS 22.0 software, and plotted using GraphPad Prism10 software.

[0067] 2 Results and analysis

[0068] 2.1 Effect of different mixed planting modes on forage yield in the planting year

[0069] For example Figure 1As shown, compared with single cropping of forage oat, the yield of forage oat / forage soybean 2:1 mixed cropping, forage oat / alfalfa 2:1 mixed cropping and forage oat / arrow pea 3:1 mixed cropping increased by 1.5%, 114% and 34% respectively. Among them, the yield of forage oat / alfalfa 2:1 mixed cropping was the highest, which could reach 4110.6 kg / hm2 on average; the yield of forage oat / alfalfa 3:1 mixed cropping and forage oat / arrow pea 2:1 mixed cropping decreased; compared with single cropping of forage soybean, the yield of forage oat / forage soybean 2:1 mixed cropping decreased by 64%; compared with single cropping of alfalfa, the yield of forage oat / alfalfa 2:1 mixed cropping increased by 63% compared with single cropping, but the yield of forage oat / alfalfa 3:1 mixed cropping decreased by 25% compared with single cropping; compared with single cropping of arrow pea, the yield of single cropping of arrow pea was higher than that of forage oat / arrow pea 2:1 mixed cropping and forage oat / arrow pea 3:1 mixed cropping, and the yield of mixed cropping decreased.

[0070] In summary, from the perspective of forage yield, the yield of forage oat / alfalfa 2:1 mixed cropping was the highest, and the production advantage was obvious compared with single cropping of forage oat and single cropping of alfalfa.

[0071] 2.2 Effects of different mixed cropping modes on plant height, stem-leaf ratio and tiller number of forage oat in the planting year

[0072] Plant height is the main factor determining the single plant biomass of forage grass, such as Figure 2 As shown in the table Figure 2 Among them, a, b and c represent the significance of difference, and the same letter above the column represents no difference, and different letters above the column represent significant difference, Figures 3-4 Among them, a, b, c, d, e and f all mean this), under different mixed cropping treatments, the plant height of forage oat in forage oat / forage soybean 2:1 mixed cropping and forage oat / arrow pea 2:1 mixed cropping was significantly higher than that in single cropping of forage oat (P<0.05), among them, the plant height of forage oat in forage oat / arrow pea 2:1 mixed cropping increased by 17.4% compared with single cropping. But there was no significant difference between forage oat / forage soybean 2:1 mixed cropping and forage oat / arrow pea 2:1 mixed cropping (P>0.05). The plant height of forage oat in forage oat / alfalfa 3:1 mixed cropping was the lowest, and the difference was significant (P<0.05). There was no significant difference in the rest of the mixed cropping treatments. There was no obvious difference in the plant height of forage oat in forage oat / alfalfa 2:1 mixed cropping compared with single cropping.

[0073] As for the stem-leaf ratio, from Figure 3The stem-leaf ratio of the forage oat in the forage oat / alfalfa 3:1 mixed planting treatment and the forage oat / arrow pea 2:1 mixed planting treatment was significantly lower than that in the forage oat monoculture treatment, and the stem-leaf ratio of the forage oat in the other mixed planting treatments was significantly higher than that in the monoculture treatment (P<0.05). The quality of the forage oat was higher in the forage oat / forage soybean 2:1 treatment, the forage oat / arrow pea 3:1 treatment, and the forage oat / alfalfa 2:1 mixed planting treatment.

[0074] As shown in Table 2, different planting methods had no significant effect on the tiller number of the forage oat (P>0.05). Figure 4

[0075] In the forage oat monoculture and different mixed planting modes, the forage oat / alfalfa 2:1 mixed planting treatment had no significant effect on the height and tiller number of the forage oat, but the stem-leaf ratio of the forage oat was significantly higher than that in the monoculture treatment, and the quality of the forage oat was improved.

[0076] 2.3-year forage oat / alfalfa mixed planting (intercropping) effect on forage yield

[0077] Through the comparison of the effects of the mixed planting methods in the planting year on the forage yield, it was found that the forage oat / alfalfa mixed planting (intercropping) had higher comprehensive benefits than the forage oat / yearling forage soybean and arrow pea mixed planting in the semi-arid region of the north. Therefore, from the second year, the effects of the forage oat monoculture, the alfalfa monoculture, the one-row alfalfa + two-row forage oat mixed planting, and the one-row alfalfa + three-row forage oat mixed planting on the total fresh forage yield were compared in the selected forage oat / alfalfa mixed planting (intercropping) planting mode. It was found that the total fresh forage yield in the one-row alfalfa + two-row forage oat mixed planting was the highest, reaching 2533.3 kg / acre, which was increased by 26.2%, 93.2%, and 86.4% compared with the one-row alfalfa + three-row forage oat mixed planting, the alfalfa monoculture, and the forage oat monoculture, respectively. In summary, the forage yield of the one-row alfalfa + two-row forage oat mixed planting was the highest in the two consecutive years under the experimental conditions, and the economic benefit was considerable.

[0078] Table 1 Change characteristics of forage yield in the second year under different planting methods

[0079] Planting pattern Fresh grass yield of the first crop (kg / acre) Fresh grass yield of the second crop (kg / acre) Total fresh grass yield (kg / acre) Feed oat monoculture - 1359.2 1359.2 Alfalfa monoculture 932.5 378.9 1311.4 One row of alfalfa + two rows of feed oat 1486.1 1047.2 2533.3 One row of alfalfa + three rows of feed oat 1113.9 893.8 2007.7

[0080] Note: "-" indicates that the forage oat is an annual forage, and therefore can only be harvested once a year; while the alfalfa is a perennial forage, and can be harvested twice a year in the experimental planting area.

[0081] ​Finally, it should be noted that the above is only to illustrate the technical solutions of the present application, and is not a limitation on the scope of protection of the present application, and simple modifications or equivalent replacements of the technical solutions of the present application by those skilled in the art do not deviate from the essence and scope of the technical solutions of the present application.

Claims

1. A method of increasing productivity of dryland alfalfa fields in semiarid regions, characterized in that It comprises the following steps: 1) suitable region selection Selecting the abandoned land or low-yield land without irrigation in the farming-pastoral ecotone of the semi-arid region in the north of China; 2) preparation before sowing In the autumn of the previous year, plough the land, remove the residues of the previous crops before sowing, and apply fertilizers; 3) sowing in the first year Selecting the alfalfa and feed oat varieties suitable for planting in the semi-arid region in the north of China, and sowing the seeds on the same day after the seed treatment; under the dry farming condition, sowing is carried out in the middle to late May when the rainy season comes; the sowing is carried out in the same period by strip sowing with one row of alfalfa and one row of feed oat every two rows; 4) field management in the first year Weeding, fertilization, and pest control; 5) harvesting and storage in the first year In the first year, only one batch of mixed forage of alfalfa and feed oat is harvested before the first frost to ensure the safe overwintering of alfalfa; the harvesting is carried out in clear weather, and the stubble height is 6-8 cm; after the harvesting, the land is not ploughed, which is beneficial to the accumulation and transformation of more organic matter by the alfalfa and feed oat root systems in the winter; 6) sowing in the second year In the late April to early May of the second year, two rows of feed oat are sown in the alfalfa rows without ploughing after the alfalfa turns green; 7) field management in the second year In the second year, the perennial alfalfa has been successfully planted, and the growth of other weeds in the field is very weak, so no weeding is carried out; fertilization and pest control are carried out; 8) harvesting and storage in the second year 2-3 batches of forage are harvested in the north of China; the first batch of mixed forage of alfalfa and feed oat is harvested: in the late June when the alfalfa is in the initial flowering period, the harvesting is carried out in clear weather, and the stubble height is 6-8 cm; the second batch and the third batch of alfalfa forage are harvested: in the late July and the late August, respectively, when the alfalfa is in the initial flowering period, the harvesting is carried out in clear weather, and the stubble height is 6-8 cm; 9) sowing in the third year and the following years In the third year and the following years, after the alfalfa turns green, two rows of feed oat are sown in the alfalfa rows without ploughing in the late April to early May when the rainfall comes, and no seed fertilizer is applied from the third year; 10) field management in the third year and the following years In the third year and the following years, the perennial alfalfa has been successfully planted, and the growth of other weeds in the field is very weak, so no weeding is carried out in the third year and the following years; fertilization and pest control are carried out; 11) harvesting and storage in the third year and the following years In the third year and the following years, 2-3 batches of forage are harvested in the north of China every year; the first batch of mixed forage of alfalfa and feed oat is harvested: in the late June when the alfalfa is in the initial flowering period, the harvesting is carried out in clear weather, and the stubble height is 6-8 cm; the second batch and the third batch of alfalfa forage are harvested: in the late July and the late August, respectively, when the alfalfa is in the initial flowering period, the harvesting is carried out in clear weather, and the stubble height is 6-8 cm.

2. The method for increasing productivity of alfalfa grassland in semi-arid region according to claim 1, characterized in that: In the step 9), the sowing amount of feed oat is 10-15 kg per mu, and the sowing depth is 4-5 cm, and after sowing, the land is shallowly covered and timely pressed.

3. The method for increasing productivity of alfalfa grassland in semi-arid region according to claim 1, characterized in that: In the step 10), fertilization: when the alfalfa is in the branching period, 150 kg of urea per hectare is applied by scattering with rainfall; pest control: according to the occurrence condition, the pesticide is sprayed by using the unmanned aerial vehicle, and the pesticide is stopped 10 days before the harvesting.

4. The method for increasing productivity of alfalfa grassland in semi-arid region according to claim 1, characterized in that: In the step 2), the plowing depth of the abandoned land or the low-yield field is 30 cm, and the land is leveled after plowing; weeds are removed 15 days before sowing by using a herbicide, and the residues of the previous crop are removed; organic fertilizer is applied before sowing, and the application amount is 10,000-15,000 kg / hm2.

5. The method for increasing productivity of alfalfa grassland in semi-arid region according to claim 1, characterized in that: In the step 3), the alfalfa is selected from the varieties with the dormancy level of less than or equal to 4 and the cold resistance index of less than or equal to 2, and the forage oat is selected from the varieties with the middle-late maturity, strong stress resistance and high yield and quality; the purity of the selected seeds is more than 98%, and the germination rate is more than 85%; the seed treatment is that a commercial alfalfa nodule bacteria agent is prepared into a bacteria solution according to the usage instruction, the bacteria solution is sprayed on the alfalfa seeds, and the seeds are uniformly stirred, or the seeds are directly treated by using dry powder; the seeds are sown by using a precision seeder, the sowing row spacing is 20 cm, the sowing amount of the alfalfa is 2-2.5 kg / mu, and the sowing depth is 1-2 cm; the sowing amount of the forage oat is 10-15 kg / mu, the sowing depth is 4-5 cm, and a composite seed fertilizer is integrally strip-applied at a rate of 15 kg / mu; and the land is shallowly covered and timely pressed after sowing.

6. The method for increasing productivity of alfalfa grassland in semi-arid region according to claim 1, characterized in that: In the step 4), weed control: when the alfalfa is at the seedling stage with a height of 10-15 cm, the weeds are removed once by intertillage; fertilization: when the alfalfa is at the branching stage, 150 kg of urea is applied per hectare by using a scattering method; disease and pest control: the disease and pest control is mainly prevention, a pesticide is sprayed by using a drone according to the occurrence condition, and the pesticide is stopped from being used 10 days before harvesting; and other measures: livestock and poultry are prevented from entering the grassland to forage during the growth of the forage grass.

7. The method for increasing productivity of alfalfa grassland in semi-arid region according to claim 1, characterized in that: In the step 6), the sowing amount of the forage oat is 10-15 kg / mu, the sowing depth is 4-5 cm, a composite seed fertilizer is integrally strip-applied at a rate of 15 kg / mu during sowing, and the land is shallowly covered and timely pressed after sowing.

8. The method for increasing productivity of alfalfa grassland in semi-arid region according to claim 1, characterized in that: In the step 7), fertilization: when the alfalfa is at the branching stage, 150 kg of urea is applied per hectare by using a scattering method; and disease and pest control: the disease and pest control is mainly prevention, a pesticide is sprayed by using a drone according to the occurrence condition, and the pesticide is stopped from being used 10 days before harvesting.

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