Effects Of Common Vetch/Oat Intercropping On Yield And Nutrient Components And Its Mechanism

Common vetch/oat intercropping has been one of the main forage production modes in the Qinghai–Tibetan Plateau,China.This practice is characterized by high yield and good profit.Intercropping plays an important role in solving the shortage of livestock forage in winter and spring in this region.However,little has been reported about the yield and quality of the two crops under different intercropping scenarios,or about the mechanisms whereby the yield of the two crops is increased.The experiment was carried out in Xiahe County,Gannan Tibetan Autonomous Prefecture,Gansu Province from 2019 to 2020,with the common vetch（Vicia sativa）cultivar Lanjian No.2 and the oat（Avena sativa）cultivar Qingyin No.2 as the plant species studied.A total of 12 intercropping configuration processes were set up.The effects of different intercropping systems on yield and nutrient composition were studied,and the mechanism of intercropping effect was discussed by combining the determination of light energy utilization efficiency,nitrogen fixation amount and nitrogen transfer amount.The main results are as follows:1.Different intercropping treatments had significant effects on above ground biomass of oat and common vetch harvested during the vetch flowering and pod bearing（oat grain-filling）stages（P<0.05）.The total aboveground biomasses of the two crops at the flowering stage and pod forming stage ranged from 6097–7560 kg hm^-2 and7831–9793 kg hm^-2,respectively,which was 37%–39%and 29%–41%higher,respectively,than the weighted average forage yield of the monoculture crops at the same growth stage.Among the different intercropping treatments,the highest forage yield at the vetch flowering stage was 7560 kg hm^-2 for treatment R1*40.The highest forage yield at the setting stage（oat grain-filling stage）was 9793 kg hm^-2 for treatment R1*20.In addition,different intercropping treatments had significant effects on seed yield of oats and common vetch（P<0.05）.The seed yields of the two crops were 7101–9295 kg hm^-2 and 1244–1875 kg hm^-2,respectively.In the intercropping treatments,compared with treatment SO,the seed yield of oats was increased by 38.6–81.4%,while common vetch seed yield decreased by 9.0–36.8%（P<0.05）.For different intercropping configurations,the highest seed yield of oat was 9295 kg hm^-2 under the1:3 oat:common vetch intercropping ratio with row spacing of 20cm.The seed yield of common vetch was highest(1969 kg hm^-2)under treatment SV.2.Different intercropping configurations significantly increased the crude protein content of the overall crop in intercropping treatments（P<0.05）and decreased the crude fiber content of oat.Combining the results of two years of field research,at the flowering stage the crude protein content was highest,the crude fiber content was lowest,and profitability was optimized when the oat:vetch seeding ratio was S3*0.As noted above,the highest crude value occurred in treatment R1*40,while the next highest occurred in treatment R1*0 at grain filling maturity（threshing）growth stages.For the combined forage and grain yield of the intercropping treatments,the total crude protein yield ranged from 534–664kg hm^-2,544–833 kg hm^-2 and 544–759 kg hm^-2,respectively,at the flowering,grain filling and post-threshing growth stages.Compared with the weighted average of SO and SV treatments,this increase was,respectively,1.62–39.07%,2.44–13.15%and 5.26–21.79%.For these three growth stages,the highest crude protein yield occurred in treatments R1*40,S4*20,and S4*40,respectively.3.The increase in forage yield of intercropping treatments compared to SO and SV was due in part to increased plant height and increased total photosynthetic use efficiency（PUE）,compared to monocultures.The average plant height of common vetch at 70–73 d（flowering stage）and 113–115 d（maturity stage）after sowing was46.0–65.1 cm and 61.1–95.4 cm,respectively,which was 1–40%and 5–61%higher than in monoculture.At the flowering stage,treatment R1*0 was optimal.However,treatment S2*0 was optimal at the maturity.On the other hand,the average plant height of oats at maturity was 136.7–151.8 cm,which was 1%–12%higher than that of monoculture in the same period.Treatment S2*0 had the highest plant height,attaining151.8 cm.The average plant height of oats at other growth stages was not significantly different from that of oat monoculture（P>0 0.05）.The range for total photosynthetic use efficiency of different intercropping configurations was 0.76–0.97 g MJ^-1,which was 15.66–46.65%higher than the weighted average of the two monocultures（P<0.05）.The highest photosynthetic use efficiency was 0.97 g MJ^-1 in treatment R1*40,followed by 0.95 g MJ^-1 in treatment R1*20.4.The average nitrogen fixation of common vetch measured at the flowering stage was 34.0–41.4 kg hm^-2,and the percentage of biological nitrogen fixation(%N_dfa)ranged from 39.5–48.5%under different mixed or intercropping treatments.Under different intercropping configurations,the total N fixation of common vetch increased with increasing oat sowing ratio per unit area,and the highest N fixation rates of 41.4 kg hm^-2(48.5%N_dfa)was observed in treatments R1*20.The percentage of N(%Ntr_（OAT）)transfered by common vetch to total N varied significantly with sowing proportion（P<0.05）.The range for%Ntr_（OAT）was 11.8–17.8%,and the quantity of nitrogen transferred was 9.52–16.50 kg hm^-2.Among the intercropping arrangements,the highest%Ntr_（OAT）of 17.78%was observed in treatment S4*20.For the purpose of hay mixing,R1*40 was the best treatment during the flowering period,which had the highest yield,light energy utilization efficiency,the highest protein content,relatively low crude fiber content,and the best quality.At the same time,the common vetch had high nitrogen fixation and good nitrogen transfer.According to the results of two years of forage yield,the content of main nutrients and the nitrogen fixation effect and nitrogen fixation turnover of common vetch,the reasonable intercropping distance and the ratio of the number of rows were significantly related to the high quality and high yield of oat and common vetch.