Productivity And Natural Resource Use Efficiency Of Common Vetch–oat Intercropping System

Common vetch?Vicia sativa?-oat?Avena sativa?intercropping is a widely practiced production system in many temperate regions around the world.Compared with monocrops,this intercropping system has greater productivity and benefits.It also plays an important role in providing high-quality forage for grass-feeding livestock and ensuring food safety.To provide theoretical and technical support for common vetch-oat intercropping systems,two field experiments were conducted over a four-year period from 2014–2017 in Xiahe County,Gannan Tibetan Autonomous Prefecture in Gansu Province.The study area is a typical alpine region.In Experiment 1?a three-year field experiment during the growing seasons in 2014–2016?three newly developed common vetch cultivars?Lanjian No.1,Lanjian No.2,and Lanjian No.3?and an oat cultivar?Qingyin No.2?were selected for study and planted either as monocultures?three vetch cultivars and one oat cultivar?,or with vetch and oats intercropped in alternate rows?three vetch-oat cultivar combinations?.In Experiment 2?a two-year field experiment during the growing seasons in 2016–2017?common vetch cultivar Lanjian No.2 and oat cultivar Qingyin No.2 were selected for study and planted as monocultures and in seven different vetch:oat intercropped planting configurations;alternate rows?vetch:oat row configuration 1:1,RI?and six‘alternate strip'treatments with vetch:oat row configurations 2:1?S21?,3:1?S31?,3:2?S32?,4:2?S42?,4:3?S43?,and 5:3?S53?.In both experiments,system productivity,photosynthetic characters and radiation use efficiency of the two crop species were evaluated,and laboratory analyses of plant and soil nutrient status in the various treatments were conducted.The main results were as follows:1.In Experiment 1,common vetch-oat alternate-row intercropping significantly increased the system productivity,with the intercropping advantage differing between common vetch cultivars.For the intercropped vetch-oat systems harvested at flowering,the average aboveground biomass yield of oats intercropped with the three common vetch cultivars Lanjian No.1,Lanjian No.2 and Lanjian No.3 were,respectively,51%,70%,and 79%greater than the oat monoculture on an equivalent basis of comparable land area?P<0.05?.Meanwhile,biomass yields of Lanjian No.1,Lanjian No.2 and Lanjian No.3 in intercropping systems were 37%,26%,and 24%lower,respectively,than the corresponding common vetch monoculture on an equivalent basis of comparable land area?P<0.05?.Thus,the weighted average values of aboveground biomass advantage for the three intercrop systems were,respectively,7638 kg ha^-1,8197 kg ha^-1,and 8555 kg ha^-1 and these values were,respectively,21%,44%,and 52%greater than the corresponding monocultures.The land equivalent ratios?LER?of the Lanjian No.1,2,and 3 intercropping systems were 1.07,1.21,and 1.27,respectively.The latter two values were significantly greater?P<0.05?than that of Lanjian No.1.2.In Experiment 2,intercropping of vetch cultivar Lanjian No.2 with oats harvested at the flowering stage again significantly increased the system productivity and the intercropping advantage differed between the seven row configurations.For the intercropped vetch-oat systems harvested at flowering,the average aboveground biomass yield of oats intercropped with the common vetch cultivar Lanjian No.2 was increased of 64%–94%compared with the oat monoculture on an equivalent basis of comparable land area?P<0.05?.Meanwhile,the biomass yield of Lanjian No.2 in the seven intercropped treatments was decreased of 6%–24%compared with the vetch monoculture on an equivalent basis of comparable land area.The weighted average values of aboveground biomass advantage for the seven intercropping systems were6073 kg ha^–1–8130 kg ha^–1 which was 35%-45%greater than the corresponding monocultures.Among the seven intercropping systems,the aboveground biomass advantage was highest in RI(8130 kg ha^-1)and S32(7588 kg ha^-1).The LER of the various seven intercropping systems ranged from 1.13–1.23,with the highest being S32.3.In both experiments,intercropping systems increased system productivity through increase in plant height,and changed photosynthetic performance and radiation use efficiency?RUE?of both crops.Specifically,in Experiment 1,in alternate-row intercropping systems,the average plant heights of the common vetch cultivars ranged from 105–112 cm,and these values were 28%–44%greater than those of the corresponding monocultures?P<0.05?,while the plant height of oats averaged 162 cm,which was a 13%increase compared to oats in monoculture.In Experiment 2,across the seven row configurations of the intercropped vetch-oat intercropping systems,the plant height of Lanjian No.2 averaged 78–103 cm,which was 2%–35%greater than for monocrops.Lanjian No.2 plant height in the alternate-row,and in S21,S31 and S32treatments was significantly greater than in the monocrops.The plant height of oats was158–164 cm on average,which was 8%–12%greater?P<0.05?than for oats in monoculture.In all the intercropped treatments in both experiments,the net photosynthetic rate?Pn?of common vetch was decreased compared to values in monoculture,with the Pn of Lanjian No.1 decreased by 22%compared to the monocultures?P<0.05?.Meanwhile,the Pn of oats was increased by 15%and 23%?P<0.05?,respectively,in Experiment 1 and Experiment 2 intercropped systems.In both experiments,the RUE of common vetch was decreased compared to the monocultures,but differences between treatments were not statistically significant in most cases.In contrast,the RUE of oats was increased by 44%and 65%?P<0.05?,respectively,in both Experiment 1 alternate-row and the seven Experiment 2 alternate-row and alternate-strip planting configurations.4.Intercropping systems affected the leaf nitrogen content,shoot nitrogen content and shoot phosphorus content of both vetch and oats.In Experiment 1,the leaf nitrogen content of the three common vetch cultivars was decreased by 4.3%–8.5%,compared with the corresponding monocrops;in both experiments,the shoot nitrogen and phosphorus contents of common vetch showed decreases?P<0.05?of between 4.0%and 8.4%,for shoot nitrogen and between 11%and 23%for shoot phosphorus.In Experiment 1,the leaf nitrogen content of oats was increased by 33%–42%in intercropped systems,compared to monocrops,while in both experiments,the shoot nitrogen and phosphorus contents of oats were increased?P<0.05?by amounts ranging from 10%–28%for nitrogen and 17%–45%for phosphorus.In Experiment 1,the crude protein yields in Lanjian No.1,Lanjian No.2 and Lanjian No.3 alternate-row intercropping systems were 673 kg ha^–1,732 kg ha^–1,and 755 kg ha^–1,and these values were,respectively,1.9%,29%,and 37%greater than the weighted average of the corresponding monocrops at the flowering stage.In Experiment 2,the crude protein yields in all seven intercropping systems were 686 kg ha^–1–736 kg ha^–1,which were greater than for the Lanjian No.2 and oat monocrops.In both experiments,intercropping systems had no significant effect on the soil organic carbon content,soil total nitrogen content,or soil total phosphorus content,for the 0–20 cm,20–40 cm,and40–60 cm soil layers,compared with the weighted average of corresponding monocrops.Soil nutrient levels did change between years,but without any obvious pattern.In summary,this study showed that a common vetch-oat intercropping system can significantly increase productivity compared to the corresponding monocultures.Row intercropping and three rows of common vetch alternate strip with two rows of oat performed better.The mechanism of action was mainly through change in photosynthetic characteristics,border row effect,RUE,and soil nutrient utilization in the intercropping systems.