Effects of nitrogen application and intercropping ratio on dry matter production and nitrogen use efficiency of the oat and common vetch intercropping system

Objectives This paper investigated the effects of nitrogen application and different intercropping ratios on dry matter yield, land equivalent ratio (LER) and nitrogen use efficiency of the oat and common vetch intercropping system, in order to provide a theoretical basis for the diverse production of grain and feed crops in the region.

Methods A field experiment was conducted in the oat (Vicia sativa L.) and common vetch (Avena sativa L.) intercropping plots located inside the Qingyang Loess Plateau Experiment Station of Lanzhou University in 2012. Seven oat to vetch intercropping ratios were set up, including 1∶0, 4∶1, 2∶1, 1∶1, 1∶2, 1∶4 and 0∶1 under the condition of N application rate of N 46 kg/hm² (N₄₆) and no nitrogen application (N₀). The dry matter yield, land equivalent ratio, nitrogen uptake were measured in the flowering and milk-ripe stage of common vetch, the amount of biological nitrogen fixation of common vetch was analyzed in the flowering stage, and the partial factor productivity from applied N (PFPN) of the intercropping systems was analyzed in the milk-ripe stage of common vetch.

Results The average total dry matter yields of the intercropping system under N₄₆ were significantly increased by 31.6% and 24.2% compared with those under N₀ at the 60 d (flowering stage) and 90 d (milk-ripe stage) after the emergence. Compared with the common vetch monoculture, at the 60 d and 90 d after the emergence, the dry matter yields of the intercropping system at the N₀ level reached the maximum at the intercropping ratios of 2∶1 and 1∶0, which were increased by 102.5% and 107.9%; at the N₄₆ level those were increased by 103.5% and 111.1% at 1∶ 1 and 4∶1. At the 60 d, the LER values were greater than 1 in all intercropping ratios in the N₀ level, and at the 90 d, the LER values of the intercropping system were less than 1 except for 4∶1 intercropping ratio at the N₄₆ level. The biological nitrogen fixation (BNF) of the common vetch was decreased by 50.6%, and the average N uptake rate of oats was increased by 17.2% after the nitrogen application. The partial factor productivity from the applied nitrogen (PFP_N) of the intercropping system was the highest in the 4∶1 intercropping ratio. Regardless of applied nitrogen or not, compared with common vetch the ratio of nitrogen nutrition competition (CR_OV) of oats was the highest in the 4∶1 intercropping ratio, and then decreased with the increase of the cultivation proportion of common vetch.

Conclusions The nitrogen fertilization promoted the N uptake ratio of oat and the total dry matter production of the system, but decreased the nitrogen fixation amount of the common vetch. The intercropping system had higher crop yield, land equivalent ratio and nitrogen use efficiency in the 4: 1 intercropping ratio.