Intercropping combined with nitrogen input promotes proso millet (Panicum miliaceum L.) growth and resource use efficiency to increase grain yield on the Loess plateau of China

Field experiment was performed on the Loess Plateau of China in 2018 and 2019 to investigate the effects of intercropping with nitrogen (N) management on proso millet growth and resource utilization. A split-plot experimental design for the planting pattern (sole proso millet (SP) and proso millet/mung bean intercropping (PM)) and N fertilizer application rate (N0, 0 kg N ha(-1); N60, 60 kg N ha(-1); N120, 120 kg N ha(-1); and N180, 180 kg N ha(-1) for proso millet) was used. Results showed that intercropping combined with N fertilization enhanced the leaf photosynthetic efficiency of proso millet by facilitating stomatal opening, and such improvements were conducive to increasing the maximal quantum yield of PSII photochemistry and the photochemical quenching coefficient. Specifically, intercropping combined with the N120 treatment was an efficient farming practice that increased radiation use efficiency by 18.1 % and 17.9 %, water use efficiency by 60.2 % and 61.8 %, and N uptake by 96.0 % and 71.6 % in 2018 and 2019, respectively, compared with those parameters in the N0 treatment in the sole planting system. Similar improvements were observed for grain yield, which reached maximum values at N120 (6331.8 kg ha(-1) and 6531.3 kg ha(-1) in 2018 and 2019, respectively) in the PM treatment. These responses resulted in an increased harvest index and land equivalent ratio. Consequently, intercropping combined with moderate N inputs reduces the chemical fertilizer application rate and increases crop productivity and is considered to be a reasonable strategy for field management.