Abstract:

The aims of this study were to clarify the effects of grass intercropping density in a jujube （Zizyphus jujuba）-grass intercropping system， and to elucidate the mechanisms by which grass intercropping density regulates system productivity， resource competition and complementarity， and sustainability. We aimed to determine the optimal between-row intercropping density of ryegrass （Lolium perenne） in a Lingwu Changzao jujube orchard located in the arid， sandy region of northwestern China. Field experiments were conducted in 2023 and 2024 in a representative Lingwu Changzao orchard. The experiment had five treatments： jujube monoculture （J）， ryegrass monoculture （G）， and intercropping with ryegrass sown at 15.0 kg·ha^-1 （J-G15）， 22.5 kg·ha^-1 （J-G22.5）， and 30.0 kg·ha^-1 （J-G30）. The impact of ryegrass sowing density in the intercropped strip on the land equivalent ratio （LER）， productivity， and competitive interactions and sustainability of the jujube-grass intercropping system was evaluated. The results show that the density of ryegrass intercropping significantly affected jujube and grass yields， as well as LER （P<0.05）. The yields of both jujube and grass were highest in the J-G22.5 treatment， with the 2-year jujube yields increased by 53.69% and 29.62%， while grass yields increased by 12.14% and 12.26%， respectively， compared with those in J and G. There were highly significant interannual differences in the yields of both jujube and grass （P<0.001）， with higher overall values in 2024 than in 2023. All intercropping treatments had a LER of >1， demonstrating a clear intercropping advantage. The maximum values of LER （2.51 and 2.42） were in the J-G22.5 treatment. This treatment also outperformed the others in terms of yield increase rate， competitive index （CI）， net effect， complementarity effect， and selection effect. Principal component and correlation analyses indicated that yield was strongly and positively correlated with net effect， complementarity effect， and CI （P<0.001）. This suggests that interspecific complementarity and coordinated resource use are key mechanisms underlying yield gains in this intercropping system. The sustainability analysis showed that the J-G22.5 and J-G30 treatments were more sustainable than the J-G15 treatment， with CI and the selection effect being the primary weighting factors. Overall， integrating productivity， competition， complementarity， and sustainability， 22.5 kg·ha^-1 is recommended as the optimal between-row sowing density for intercropped ryegrass in Lingwu Changzao jujube orchards in the arid sandy region of northwest China.

Key words: jujube-grass intercropping system, grass intercropping densities, yield, productivity, sustainability