Abstract: 【Objective】An experiment was carried out to investigate the effects of relay intercropping of spring-sown maize and summer-sown maize on dry matter yield and nutritive values of whole-crop forage at different nitrogen level compared with sole cropping.【Method】The effects of relay intercropping at different nitrogen levels on dry matter yield, crude protein yields and crude fat yields of the spring-sown maize, summer-sown maize, and the whole year were studied in a randomized block design. And the reasons of these effects were analyzed from the changes of nitrogen uptake and field microclimate.【Result】Relay intercrops were higher in the annual yields of dry matter, crude protein, and crude fat than either spring-sown maize or summer-sown maize grown as sole crops. The land equivalent ratios of crude protein yield of whole-crop for N1 (187.5 kg•ha-1) and N2 (375 kg•ha-1) were 1.54 and 1.77, respectively. And the land equivalent ratios of crude fat yield of whole-crop for N1 and N2 were 1.39 and 2.55, respectively. In general, the dry matter yield and nutritive values of relay intercrops were lower than those of sole crops. But at N2, the crude fat yield of spring-sown maize in relay intercropping system was higher than that of sole cropping; and no significant differences were observed between the crude protein yield of summer-sown maize relay intercropping and that of sole cropping. The nitrogen uptake of relay intercrops were lower than that of sole crops, but increased with nitrogen applied more quickly. 【Conclusion】 Compared with sole cropping, relay intercropping of spring-sown maize and summer-sown maize can increase the annual nutritive values, which are mainly resulted from nitrogen uptake and field microclimate. In the relay intercropping system, the nutritive values of spring-sown maize are affected greater, while those of summer-sown maize are affected less, because of their different growth stages in coexistence. Increased the application of nitrogen can relax the competition in relay intercropping system, and improve the yield and nutritive values of whole-crop forage.

Key words: maize, mono-cropped, relay-cropped, nitrogen nutrition, nutritive values