This study aimed to investigate the response of maize grain yield, quality and water use efficiency (WUE) in the dryland of the Loess Plateau to different ways of carbon returning, and to provide a theoretical basis for high-yield and high-efficiency cultivation of maize in this region.

A maize field experiment was carried out in Dingxi City, Gansu Province, from 2022 to 2023, with one no-carbon returning and four different carbon-increasing treatments of equal carbon amounts: CK, control treatment without carbon returning; S1, biochar returning treatment (0.5×10⁴ kg·hm^-2); S2, straw returning treatment (1.2×10⁴ kg·hm^-2); S3, organic returning treatment (2.0×10⁴ kg·hm^-2); S4: 50% straw returning (0.6×10⁴ kg·hm^-2) combined with 50% organic returning treatment (1.0×10⁴ kg·hm^-2) to study the effects of carbon returning methods on soil moisture, dry matter accumulation and translocation, yield, water use efficiency and grain quality of maize in dryland of Loess Plateau.

Carbon returning treatments reduced soil bulk weight and increased soil porosity in the 0-30 cm soil layer, where S1 treatment significantly increased soil water content in the 0-300 cm soil layer compared with CK treatment. Compared with the CK treatment, S1 treatment significantly decreased the SPAD value and leaf area index (LAI) at flowering stage, whereas S2, S3 and S4 treatments significantly increased the LAI of maize. The aboveground dry matter accumulation at harvest and the maximum rate of dry matter accumulation under S2, S3 and S4 treatment were significantly increased by 10.83%-21.05% and 8.47%-17.13%, respectively, while the dry matter accumulation of maize after anthesis and the contribution of post-flowering dry matter to grain yield significantly increased by 28.58%-54.02% and 11.18%-19.43%, respectively. And then, maize yields significantly increased by 17.22%-29.66%, with S3 demonstrating the most pronounced yield improvement. Conversely, compared with CK, S1 treatment significantly reduced the maximum rate of dry matter accumulation and dry matter accumulation at harvest by 5.31% and 10.32%, respectively, and then decreased grain yield by 7.05%. The S3 treatment significantly increased water use efficiency for grain yield by 23.71% relative to CK, while S1, S2, and S4 showed no significant differences in water use efficiency when compared with CK. Furthermore, compared with CK, S2 treatment significantly reduced grain protein content, while S2, S3, and S4 significantly decreased grain cellulose content. In contrast, S1 treatment significantly increased grain cellulose content compared with CK treatment.

Under carbon applications of 0.5×10⁴ kg C·hm^-2, organic manure application was more effective in improving maize yield and water use efficiency than straw return and biochar return.