Effects of straw incorporation and nitrogen application rate on winter wheat yield and nitrogen utilization

Objectives This study explored the effects of summer maize straw returning and nitrogen (N) application rate on winter wheat yield and N utilization to provide a theoretical basis for efficient summer maize straw and N management.

Methods The experiment was conducted in the Experimental Farm of Shandong Agricultural University from 2019 to 2021. There were six experimental treatments: incorporation of whole maize straw combined with N 210 kg/hm² (SN) and 178.5 kg/hm² (S–15%N), half of the maize straw combined with N 210 kg/hm² (1/2SN) and 178.5 kg/hm² (1/2S–15%N), and no maize straw incorporation with N 210 kg/hm² (CKN) and 178.5 kg/hm² (CK–15%N). The aboveground N accumulation, N nutrition index (NNI), and N fertilizer utilization efficiency of each treatment were analyzed to understand the impact of maize straw returning on wheat yield and N utilization efficiency.

Results The yield of SN, S–15%N, and 1/2SN (P<0.05) were increased by 12.79%, 11.24%, and 12.63%, compared with CKN. The aboveground N accumulation of SN, S–15%N, and 1/2SN (P<0.05) increased by 24.45%, 22.81%, and 23.51%, compared with CKN. The accumulation of soil inorganic N in SN and 1/2SN increased by 4.81% and 3.19% compared with CKN; S–15%N and 1/2S–15%N increased by 8.28% and 5.15% compared with CK–15%N. At the jointing stage, the NNI (P<0.05) decreased, which was 8.14%–25.56% lower than CKN (0.90). The NNI of SN (>1) at post-flowering increased by 28.66% compared with CKN, suggesting that N was surplus in the soil. While the NNI of S–15%N and 1/2SN were 0.98 and 1.08, respectively, the corresponding values increased by 20.66% and 17.45% compared with CKN. This indicated the optimum N content in the soil at the post-flowering stage of wheat. The UPE of wheat (P<0.05) increased with the maize straw returning. The values recorded for SN (16.99%), S–15%N (42.65%), and 1/2SN (27.15%) were higher than CKN. The UTE of SN and S–15%N were (P<0.05) lower than CKN by 10.68% and 8.29%. The NUE of SN, S–15%N, and 1/2SN increased by 10.41%, 29.55%, and 14.19%, compared with CKN.

Conclusions Without reducing the rate of N fertilizer (N 210 kg/hm²), there was no significant difference in wheat yield between the half and full return of summer maize straw. Reduced N fertilizer application by 15% with full maize straw return to the field did not reduce wheat yield but increased N utilization efficiency. Returning half of the maize straw to the field with the same amount of N reduction, on the other hand, reduced wheat yield.