Exploring the effect of plant nitrogen concentration on the nitrogen nutrition index of winter wheat under controlled irrigation conditions

Mingxia Wang¹Ben Zhao^2*Wanqiang Chu¹Guijun Lv¹Xiaoli Niu³

• ¹School of Hydraulic Engineering, Yellow River Conservancy Technical University, kaifeng, China
• ²College of Tobacco, Henan Agricultural University, Zhengzhou, Henan Province, China
• ³College of Agricultural Equipment Engineering, Henan University of Science and Technology, luoyang, China

The nitrogen nutrition index (NNI) of winter wheat decreases under water deficit conditions, primarily due to an increase in the critical nitrogen concentration (%Nc) associated with a reduction in shoot biomass (SB). However, the influence of plant nitrogen concentration (PNC) on NNI under water deficit conditions remains unclear. This study aimed to: (1) determine whether significant differences exist in PNC and leaf nitrogen concentration (LNC) of winter wheat among different irrigation treatments under rainout shelter conditions; (2) analyze the reasons for changes in PNC and LNC under water deficit conditions; and (3) assess the stability of relationships between PNC and LNC, as well as between plant nitrogen accumulation (NAp) and leaf area index (LAI), across different water treatments. For this purpose, rainout shelter experiments were conducted during the winter wheat growing seasons from 2018 to 2021. The results indicated that water deficit treatments resulted in reduced PNC and LNC values at specific growth stages of winter wheat under controlled conditions. However, such severe water deficits were unlikely to occur in typical field conditions; thus, PNC was not identified as the primary factor affecting NNI in field environments experiencing water deficit. Component analysis clarified the causes behind the decline in PNC and LNC. The reduction in specific leaf area (SLA) and leaf biomass fraction (LBF) contributed to the decrease in PNC, with SLA accounting for more variation than LBF. Similarly, declines in both SLA and specific leaf nitrogen (SLN) resulted in reduced leaf nitrogen content (LNC), with SLN explaining more variation in LNC than SLA across different water treatments. LNC was jointly controlled by PNC and the SLN to LBF ratio. Additionally, the water deficit did not change the proportional linear relationship between NAp and LAI, indicating that the effect of water deficit on PNC and LNC was limited, thus enhancing the understanding of the factors contributing to the decline of NNI.