Effects of Nitrogen Reduction and Potassium Enhancement Fertilization Mode on Photosynthetic Fluorescence Characteristics and Photosynthetic Product Accumulation of Maize in Ningxia Yellow Irrigation Area

Focusing on the effects of nitrogen reduction and potassium increase fertilization mode on photosynthetic fluorescence characteristics and dry matter accumulation of maize, this paper aimed to elucidate its internal physiological mechanism and provide the theoretical support for the precise fertilization management and green high-yield cultivation of maize nitrogen and potassium.

Field experiments were carried out in Pingjibao Farm, Ningxia from 2023 to 2024, using maize variety Xianyu 1321 as experimental material. The experiment adopted the crack zone design, and the main area was set to different nitrogen application rates, with a total of two levels, namely conventional nitrogen application of 450 kg·hm^-2 (N0) and nitrogen reduction of 30% (N1, 315 kg·hm^-2). The secondary area was 4 gradients with different potassium application rates, namely conventional potassium application of 45 kg·hm^-2 (K0), potassium increase of 50% (K1, 68 kg·hm^-2), potassium increase of 100% (K2, 90 kg·hm^-2), and potassium increase of 150% (K3, 113 kg·hm^-2). The photosynthetic fluorescence parameters, dry matter accumulation and transport and yield components of maize were systematically measured, and the synergistic effects of nitrogen reduction and potassium increase were comprehensively analyzed.

Photosynthetic and fluorescence parameters of maize showed a trend of increasing first and then decreasing with growth period, and N1K2 treatment performed the best. Data from a two-year experiment at tasseling stage showed that net photosynthetic rate (P_n) under N1K2 treatment was increased by 17.53%, 6.74% and 8.16% compared with N1K0, N1K1 and N1K3 treatments, respectively. Transpiration rate (T_r) was significantly increased by 11.57% and 10.89% compared with N1K0 and N1K3 treatments, with no significant difference from N1K1, indicating that appropriate potassium application could effectively improve leaf transpiration efficiency. Maximum photochemical efficiency of PSII (F_v/F_m) was increased by 4.93%-12.71% compared with N1K0, N1K1 and N1K3 treatments. Performance index on absorption basis (PI) was increased by 2.53%-7.81% compared with N1K0, N1K1 and N1K3 treatments. Dry matter accumulation and transport analysis revealed that the N1K2 treatment significantly enhanced pre-harvest dry matter transport to grains, with pre-harvest dry matter accumulation, transport rate, and grain contribution rate increasing by 61.90%, 21.14%, and 27.73% compared with N0K0 treatment, respectively. Yield analysis showed that with production followed a pattern of initial increase followed by decline with nitrogen reduction and potassium increase, achieving peak yields of 18586.39 and 19279.5 kg·hm^-2 over two years under the N1K2 treatment. Correlation analysis and principal component analysis further confirmed the significant positive correlation between photosynthetic fluorescence parameters and yield under the nitrogen-reduction and potassium-increase pattern.

Reducing nitrogen by 30% and increasing potassium by 100% was the optimal fertilization mode for maize production in the Yellow River diversion irrigation area of Ningxia. N1K2 treatment significantly improved leaf photosynthetic performance and photochemical efficiency, promoted the efficient transport of post-flowering photosynthetic products to grains, increased dry matter accumulation, significantly improved nitrogen fertilizer utilization rate for ensuring high yield of maize, realized the synergistic optimization of photosynthetic efficiency and nutrient use efficiency, and provided a reliable fertilization basis for local maize green production.