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.

In order to explore the mechanism of nitrogen application under high temperature on the antioxidant characteristics of dryland potato in the mountainous area of southern Ningxia, and to elucidate the mechanism of nitrogen regulation, so as to provide the reference for the local development of nitrogen application measures favorable to alleviate high temperature stress.

A 2-year field in situ experiment was conducted in Dazui Village, Haiyuan County, Ningxia, from 2020 to 2021, using a split-zone experimental design with four N application levels as the main zones, namely 0 (N0), 75 kg·hm^-2 (N1), 150 kg·hm^-2 (N2), and 225 kg·hm^-2 (N3), and two temperature gradients as the sub-zones, namely (35±2) ℃ (HT) and (30±2) ℃ (CK). The effects of post-flowering high temperature stress on potato leaf area index (LAI), relative chlorophyll content (SPAD), antioxidant properties, membrane lipid peroxidation products and non-enzymatic protective substances were analyzed.

The 2-year results showed that potato LAI, SPAD, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) showed a decreasing trend from 30d-35d after flowering under the nitrogen fertilizer×temperature intercropping condition; at the same time, the cell membrane permeability, malondialdehyde content (MDA) and proline content (Pro) of potato leaves showed an increasing trend. Taking 35d after flowering as an example, after high temperature stress, potato LAI decreased by 11.22%-21.20%, SPAD decreased by 23.29%-26.05%, SOD decreased by 12.27%-16.87%, POD decreased by 13.69%-17.71% and CAT decreased by 13.80%-18.39% compared with room temperature; while cell membrane permeability, MDA content and Pro content increased significantly. Meanwhile, after high temperature stress, LAI and SPAD were significantly increased, while SOD, POD, CAT as well as yield reached the highest under N2 treatment (150 kg·hm^-2) compared with other treatments and N2 could also reduce cell membrane permeability and MDA content to alleviate high temperature hazards and increase potato yield. To further explore the correlation between potato yield and N application, a quadratic relationship between yield and N application was found, which led to the derivation of the corresponding parameter values for the economically optimal N application rates of 132-142 kg·hm^-2 (HT) and 185-210 kg·hm^-2 (CK). Pearson's correlation analysis showed that under high temperature stress, yield was only related to leaf LAI, POD, and CAT. LAI, POD and CAT reached significant positive correlation and significant negative correlation with MDA and Pro, while it did not reach significant level with SOD, SPAD and cell membrane permeability. Meanwhile, through the principal component analysis, it was found that after 2 years of high temperature stress, the composite scores of different nitrogen application levels were N2>N3>N1>N0.

The application of nitrogen at 150 kg·hm^-2 could continue to improve the physiological and antioxidant characteristics of potato leaves and to optimize its yield effectively, and it was also consistent with the theoretical estimation of 2 years of post-flowering high temperature. It was found that the N application rate of 150 kg·hm^-2 could continuously improve the physiological characteristics of potato leaves and effectively optimize the yield, and the difference was very small with the theoretically estimated 2-year economic optimum N application rate (132-142 kg·hm^-2). Therefore, the present experiment could also take 150 kg·hm^-2 as the recommended N application rate for safe potato production in Ningnan mountainous area to cope with the increasingly serious local high temperature hazard.

The effects of postponing nitrogen fertilizer on membrane lipid peroxidation, antioxidant enzyme activity, osmotic adjustment substance content in flag leaves and yield of spring wheat (Triticum aestivum L.) under high temperature stress were investigated, and the scientific fertilization methods to alleviate high temperature premature senescence of spring wheat after anthesis were screened.

From 2022 to 2023, Ning 3015 was used as the test material, and the test was carried out in the test base of the sixth team of Pingjipu Agricultural Reclamation in Ningxia. The split-plot experiment design was adopted. The main plot was temperature, with (25±2)℃ (normal temperature, RT) and (35±2)℃ (high temperature, HT), and the sub-plot was nitrogen fertilizer operation. The total amount of nitrogen application was constant, with 300 kg·N·hm^-2: in 2022, G1 (30% of nitrogen application at tillering stage), G2 (30% of nitrogen application at jointing stage), G3 (30% of nitrogen application at booting stage), G4 (20% of nitrogen application at heading stage) and G5 (20% of nitrogen application at filling stage) were set up; in 2023, a total of three fertilization methods, including G1, G3 and G5, were selected from the previous year 's test results. Samples were taken every 5 days from the flowering stage to determine the indexes of membrane lipid peroxidation, antioxidant enzyme activity and osmotic adjustment substances in flag leaves.

Superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activities, proline (Pro) content in flag leaves and yield in two consecutive years of Nitrogen Fertilizer Transportation Experiment (NFTO) reached the highest under the G5 treatment, while malondialdehyde (MDA) and membrane permeability were the lowest under the G5 treatment, which were significantly different from the G1 treatment (P<0.01). According to Pearson's (Pearson) correlation analysis, it was shown that spring wheat grain yield was significantly positively correlated (P<0.05) with SOD, POD, CAT activities and proline content, while it was significantly negatively correlated (P<0.05) with MDA content and membrane permeability. Comprehensive evaluation showed that the ordering of the principal component scores of nitrogen fertilizer transport in 2022 and 2023 was G5>G3>G4>G2>G1 and G5>G3>G1, respectively, and the trend of the results of the two-year test was consistent.

Appropriate nitrogen fertilizer postponing could reduce the membrane lipid peroxidation of spring wheat flag leaves under high temperature stress, increase the activity of antioxidant enzymes and the content of osmotic adjustment substances, and then increase the yield. In this experiment, the treatment of 20% total nitrogen application at filling stage was more suitable.