The purpose of this study was to elucidate the regulatory mechanisms of planting density on fertilization and kernel-setting characteristics in summer maize under drip fertigation conditions, and to clarify the relationship between planting density and kernel number per ear as well as yield formation under integrated water-fertilizer management.

In 2023-2024, this experiment selected the medium-large ear type maize variety Denghai 605 (DH605) and the small ear type maize variety MY73 as test materials. It set up a traditional water and fertilizer management method (QG) with border irrigation and one-time base application of fertilizer before sowing, as well as a drip irrigation integrated water and fertilizer management method (DG). With a gradient of 15 000 plants/hm², a total of 8 planting densities ranging from 15 000 to 120 000 plants/hm² were set up to explore the impact of planting density on the fertilization and seed-setting characteristics and yield formation of summer maize under the integrated water and fertilizer management of drip irrigation.

Compared with the QG treatment, the plant height and specific leaf area density (SDLA) of both DH605 and MY73 varieties increased under QG treatment, and the differentiation process of male and female spikes accelerated. The number of florets on the male spike increased, while the abortion rate decreased. The number of filaments, total florets, and fertilized florets on the female spike increased, and the seed setting rate and total seed setting rate improved too. The anthesis-silking interval (ASI) shortened by about 1 day, the empty spike rate decreased, and the maximum yields increased by 7.6% and 6.4%, respectively. Under different water and fertilizer management conditions, as planting density increased, the plant height and SDLA of both varieties increased, but the development of male and female spikes was inhibited: the number of florets on the male spike decreased, and the abortion rate increased; the number of silk-spinning and fertilized florets on the female spike decreased, and the fertilization rate and total fertilization rate of florets first increased and then decreased; under high-density conditions, the ASI extended by about 1 day, the empty spike rate and bald tip length increased, and the yield showed a trend of first increasing and then decreasing. In addition, the differentiation process of male and female spikes in MY73 was faster than that in DH605, with a shorter ASI, lower plant height, and larger SDLA. The decrease in the seed setting rate and total seed setting rate with increasing SDLA was not significant, and the planting density for achieving maximum yield was higher.

Under the conditions of this experiment, excessive planting density would have a significant negative impact on fertilization and fruiting characteristics, thereby affecting the establishment of grain number per ear and hindering yield improvement. Compared with traditional irrigation methods, drip irrigation water fertilizer integration technology could effectively alleviate the negative impact of high-density conditions on the fertilization and fruiting characteristics of summer maize, thereby increasing yield. DH605 and MY73 reached their maximum yields at planting densities of 60 000 plants/hm² and 75 000 plants/hm², respectively.

To optimize the soybean-maize intercropping system in the Huang-Huai-Hai region, this study aimed to evaluate the effects of different row ratio configurations on crop agronomic traits, canopy structure of the population, yield components, edge effects, and overall economic benefits. The goal was to identify suitable row ratio configurations, thereby improving land resource use efficiency and economic returns.

Three row ratio configurations were implemented: 4 rows of soybean intercropped with 2 rows of maize (4:2), 6 rows of soybean intercropped with 4 rows of maize (6:4), and 4 rows of soybean intercropped with 4 rows of maize (4:4), using monoculture soybean (SCK) and monoculture maize (MCK) as controls. Crop dry matter accumulation, leaf area index (LAI), relative chlorophyll content (SPAD), canopy light transmittance, and yield components were measured. The inner and outer row sampling approach was adopted to evaluate edge effects and overall economic benefits.

Compared with monoculture, intercropping significantly decreased per-plant dry matter accumulation in maize during the filling, milking, and maturity stages, and in soybean during the full flowering, full pod, grain filling, and full maturity stages. Among the row ratio configurations, maize exhibited maximum per-plant dry matter accumulation under the 4:4 pattern, whereas soybean achieved its highest accumulation under the 6:4 pattern. Row ratio configurations significantly influenced inter-row variations in dry matter accumulation and yield for both crops. Maize yield followed the order 4:4 pattern>4:2 pattern>6:4 pattern, representing reductions of 15.22%, 18.02%, and 12.62% relative to MCK, respectively; soybean yield followed the order 6:4 pattern>4:4 pattern>4:2 pattern, corresponding to reductions of 55.99%, 50.43%, and 56.00% compared with SCK, respectively. Intercropped maize exhibited pronounced edge advantage, with border row maize yields significantly exceeding those of inner rows. Within the intercropping system, both maize and soybean demonstrated lower canopy light transmittance, LAI, and SPAD values compared with their monoculture counterparts. Maize canopy light transmittance, LAI, and SPAD values followed the consistent ranking: 4:4 pattern>4:2 pattern>6:4 pattern; soybean canopy light transmittance followed 4:4 pattern>6:4 pattern>4:2 pattern, while its LAI and SPAD values mirrored the ranking pattern observed in maize. Maize LAI was significantly influenced by row ratio configuration, whereas no significant inter-row variations were detected for maize SPAD values or for soybean LAI and SPAD values. In evaluations of economic returns and intercropping advantages, the 4:4 pattern configuration demonstrated superior performance, achieving the highest values for land equivalent ratio (LER), relative crowding coefficient (K), and economic benefits. Maize in intercropping exhibited higher LER and K values relative to soybean, with the maize competition ratio (CR_m) being significantly greater than that of soybean (CR_s) (CR_m>1, CR_s<1), demonstrating maize's competitive dominance in interspecific competition.

Although intercropping reduced per-plant dry matter accumulation, LAI, and SPAD values for both crops compared with monoculture, it significantly increased the land equivalent ratio (LER) and overall economic benefits. Under the experimental conditions, the 4:4 pattern exhibited more optimal canopy architecture, with maize demonstrating pronounced edge advantage. This system maintained maize yield while generating additional soybean income, thereby achieving the synergistic enhancement of total productivity and economic returns.

The effects of different nitrogen forms on filling characteristics, grain quality and yield of summer maize were studied, so as to provide the scientific basis for selecting suitable nitrogen fertilizer types and improving the yield and grain quality of summer maize.

The experiment was conducted in Taian, Shandong Province from 2022 to 2023. Denghai 605 (DH605) was selected as the experimental material, with a nitrogen application rate of 210 kg N·hm^-2. The experiment included five treatments: amide nitrogen (Urea, UREA), nitrate nitrogen (Calcium nitrate, NN), ammonium nitrogen (Ammonium chloride, AN), co-application of nitrate and ammonium nitrogen (1:1, HH), and urea ammonium nitrate solution with a blend of amide nitrogen, nitrate nitrogen, and ammonium nitrogen (2:1:1, UAN). The effects of different nitrogen forms on the yield and quality of summer maize were investigated by determining the grain filling characteristics, grain quality characteristics and grain capacity of summer maize.

Compared with the conventional application of amide nitrogen in UREA, both the maize yield and grain quality under NN decreased. The maize yield under AN increased, but the grain quality decreased. HH significantly increased maize yield without affecting grain quality. UAN significantly increased maize yield and improved grain quality. Over the two years, the highest maize yield achieved with the co-application of the three nitrogen forms, significantly increasing by 13.7% to 16.3% compared with UREA. The Next the highest maize yield were from AN and HH, which significantly increased maize yield by 5.2% to 6.8% and 7.3% to 10.6%, respectively, compared with UREA. The maize yield under NN decreased by 5.4% to 5.8% compared with UREA. Compared with UREA, the growth amount at the maximum filling rate (W_max) under UAN was enhanced by 6.3% to 9.7%, and the active filling period (D) was extended by 7.7% to 10.9%. Both AN and HH increased W_max and prolonged D, thereby promoting the accumulation of grain weight and increasing yield. The W_max, D, grain filling rate, and dehydration rate of NN were significantly lower than those in the other treatments. The crude protein content was lower with NN and AN, decreasing by 20.6% to 22.0% and 15.2% to 17.4% than that under UREA, respectively. The rude fat content with NN was significantly higher than that of other treatments, increasing by 23.6% to 30.9% than that under UREA. Compared with UREA, UAN improved grain quality, with total starch and amylopectin content increasing by 4.9% to 5.2% and 11.7% to 14.4%, respectively, compared with UREA, and the ratio of amylopectin to amylose increased by 31.0% to 39.1%. The amylose content decreased by 14.1% to 16.8%. The crude protein content of UAN increased by 11.7% to 24.1%. The grain bulk weight under UAN was significantly higher than that under other treatments.

Compared with the conventional application of amide nitrogen, the treatment with nitrate nitrogen inhibited grain filling, reduced grain weight, and decreased yield. In contrast, ammonium nitrogen or the co-application of multiple nitrogen forms enhanced the grain filling process, increased grain weight, and thereby improved yield. Furthermore, compared with the application of a single nitrogen form, the co-application of three nitrogen forms could achieve a synergistic improvement in both yield and grain quality.

The purpose of this study was to investigate the regulation mechanism of planting density and spraying ethephon on lignin metabolism and lodging resistance characteristics and to explore the mechanism of planting density and ethephon application on lodging resistance characteristics of summer maize.

In this study, the summer maize hybrid, Xundan20, was grown by spraying water or ethephon at the seven-expanded-leaf stage under three different plant densities (60 000 plants/hm², low density, L; 75 000 plants/hm², medium density, M; 90 000 plants/hm², high density, H) in order to explore the effects of density and ethephon on plant morphology, the third internode microstructure, lignin metabolism and yield, etc.

Compared with LCK at milking stage, the internode length of the third stem under HCK increased by 19.75%. The stem diameter, stalk rind penetration strength, small vascular bundle number, small vascular bundle area and cortex thickness under HCK were 8.00%, 43.46%, 20.41%, 26.92% and 22.05% lower than those under LCK, respectively. The lignin accumulation and enzyme activity of PAL, 4-CL, CAD and POD under HCK were 24.04%, 33.81%、10.92%, 49.06% and 20.78% lower than those under LCK, respectively. Compared with HCK at milking stage, the internode length of the third stem under HE decreased by 34.84%. The stem diameter, stalk rind penetration strength, small vascular bundle number, small vascular bundle area and cortex thickness of HE were 14.22%, 66.10%, 22.71%, 22.11% and 35.96% higher than those under HCK, respectively. The lignin accumulation and enzyme activity of PAL, 4-CL, CAD and POD of HE were 28.28%, 30.74%, 13.01%, 59.26% and 16.99% higher than those under HCK, respectively.

Lodging resistance of summer maize decreased with the increasing of planting density. After the application of ethephon, the stem strength and lignin metabolism of summer maize were enhanced, the lodging resistance was enhanced, and finally maize yield was increased. The effect of spraying ethephon on the lignin metabolism and lodging resistance of XD 20 was the most significant when the planting density was 90 000 plants/hm², and yield was the highest.

Climate change has led to global warming, with frequent occurrences of high temperatures and droughts, and high temperatures often accompany droughts during production. This study aimed to explore the physiological mechanism of the compound stress of high temperature and drought in different growth periods affecting the yield and photosynthetic characteristics of summer maize.

DH605 was selected as the experimental hybrid. High temperature treatment (T), drought treatment (D) and the compound stress (T-D) treatment were set in different growth periods. In 2019, it was carried out at the third leaf stage (V3), the sixth leaf stage (V6) and flowering stage (VT); In 2020, it was carried out at the third leaf stage (V3), the twelfth leaf stage (V12) and flowering stage (VT). This experiment took natural temperature and normal moisture treatment as control (CK). The effects of high temperature and drought compound treatments on yield, photosynthetic characteristics, dry matter accumulation and distribution of summer maize were studied, and the differences of photosynthetic characteristics and yield between single treatment and compound treatment were compared.

After the combined stress treatment of high temperature and drought in different growth stages, the LAI and SPAD of summer maize decreased significantly, which affected the net photosynthetic rate (P_n) and it decreased significantly. Among that, the compound stress during the VT period had the most significant effect on P_n. The P_n under T-D treatment in the VT period decreased by 39.0% on average compared with CK, while the net photosynthetic rate of summer maize after the combined treatment of high temperature and drought decreased more than that under single stress such as high temperature and drought. The combined treatment of high temperature and drought caused the photosynthetic performance of summer maize to decrease, and it led to the decrease of dry matter accumulation capacity and distribution ratio of summer maize to grains, which in turn led to a significant decrease in yield. In 2019, the output of T-D at V3, V6, and VT decreased by 27.4%, 18.3%, and 66.5%, respectively, compared with CK; in 2020, the output of T-D treatment at V3, V12, and VT decreased by 14.5%, 14.6% and 68.7%, respectively, compared with CK.

After the combined stress of high temperature and drought, the leaf area index and chlorophyll content was decreased, gas exchange was inhibited, leading to the decrease of photosynthetic performance, and thus hindered the accumulation and distribution of photosynthetic compounds, resulting in a significant yield reduction of summer maize. The combined stress of high temperature and drought during the flowering stage had the greatest impact on the yield and photosynthetic characteristics of summer maize, and the combined stresses had greater impacts than that of single stress.

Supplying nitrogen timely and effectively could delay leaf senescence and improve grain filling characteristics of maize. The effects of controlled-release fertilizers with different controlled nitrogen ratio on leaf senescence, grain filling and yield of summer maize were studied to explore the appropriate controlled nitrogen ratio for summer maize in Huang-Huai-Hai region.

This study was conducted in 2019-2021 cropping seasons, using the middle-early maturing hybrid Denghai 518 (DH518) and the middle-late maturing hybrid Denghai 605 (DH605) as experimental materials. The types of nitrogen fertilizer are controlled release urea and ordinary urea mixed, ordinary urea. Five controlled nitrogen ratios: 10% (T1), 20% (T2), 30% (T3), 40% (T4) and 50% (T5) were set for studying the effects of controlled-release fertilizers on leaf senescence, grain filling characteristics, and their inter-relationship of summer maize, using urea fertilizer treatment as control (CK).

The results showed that using controlled release fertilizers could significantly increase the yield of summer maize. Among these, the yield increased most significantly in T3 treatment. Compared with CK, using controlled release fertilizers significantly increased the leaf area index (LAI), SPAD value, and the antioxidant enzymes activities, thus improving the grain filling characteristics. Among these, T3 treatment increased the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in summer maize leaves at the late growth stage, reducing the accumulation of malondialdehyde (MDA), thus delaying leaf senescence most significantly. In addition, the maximum growth (W_max), grain filling rate (G_max), days of active filling period (P), and grain dehydration rate were increased mostly in T3 treatment, accordingly the 1000-kernel weight and grain yield of summer maize were increased mostly. Correlation analysis showed that the yield was positively correlated with W_max and G_max; W_max and G_max was positively correlated with the activities of SOD and POD, but negatively correlated with MDA content. Grain dehydration rate and grain filling rate were positively correlated with the activities of SOD and CAT, but negatively correlated with MDA content. The water content of kernels was negatively correlated with the activities of SOD and CAT, and positively correlated with MDA content. Therefore, using controlled release fertilizers, especially T3 treatment, effectively optimized the grain filling characteristics by increasing the antioxidant enzyme activities, thus increasing the grain yield of summer maize.

Using controlled-release fertilizer could effectively increase the activities of leaf antioxidant enzymes, thus delaying leaf senescence, improving grain filling characteristics and increasing grain yield of summer maize. Among these, T3 treatment increased the grain yield most significantly.