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In China, the most common grain crop is maize (Zea mays). The increasing pressure to meet the food demands of its growing population has pushed Chinese maize farmers toward an excessive use of chemical fertilizers, a practice which ultimately leads to a massive waste of resources and widespread environmental pollution. As a result, increasing the yield and improving the nitrogen (N) use efficiency of maize has become a critical issue for agriculture in China. This study, which analyzes the combined data from a simulation carried out using the Decision Support System for Agrotechnology Transfer (DSSAT), a field experiment, and a household survey, explored the effectiveness of several approaches aimed at narrowing the maize yield gap and improving the N utilization efficiency in the Huang-Huai-Hai Plain (HHHP), the most important area for the production of summer maize in China. The various approaches we studied deploy different methods for the integrated management of N fertilizer input and the planting density. The study produced the following results: (1) For the simulated and actual maize yields, the root mean square error (RMSE), the normalized root mean squared errors (NRMSE) and the index of agreement (d) were 1,171 (kg ha–1), 12% and 0.84, respectively. These results show that the model is viable for the experiment included in the study; (2) The potential yield was 15.58 t ha–1, and the yields achieved by the super-high-yield cultivation pattern (SH), the optimized nutrient and density management pattern (ONM), the simulated farmer's practice cultivation pattern (FP) and actual farmer's practice (AFP) were 11.43, 11.06, 10.33, and 7.95 t ha–1, respectively. The yield gaps associated with the different yield levels were large; (3) For summer maize, the high yield and a high N partial factor productivity (NPFP) was found when applying a planting density of 9 plants m–2 and an N application amount of 246 kg ha–1. These results suggest that the maximum yield that can actually be achieved by optimizing the N application and planting density is less than 73% of the potential yield. This implies in turn that in order to further narrow the observed yield gaps, other factors, such as irrigation, sowing dates and pest control need to be considered. [ABSTRACT FROM AUTHOR]

Controlled release urea (CRU) has been widely adopted to increase nitrogen (N) use efficiency and maize production, but the impacts can range widely depending on water availability in the soil. In an experiment using Zhengdan 958 (a popular summer maize hybrid), three levels of water treatments (adequate water condition [W3], which maintained soil moisture at about 75% ± 5% of the soil’s field capacity; mild water stress [W2], which maintained moisture content at 55% ± 5% of field capacity; and severe water stress [W1], which had a moisture content of 35% ± 5% of field capacity) and four levels of controlled release urea fertilizer (N0, N1, N2 and N3 were 0, 105, 210 and 315 kg N ha–1, respectively) were compared in a rainout shelter system with soil. The results revealed that CRU had significant effects on maize yields and N use efficiencies under different water conditions. The mean yields increased with increasing water levels and showed significant differences. Under W1, the accumulation of dry matter and N were limited, and N internal efficiency (NIE) and the apparent recovery efficiency of applied N (REN) decreased with N increases; yields of N1, N2, and N3 were similar. Under W2, the dry matter and N accumulation, as well as the yield, showed an increasing trend with an increase in N application, and the NIE and REN of N3 showed no difference from N2. Under W3, yields of N2 and N3 were similar and they were significantly higher than that of N1, but the agronomic N use efficiency (ANUE), REN, and the physiological NUE (PNUE) of N2 were 54.2, 34.9, and 14.4% higher, respectively, than those of N3. N application beyond the optimal N rate did not consistently increase maize yield, and caused a decrease in N use efficiencies. Highest overall dry matter, N accumulation, and yields were observed with N3 under W2, and those showed no differences with N2 and N3 under W3. Under this experimental condition, the CRU of 210 kg ha–1 was optimized when soil moisture content was 75% ± 5% of field capacity, but an N rate of 315 kg ha–1 was superior when soil moisture content during the entire growing season was maintained at 55% ± 5% of field capacity. [ABSTRACT FROM AUTHOR]

A field experiment was conducted to study the effects of shading on tassel and ear development and yield formation of three summer maize hybrids Zhenjie 2 (ZJ2), Denghai 605 (DH605), and Zhengdan 958 (ZD958). The ambient sunlight treatment was used as control (CK) and shading treatments (40 % of ambient sunlight) were applied at different growth stages from silking stage (R1) to physiological maturity stage (R6) (treatment S1), from the sixth extended leaf stage (V6) to R1 (treatment S2) and from seeding to R6 (treatment S3). Shading had no significant effect on the time from seeding to shoot emergence (VE); however, subsequent growth and development were delayed with shading beyond this point. The differentiation time of both tassel and ear delayed, and female spike (tassel) floret differentiation, sexual organ formation time, and anthesis-silking interval (ASI) were lengthened. After shading, the total number of floret, silk, and fertilization floret reduced significantly; the number of abortive seeds increased, and the total setting percentage among different treatments showed that CK>S2>S1>S3; and the total setting percentages in S1, S2, and S3 of ZD958 were 44, 72, and 15 % respectively. The total floret number of tassel primordium differentiation, fertility rate, and seed setting rate of florets in S3 treatment was the minimum; kernels per ear decreased seriously and single ear setting percentage was only 16 %; although floret degeneration number of S2 during ear differentiation stages increased and floret fertility rate reduced than that of CK, fertilization flower seed production increased and abortive seed decreased after canceling shading. Aborted kernel of S1 increased and kernel dry weight reduced, resulting in a significant decrease of kernel number per ear and kernel weight, and the grain abortive rate of 40-62 %. In conclusion, shading changed the growth and development process and caused infertility of tassel and ear; tassel branches decreased, reducing pollen vitality and silks differentiation cut down; and grain dry matter accumulation and setting percentage decreased, causing yield reduction. Grain yield and biomass reduced 66, 36, and 93 % compared to the control by shading treatments of S1, S2, and S3, respectively. [ABSTRACT FROM AUTHOR]

Clarification of influencing factors (cultivar planted, cultivation management, climatic conditions) affecting yields of summer maize ( Zea mays L.) would provide valuable information for increasing yields further under variable climatic conditions. Here, we report actual maize yields in the Huanghuaihai region over the past 50 years (1957-2007), simulated yields of major varieties in different years (Baimaya in the 1950s, Zhengdan-2 in the 1970s, Yedan-13 in the 1990s, and Zhengdan-958 in the 2000s), and factors that influence yield. The results show that, although each variety change has played a critical role in increasing maize yields, the contribution of variety to yield increase has decreased steadily over the past 50 years (42.6%-44.3% from the 1950s to the 1970s, 34.4%-47.2% from the 1970s to the 1990s, and 21.0%-37.6% from the 1990s to the 2000s). The impact of climatic conditions on maize yield has exhibited an increasing trend (0.67%-22.5% from the 1950s to the 1970s, 2.6%-27.0% from the 1970s to the 1990s, and 9.1%-51.1% from the 1990s to the 2000s); however, interannual differences can be large, especially if there were large changes in temperature and rainfall. Among climatic factors, rainfall had a greater positive influence than light and temperature on yield increase. Cultivation measures could change the contribution rates of variety and climatic conditions. Overall, unless there is a major breakthrough in variety, improving cultivation measures will remain important for increasing future summer maize yields in the Huanghuaihai region. [ABSTRACT FROM AUTHOR]

Excising the upper leaves strata of maize crops cultivated at high stand densities could possibly optimize canopy architecture to achieve enhanced canopy apparent photosynthesis, a more favorable distribution of 13 C-photosynthates to grain, and ultimately higher grain yields. To test this hypothesis, we conducted a leaf removal experiment in 2012 and 2013 growing seasons in Shandong, a province in the North China Plain. Jinhai5, a corn cultivar planted widely across China, was grown at a density of 105,000 plants ha −1 until 3 days after silking (DAS), when plants were subjected to the removal of the uppermost and next leaves (S 2 ), the four uppermost leaves (S 4 ) or the six uppermost leaves (S 6 ), with no leaf removal as control (S 0 ). In the S 2 treatment we found a longer duration of canopy apparent photosynthesis (CAP) and green leaf area index (LAI), higher total dry matter weight at physiological maturity as well as greater harvest index (HI) compared to the control, whereas those in the excessive leaf removal treatments (S 4 and S 6 ) declined substantially. In addition, modification of the number of leaves above the ear leaf led to different patterns of allocation of 13 C-photosynthates. Excising two leaves promoted the distribution of 13 C-photosynthates to grains, while that allocation decreased in the S 4 and S 6 treatments, which can be interpreted as a result of increased retention of 13 C-photosynthates in the stem and ear bracts. Plants in S 2 treatment displayed a yield advantage under high plant density due to higher kernel weight and more harvested ears. Relative to control, plants in the S 2 treatment had 15% and 12% higher grain yields in 2012 and 2013, respectively. However, the removal of four or six leaves at the very early grain filling period, when kernel sink capacity is being established, caused a marked reduction in yields due to decreased both kernel number per plant and kernel weight, despite a relatively higher biomass availability per kernel. In conclusion, excising two leaves (the uppermost and next leaves) of maize crops cultivated at high plant density delayed leaf senescence, enhanced canopy photosynthesis and dry matter accumulation, leading to a higher post-silking source–sink ratio with its positive impact on kernel weight and higher grain yield. [ABSTRACT FROM AUTHOR]

• Controlled-release urea with irrigation affects maize biomass and N accumulation. • Optimum controlled-release urea improved photosynthetic capacity for each irrigation level. • The interaction of irrigation and controlled-release urea on maize yield was significant. Effective irrigation and nitrogen (N) management is crucial for sustainable agricultural development. Controlled-release fertilizer has been widely used to improve N use efficiency and save labor in one-off application. A specially designed soil column and field trial were conducted to investigate the effect of the interaction of irrigation management and nitrogen on yield, N uptake, and photosynthetic characteristics of summer maize. In the soil column experiment, severe water stress (W1) significantly decreased the leaf area index, relative chlorophyll content, and net photosynthesis and delayed maize growth, resulting in significant yield loss. Under mild water stress (W2), increased controlled-release urea (CRN) application counteracted the inhibition of maize growth. Under adequate water condition (W3), the yield and maize growth exhibited no significant difference between CRN 210 and 315 kg N ha–1. In the field experiment, CRN 210 and 315 kg N ha–1 also exhibited similar yield and were significantly higher than common urea 315 kg N ha–1 under conventional irrigation (CI). Under half-reduced conventional irrigation (RI), yields of CRN 315 kg N ha–1 increased by 10.5% and 7.5% compared with that of CRN 210 kg N ha–1 in 2014 and 2015. The interaction between irrigation and CRN could effectively alleviate the adverse effects of mild drought on summer maize by delaying leaf senescence, increasing chlorophyll content, and improving photosynthetic performance during the grain-filling period. These characteristics allowed more water and nutrients for maize plant and ultimately increased the yield. In areas with adequate irrigation conditions, CRN reduced to 210 kg N ha–1 could satisfy maize growth. In mild water stress and half-reduced conventional irrigation area, the CRN rate of 315 kg N ha–1 used by traditional farmers showed superior benefits. [ABSTRACT FROM AUTHOR]