Field Crop 2024, Vol.7, No.3, 158-170 http://cropscipublisher.com/index.php/fc 163 Additionally, extreme weather events, such as excessively wet or dry seasons, can drastically affect maize yield and grain composition. During extremely wet years, excessive irrigation can reduce grain yield due to water stress, while in dry years, appropriate irrigation can significantly boost yield (Marković et al., 2021). Moreover, climate change impacts, such as increased minimum temperatures and decreased solar radiation, have been found to affect maize yield differently across various agro-ecological zones, necessitating adaptive agronomic strategies (Zhang et al.. 2020). 5.2 Soil types and characteristics Soil fertility and characteristics play a crucial role in determining the effectiveness of agronomic practices on maize protein and starch contents. Integrated agronomic practices (IAP), which include optimal planting density, split fertilizer application, and subsoiling tillage, have been shown to increase maize grain yield and nitrogen use efficiency (NUE) more effectively in high soil fertility (HSF) fields compared to low soil fertility (LSF) fields (Zhou et al., 2019). The type of fertilization also impacts starch properties, with conventional fertilization methods leading to larger starch granules and higher relative crystallinity compared to slow-release fertilizers (Wang and Lu, 2022). Additionally, soil mineral nitrogen content and root length are critical factors that enhance post-silking dry matter and nitrogen accumulation, thereby improving grain yield and NUE, especially in HSF fields (Zhou et al., 2019). 5.3 Interaction effects on protein and starch contents The interaction between agronomic practices and environmental factors significantly affects maize protein and starch contents. Nitrogen fertilization consistently increases grain protein concentration, with higher fertilizer levels resulting in greater protein content (Correndo et al., 2021). However, the impact of irrigation on grain quality components such as protein, starch, and oil concentrations can vary depending on the duration, timing, and intensity of water stress treatments (Correndo et al., 2021). For instance, irrigation combined with high nitrogen levels can lead to increased protein yield, but excessive irrigation during wet years can reduce grain yield due to water stress (Figure 2) (Marković et al., 2021). Furthermore, the combination of appropriate agronomic practices and favorable climate conditions can enhance maize yield and stability, particularly in low-yielding zones (Zhang et al.. 2020). The optimization of genotype-environment-management interactions is essential for developing sustainable intensification options that improve yield and grain quality with minimal environmental impact (Zhang et al., 2020). Marković et al. (2021) found that proper irrigation and fertilization strategies are crucial for optimizing maize quality and yield. Irrigation and nitrogen fertilization significantly affect maize yield and nutritional components, especially under extreme weather conditions. Their study examined the effects of different irrigation regimes (rainfed, 60%~100% field capacity, 80%~100% field capacity) on various variables under extremely wet, extremely dry, and average years (Figure 2a-d). The results showed that in extremely dry conditions, increasing irrigation significantly improved yield and starch content (P<0.01), but had little effect on protein and oil content. Figure 2(e-h) illustrates the impact of different nitrogen fertilization rates (b1: 0 kg N ha−1, b2: 100 kg N ha−1, b3: 200 kg N ha−1) on various variables under different weather conditions. The results indicated that increasing nitrogen fertilization significantly enhanced yield and protein content (P<0.01), while the effects on starch and oil content were less pronounced. In summary, the interplay between agronomic practices and environmental factors such as climate conditions and soil characteristics is critical in determining maize protein and starch contents. Effective management strategies that consider these interactions can lead to significant improvements in maize yield and grain quality. 6 Advances in Research and Technology 6.1 Genomic approaches and breeding Recent studies have highlighted the limited contribution of genetic technologies to maize yield potential in favorable environments. A comprehensive analysis of maize production in Nebraska from 2005 to 2018 revealed that only 13% of yield gains were attributable to genetic improvements, with the majority of gains resulting from
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