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The rising demand for animal protein has intensified forage shortages and restricted pasture availability, underscoring the critical need for effective dual-purpose animal feeds. This study aims to evaluate the potential of vegetative soybeans as animal feed by assessing their nutritional value and productivity. Specifically, it explores the feasibility of using late-maturing soybean varieties, adapted to low latitudes, as forage in high-latitude regions and examines the impact of different planting dates on their growth and effectiveness during limited growing seasons. To achieve these objectives, a series of field and controlled experiments were conducted. The first experiment assessed 418 mid-maturing soybean varieties from the Huang-Huai-Hai Basin in China for their nutritional value as forage during 2020 and 2021. The second experiment tested late-maturing and photoperiod-sensitive soybean varieties, including "ZGDD" and the methionine-enhanced material "Ox-CGS," under tropical conditions with extended daylight. The third experiment evaluated forage soybeans sown on June 19th, July 14th, and August 8th, 2022, to determine their yield and protein content. Results showed that the first experiment yielded an average protein content of 24.7 %, ether extract content of 1.9 %, neutral detergent fiber content of 41.9 %, and acid detergent fiber content of 27.3 %, with a relative feeding value of 153, surpassing local standards for high-quality leguminous forage. The second experiment demonstrated that extended daylight increased crude protein yield by 3.7 times compared to Chinese soybean seed yields, and "Ox-CGS" showed a 24.2 % increase in methionine content. The third experiment revealed that forage soybeans achieved a crude protein yield of 0.95 t/ha within 60 days, exceeding the 2022 average of 0.68 t/ha for seed soybeans in China. The findings indicate that photoperiod-sensitive soybeans can be effectively used as forage over extended periods, utilizing artificial lighting or cultivation in higher latitudes, and that short growth cycles enhance crude protein accumulation. This research highlights the potential of soybeans to alleviate forage shortages, improve land use efficiency, and contribute to food security and agricultural development, especially on marginal lands and in regions with limited growing seasons. [Display omitted] • Soybean varieties (418 total) showed 24.7 % protein, exceeding quality standards. • Genotypes "ZGDD" and "Ox-CGS" tripled protein yield over soybean seed in tropics. • Genotype "Ox-CGS" is a promising forage option with high methionine (24.2 %) content. • Forage soybeans exacel in short 60-day periods, outdoing seed protein yield. • A strategy for planting soybeans as forage based on maturity groups has been proposed. [ABSTRACT FROM AUTHOR]

• Crude protein, oil and 11 categories of functional components were quantified in 1792 soybean samples collected from a vast range of soybean planting regions across China. • The geographic distributions of soybean nutritional compositions were mapped. • Regions with high seed protein, oil and functional components were highlighted. • A significant regionalization scheme of soybean seed quality for guiding high-quality edible soybean production was proposed. As one of major food crops, soybean is grown over a broad ecological region in China with considerable variations in environmental conditions, and the seed compositions of soybeans are diverse among different regions. To clarify the spatial patterns of soybean seed compositions, crude oil, protein, and 11 categories of functional components were quantified in 1792 soybean samples collected from a vast range of soybean planting regions across China spanning from 2010 to 2017. The Kriging interpolation maps presented a clear north-to-south (high latitude to low latitude) increasing trend in contents of crude protein and dietary fiber and decreasing trend in contents of crude oil, phospholipids, saponins, and carotenoids. Soybeans with high-level of total oligosaccharide were concentrated in the central region. Based on the geographical distribution of soybean nutritional components, weather conditions, and cultivation systems, the soybean production areas in China were divided into three regions and 10 subregions. This study highlights the geographic distribution of soybean nutritional compositions and provides scientific evidence for guiding the construction of high-quality edible soybean production bases in China. [ABSTRACT FROM AUTHOR]