Molecular Soil Biology 2025, Vol.16, No.3, 126-136 http://bioscipublisher.com/index.php/msb 129 also increase the types of nutrients in the soil and enrich the microorganisms in the soil (Wang et al., 2025; Oueda et al., 2025). Although the yield-increasing effect of organic fertilizers may not be as obvious as that of chemical fertilizers, it can improve soil health, is suitable for long-term use, and is also beneficial to sustainable planting (Tonitto and Ricker-Gilbert, 2016; Oueda et al., 2025). 4.3 Integrated Nutrient Management (INM): Combination of organic and inorganic Integrated nutrient management, that is, the combination of organic and inorganic fertilizers, is a more comprehensive approach. It can not only increase yields, but also do not damage the soil, and maintain the diversity of soil ecology. Many studies have found that this combination is very effective. For example, the combination of poultry manure plus diammonium phosphate, straw plus NPK fertilizer, can not only increase sorghum yield, but also improve protein and other quality parameters (Tonitto and Ricker-Gilbert, 2016; Ivanina et al., 2019; Akinseye et al., 2023; Oueda et al., 2025; Wang et al., 2025). For example, returning straw to the field and appropriately reducing nitrogen fertilizer, or using poultry manure and fertilizer together, can not only make sorghum grow well, but also improve soil quality, and it is more cost-effective (Ivanina et al., 2019; Akinseye et al., 2023; Wang et al., 2025). 4.4 Biofertilizers: Nitrogen-fixing and phosphorus-solubilizing microbes Biofertilizers use beneficial microorganisms to help sorghum absorb nutrients, such as nitrogen-fixing and phosphate-solubilizing bacteria. They can help sorghum grow better, absorb more nutrients, and increase yields. Some studies have used biofertilizers together with chemical fertilizers and organic fertilizers, and found that sorghum grows stronger and has higher yields and quality. These microorganisms can improve the environment around the roots, making it easier for nutrients to be converted and absorbed. Biofertilizers are particularly suitable for use in organic farming and integrated management systems, and they perform well. 5 Effects of Nitrogen Fertilization 5.1 Nitrogen’s role in vegetative growth and grain protein content Nitrogen fertilizer is very important for sorghum, both for making it grow well and for improving its quality. As long as there is enough nitrogen fertilizer, the sorghum will be taller, with larger leaves and thicker stems. There will also be more chlorophyll in the leaves, stronger photosynthesis, and more vigorous growth of the whole plant (Elnasikh and Ibrahium, 2015; Bartzialis et al., 2023; Ismaeil et al., 2024; Wang et al., 2024). Nitrogen fertilizer can also increase the protein content in grains and forage, and improve nutritional content such as protein and starch, which is good for both eating and making feed (Modisapudi and Sebetha, 2022; Bartzialis et al., 2023; Ismaeil et al., 2024). Different nitrogen fertilizers have different effects. For example, lime ammonium nitrogen and urea can significantly increase the protein content in grains, but the differences between them are also worth noting. 5.2 Influence on biomass, tillering, and yield response curves If nitrogen fertilizer is used properly, the biomass and yield of sorghum will increase. Appropriate nitrogen fertilizer can make the aboveground part grow more, whether it is the weight of the ear, or the fresh weight and dry weight. Tillering will also increase, and ultimately more ears and grains can be harvested. However, nitrogen fertilizer should not be too much or too little. Too little is not enough, and too much is counterproductive. The change in yield is usually a trend of "first rise and then fall". Studies have found that the range of 144 to 160 kg/hectare is an ideal dosage, which not only has high yields, but also does not accumulate too much nitrate in the soil (Majrashi et al., 2022; Bartzialis et al., 2023; Wang et al., 2024; Obour et al., 2025). Under different farming methods, the effect of fertilization will also be different. For example, if no-till plots are combined with 45 to 90 kg/hectare of nitrogen fertilizer, the harvest can also be good and relatively stable (Majrashi et al., 2022; Obour et al., 2025). 5.3 Risks of overapplication (lodging, nitrate accumulation) Although nitrogen fertilizer is important, there are many problems if it is used too much. First, too much nitrogen fertilizer will make sorghum grow too high and too fast, and the stems will become soft and easy to fall over. This will affect mechanical harvesting and may also affect yield (Shehab and Guo, 2021; Majrashi et al., 2022; Wang et
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