Plant Gene and Trait 2025, Vol.16, No.3, 133-141 http://genbreedpublisher.com/index.php/pgt 136 4.2 Timing strategies: pre-planting, flowering, fruit set, and ripening The key to applying nitrogen fertilizer in different parts is to choose the right time for fertilization. Apply a portion before planting to help the seedlings take root and grow leaves during the seedling stage (Ayankojo and Morgan, 2021). When flowering, not much nitrogen is used. The nitrogen in the soil is sufficient. Excessive application is prone to waste (Wang et al., 2025). When tomatoes start to bear fruit, their demand for nitrogen increases, and appropriate topdressing helps the fruit grow (Wabela, 2018; Wang et al., 2025). When the fruits are nearly ripe, a little nitrogen can also be supplemented to maintain the quality, but not too much, otherwise it will affect the fertilizer efficiency (Luo et al., 2023; Wang et al., 2025). Studies have shown that applying nitrogen fertilizer in a ratio of “50% before sowing + 50% during growth” or “25% before sowing + 75% during growth” can yield more fruits and have better quality (Wabela, 2018; Ayankojo and Morgan, 2021). 4.3 Methods of application: fertigation, foliar sprays, side-dressing There are many ways to apply nitrogen fertilizer separately. For example, irrigation fertilization involves dissolving fertilizers in water and applying them together. It is often used in drip irrigation systems, which can supply fertilizers evenly and is particularly economical (Du et al., 2020; Liu et al., 2020; Bello et al., 2024). Foliar fertilization involves spraying fertilizer onto leaves, which is suitable for rapid nitrogen supplementation during critical periods and can enhance the resistance and fruit quality of plants (Luo et al., 2023). There is also furrow topdressing, which involves digging small furrows beside the seedlings for fertilization. It is often used in conjunction with watering and is suitable for field cultivation (Wabela, 2018; Ayankojo and Morgan, 2021). 5 Impact of Application Timing on Tomatoes Physiology 5.1 Effects on root-to-shoot ratio and biomass allocation Applying nitrogen fertilizer in multiple installments can make the roots and above-ground parts of tomatoes grow more reasonably and also increase the total weight of the plants. Studies have found that applying a portion of the fertilizer before planting and supplementing it later can help tomatoes grow faster and have deeper root systems in the early stage. Especially under the condition of reasonable irrigation, this method enables more roots to grow into the deep soil, which is conducive to the absorption of water and nutrients, and finally increases the yield (Ayankojo and Morgan, 2021; Nie et al., 2022). Moreover, a reasonable arrangement of the dosage and timing of nitrogen fertilizer can also enable roots and stems to grow better and accumulate more dry matter (Nie et al., 2022). 5.2 Influence on flower development and fruit set Applying nitrogen in batches can also help flowers develop well and increase the fruit setting rate. Studies have pointed out that supplementing nitrogen fertilizer during the flowering and fruiting periods of tomatoes can enable normal flower development and smooth pollination, thereby increasing the number of fruits (Wabela, 2018; Wang et al., 2025). Adding nitrogen fertilizer in the middle and later stages is also conducive to fruit growth, reduces flower and fruit drop, and increases the yield per plant (Wabela, 2018; Wang et al., 2025). 5.3 Delaying senescence and extending harvest duration In addition to promoting growth, applying nitrogen fertilizer in installments can also slow down the aging of leaves and prolong the harvest time. Timely nitrogen supplementation can maintain strong photosynthesis and higher chlorophyll content, keep the leaf function for a longer time, and also prolong the fruit development and harvest time (Nie et al., 2021; Nie et al., 2022). In addition, reasonable nitrogen fertilizer management can also enable tomatoes to absorb nitrogen more efficiently and grow more vigorously throughout the growth period, which is conducive to maintaining a good yield and quality all the time (Du et al., 2020; Wang et al., 2025). 6 Yield and Quality Benefits of Optimized Nitrogen Scheduling 6.1 Total and marketable yield improvements Applying nitrogen fertilizer in batches can significantly increase the total yield of tomatoes and the number of commercial fruits. Research has found that applying nitrogen fertilizer in two installments, such as once during transplanting and again during growth, with half each time, can achieve the highest yield, reaching 39.33 tons per hectare, which is much better than applying it all at once (Wabela, 2018). Among different fertilization levels,
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