Bioscience Methods 2025, Vol.16, No.6, 270-279 http://bioscipublisher.com/index.php/bm 2 71 This study aims to evaluate the field performance of rice varieties that efficiently utilize nitrogen fertilizers under different fertilization schemes. It integrates agronomic experiments, genetic analysis, and nitrogen fertilizer utilization rate (NUE) assessment to screen out varieties that can maintain yield and quality at lower nitrogen input, and quantify the yield and nitrogen fertilizer utilization rate responses of different rice genotypes under different fertilization gradients. Clarify the genotype-environmental interactions that affect nitrogen fertilizer utilization rate. This study aims to promote sustainable rice production by guiding breeding programs and fertilizer recommendations, and ultimately contribute to global food security and environmental protection. 2 Physiological Basis of Nitrogen-efficient Rice Varieties 2.1 Molecular mechanisms of nitrogen uptake, transport, and assimilation For rice to make efficient use of nitrogen fertilizer, it does not rely on a single link but on a complete set of internal operation procedures. Absorbing nitrogen from the soil is just the first step. Next, a series of molecular mechanisms are needed to truly "utilize" this nitrogen. Like OsNRT1.1B, OsNPF6.1 and OsAMT1; These transport proteins are used to transport nitrates and ammonium. Enzymes such as NR, NiR, GS, and GOGAT are responsible for converting nitrogen into amino acids and proteins needed by crops (Shen, 2025). Interestingly, these molecules themselves are also controlled by regulatory factors, such as OsNAC42, and gene loci like DNR1 and DEP1, which determine whether rice can "intelligently" absorb and utilize nitrogen in different environments (Figure 1) (Tang et al., 2019). Not all rice varieties have this ability. Some varieties are just good at regulating and thus have a higher utilization rate. 2.2 Genetic basis of nitrogen use efficiency variation among varieties Why can some rice varieties achieve "low fertilizer consumption and high yield" while others cannot? This is inseparable from genetic differences. In the past, through analyses such as QTL and GWAS, researchers have identified a number of key loci related to nitrogen efficiency, such as qTGW11, OsNR2, OsNRT1.1B and OsTCP19, which all affect nitrogen uptake, nitrogen utilization and final yield performance of rice (Liu et al., 2022; Shen et al., 2025). Especially between indica rice and japonica rice, some natural allelic differences can affect the pathways of nitrate assimilation or hormone regulation, thereby directly causing differences in expression (Gao et al., 2019). The good genes "dug" out from wild rice or local old varieties were later introduced into modern varieties, and indeed some varieties performed more stably in low-nitrogen environments. So, when it comes to breeding, the selection of genetic materials is really crucial. 2.3 Evaluation indices and phenotypic traits related to nitrogen efficiency Ultimately, to determine whether a rice variety has a good nitrogen efficiency or not, one needs to observe how it performs in the field. Efficiency indicators like NUpE and NUtE may sound academic, but in fact, they are about how much nitrogen is absorbed, how much nitrogen is used, and how much grain is finally produced (Shanmugapriya et al., 2025). For some varieties, even with low fertilizer application, the root structure can hold up, and the photosynthetic capacity of flag leaves is not compromised. Parameters such as Fv/Fm and ΦPSII also perform well (Natarajan et al., 2024). Nowadays, there are still some high-throughput tools, such as unmanned aerial vehicles with multispectral cameras flying around, which can directly monitor the changes in canopy nitrogen content. These phenotypic characteristics and technical means are increasingly being used to select superior genotypes suitable for low-nitrogen cultivation, which not only saves fertilizer but also ensures yield, providing significant assistance for sustainable rice production (Zhu, 2025). 3 Fertilization Regimes and Their Agricultural Implications 3.1 Comparison of conventional, reduced, and slow-release fertilizer strategies For a long time, the conventional practice in rice fields has been to apply quick-acting urea multiple times. To put it bluntly, it's for convenience and quick results. However, the result of doing so is that the utilization rate of nitrogen fertilizer is not high and it is also prone to loss. A considerable amount of nitrogen was carried away with water and entered the atmosphere and water bodies, and environmental pressure followed (Lee et al., 2025). So, reducing the amount of fertilizer application seems like a solution, especially on the basis of adjusting the timing of fertilizer application. However, this approach is not a panacea. If not used properly, the yield may even drop.
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