Molecular Soil Biology 2025, Vol.16, No.2, 91-102 http://bioscipublisher.com/index.php/msb 96 measurement, soil and plant analysis. At the same time, local farmers also participated in observing and evaluating the actual performance of the varieties (Witt et al., 1999; Silva et al., 2022). In some areas, the experiment also cooperated with field schools and technical observation activities to improve farmers' understanding and operational capabilities of low-nitrogen management (Silva et al., 2022; Suman et al., 2024). 5.2 Results of farmers' participation in variety screening In these experiments, farmers directly participated in variety selection activities and achieved good results. For example, in Indonesia and Vietnam, farmers selected new varieties with stable yields and strong adaptability under low nitrogen by visiting the site and evaluating varieties (Silva et al., 2022). In Bago, Myanmar, the yield difference between the low-nitrogen treatment group and the control group was large, indicating that the region still has potential for improvement; while in Can Tho, Vietnam, the yield difference was small, indicating that there are good management measures and limited room for improvement. Farmers not only value yield, but also compare other characteristics such as disease resistance, rice quality, length of harvest period and whether it is easy to manage (Silva et al., 2022). From the feedback, saving nitrogen fertilizer, reducing costs and improving benefits are important reasons for them to choose new varieties (Silva et al., 2022; Suman et al., 2024). Their enthusiasm for participation also makes these new technologies landed faster and promoted more smoothly in the local area (Suman et al., 2024). 5.3 Promotion policies and supporting measures To promote the application of low-nitrogen varieties, governments encourage farmers to use these technologies through subsidies, training and promotion activities (Begho et al., 2022). Studies have shown that education and agricultural technical services, coupled with necessary financial support, are important factors affecting whether farmers adopt new technologies. IRRI also cooperates with research institutions in various countries to promote farmer field schools, set up demonstration sites, and compile technical materials to help farmers master low-nitrogen management methods (Begho et al., 2022; Suman et al., 2024). There are still problems with seed promotion. The main difficulties are insufficient seeds of excellent varieties, imperfect distribution channels, and some farmers are unfamiliar with new varieties (Begho et al., 2022). To solve these problems, it is necessary to strengthen the connection between seed companies and farmers, improve the seed certification system and circulation system, and ensure that farmers can easily buy suitable seeds. 6 Challenges and Limitations of Breeding in Low Nitrogen Environments 6.1 The contradiction between yield potential and nitrogen use efficiency (NUE) In crops such as rice, improving nitrogen use efficiency (NUE) requires improving nitrogen absorption, transport and utilization, which are regulated by complex genetic and physiological mechanisms (Van Bueren and Struik, 2017; Ranjan and Yadav, 2020; Chen et al., 2022). Although there is a certain amount of genetic variation in modern crop varieties that can be used to improve NUE, most of the related traits are quantitative traits controlled by multiple genes and are difficult to improve quickly through a single method (Cormier et al., 2016). In low nitrogen environments, the heritability of crop yield is lower than that under high nitrogen conditions. This phenomenon is partly due to the smaller differences between genotypes, which affects the efficiency of selection (Bänziger et al., 1997; Ertiro et al., 2020). For example, in maize, yield heritability under low nitrogen conditions is 29% lower than that under high nitrogen conditions (Bänziger et al., 1997). Traits closely related to NUE, such as root activity and nitrogen redistribution, are more critical in low nitrogen environments, but these traits are difficult to phenotype and genetic improvement is slower (Ranjan and Yadav, 2020; Chen et al., 2022). In practical applications, farmers want varieties to maintain high yields under low nitrogen conditions and also require them to maintain high yields in high nitrogen environments. However, some studies have shown that as the degree of nitrogen stress increases, the correlation between low nitrogen and high nitrogen yields weakens, indicating that some genotypes perform inconsistently under different nitrogen conditions (Begho et al., 2022; Amegbor et al., 2022x). There are few varieties that can perform well under both conditions, and breeding must
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