Composition of Primary Metabolites in Winter Barley Grain as Affected by NPK Fertilization of Reclaimed Land

Optimizing nutrient management is critical for enhancing crop productivity and grain nutritional quality in reclaimed soils, where poor soil fertility and salinity often limit barley cultivation. In that context, this study evaluated the effects of NPK fertilization on barley grain metabolism in reclaimed soil, using four barley cultivars (Betaone, Heuknuri, Nurichal, and Sogang) under fertilized (F) and non-fertilized (NF) conditions. Chemical fertilization (N–P2O5–K2O = 88–72–36 kg ha−1) increased crude protein (CP) concentrations in Heuknuri and Sogang by over 30%, while reducing the soluble sugar content by 15–24%. In contrast, starch content remained relatively stable across all cultivars. Gas chromatography–mass spectrometry (GC–MS) profiling revealed that fertilization caused only modest changes in grain primary metabolism, including increased fatty acids (oleate, linoleate), alongside consistent accumulation of amino acids related to nitrogen assimilation (asparate, asparagine, glutarate, proline). Two-way ANOVA and principal component analysis (PCA) revealed that the cultivar identity, rather than fertilization, was the dominant factor shaping metabolic variation, affecting 23 of 28 detected metabolites. Notably, Betaone and Heuknuri exhibited higher overall metabolite accumulation and stable metabolic profiles across treatments, suggesting better physiological adaptation to nutrient-deficiency stress. These results indicate that NPK fertilization under reclaimed soil conditions promotes nitrogen assimilation more than carbon storage, and grain metabolic changes are largely cultivar-dependent. However, the underlying regulatory mechanisms controlling carbon–nitrogen allocation and lipid metabolism under fertilization were not fully investigated and require further multi-omics and long-term field studies.