Optimizing Nitrogen, Phosphorus, and Potassium Use Efficiency in Temperate Vegetable Production in Latvia’s Agroecological Conditions

Optimizing nutrient uptake efficiency (NUE) through an understanding of system-level dynamics and crop-specific physiological thresholds is essential for the resilience of North European vegetable production under shifting climatic conditions. This study evaluated the uptake and efficiency of macro- and secondary nutrients (N, P, K, Ca, Mg) in cabbage, carrot, red beet, and onion over a five-year period (2021–2025) in Latvia, comparing organic and integrated management systems. It was hypothesized that NUE on commercial farms is currently suboptimal due to standardized bulk applications and that systems integrating sustainable practices would demonstrate higher nutrient uptake efficiency than those relying exclusively on mineral fertilization. The results revealed a notable yield–input divergence, where increased fertilization rates failed to provide proportional yield gains, as evidenced by the lack of a strong linear relationship (R2 < 0.07) and variable correlation coefficients (e.g., r = 0.52 for N in cabbage and r = −0.47 for Ca in carrot). These findings suggest that abiotic stressors and technical constraints may outweigh the influence of nutrient volume alone. This divergence was less pronounced in organic farming systems compared to integrated ones and varied notably by crop. Such species-specific responses indicate a complex role for mineral nutrition in root crops that requires further physiological investigation. No consistent differences in nutrient concentrations were observed between farming systems, indicating that inter-annual climatic variability is the dominant driver of nutrient dynamics. Furthermore, the integration of green manures and supplemental irrigation triggered extreme apparent system-level N-NUE values (exceeding 500% in some cases), reflecting the successful mineralization of legacy nitrogen and enhanced mass flow to the root zone. The study concludes that current fertilization methodologies in the Baltic region may lead to over-application. To ensure climate-resilient horticulture, management strategies must transition toward balancing ionic ratios (Ca:K) and synchronizing inputs with specific crop removal rates, rather than relying on standardized bulk applications.