Integrating preceding crop sequences with foliar-applied boron to enhance soil fertility, yield formation, and sugar beet quality in a semi-arid ecosystem

Abstract

Abstract Background Optimizing sugar beet productivity and sustainability requires integrating nutrient management with preceding crop sequence (PCS) strategies. However, foliar boron (B) efficacy relies heavily on the biological legacy and fertility status created by the PCS, which alters soil fertility and plant physiological responses. This study evaluated the interactive effects of PCS and foliar B on soil properties, sugar beet yield, and system sustainability. Methods A two-season strip-plot field experiment (2023/24 and 2024/25) in a complete randomized block design with three replications was conducted in Egypt using sugar beet cv. “BTS 195”. The vertical strips were assigned to four PCS treatments: rice-fallow (PCS-I), rice-clover (PCS-II), soybean-fallow (PCS-III), and soybean-clover (PCS-IV), whereas the horizontal strips were allocated to four foliar-applied B at 0 (B 0 ), 100 (B 100 ), 200 (B 200 ), and 300 (B 300 ) mg L⁻¹, applied 60- and 80-days post-sowing. Soil chemistry, plant physio-biochemical traits, sugar yield, and economic sustainability indices were assessed. Multivariate analyses (correlation heatmap and PCA) were performed. Results PCS fundamentally shaped the agronomic baseline, while B acted as a physiological regulator. Compared to PCS-I, PCS-IV enhanced soil organic carbon by 7.0%, soil fertility index by 10.0%, and available N and P (by 17.0% and by 34.0%, respectively). However, this soil enrichment under PCS-IV did not translate to optimal yield; instead, it increased root K⁺ and Na⁺ accumulation, which raised sugar loss to molasses by 31.4%. Conversely, PCS-III maximized crop performance relative to PCS-IV, significantly increasing leaf area index (LAI; by 65.4%), shoot biomass by 49.0%, and root yield by 12.7%, which drove a 14.7% increase in gross sugar yield due to superior assimilate partitioning. Boron applications were trait-specific: 200 mg L⁻¹ optimized canopy growth (LAI by 27.8%) and biomass, whereas 300 mg L⁻¹ maximized root and sugar yields (by 7.5% and 9.3% over 100 mg L⁻¹, respectively). Significant PCS × B interactions revealed a productivity-driven pathway (PCS-III combined with 200–300 mg L⁻¹ B) generating the highest physiological efficiency, and a soil-fertility-driven pathway (PCS-IV with 300 mg L⁻¹ B). Economically, the PCS-II × 300 mg L⁻¹ B interaction balanced rotation performance, achieving the highest net profit and sustainability index (by 18.6% over control), while PCS-II and PCS-IV improved land-use efficiency. Multivariate analyses identified a productivity-driven pathway (PCS-III × 200 mg L⁻¹ B) and a soil-fertility-driven pathway (PCS-IV × 300 mg L⁻¹ B). Conclusions The interplay between crop sequence and boron nutrition strongly dictates sugar beet outcomes. PCS-III, combined with moderate-to-high B (200–300 mg L⁻¹), optimally maximizes physiological activity, biomass, and sugar yield. Alternatively, PCS-IV best enhances soil fertility, though it comes with trade-offs in sugar extractability. Systemically, integrating a rice-clover sequence (PCS-II) with 300 mg L⁻¹ B delivers a superior economic and sustainability profile. This study underscores that aligning crop succession, specifically adopting a soybean-fallow (PCS-III) sequence for maximum yield or a rice-clover (PCS-II) sequence for peak economic profitability, with targeted B management is essential for optimizing productivity, sustainability, and soil health in sugar beet agroecosystems.