Efficient nutrient management is vital to sustaining rice production in the sandy soils of Northeast Thailand, where zinc (Zn) deficiency and low organic matter often constrain yield. This study evaluated the effects of Zn fertilization on the growth, yield, and Zn use efficiency (ZUE) of rice (Oryza sativa L. cv. Chai Nat 1) grown under greenhouse conditions in contrasting soil textures (loamy sand and clay). Four Zn rates were applied: 0, 5, 10, and 15 kg ZnSO₄·7H₂O ha⁻¹ (0, 0.013, 0.026, and 0.039 g ZnSO₄·7H₂O pot⁻¹). Clay soil, with higher organic matter, nitrogen, and available Zn, supported greater vegetative growth, biomass, and yield than loamy sand. Zinc fertilization significantly increased plant height, tiller number, chlorophyll content, biomass, panicle number, grain number, and filled grain weight. Yield improvement in loamy sand was associated mainly with reproductive efficiency, whereas in clay it was driven by vegetative vigor, biomass accumulation, and Zn uptake. Thousand-grain weight was not affected by Zn. ZUE peaked at 5 kg ha⁻¹ in loamy sand and 10 kg ha⁻¹ in clay, with clay showing a greater overall increase in ZUE across Zn rates and loamy sand exhibiting diminishing returns at higher application rates, reflecting differences in Zn availability and retention capacity. Correlation, PCA, and SEM analyses confirmed soil-specific yield mechanisms. Overall, Zn fertilization improved rice productivity and tissue Zn concentration, with optimal rates differing by soil texture. These findings highlight the importance of site-specific Zn management in enhancing yield, nutrient efficiency, and biofortification in rice-based systems of Northeast Thailand.

Cultivar-dependent responses of Jerusalem artichoke (Helianthus tuberosus L.) to combined potassium (K) and zinc (Zn) fertilization remain poorly understood, particularly under low-fertility sandy loam conditions in tropical environments. This study evaluated growth, yield, and tuber-quality responses to K and Zn fertilization in a greenhouse. A 2 × 4 × 3 factorial experiment included two cultivars [CN 52867 × JA6-23 (V1) and JA37 × HEL65 (V2)], four supplemental K application rates (0, 0.61, 1.22, and 1.83 g K pot⁻¹) and three supplemental Zn application rates (0, 0.05, and 0.10 g Zn pot⁻¹). Potassium exerted a more consistent influence on growth and tuber production than Zn, whereas Zn responses varied with cultivar, trait, and nutrient combination. Significant cultivar × K × Zn interactions were detected for tuber number (p < 0.001) and tuber dry weight (p = 0.016). At the highest K rate (1.83 g K pot⁻¹), increasing Zn reduced tuber number in V1 from 38.00 to 19.00 tubers plant⁻¹, whereas in V2 it increased from 17.33 to 26.67 tubers plant⁻¹. Across cultivars and Zn treatments, tuber dry weight increased from 38.53 g plant⁻¹ without supplemental K to 45.91 g plant⁻¹ at 1.83 g K pot⁻¹ and was positively correlated with aboveground biomass (r = 0.77) and stem diameter (r = 0.76). Multivariate analysis further illustrated associations among growth, yield, physiological, and quality traits. From a practical perspective, these results indicate that K and Zn management in Jerusalem artichoke should consider cultivar-dependent nutrient responses rather than assuming a uniform fertilizer response. However, these findings are specific to the tested fertilizer rates and controlled pot conditions and require field validation before cultivar-specific fertilizer recommendations can be established.

Nitrogen (N) management is critical for improving rice productivity, but increasing N inputs may reduce N-use productivity when grain production does not increase proportionally. This study evaluated the effects of urea rate and application method on grain weight and partial factor productivity of N (PFPN) of rice (Oryza sativa L. cv. RD49) grown in low-fertility sandy loam soil under controlled greenhouse pot conditions. Three urea rates (0.53, 1.07, and 1.60 g pot⁻¹) and two application methods—basal application (BD) and basal plus topdressing (BTD)—were evaluated across two growing seasons. Grain weight was significantly affected by urea rate, application method, and their interaction. The lowest urea rate (N1; 0.53 g pot⁻¹) maintained grain weight comparable to the highest rate (N3; 1.60 g pot⁻¹) while producing the highest harvest index and substantially greater PFPN. Grain weight exhibited a significant quadratic response to urea rate, whereas PFPN, calculated on the basis of total fertilizer N applied, showed significant linear and quadratic responses and declined markedly with increasing urea rate. BTD resulted in greater mean grain weight and PFPN than BD. These findings indicate that the lowest tested urea rate provided a favorable balance between grain production and fertilizer-N input under the conditions evaluated, while the greater grain weight and PFPN under BTD highlighted the importance of coordinating N rate and application timing. These findings provide a basis for targeted field validation of N rate and application timing for RD49 rice grown in low-fertility, coarse-textured soils.