Climatic factors determine the yield and quality of Honghe flue-cured tobacco

Flue-cured tobacco is a key cash crop in Yunnan, producing about half of China’s total tobacco leaf yield. Owing to its unique climate and geography, Yunnan produces high-quality leaves but tobacco is sensitive to environmental conditions. Prior work shows that climate (light, temperature, water) and soil (pH, fertility, microbes) strongly influence yield and quality, with temperature and moisture affecting growth, curing quality, disease resistance, and leaf chemistry (sugars, nicotine, potassium). However, the combined effects and relative contributions of climatic and soil factors in Honghe remain unclear. In 2015, most flue-cured tobacco in the Honghe Tobacco Zone was planted across four counties (Luxi, Mile, Jianshui, Shiping) using three cultivars (K326, Honghuadajinyuan/Hongda, and Yunyan87/Yun87). This study aimed to determine: (1) whether yield and quality of these cultivars differ among the four sites, and (2) which environmental variables (climatic vs soil) most strongly explain differences in yield and quality.

The paper reviews evidence that ecological conditions substantially affect tobacco yield and quality. Temperature influences soil carbon mineralization and plant resistance, while both low and high temperatures can reduce yield and quality (e.g., early flowering, curing defects, forced ripening). Moisture strongly affects biomass, leaf area, sugar, nicotine, and disease incidence; tobacco is particularly sensitive to water deficits, with varied proteomic responses among cultivars (e.g., Yunyan87 vs Yuyan6). Prior studies in Guizhou found positive correlations of total and reducing sugars, total nitrogen, and potassium with irrigation, and negative relationships of nicotine, protein, and chlorine with irrigation. Soil properties (pH, organic matter, nutrient balance, microbial communities) also shape growth and chemistry; inappropriate nitrogen can cause excessive growth and degrade quality. While individual effects are known, the combined and relative impacts of climate and soil on tobacco leaf quality in Honghe have not been fully quantified.

Study area: Hani-Yi Autonomous Prefecture of Honghe, Yunnan, China (22.43–24.75°N, 101.78–104.27°E), plateau subtropical monsoon climate; average annual rainfall ~1491 mm; annual sunshine 1065–2300 h. Temperatures during growing season: >20 °C (May–Aug), 20.4–24.6 °C in September. Cultivars and sites: Three cultivars (K326, Yunyan87/Yun87, Honghuadajinyuan/Hongda) planted at four sites: Jianshui (JS), Luxi (LX), Mile (ML), and Shiping (SP). Site characteristics (ranges): Elevation approx. 1206–2198 m; various soil types (red, yellow, paddy; ML also clay, purple). Field-period (May–Aug) climate summaries and soil properties (clay, pH, SOM, AN, AP, AK, SCL) are tabulated (Table 1). Field management: Standard Virginia tobacco practices per Tobacco Institute of Yunnan. Seedling stage: floating breeding (Mar 1–10). Transplanting under plastic film (Apr 10–20), spacing 120 cm × 50 cm; density 15,000–16,500 plants/ha. Irrigation sources varied (water cellars, ponds, reservoirs, rivers, springs/wells; some fields without facilities). Dominant rotation: tobacco→corn→tobacco (75.33%). Fertilization: K326 and Yun87 received 90–110 kg N/ha with N:P2O5:K2O of 1:1:2.5–3.0 and 1:1:3.0–3.5, respectively; Hongda received 60–75 kg N/ha with 1:1:3.0–5.0. Integrated pest and disease management used physical, biological (priority), and chemical (supplementary) measures. Topping: K326/Yun87 around June 5; Hongda around May 30; plant heights post-topping ~90–110 cm. Harvesting: staged from June 30 to Sept 10; middle leaves (C3F grade) collected in August after 85–95 days growth and 30–40 days after topping; cured using intelligent baking regimes. Grades followed GB2635-1992; economic value computed from grade values and yield; proportion of superior middle and superior grades estimated from national purchasing data. Sampling: Soil—39 (JS), 76 (LX), 87 (ML), 42 (SP) samples (0–20 cm layer, S-shaped composite of 10 subsamples), GPS-located; sieved to 2 mm and stored cold before lab analyses. Tobacco plant samples of the three cultivars collected at the same sites. Measurements: Leaf chemistry on C3F grade middle leaves. PTN (YC/T161-2002), PTK (YC/T173-2003), PCL (YC/T162-2011), PTS and PRS (YC/T159-2002), PN (LY/T1228-2015), starch PS (NY/T1121.7-2014), petroleum ether extract PPE (NY/T889-2004). Ratios computed: PSA (sugar/alkaloid = total sugar/total alkaloids) and PNA (total N/total alkaloids). Soil: clay fraction <0.001 mm (NY/T1121.3-2006), pH (NY/T1377-2007), SOM (NY/T1121.6-2006), AN (LY/T1228-2015), AP (NY/T1121.7-2014), AK (NY/T889-2004), SCL (NY/T1378-2007). Meteorology: Historical (1980–2010) and monitoring (2013–2015) data from Yunnan Meteorological Observatory via Honghe Tobacco Company. Standardized to derive field-period (May–Aug) average temperature and relative humidity, and cumulative sunshine hours and rainfall. Statistics: Checked residual normality (kurtosis, skewness) and homoscedasticity; rank-transformed yield, proportion, and SCL where needed. ANOVA with Duncan’s test (p<0.05) for site, cultivar, and interaction effects. Pearson correlations between yield/quality variables and environmental (soil, climate) factors. Redundancy analysis (RDA) to relate yield/quality to ecological variables; forward selection with Monte Carlo permutation (499 iterations) to identify significant predictors (p<0.05). Software: SPSS 17.0 and Canoco 4.5.

• Yield and economics: Site × cultivar interactions significantly affected yield, economic value, proportion of superior middle tobacco, and number of left leaves. Generally, K326 had more left leaves and higher proportion of superior middle tobacco but lower yield and economic value than Hongda; Hongda achieved higher economic value despite fewer left leaves and lower superior middle proportion. K326 and Yun87 had higher yield and economic value at ML, with yield +8.00–18.18% and economic value +7.54–16.23% compared to other sites.
• Climatic drivers of yield: Yield was negatively correlated with field rainfall and relative humidity and positively correlated with field temperature and sunshine hours, indicating higher yields in sunnier, drier conditions.
• Site effects on quality traits (Table 3): PN in K326 and Hongda was higher at JS and SP than at LX and ML; Yun87 PN showed no significant site difference. PRS in Hongda and Yun87 was higher at ML and SP; K326 PRS did not differ among sites. PPE was lowest at LX for all cultivars. PTK was higher and PCL lower at ML and SP; across cultivars, PTK and PCL ranked K326 > Hongda > Yun87. PTN was higher and PSA lower at JS and SP; PTN lower and PSA higher at LX and ML. PSA > 11 and PNA < 1 for all cultivars (K326 had the highest average PSA and PNA among cultivars).
• Correlations with soil factors: PTS, PRS, PTK, PCL, and PPE were negatively related to soil pH; PRS and PTK were positively correlated with AN. PCL and PPE were negatively correlated with soil clay content and positively with SCL. Several components (PTS, PRS, PTK, PCL, PPE) were negatively associated with SOM and clay content.
• Correlations with climate: Besides PTS, most chemical components were significantly associated with climate. PN and PRS were positively related to sunshine hours; rainfall was negatively correlated with PTN and PRS but positively with PS. PSA and PNA were negatively correlated with temperature and positively with relative humidity. PCL and PS were positively associated with moisture (rainfall, humidity) and negatively with temperature/sunshine.
• RDA (variance explained by first two axes): K326—axes 1 and 2 explained 53.1% and 17.2%; key predictors: field rainfall (29%) and AN (12%). Hongda—axes 1 and 2 explained 53.7% and 13.3%; key predictors: field temperature (25%), clay (18%), AP (18%). Yun87—first two axes explained 69.1%; key predictors: field rainfall (21%), field sunshine hours (12%), and SCL (21%).
• Ecogeographic patterns: High-latitude/high-altitude sites (ML, LX) favored higher PTS, PPE, and PS (carbon supply), while low-latitude/low-altitude sites (JS, SP) with higher temperature and longer sunshine favored higher PTN and PN (nitrogen supply). Overall, climatic factors affected 11 variables versus 7 for soil factors.

The study addressed whether yield and quality differ among major Honghe sites and which environmental variables dominate these outcomes. Results show that climate—particularly temperature, sunshine, rainfall, and relative humidity—more strongly regulates yield and most quality components than soil does. Yield increased with warmth and sunshine and decreased with rainfall and humidity, aligning with known physiological sensitivities of tobacco to temperature and water status. Quality traits responded differentially: components tied to nitrogen metabolism (PTN, PN) increased under warmer, sunnier, drier conditions, while those reflecting carbon accumulation (PTS, PPE, PS) were higher in cooler, moister, higher-altitude/latitude conditions. Soil properties still played notable roles: pH, clay content, AN, AP, and SCL influenced several chemical indices (e.g., pH negatively related to PTS/PRS/PTK/PCL/PPE; AN positively to PRS and PTK; SCL to PCL and PPE). RDA clarified cultivar-specific sensitivities: K326 quality and yield were more moisture-driven (rainfall) and responsive to AN; Hongda was primarily temperature-driven and influenced by clay and AP; Yun87 was shaped by rainfall, sunshine, and SCL. These findings inform site–cultivar matching and management: positioning temperature-sensitive cultivars (e.g., Hongda) in warmer microclimates and managing moisture for K326 and Yun87 can optimize both yield and leaf chemistry. The results underscore the need to integrate climatic risk and soil nutrient/chlorine management for quality stabilization.

Thirteen variables affecting yield and internal chemistry were identified, with climatic factors influencing 11 variables and soil properties influencing 7. Key soil determinants were pH, clay, AN, AP, and SCL. Higher temperatures and longer sunshine enhance yield and elevate PTN and PN, while lower temperatures, shorter sunshine, and higher rainfall increase PTS, PPE, and PS. Economic value did not increase with more left leaves or higher proportions of superior grades. Cultivar responses differed: K326 and Yun87 were mainly influenced by moisture-related factors, while Hongda was primarily affected by temperature. Overall, climatic conditions are the principal drivers of yield and quality of Honghe flue-cured tobacco, suggesting that cultivar deployment and management should prioritize local climatic regimes alongside targeted soil nutrient and chlorine management.

• Spatial heterogeneity: At the SP site, dispersed sampling points may have affected analyses of AN, SOM, and SCL.
• Management variability: Although standard practices were used, field-to-field differences in fertilizer rates and irrigation sources likely introduced variability not fully controlled for, potentially confounding environmental effects.
• Observational constraints: Relationships are largely correlational; mechanistic validation (e.g., controlled experiments on drought/temperature responses) is needed, especially to distinguish cultivar-specific stress responses.
• Agronomic factors: Effects of specific agronomic practices (e.g., precise irrigation scheduling, nitrogen form/timing, leaf removal regimes) were not experimentally manipulated here; future work will test optimal agronomy per cultivar and assess plant–soil interactions within the same fields.