| Flue-cured tobacco（Nicotiana tabacum L.）is one of the most important cash crops in southern Shaanxi province.Soil moisture is the main environmental factor affecting agricultural production.Water deficit is caused by unreasonable distribution of rainfall and the decrease of soil water holding capacity due to poor soil structure caused by long-term application of chemical fertilizers in southern Shaanxi tobacco-growing areas,which inhibit the growth and development of flue-cured tobacco and diminish the yield and quality of tobacco leaves.Applying organic materials is a simple and effective agronomic measure which maintain soil moisture in agricultural planting.Many studies have shown that humic acid,vermicompost,biochar and other organic materials have been widely used in the production of some crops,which can reduce the adverse reactions of water deficiency on plants and enhance their stress resistance.At the same time,soil physical structure and water characteristics can be improved effectively,and soil water holding capacity can be enhanced.In this study,five formulations of three organic materials were obtained by uniform design,namely,T1（potassium humate 71.13%,vermicompost 21.65%,biochar 7.22%）,T2（potassium humate 50.00%,vermicompost 20.83%,biochar 29.17%）,and T3（potassium humate 35.45%,vermicompost 59.17%,biochar 5.38%）,T4（potassium humate 23.62%,vermicompost 44.55%,biochar 31.82%）and T5（potassium humate13.40%,vermicompost 21.65%,biochar 64.95%）,with CK（pure chemical fertilizer control）.Through pot and field experiments,there were studied in the effects of different organic material formulations on soil moisture characteristics,antioxidant properties and leaf quality of flue-cured tobacco.The main results are as follows:1.Combined application of organic materials can improve the osmotic adjustment and antioxidant capacity of tobacco leaves under water deficit,and reduce the accumulation of reactive oxygen species in tobacco leaves.The contents of osmotic adjustment substances such as proline（Pro）,soluble protein and soluble sugar in tobacco leaves were significantly increased by combined application of organic materials,and the contents of Pro and soluble sugar in T3 treatment were increased by 91.53%and 13.08%respectively compared with CK-G（pure chemical fertilizer treatment under water deficit）.The combined application of organic materials could also improve the activities of antioxidant enzymes such as superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）,and the contents of antioxidants such as ascorbic acid（As A）and reduced glutathione（GSH）in tobacco leaves,enhance the antioxidant defense of tobacco leaves,and alleviate the oxidative damage caused by water deficit.Among them,the SOD activity of T2 treatment was 50.88%higher than that of CK-G treatment,and the POD activity of T3 treatment increased by 58.80%compared with CK-G treatment.In addition,the application of organic materials could significantly reduce the content of reactive oxygen species in tobacco leaves,the contents of superoxide anion(O2·-)and malondialdehyde（MDA）in T2 treatment decreased by50.32%and 38.30%compared with CK-G.In summary,The T2 and T3 treatments had better effects on alleviating oxidative damage and enhancing antioxidant capacity of flue-cured tobacco under water deficit.2.The combined application of organic materials could improve the soil physical properties of tobacco-growing soil and enhance the water retention of soil.Compared with CK treatment,the combined application of organic materials could effectively improve the bulk density,total porosity and capillary porosity of tobacco-growing soil at rosette stage,vigorous stage and dome stage,and optimize the proportion of soil solid phase,liquid phase and gas phase.The T2 and T3 treatments were better.At the same time,the combined application of organic materials can significantly improve the field capacity,capillary capacity,available water capacity and soil moisture absorption coefficient of tobacco-growing soil in the later stage of flue-cured tobacco growth,and enhance soil water holding capacity.In the flue-cured tobacco dome stage,the soil field capacity of T2treatment was 14.51%higher than that of CK treatment,and the soil capillary capacity of T3 treatment increased by 12.80%compared with CK treatment.3.The combination of organic materials could effectively improve the quality and yield of flue-cured tobacco.The combined application of organic materials could increase the contents of nicotine,total nitrogen and potassium in flue-cured tobacco leaves,and improve the ratio of reducing sugar to nicotine and the ratio of nitrogen to nicotine.The improvement effect of T3 treatment was better.The combined application of organic materials could also increase the contents of total phenols,free amino acids and other aroma precursors in flue-cured tobacco leaves,and the treatment effects of T1 and T3 were better.The application of organic materials could improve the contents of neutral aroma components in flue-cured tobacco leaves,among which T3 treatment had better effect on improving the contents of aroma components degraded from phenylalanine and Products degraded by cembrane.The combined application of organic materials can increase the economic traits such as yield and output value of flue-cured tobacco leaves,and increase the input-output ratio of flue-cured tobacco planting,and the T2 treatment has better performance.Finally,the combination application of organic materials can alleviate oxidative damage produced by water deficit in plants.It can improve soil water retention,improve the quality of flue-cured tobacco,and boost tobacco yield.Overall comparison shows that T3 treatment has better comprehensive lifting effect.The findings provided a technical support for enhancing water holding capacity of tobacco-growing soil,improving crop drought resistance and improving tobacco yield in southern Shaanxi tobacco-growing region. |
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