Effect Of Partial Root-Zone Irrigation On Growth, Water And N K Use Of Flue-Cured Tobacco

Partial root-zone irrigation (PRI) such as fixed partial root-zone irrigation andalternate partial root-zone irrigation, is a new water-saving and high-quality technique.The pot and field experiments were conducted to investigate the effects of PRI on thegrowth, physiological characteristics, dry mass accumulation, yield, water, nitrogen (N)and potassium (K) use of flue-cured tobacco (Nicotiana tabacum L.) under differentwater and fertilization condition. Three irrigation methods, i.e. conventional irrigation(CI), fixed partial root-zone irrigation (FPRI) and alternate partial root-zone irrigation(APRI) were designed for all experiments. Four N levels, i.e. 0, 0.10 g N kg^-1, 0.20 g Nkg^-1 and 0.30 g N kg^-1 were designed for Experiment 1. Two K levels, i.e. 0.6 g K₂O kg^-1and 0.8 g K₂O kg^-1, and three ammonium-N and nitrate-N ratios (NH₄/NO₃ ratios), i.e.2:1, 1:1 and 1:2, were designed for Experiment 2. Two irrigation levels, i.e. lowerirrigation water and higher irrigation water, and three K levels, i.e. 0.4 g K₂O kg^-1, 0.6 gK₂O kg^-1 and 0.8 g K₂O kg^-1, were also designed for Experiment 3. Three irrigationmethods i.e. conventional furrow (CF), fixed furrow (FF) and alternate furrow (AF),were designed for field experiment. Main results are outlined as follows:(1) Compared to CI, mean photosynthesis rate, transpiration rate and stomataconductance in FPRI and APRI treatments are reduced by 9.2% and 6.5%, 18.9% and12.7%, 13.2% and 17.1% 54d after transplanting (at the mid time of growing stage)under different NH₄/NO₃ ratios, respectively, indicating that the reduction of photosynthesis rate is lower than that of transpiration rate and then leaf water useefficiency (WUE) increases. FPRI and APRI treatments reduce maximal leaf area by14.4% and 13.7% 51d after transplanting under N fertilization condition, respectively.However, FPRI and APRI treatments increase the maximal leaf area 55d aftertransplanting under different NH₄/NO₃ ratios and 62d after transplanting underdifferent K fertilization condition.(2) Compared to CI, mean total yield in FPRI and APRI treatments during thewhole growth period respectively reduce by 16.5% and 14.5% under N fertilizationcondition. Under different NH₄/NO₃ ratios, FPRI treatment increases total yield by 8.6%but APRI treatment reduces it by 0.8% during the root developing and ripening stages.FPRI and APRI treatments respectively reduce yield by 9.6% and 11.1% in the rootdeveloping and ripening stages under different K fertilization condition. In the fieldexperiment, FF and AF treatments reduce total yield by 2.3% and 0.7%, respectivelywhen compared to CF treatment.(3) Compared to CI, PRI reduces water consumption but increases tobacco WUE.PRI reduces the water consumption by 19.3-22.9%, but FPRI and APRI treatmentsrespectively increase WUE by 7.5% and 11.2% under different N fertilization levels.FPRI and APRI treatments increase WUE by 10.2% and 2.0% under different NH₄/NO₃ratios and by 19.8% and 19.5% under different K fertilization levels, respectively.(4) PRI can improve leaf N and K content, which are in the suitable N and Kcontent. Compared to CI treatment, FPRI treatment enhances middle leaves N contentunder 0.20 g N kg^-1 and 0.30 g N kg^-1 levels. Under different N fertilization condition,APRI treatment enhances middle leaf N content by 25.4%, and FPRI and APRI increasemiddle leaf K content by 30.4% and 73.2%, respectively. Under different NH₄/NO₃ratios, FPRI and APRI treatments enhance middle leaf N and K content by 7.8% and0.9%, 4.5% and 6.5%, respectively. While under different K fertilization levels, FPRIand APRI increased middle leaf N content by 45.9% and 61.3% and leaf K content by19.1% and 16.9%, respectively. In the field experiment, FF and AF treatments increasemiddle leaf N and K content compared to CF treatment.(5) In a certain N fertilization levels, FPRI and APRI treatments slightly increase middle leaf protein, nicotine and reduing sugar content, but reduces N/nicotine ratiowhen compared to CI treatment. And FPRI treatment reduces sugar/nicotine ratio, butAPRI treatment increases slightly. The content of several above-mentioned chemicalcomponents falls in the suitable content or is close to the ideal ratio of tobaccoproduction.The above-mentioned results indicate that PRI can be used in the production offlue-cured tobacco. It can reduce water use and improve WUE and K content withoutsignificant effect the growth and yield of flue-cured tobacco. However, partial root-zoneirrigation in different growth stages may have different effect on tobacco productionunder different water and fertilization condition.