Regulating Effect Of Irrigation And Nitrogen Supply On The Photosynthetic Characteristics, Yield And Quality Of Stevia Rebaudiana

In recent years, the shortage of water resources and excessive applying nitrogenfertilizer were major factors to restrict oasis agricultural development of Hexi, Gansu.A field experiment was carried out to study the effects of different irrigation andnitrogen supply on photosynthetic characteristics, dry leaf yield, glycoside content,water and nitrogen use efficiency of Stevia rebaudiana in Gansu State FarmsAcademy of Agricultural Reaserches of Hexi during2010to2011. The experimentdesigned three irrigation volume levels (conventional,320mm and340mm;20%water-saving,256mm and272mm;40%water-saving,192mm and204mm) andfour nitrogen application levels N0, N100, N200,N300(equivalent to pure nitrogen:0、100、200、300kg·hm-2). The main results were follows:1. In the oasis irrigation agriculture area of Hexi, Gansu, China, Pn, Tr and Gs ofStevia rebaudiana was a single peak curve which appeared “low-high-low” during thewhole growth period, Pn、Tr and Gs reached high peak in squaring period, while Citaked on “high-low-high”, its low peak also appeared in squaring period.2. There was significant interaction effect between irrigation and nitrogen supply(P＜0.05or P＜0.01), irrigation and nitrogen had the significant regulating effect onPn, Tr, Gs and Ci of Stevia rebaudiana (P＜0.05), as the growth period continued, Pn,Tr and Gs appeared first increased and then decreased with the decrease of irrigationvolume, while Ci appeared first decreased and then increased. Under20%watersaving (I256, I272) Pn, Tr and Gs were the highest, Ci was the lowest. With the increaseof nitrogen, in each growing stage, Pn and Gs appeared first increased and thendecreased, while Tr continued to rise, Ci apperad first decreased and then increased.Under20%water-saving (I256, I272) and nitrogen application200kg·hm-2comparedwith other nitrogen treatments (0,100and300kg·hm-2), Pn and Gs were increased by23.21,10.63,0.29%and5.51,2.13,0.24%respectively, while Ci accordinglydecreased by7.61,2.76and0.53%, when nitrogen supply increased to300kg·hm-2,compared with other three nitrogen treatments (0～200kg·hm-2), Tr was increased by42.76,34.48and19.08%respectively. Correlation analysis showed that Pn and Tr, Gswas extremely significant positive correlation, correlation coefficient was0.838and0.815respectively, while Pn and Ci was extremely significant negative correlation (r=-0.581). 3. Different irrigation and nitrogen supply had significant regulating effect on drymatter accumulation of Stevia rebaudiana (P＜0.05or P＜0.01) in each growth stage.Dry matter accumulation had very significant positive correlation with dry leaf yieldduring seedling to branching stage, branching to squaring stage and squaring toharvest stage, dry matter accumulation and dry leaf yield had the highest degree ofcorrelation during branching to squaring stage(r=0.933). Dry matter accumulationpromoted with the nitrogen supply increase, when nitrogen application was more than200kg·hm-2, dry matter accumulation gradually reduced or rised a little. Under40%water-saving(I192, I204), dry matter accumulation of each nitrogen supply treatmentwas significant higher than that of no nitrogen fertilizer treatment, but dry matteraccumulation was lower than that of the same nitrogen supply treatment with differentirrigation.4. Irrigation and nitrogen application had the significant regulating effect on dryleaf yield and dry weight of leaf per plant of Stevia rebaudiana(P＜0.05or P＜0.01),there was a significant positive correlation between dry leaf yield and dry weight ofleaf per plant(r=0.635). When nitrogen supply increased from100kg·hm-2to300kg·hm-2, dry leaf yield and dry weight of leaf per plant appeared first increased andthen decreased with the irrigation volume reduce, there were significant differencesbetween different irrigation treatments, under different nitrogen supply treatment withthe same irrigation level, dry leaf yield and dry weight of leaf per plant promoted withthe nitrogen supply increase, when nitrogen supply was more than200kg·hm-2, theincreasing trend became slow obviously, when20%water-saving(I256, I272), nitrogensupply300kg·hm-2, dry leaf yield and dry weight of leaf per plant were the highestwhich were increased by10.54,3.21,0.02%and13.97,2.37,1.17%respectivelycompared with nitrogen supply0,100,200kg·hm-2treatments.5. Irrigation and nitrogen application had the significant regulating effect on SGscontent of Stevia rebaudiana (P＜0.05). There were significant positive correlation ofSGs with St, R-A and R-C,(r=0.907,0.830and0.832). The change of SGs wassignificant difference between different irrigation and nitrogen supply, when nitrogensupply increased from100kg·hm-2to300kg·hm-2, SGs appeared first increased andthen decreased with the irrigation volume reduce, under the same irrigation volume,SGs also gradually increased with nitrogen supply increase. When nitrogen supplyreached to200kg·hm-2,20%water-saving (I256, I272) treatment SGs content was the highest which was increased by6.09,2.13and0.22%respectively compared withnitrogen supply0,100,300kg·hm-2treatments. With the irrigation volume decreaseor nitrogen supply increase, Stevioside all appeared first increased and then decreased,there were significant differences between different treatments, But irrigation andnitrogen supply had little effects on R-A and R-C, there were no significantdifferences between irrigation and nitrogen supply treatments.6. Irrigation and nitrogen supply had significant regulating effect on WUE ofStevia rebaudiana (P＜0.05) and had significant positive correlation with dry leafyield(r=0.654). When nitrogen supply increased from100kg·hm-2to300kg·hm-2,WUE appeared first increased and then decreased with the irrigation amount reduce,with nitrogen supply increase, WUE also appeared first increased and then decreased.When20%water-saving (I256, I272), WUE was the highest under nitrogen supply200kg·hm-2, which was increased by22.14,11.42and4.34%respectively compared withnitrogen supply0,100and300kg·hm-2.7. Different irrigation and nitrogen application had significant regulating effecton the nitrogen apparent efficiency and nitrogen fertilizer production efficiency ofStevia rebaudiana (P＜0.05). Under the same nitrogen application, nitrogen apparentefficiency appeared first increased and then decreased with the irrigation amountreduce, and20%water-saving (I256, I272), nitrogen apparent efficiency was significanthigher than that of conventional irrigation (I320, I340) and40%water-saving (I192, I204),it was increased by9.96and24.75%respectively. Nitrogen apparent efficiencypromoted with nitrogen supply increase, when nitrogen supply was more than200kg·hm-2, nitrogen apparent efficiency gradually reduced or rised a little. Under thesame nitrogen supply, the nitrogen fertilizer production efficiency were significantdifferences between different irrigation treatments, under the same irrigation level,there were also significant differences between different nitrogen supply treatments.8. Under different irrigation and nitrogen supply, in each growth stage, there wassignificant positive effect between Pn and Gs of Stevia rebaudiana (R2=0.74), therewas significant negative effect between Pn and Ci (R2=0.80), there was significantpositive effect between Pn and dry matter accumulation (R2=0.64,0.84and0.93). Theincrease of Pn played a significant promoting role on dry leaf yield (R2=0.9364), ithad significant effect on WUE and nitrogen apparent efficiency, but it had no obviouseffect on SGs. 9. In summary, considering water resources saving, reducing environmentalpollution caused by excessive application of nitrogen, increasing plant yield, waterand nitrogen use efficiency etc,20%water-saving and nitrogen supply200kg·hm-2was more appropriate combination of water and fertilizer cultivation mode in oasisirrigation area of Hexi, Gansu, it not only developed water-nitrogen interaction andstrengthened photosynthesis in plants but also increased dry leaf yield, SGs content,water and nitrogen use efficiency.