| Border irrigation is used plenty for Isatis indigotica planting in northwest arid region,but it is huge waste of water for lower yield and quality.The result is that the yield and water use efficiency is low and unstable,so the sustainable development of the Isatis indigotica planting is restricted.Four soil moisture gradients were designed for the study Isatis indigotica as the research object,using the drip irrigation of Regulated Deficit Irrigation and combining field experiment and theoretical analysis.There were full irrigation,light water deficit,moderate water deficit and severe water deficit,all 10 water regulation treatment.The characteristics of water consumption and photosynthetic physiological indexes were studied,and the effects of different reproductive water stress on the yield and quality were analyzed,then a system of high yield and high quality irrigation will be established.The results are as following.(1)The change of water consumption intensity of Isatis indigotica was the smallest in the seedling stage,larger in fleshy root maturity,the largest in vegetative stage and fleshy root growth stage.Water consumption was affected significantly by water deficit.CK had the highest water consumption during the whole growth period(374.04mm in 2016,381.75mm in2017).Other treatments were significantly different from CK.The water consumption of light and moderate water deficit was significantly reduced by 6.74%~14.32%compared with CK.Severe water deficit had the lowest water consumption(WD8 and WD9),decreased significantly by 15.62%~17.69%.The effect of light water deficit on soil moisture of the root was not significant(p>0.05),but moderate and severe water deficit affect significantly the water content in the root soil layer.The soil moisture content of WD3,WD8 and WD9 was significantly decreased by 4.53%~8.92%(p<0.05).(2)The photosynthesis of Isatis indigotica was inhibited by moderate and severe water deficit.Compared with CK,the net photosynthetic rate of light water deficit was increased by1.82%~5.51%,stomatal conductance was increased by 2.1%~3.9%,and transpiration rate was increased by 0.9%~4.6%,but there was no significant difference(p>0.05).Moderate and severe water deficit reduced the net photosynthesis rate of Isatis indigotica by 7.8%~19.1%(p<0.05),and the stomatal conductivity was decreased by 5.8%~19.5%,and transpiration rate was decreased by 13.6%~26.6%significantly.The severe water deficit(WD3,WD8,WD9)had the greatest negative impact on the net photosynthetic rate,stomatal conductance and transpiration rate of Isatis indigotica.(3)The effect of light water deficit for Isatis indigotica was not significant(p>0.05),and moderate water deficit inhibited the growth of Isatis indigotica.Severe water deficit had a significant effect on the growth and dry matter(p<0.05),just as plant height,stem leaf biomass,root stem weight less than CK significantly.The root cap ratio of WD4 and WD1was significantly increased by 23.27%and 15.09%compared with CK.The light water deficit can regulate accumulation of dry matter,improving the root ratio significantly.The severe water deficit treatment of WD8 and WD9 was reduced by 12.21%and 15.89%significantly.The dry matter of moderate water deficit was reduced in WD5,WD6 and WD7 compared to CK,and the severe water deficit reduction was significantly lower than CK,with a decrease of 12.5%~31.1%.(4)The water use efficiency of Isatis indigotica was improved by light water deficit effectively,and economic output was obtained similar to the full irrigation.The light water deficit(WD1 and WD4)had no significant effect on the yield of Isatis indigotica(p>0.05).All the other water deficit treatments reduced the yield of Isatis indigotica,particulariy,WD3,WD7,WD8 and WD9 treatments with severe water deficit were significantly different from CK(p<0.05),decreased by 17.09%~37.42%.The total biomass of CK was the largest,and the total biomass of the remaining treatments decreased by 0.11%~33.68%compared with CK.The water deficit had a significant effect on water use efficiency.The WUE of WD1 and WD4 treated with light water deficit was increased significantly,which was 6.74%~8.45%higher than CK,and other treatments have reduced WUE,which WD2,WD3,WD7,WD8 and WD9 were significantly lower than CK,reduced by 6.47%~25.41%.The maximum yield is 8140kg/hm~2 when the water consumption is 370mm in 2016.The maximum yield is 8193kg/hm~2 when the water consumption is 381mm in 2017.When the water consumption increases more than this critical value,the yield of the Isatis indigotica reaches the maximum and no longer increases.(5)Based on the Blank addition model and Jensen multiplication model,the correlation coefficient R of the water production function model of Isatis indigotica was 0.988 and0.932 respectively,therefore,Blank model and Jensen model was reflected the relationship between the yield and the water consumption.The water sensitivity coefficient of each stage obtained under two models is seedling stage,fleshy root growth stage,vegetative stage and fleshy root maturity stage from large to small order.(6)There were significant differences for available nitrogen,available phosphorus and available potassium in the treatment between different water deficit in the soil after Isatis indigotica harvest(p<0.05).The available nitrogen,available phosphorus and available potassium of severe water deficit were similar to that before sowing,however,the content of alkaline nitrogen,available phosphorus and available potassium was significantly reduced in light and moderate water deficit.The number of bacteria,fungi and actinomycetes in soil gradually was decreased with the increase of soil depth.The water deficit did not affect significantly the amount of soil fungus and actinomycetes in the 0~20cm soil layer(p>0.05)in vegetative stage,and light water deficit increased the number of fungi and actinomycetes in the soil.The moderate and severe water deficit did not affect significantly the amount of fungi and actinomycetes in the soil in fleshy root growth stage.The activity of urease and sucrase in soil gradually decreased with the increase of soil depth.The full irrigation and light water deficit will not affect significantly urease activity in the 0~20cm soil layer,and it may improve the activity of sucrase in the soil layer of 0~20cm.(7)The water deficit treatment can increase the content of active ingredients and improve the quality of Isatis indigotica.However,the severe water deficit was not conducive to accumulation of active ingredients.The effecting of(R,S)-goitrin on water deficit treatment was the content(R,S)-goitrin of WD3 and WD8,WD9 lowered 8.59%~13.23%than CK significantly(p<0.05).In addition,the content(R,S)-goitrin was increased in fleshy root growth stage,vegetative stage by water deficit.The treatment of WD4 and WD5 was increased by 5.43%~7.94%significantly.The effecting of indirubin on water deficit treatment was that the light and moderate continuous loss is beneficial to the improvement of indirubin content.The differences between WD4,WD5,WD6 and WD7 from CK were significant,with the increase of 3.6%~9.9%.The calculation of comprehensive evaluation showed that WD4 and WD1 of light water deficit can not only obtained higher yield and WUE,but also improved the quality of Isatis indigotica.(8)Evaluation factors of comprehensive evaluation are economic yield,WUE,IWUE and(R,S)-goitrin for RDI drip irrigation.It was concluded that the comprehensive IEI was the highest in WD4 with light water deficit,WD1 second.There was no significant difference between WD4 and CK(p>0.05),however,WUE and IWUE were 8.0%and 7.2%higher than CK.Therefore,WD4 is treated as the optimal irrigation system under this test scheme. |
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