| China is the largest apple production country in the world, while Shanxi province is one of the domestic high-quality apple production bases. In North China, water shortage issue has become the major limiting factor of orchard industry development. Water storage pit irrigation is a new tridimensional irrigation method with the advantages of water saving and drought resistence. Based on the current research situation of water storage pit irrigation, this paper established 6 water storage pit irrigation treatments in the apple orchard of Shanxi Academy of Agricultural Sciences. To illustrate, T1 treatment’s upper and lower irrigation limit in whole growing stages is 70% and 100% of field capacity, resepctively; T2 treatment’s upper and lower irrigation limit in whole growing stages is 60% and 90% of field capacity, respectively; T3 treatment’s upper and lower irrigation limit in whole growing stages is 50% and 80% of field capacity, respectively; T5 treatment’s upper and lower irrigation limit in germination stage is 70% and 100% of field capacity while 50% and 80% of field capacity in other growing stages, respectively; T6 treatment’s upper and lower irrigation limit in branch shooting stage is 70% and 100% of field capacity while 50% and 80% of field capacity in other growing stages, respectively; T7 treatment’s upper and lower irrigation limit in fruit expanding stage is 70% and 100% of field capacity while 50% and 80% of field capacity in other growing stages, respectively. The control treatment T4 was made according to the traditional land surface irrigation in local orchard. The irrigation amount per tree under T1~T7 treatments were 3200 L, 1600 L, 800 L, 2160 L, 1200 L, 1600 L, 1600 L, respectively.In this paper, hydrogen and oxygen stable isotope techniques were applied to research the root water uptake rules under different water storage pit irrigation treatments. Combined with the research results of apple trees’ SPAC system water potential, water consumption characteristics, branch growth situation, yield and fruit quality under different water storage pit irrigation treatments, the most suitable water storage pit irrigation treatments for the local orchard were selected after comprehensive comparison. The research results provide a scientific basis and reference for the irrigation regime establishment and application of water storage pit irrigation method. The conclusions of this paper are as follows:(1) Through comparing the assumptions, principles and model output of 4 commonly used hydrogen and oxygen stable isotope techniques analysis methods, multiple-source linear model was proved to be of strong applicability and high accuracy. According to multiple-source linear model analysis results, the main root water uptake depth of apple trees under water storage pit irrigation and land surface irrigation can be summarized as concentrated on the surface soil in germination stage, gradually increased in branch shooting stage and returned to surfaced again after fruit expanding stage. Under the water storage pit moderate water irrigation treatment T2 and land surface treatment T4, the main water uptake depths and water contribution is shown as follows: 0~20cm(51.3%) and 0~20cm(59.5%) in germination stage; 0~20cm(33.4%), 20~40cm(19.6%) and 0~20cm(42.9%), 20~40cm(11.1%) in June of branch shooting stage; 20~40cm(14.3%), 60~80cm(14.6%), 80~100cm(14.8%) and 0~20cm(24.3%)、20~40cm(29.1%) in July of branch shooting stage; 40~60cm(13.5%), 60~80cm(14.5%), 80~100cm(14.7%) and 0~20cm(23.6%)、20~40cm(37.1%)、40~60cm(11.6%) in August of fruit expanding stage; 0~20cm(18.9%), 20~40cm(19.1%), 60~80cm(16.3%) and 0~20cm(26.3%) 、 20 ~ 40cm(27.3%) 、 40 ~ 60cm(13.8%) in September of fruit expanding stage. After comparing the main root water uptake depths of different water storage pit irrigation treatments to the land surface control treatment, it shown that T2 and T6 treatments could save irrigation water amount and promote water absorption in medium-deep soil layers blow 60 cm.(2) Root length density and root activity of apple trees under both water storage pit irrigation and land surface treatment peaked in July of branch shooting stage. Water storage pit irrigation T2 and T6 treatments significantly promoted root growth in deep soil layers and strengthened the overall root development. It was showed that root water absorption is a complex process by the correlation analysis results of water uptake depth, root length density, root activity and soil water content in the different growth stages of the apple trees. Root water uptake depth was synthetically determined by root length density, root activity and soil water content. In germination and early branch shooting stages, the main impact factors were root length density and root activity; in late branch shooting stage the main impact factors were root length density, root activity and soil water content; in ealy fruit expanding stage the main impact factor was soil water content while in late fruit expanding stage the main impact factor was root length density.(3) T2 treatment saved 560 L irrigation water per tree than the control treatment while the leaf water potential and soil water potential between them did not arrive at the significant level. T1 treatment had the largest soil-leaf water potential gradient while irrigated 1040 L more water per tree than the control treatment. According to the water potential comparison between different water storage pit irrigation treatments, irrigation during branch shooting stage had the largest impact on water potential maintenance of apple tress while irrigation in germination stage only had minor influence. In addition, water potential threshold value under water storage pit irrigation was below that of land surface irrigation treatment(lower than 0.48Mpa), which showed the drought resistance of water storage pit irrigation method.(4) The per sapwood area’s sap flow intensity of T1, T2, T3 and T4 treatments peaked in July and August, which indicated the largest water demand of apple trees during these periods. The sap flow velocity of T1 treatment was significantly higher than that of other treatments. T2 treatment maintained the similar sap flow velocity with T4 treatment while the irrigation amount of T2 treatment was less than that of T4 treatment. Comparing the water consumption and irrigation amount of different irritation treatments from May to October, it was found that T1 treatment had the highest water consumption and irrigation amount while the water use efficiency is low; For T3 treatment, the sap flux was too low to sustain the normal growth and development of apple trees; T2 and T6 treatments saved 560 L water per tree than land surface irrigation T4 treatment while maintained the similar water consumption,which contributes to the high water use efficiency.(5) The apple trees branch under different water storage pit irrigation treatments grew slowly in germination stage, rapidly in branch shooting stage and almost stable after late July. T1 treatment had the largest growing length, however the excessive growth of branches may cause tree canopy closure. The branch length of T3, T5 and T7 treatments were less than that of control treatment T4 because of water deficit in branch shooting stage. T2 and T6 treatments had the similar branch length with T4 treatment. The fruit yield and fruit quality analysis results showed that compared to traditional land surface irrigation, water storage pit irrigation T6 treatment saved irrigation water amount, significantly enhanced fruit yield, fruit shape index, yield of individual tree, fruit weight, soluble solid content and sugar acid ratio; water storage pit irrigation T2 treatment significantly increased the indicators above compared to T4 treatment except for fruit shape index.(6)Through comprehensive comparison on root distribution, root water uptake depth, SPAC water potential system analysis, water consumption rule, tree growth situation, fruit yield and quality of apple tress under different water storage pit irrigation treatment, it shown that water storage pit irrigation T2(irrigation lower and upper limits were 60% and 90% of field water capacity in germination stage, branch shooting stage, fruit expanding and ripening stage) and T6 treatment(irrigation lower and upper limits were 50% and 80% of field water capacity branch shooting stage, fruit expanding and ripening stage while 70% and 100% of field water capacity in germination stage) reduced 560 L irrigation water per tree than the traditional land surface irrigation T4 treatment while maintained moderate SPAC system water potential and transpiration water consumption; promoted root growth and water absorption in medium-deep soil layers blow 60cm; improved fruit yield per plant, fruit weight, soluble solids, sugar to acid ratio and other indicators. Therefore, T2 and T6 treatments were the most suitable water storage pit irrigation treatments for the local orchard. |
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