| Drip fertilization is a major technical means to improve the efficiency of water and fertilizer use and develop water-saving agriculture.At present,the technology of drip fertilization has achieved good application on a variety of crops.Faced with the problems of excessive fertilization,decreased fruit quality,low water and fertilizer utilization efficiency,and increased environmental pollution risk in apple planting in Shaanxi,drip irrigation technology has received increasing attention.How to use technical means to optimize the effect of drip fertilization is closely related to the selection of the technical parameters of irrigation and fertilization such as the spacing of drippers,the arrangement of drip lines,and the fertilization cycle.Different technical parameters of drip fertilization have a direct impact on water and fertilizer supply and distribution,and water and fertilizer conditions significantly affect the growth and development of the root system,and at the same time,the root system growth has an effect on nutrient absorption of apple trees.Therefore,discussing the effect of drip fertilization technology parameters on the growth and distribution of apple tree roots can provide a theoretical basis for the optimization of drip fertilization technology in orchards.In this paper,from October 2017 to October 2019,dwarfing,compact and initial fruit period apple trees were taken as the research object to carry out a field drip irrigation fertilization experiment.The experiment is a complete combination design of three factors and two levels of dripper spacing,arrangement of drip lines,and fertilization cycle.The arrangement of drip lines included one pipe(P1),two pipes(P2)per row.The dripper spacing included 30cm(D1)and 50cm(D2).The fertilization cycle included 15 days(T1)and 30 days(T2),a total of 8 Treatment combinations.The soil drilling method was used to collect samples of fine roots(diameter <2mm)of fruit trees at different horizontal distances and different vertical depths around the apple tree during the apple harvest period in 2018 and the germination period,new shoot growth period and harvest period in 2019.Analyze the growth and distribution of fine roots and the dynamic changes during the growth period,and discuss the response of root morphological indicators to the technical parameters of drip irrigation and fertilization.The main results are as follows:(1)The effect of drip fertilization technical parameters on the fine root density and root length density of apple trees shows the same pattern,showing that the root weight density of P2 is significantly increased by 13.88%～277.95% compared with P1,Root length density increased significantly by 15.28%～155.88%;the root weight density of D1 is significantly increased by 48.80%～171.79% compared with D2,Root length density increased significantly by 37.16%～103.48%;the root weight density of T1 is significantly increased by 15.9%～152.76% compared with T2,Root length density increased significantly by 22.83%～150.88%.The effect of drip irrigation technology parameters on root length is not very obvious.Different drip irrigation technical parameters have different effects on the root morphology index.The arrangement of drip lines has the greatest influence on the root morphology index,and the drip spacing and fertilization cycle have little effect on the root morphology index.In the previous harvest period-the next year’s germination period-new growth period-harvest period,as the apple tree growth period progressed,the root weight density of fine roots showed a trend of firstly constant and then decreased and then increased.Root length density basically shows a tendency to increase first and then decrease and then increase.There is no obvious regularity of the dynamic change of the specific root length.The effect of drip irrigation and fertilization technical parameters on the variation of root morphology indexes during the growth period as follows: P2 compared to P1,D1 compared to D2,T1 and T2,conducive to root growth and development and stably maintain higher root density.(2)The influence of drip fertilization technical parameters on the distribution of root weight density and root length density is basically the same as that on the quantify of root weight density and root length density.The root weight density distribution range of P2 is larger than that of P1 in the horizontal direction by 3～48cm and vertical by 4～45cm.The root length density distribution range of P2 is larger than that of P1 in the horizontal direction by 4～45cm and vertical by 2～45cm.The root weight density distribution range of D1 is larger than that of D2 in the horizontal direction by 10～51cm and vertical by 9～37cm.The root length density distribution range of D1 is larger than that of D2 in the horizontal direction by 10～50cm and vertical by2～35cm.The root weight density distribution range of T1 is larger than that of T2 in the horizontal direction by 5～42cm and vertical by 5～35cm.The root length density distribution range of D1 is larger than that of D2 in the horizontal direction by 3～54cm and vertical by 3～33cm.In the case of P2 and D1,the fertilization cycle is more likely to affect the distribution of root weight density and root length density.In the case of P2 and T1,the spacing of drippers is more likely to affect the distribution of root weight density and root length density.In the case of D1 and T1,the arrangement of drip line is more likely to affect the distribution of root weight density and root length density.The influence of the arrangement of drip lines and dripper spacing on specific root length distribution showed the same rules as root weight density and root length density,but the effect of fertilization cycle on specific root length distribution had no obvious regularity.(3)There is a significant correlation between the fractal dimension of apple fine roots,root density and root length density,and no obvious correlation with specific root length.The effect of drip irrigation technical parameters on the size of fractal dimension is basically the same as the effect on root density,but the degree of response of fractal dimension to drip irrigation technical parameters is significantly reduced.In different growth periods,the effect of the dripper spacing on the distribution law of fractal dimension is basically the same.The fractal dimension distribution range of D1 is larger than that of D2 in the horizontal direction by 2～40cm and vertical by 10～41cm.The influence of arrangement of drip lines and fertilization cycle on the distribution of fractal dimension is different in each growth period. |
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