Optimization Of Technical Parameters Of Drip Fertigation Based On Apple Root-zone Soil Water And Nitrogen Distribution

Facing the problems of excessive nitrogen input,low water and fertilizer use efficiencies and serious nitrate-N leaching in the process of apple planting in Shaanxi Province,how to realize water and fertilizer saving,environment-friendly and sustainable development through water and fertilizer management is the concern of many scholars.Drip fertigation could solve these problems well through controlling the amount and time of water and fertilizer reaching the root zone flexibly.Maintaining high soil moisture and nutrient status in crop root zone for a long time is the premise of good effect of drip fertigation,and which can be affected by these factors,such as the amount of irrigation and fertilizer,fertilizer type and operation mode of drip irrigation system,etc.Further more,different technical parameters of drip fertigation can directly cause different soil wetting body and dynamic changes of nitrogen in root zone.Therefore,choosing appropriate technical parameters of drip fertigation based on the relationship between spatial distribution of fine roots of apple trees and spatial distribution of soil water and nitrogen and nitrogen dynamics can provide a reference for applying drip fertigation in orchards in this area.In this study,dwarfing,compact and young apple trees were taken as the research object to carry out field experiment of drip fertigation and the experiment including three factors:arrangement of drip line,dripper spacing,fertilization cycle.The arrangement of drip lines included one pipe?P₁?,two pipes?P₂?per row.The dripper spacing included 30cm?D₁?and50cm?D₂?.The fertilization cycle included 15 days?T₁?and 30 days?T₂?.And there were eight treatments in the experiment totally.In order to analyse the effects of technical parameters of drip fertigation on the distribution of soil water and nitrogen and the nitrogen dynamics in the root zone,monitoring the soil water and nitrogen distribution around the emitter in the direction of along and vertical drip lines,and the dynamics of nitrogen in the root zone at different distances?0,30 and 60cm?from the tree rows and different soil depth during the growth period?germination stage,shoot growth stage and young fruit stage?.Consequently,suitable technical parameters of drip fertigation was selected considering of the main areas of fine root distribution.The main results were as follows:?1?The spatial distribution of fine roots at 30,60 and 90cm away from the trunk before the experiment was investigated.The fine root biomass and length density increased firstly and then decreased with the increase of soil depth,and the maximum values of both occurred in 10-20cm soil layer.The fine root biomass in 0-60cm soil layers accounted for77.26%of its total of 0-100cm soil layers.The density of root length in 0-60cm soil layers were higher than that under 60cm soil layers,and there was a significant difference between them.The specific root length were smaller in 0-30cm soil layers,and then increased below30cm soil layers as well as the value of which were close.The fine root biomass and length density gradually decreased from the trunk to the outside along the radial direction,but there was no significant difference in the specific root length.?2?The response of spatial distribution of soil moisture in the direction of vertical drip lines and along drip lines to the arrangement of drip lines and dripper spacing was studied.For the soil water distribution in the direction of vertical drip lines,horizontal wetting widths of all treatments were less than 60cm.And the total diffuse area of P₂ were larger than that in P₁ horizontally,while the vertical diffuse area was opposite.Among them,the soil moisture wetting depth was 70-80cm in P₁ and 50-60cm in P₂.Compared with D₁,the wetting range in both horizontal and vertical directions were larger when the dripper spacing was D₂.For the distribution of soil moisture along drip lines direction,the soil water distribution uniformity was more higher in P₁ than P₂.And compared with D₂,the soil water distribution uniformity was more higher in D₁.?3?The spatial distribution of soil NO₃^--N in the direction of vertical drip lines and along drip lines responded to the technical parameters of drip fertigation was studied.The distribution of soil NO₃^--N and soil water in the direction of vertical drip lines showed the same law.For the distribution of soil NO₃^--N along drip lines direction,the influence of dripper spacing on uniformity was related to the arrangement of drip lines.To be more specific,the distribution of soil NO₃^--N was more uniform at D₁ than D₂ under the condition of P₁ but the opposite was true under the condition of P₂.In addition,prolonging fertilization cycle resulted in more NO₃^--N leaching to 70-100cm soil layers.?4?Most of soil NH₄⁺-N accumulated in the range of 15cm horizontally and 18cm vertically from the emitter after fertilization with drip irrigation.P₂ made the distribution of soil NH₄⁺-N in horizontal direction more concentrated than P₁ and there was no significant effect on which in the direction of vertical drip lines.For the distribution of soil NH₄⁺-N along drip lines direction,it was more uniform in P₁ than P₂.And the dripper spacing had no significant effect on the distribution of NH₄⁺-N in soil.Moreover,The soil NH₄⁺-N content at 70-100cm soil layers was increased by prolonging the fertilization cycle.?5?The study on the dynamics of NO₃^--N in root zone soi with the growth period showed that prolonging the fertilization cycle increased the value and change degree of NO₃^--N in 0-20cm and 80-100cm soil layers,and intensified the movement of NO₃^--N to deep layers.P₂ made the distribution of soil NO₃^--N more uniform in the range of 0-60cm from tree rows during the growth period than P₁.Compared with D₁,D₂ deepened the soil layer with large fluctuation of NO₃^--N and increased the proportion of which in the80-100cm soil layer during the growth period.Among them,the combination of P₂D₁T₁ can make most of NO₃^--N remain in 0-60cm soil layers.And the influence of the dripper spacing on the horizontal diffusion range of soil NO₃^--N was related to the arrangement of drip lines.More specifically,there was no significant difference in the diffusion range of D₁ and D₂under the arrangement of P₂,however the diffusion range of D₂ was larger than that of D₁under the arrangement of P₁.?6?The study on the dynamics of NH₄⁺-N in root zone soils with the growth period showed that soil NH₄⁺-N mainly accumulated in 0-20cm soil layer.The change of NH₄⁺-N in0-20cm soil layer below drip lines was aggravated by prolonging fertilization cycle,but there was no significant effect on the change of soil NH₄⁺-N at 30cm or 60cm away from drip lines during the growth period.Different arrangement of drip lines and dripper spacing had no significant effect on the vertical and horizontal movement of soil NH₄⁺-N during the growth period.In summary,it is more appropriate to select the combination of treatment with P₂D₁T₁in actual production for dwarfing,compact and young apple orchards.