Dynamic Characteristics And Regulation Of Soil Environment And Fine Roots In Orchards In Weibei,Shaanxi Province

Due to the continuous expansion of the fruit planting scale,the excessive application of chemical fertilizers in the arborization apple orchard and the long construction time,a series of problems have occurred in the soil environment,such as the deterioration of the soil structure,which affects the root development of fruit trees.The water absorption rate is reduced,and a dry layer of soil appears.The fertilizer utilization rate decreased,causing problems such as the leaching and accumulation of nitrate nitrogen.Therefore,with the rapid development of the cultivation mode of apple dwarf stock dense planting,the spatial distribution characteristics of fruit tree roots,the dynamic changes of soil water content,the accumulation and distribution characteristics of soil mineral nitrogen in dwarf stock dense planting apple orchards are not clear,and the lack of artificial control measures in the orchard can improve the soil water,fertilizer utilization and other issues.In this study,apple orchards with different tree ages（6 a,9 a,12 a）in the Weibei region of Shaanxi Province were used as the research object.Soil and root samples were used to analyze soil moisture,mineral nitrogen and fruit tree roots,and to control soil moisture,nitrate nitrogen and fruit tree roots by deploying a variety of artificial control measures in the orchard.Research indicates:（1）The colonization zone was the main concentration area of fine roots of rootstocks of all ages,and the number and absorptive capacity of fine roots decreased gradually with the increase of tree age.In the vertical direction,the main concentration area of fine roots showed a downward trend with the increase of tree age.At the same horizontal position,the root length density,root surface area density,dry mass density and specific root length of fine roots all decreased significantly with the increase of tree age（P<0.05）,but the overall difference between older rootstocks（9 a,12 a）was not significant.The indexes of fine roots of rootstocks of the same age decreased with the increase of the radial distance from the trunk.In the vertical direction,through the analysis and research on the characteristics of root length density and root surface area density of fine roots,it is shown that the root system of rootstocks of each age is mainly concentrated in the soil layer of 0～60 cm,and the root length density in this soil layer accounts for the total the ratio of root length to density is 6 a>9 a>12 a.（2）During the same period,the soil water content of the 0～300 cm soil layer increased with the age of the orchard trees,which was 6 a<9 a<12 a.The soil water content in the orchard of the same age in different periods is as follows:summer moisture increase period>spring moisture loss period>winter moisture stabilization period,and the main soil layer depth of soil water content changes is 0～200 cm,and the soil layer below 200 cm the soil moisture content varies only within a small range.In the summer moisture increase period,the average soil water storage capacity of the three tree age orchards at 0～100 cm and 100～200 cm was 267.2 mm and 230.1 mm,respectively,while in the winter moisture stabilization period,the average soil water storage within the same soil layer range was respectively are 234.5 and 241.3 mm,indicating that the surface soil moisture has moved to a depth of 100-200 cm,which increases the water storage in this soil layer to a certain extent.In the spring moisture loss period,the average soil water storage capacity of the0-100 cm soil layer was 258.5 mm,which was higher than that of the previous period,indicating that the water storage capacity of the soil surface was restored due to the increase of natural rainfall in spring.（3）The accumulation of nitrate nitrogen in the soil layer of 0～300 cm increases with the age of the orchard,and the difference between the orchards of different tree ages is significant,which is 6 a<9 a<12 a,and the accumulation of nitrate nitrogen varies from1729 kg·hm^-2increased to 3771 kg·hm^-2.However,the content of ammonium nitrogen in orchards of different tree ages was low,which had little effect on the accumulation and spatial distribution of mineral nitrogen.In the vertical direction,there are two cumulative peaks of nitrate nitrogen,and the depth of the soil layer where the second cumulative peak is located moves down from 180 cm to 220 cm with the age of the orchard.The nitrogen content increased from 27 mg·kg^-1to 138 mg·kg^-1with the increase of tree age in the orchard,an increase of more than 400.0%.There were significant differences among orchards of different tree ages.To sum up,there is an excessive application of nitrogen fertilizer in orchards of all tree ages,and the accumulation of nitrate nitrogen leaching is very serious.During production,the amount of nitrogen fertilizer application in orchards should be reduced,and anti-seepage measures should be placed at the fertilization position to prevent nitrate nitrogen from leaching into the deep soil.（4）In the soil layer range of 0～100 cm,the treatment of the anti-seepage layer（I）,the treatment of the anti-seepage layer plus ridge（II）,and the treatment of the anti-seepage layer plus the ridge and mulch（III）can all be effective increase soil water content,reduce nitrate nitrogen accumulation and promote fruit tree root growth and development.Among the three treatment measures,the overall effect of the anti-seepage layer plus ridge and film mulching（III）is the best,which can increase the soil water content in the 0～100 cm soil layer by 24.0%and reduce the accumulation of nitrate nitrogen 13.4%,the root density of fine roots increased by 14.0%.The impermeable layer plus ridge treatment（II）increased the soil water content in the 0～100 cm soil layer by 23.7%and decreased the soil nitrate nitrogen content by collecting surface runoff 11.5%,the root density of fine roots increased by 13.1%;the impermeable layer treatment（I）can increase the soil water content in the0～50 cm soil layer by 16.4%by reducing water infiltration,but it has a poor effect on the deep soil.By hindering water infiltration,the accumulation of soil nitrate nitrogen in the0～40 cm soil layer is increased,and the water leaching effect in the 50～100 cm soil layer is reduced.The development of fine roots of 0～40 cm was significantly promoted,and the root length density increased by 8.9%.