Regulatory Mechanism Of Water And Fertilizer Coupling On Soil Nitrogen And Fine Root Distribution Of Populus Tomentosa

With the increasing demand for wood in China,it is urgent to increase the yield of fast-growing and high-yield forests.Poplar is an important fast-growing and high-yield tree species in China.The cultivated area has reached 7.57 million hectares,but its yield and quality are far lower than its potential productivity and the international medium level.The low efficiency of water and fertilizer management measures is one of the important reasons.Blind water and fertilizer supply results in waste of resources,pollution of the ecological environment,inefficient and low-quality forest production.Develop furrow irrigation cultivation and water and fertilizer coupling management techniques,pay attention to the N mineralization reaction,water and nitrogen transport in the root zone,root system distribution,absorption and utilization of the various links,as well as the dynamic relationship between each other and the overall control mechanism,looking for reasonable plantation water and fertilizer management measures to meet the requirements of modern forestry development.In this study,3-year old triploid Populus tomentosa was used as the research object in the Huangfan Plain,and the coupling of furrow irrigation and fertilizer was conducted.The experiment used a two-factor completely randomized block design,setting 3 irrigation levels(I₂₀,I₃₃,I₄₅)and 4 N application levels(F₀,F₁₂₀,F₁₉₀,F₂₆₀),and CK?no irrigation without fertilization?,a total of 13 water and nitrogen coupling treatment.The key factors affecting N mineralization,the distribution of soil water and nitrogen,the distribution of fine roots,the biomass yield and the utilization efficiency of water and fertilizer were studied.The effects of different water and fertilizer coupling measures on poplar plantations were clarified,and an optimized water and fertilizer management system for furrow irrigation of poplar plantations was proposed.The main research conclusions are as follows:1.The mineralization rate and mineral N content in rainy season and different water treatment were measured by resin core in situ culture method.The results show that,soil moisture is the key to affecting the mineralization reaction.The sufficient irrigation?-20 k Pa?treatment will easily cause the soil nutrients of the forest land to leak into the deep layer.The soil water content is in the range of 10.2%?15.8%,and the mineralization rate is accelerated with the increase of irrigation volume,and there will be no deep leakage.2.Through the observation of the movement and distribution of water and nitrogen in the soil under different water and fertilizer coupling treatment,it is found that:?1?At the same irrigation volume,the upper,lower,middle,and higher stable elliptical humid bodies are formed in the dry season and the rainy season,but the wet season humid bodies expand 67%and 100%in the vertical and horizontal directions,respectively,and can reach the range of 0?100 cm.The higher the initial moisture content of the soil,the faster the water migration rate;the kinetic energy of raindrops during the rain can also accelerate the water migration.?2?In a short period,the migration law of NO₃^--N is similar to that of soil moisture,but its migration rate lags behind water,and its content is higher than the edge inside the wetted body,mainly vertical migration;NH₄⁺-N is mainly in The soil layer of 0?40 cm is accumulated,and the distribution between the soil layers is clear.During the redistribution of water and fertilizer infiltration,about 25%of the soil water content is the node where the nitrification reaction proceeds rapidly.?3?During water nutrient transport in different treatment years,the amount of N application affects the accumulation of NO₃^--N,and the amount of irrigation affects the migration and distribution;the amount of NO₃^--N leakage in 100?140 cm soil layers increases with the amount of N application and irrigation While increasing,the immersion phenomenon of I₂₀F₂₆₀ treatment is serious.NO₃^--N accumulated in the 40?60cm soil layer,of which I₃₃F₂₆₀ treatment had the highest accumulation.3.Through the collection of forest biomass in roots,stems,branches,leaves and other parts of districts?,?and?,the corresponding differences in root distribution and forest biomass in different treatments were explored.The result shows that:?1?In the CK treatment,the root length density?RLD?in the 80?150 cm soil layer is significantly higher than that in other water-fertilizer coupling treatments.The coupling treatment of water and fertilizer makes the root system shallow,and the content of fine roots in the 0?10 cm soil layer is significant;it is concentrated in the soil with a radius of 50 cm,and the absorption roots are most concentrated at a radius of 30 cm from the tree;the horizontal and vertical directions are respectively It can be extended to 150 and 100 cm.The root growth of I₂₀ treatment is better than that of F₂₆₀ treatment,and the response of root growth to N depends on the irrigation level.Water and fertilizer management measures can change the root distribution pattern,so that the roots are distributed in a"bimodal"pattern.?2?I₂₀F₁₂₀ treatment has the highest annual biomass,biomass increase,and comprehensive utilization efficiency of water and fertilizer.The water and fertilizer utilization efficiency is as high as 1074.15,which is 47.6 times that of I₄₅F₂₆₀ treatment;I₂₀F₂₆₀ treatment,leaf and root biomass is significantly higher than other treatments;I₄₅F₂₆₀ treatment,over The high salt concentration has a toxic effect on root growth,the root length density is significantly lower than other water and fertilizer coupling treatments?P<0.05?,and the forest biomass and annual biomass increase are also low.?3?The regression relationship between the RLD and the forest biomass?TB?above the soil layer of 50 cm is well fitted,that is,the fine roots of the soil layer above 50 cm significantly affect the forest growth.Based on the results of various studies,I₂₀F₁₂₀ performed well in the treatment of forest biomass,annual biomass increase,water and fertilizer comprehensive utilization efficiency,and the deepest NO₃^--N leaching amount,which can form an appropriate amount of RLD and promote forest growth.Therefore,I₂₀F₁₂₀ treatment is the best water and fertilizer management measure for three-year-old Populus tomentosa forest.