Research On Water And Nitrogen Absorption,Water And Nitrogen Utilization Characteristics Of Populus Tomentosa Under Ditch Irrigation

Triploid Populus tomentosa has become a major timber tree species in North China because of its fast-growing,high-yield,high-quality,and high-efficiency characteristics.However,this tree species lacks reasonable water and fertilizer management measures and has low productivity.Although the coupling of water and fertilizer has been widely used in plantation cultivation at home and abroad,the effect and mechanism of regulating and controlling the absorption and utilization of water and nitrogen in poplars are still insufficient.we studied the growth and absorption and utilization of water and nitrogen in poplar trees under three irrigation gradients(W₂₀,W₃₃,W₄₅;when the soil water potential of 40 cm under the ditch reaches-20,-33 and-45 k Pa respectively,irrigate),four N applicate rate gradients(N₁₂₀,N₁₉₀,N₂₆₀,and N₀;The fertilization amount was 120,190,260 and 0 kg·hm^-2·a^-1)and natural conditions?CK?.Based on the growth status of trees,the optimal combination of irrigation level and nitrogen application rate under furrow irrigation conditions was determined.The research results are as follows:?1?Water and nitrogen coupling measures cannot change the original seasonal growth pattern of Populus tomentosa,but proper water and nitrogen coupling measures can effectively regulate the growth and development of Populus tomentosa.The increments of DBH and tree height in different water and nitrogen coupling treatments have increased to varying degrees compared with CK.Among them,W₂₀N₁₂₀(high water and low fertilizer;soil water potential-20 k Pa,N application amount 120 kg·hm^-2·a^-1)Has the highest DBH increment and the most significant increase in the productivity of triploid Populus tomentosa forest land.Its forest land productivity can reach 33.37 m³·hm^-2·a^-1.?2?The water absorption of Populus tomentosa is mainly affected by the amount of irrigation water.The W₂₀N₁₂₀ treatment has the highest water absorption and water absorption efficiency of 13268.28 t·hm^-2 and 129.4%,respectively.Increasing the amount of irrigation or N application will increase the amount of nitrogen absorbed by the trees,but the amount of nitrogen absorbed is mainly affected by the amount of N applied;the total nitrogen absorption of the total plant treated with W₂₀N₂₆₀ is the highest,reaching 112.17 kg·hm^-2·a^-1,an increase of 74.0 compared with CK%.?3?Among all treatments,W₂₀N₁₂₀ treatment had the highest partial productivity of nitrogen fertilizer,and the total partial nitrogen productivity of the plant could reach221.4 kg·kg^-1.Different irrigation and nitrogen treatments have a significant effect on irrigation water use efficiency,of which W₄₅N₂₆₀ treatment has the highest irrigation water use efficiency,reaching 13.66 g·kg^-1.Adequate irrigation can reduce the dependence of Populus tomentosa on nitrogen fertilizer,at the same time promote its absorption and utilization of nitrogen fertilizer and increase the partial productivity of nitrogen fertilizer.?4?Among the organs of Populus tomentosa,the organs with more active physiological activities,such as leaves and roots,respond more actively to irrigation and fertilization.Under W₂₀ irrigation gradient,the proportion of leaf biomass allocation increased the most than CK,and the increment was 0.05 g·g^-1.Appropriate water and nitrogen coupling measures can change the biomass distribution and nutrient distribution in Populus tomentosa,promote the growth and development of leaves,and then improve forest transpiration,enhance photosynthesis,and strengthen the absorption and utilization of Populus tomentosa roots to moisture and nitrogen fertilizer,and ultimately effectively improve Woodland productivity.?5?In order to achieve greater benefits,the local should maintain sufficient water irrigation?-20 k Pa?and relatively low nitrogen application(120 kg·hm^-2·a^-1).