| Poplar plantations are widely planted in China,but most of them are located in poor site conditions and have low stand productivity.In addition,due to the diversity of terrain,serious shortage and uneven distribution of water resources in China,the problem of water consumption in agricultural and forestry production has become an important factor hindering the economic development of China.In order to meet the requirements of modern forestry development,forest water-saving,high-efficiency,and improve productivity,drip irrigation technology and scientific irrigation system can be used to cultivate poplar plantation.In order to study the irrigation effect of poplar plantation cultivated by drip irrigation,this study takes 9-year-old poplar plantation on the sand land of Yongdinghe old road in Daxing District of Beijing as the test object.The paper studied the movement law of wet front of different dripper flow rate,the change law of soil moisture and the distribution and productivity of fine roots under drip irrigation and furrow irrigation,the growth and physiological characteristics of poplar plantation under different irrigation amount and the growth of poplar plantation under different water-fertilizer coupling treatment.The main conclusions are as follows:(1)After 6 hours of drip irrigation,the vertical migration distance of soil wetting front under4 L/h and 2 L/h dripper flow was 63.8 cm and 54 cm respectively.The soil moisture content of the main distribution layer(0-40 cm)of poplar absorbing roots under 4 L/h dripper flow was saturated,while the soil moisture content of this layer kept rising rapidly under 2 L/h dripper flow.After 6 hours of drip irrigation,the water content of 4 L/h emitter could completely cover the main soil layer of poplar root system,and would not cause deep water leakage.(2)The results showed that after single effective drip irrigation and furrow irrigation,the vertical depth of of wet body formed along the tree row was 72 cm and 143 cm respectively,and the cross-sectional area of wet body was 0.41 m~2 and 2.71 m~2,respectively.The amount of irrigation was 79.20 m~3/hm~2 and 776.47 m~3/hm~2,respectively,with the latter being 9.80 times of the former.The duration was almost same(11 d)when soil moisture went down to the level of slight water deficit(the soil moisture content=70%of the field capacity)in the 0-40 cmlayer where poplar absorption roots mainly distributed.From April to October 2019,drip irrigation was 1425.60 m~3/hm~2,18 times in total,and that of total irrigation amount of three times furrow irrigation in May,July and September was 2329.41 m~3/hm~2.No moderate water deficit happened under drip irrigation,whereas there were 109 days during which poplar trees suffered moderate water deficit(the soil moisture content?60%of the field capacity)under furrow irrigation during the whole growing season.(3)Irrigation and rainfall were the main ways of water conveyance in 2019,the input water volume of the drip irrigation management area is 6227.60 m~3/hm~2,and the water consumption is6161.64 m~3/hm~2.The input water volume of the ditch irrigation area is 7131.41 m~3/hm~2,and the water consumption is 5203.26 m~3/hm~2.The non-available water volume proportion in the drip irrigation area and the ditch irrigation area is 1.1%and 37.1%respectively,which cannot be absorbed and utilized by poplar.Under the same rainfall,the irrigation amount of furrow irrigation is far greater than that of drip irrigation,but 37.1%of water resources are wasted,which is totally inconsistent with the actual production significance.The surface area of fine roots under drip irrigation at the distance between tree trunks and row directions is larger than the surface area under furrow irrigation,and the horizontal distribution under different irrigation is basically similar in the same direction.The largest by single plants is at 1.5 m from the trunk,the difference between 1m and 1.5 m from the trunk under drip irrigation is only 15.44 cm~2.But the largest between lines is at the distance of 0.5 m from tree trunks.The surface area of fine roots by single plants is 4556.81cm~2 and 1695.19 cm~2,the area between lines were 1302.64 cm~2and 964.48 cm~2,respectively.The surface area of fine roots in the depth of soil layer between plants and rows was larger than that of furrow irrigation,and the surface area of fine roots in the depth of 10-20 cm soil layer in each direction was the largest,accounting for 23.2%and 29.8%between plants,26.7%and 34.6%between rows.The surface area of fine roots increased with the increase of soil depth,but the surface area of 50-60 cm soil layer under furrow irrigation was higher than that in the previous soil layer.Annual increment of standing volume was 38.92m~3/hm~2 and 25.43 m~3/hm~2 under drip and furrow irrigation,the former was 1.53 times of the latter.Our results suggested that different irrigation resulted in significant difference in productivity of poplar plantation.(4)The experiment of different drip irrigation amount also showed that,the photosynthetic parameters Pn,Gs,Ci and Tr of poplar leaves increased firstly and then decreased with the increase of irrigation;under slight deficit irrigation and moderate deficit irrigation treatments,the surface area of fine roots increased with the increase of soil depth,while under full irrigation treatment,the surface area of 10-20 cm increased by 193.28 cm~2 compared with 0-10 cm soil layer,and 86.6%,89.5%and 91.7%of fine roots were distributed in 0-40 cm soil layer;three kinds of irrigation amount treatments have significant effect on the DBH of poplar,and full irrigation treatment had the largest effect,which was 1.42 cm.Volume growth was also the largest under full irrigation treatment,which was 38.92 m~3/hm~2,with no significant difference from slight deficit irrigation treatment.(5)The results of different water and fertilizer coupling treatments showed that four kinds of water and fertilizer couplings have no significant effect on the DBH of poplar,but the tree height and volume growth of high fertilizer rate and full irrigation were significantly higher than those of other treatments. |
PDF Full Text Request