| In recent years,the wasting of resources and environment pollution of ecosystem caused by extensive irrigation and fertilization in the production of agriculture and forestry are becoming more and more serious.The development of drip irrigation and the water and fertilizer management technology can effectively promote the utilization of water and nutrient resources,significantly improve the forest productivity and can save resources and avoid environmental pollution caused by conventional water and fertilizer supply.which satisfied with the development requirements of modern forestry.In this study,6-year-old poplar plantation cultivated by drip irrigation was studied.The effects of 8 fertilization levels(The amount of N + P + K applied per plant was CK:0+0+0g,T1:72+12+36g,T2:108+18+54g,T3:144+24+72g,T4:180+30+90g,T5:216+36+108g,T6:252+42+126g,T7:288+48+144g)on poplar plantation were analyzed by the growth and physiological characteristics of trees,the distribution characteristics of fine roots,the productivity of woodland,the change of soil environment.And the optimal fertilization schemes of poplar plantation was established.The main results are as follows:(1)The growth of poplar plantation under different drip fertigation was measured and the results showed that the drip fertilization did not change the seasonal growth pattern of poplar plantation,the growth dynamics of DBH in different months under different fertilization treatments was similar to that of CK,the cumulative growth of DBH in June,July and August accounted for 82.9%-90.1% of the annual growth of DBH.Drip fertilization can effectively promote the growth of DBH,tree height and volume of poplar plantation,improve the stand productivity.The annual growth rate of DBH,tree height and volume in T6 treatment was the highest,and was 2.2cm,2.07 m and 0.057m3/tree respectively,compared with CK,they increased by 44.1%,22.1% and 50.9% respectively.Under CK,the productivity of forest land was 25.31 m3/hm2·a,and the productivity of T1-T7 was higher and was 1.14,1.22,1.24,1.33,1.38,1.51 and 1.34 times of CK respectively.The woodland productivity under T6 treatment was greater than of T7 treatment and it indicated that excessive fertilization or insufficient fertilization could affect the growth of poplar,and the effect of low fertilization on the growth of trees was higher than that of high fertilization.The high fertilization level could not bring the corresponding yield effect.In order to improve the productivity of poplar plantation,other factors should be considered.(2)Drip irrigation has a significant effect on the distribution of fine roots.The fine root length in different directions under DI was strains direction(50.5%)> diagonal direction(27.7%)> row direction(21.8%),and the difference was significant while the distribution under CI was strains direction(39.2%)> diagonal direction(34.9%)> row direction(25.9%),and the difference was not significant.The fine root length of DI in different directions was greater than CI and the difference was very significant.The drip irrigation affects the horizontal distribution of fine roots.In the strains direction of DI,the largest root length was at the distance of 0.5 m from the trunk and the differences at different trunk distances were very significant from that of CI.In the diagonal and row direction,the distribution of fine roots was similar to that of CI,and the largest fine root length was at 0.2 m from the trunk,the difference with CI at 0.2 and 0.5 m of the trunk was significant.The drip irrigation affects the vertical distribution of fine roots.In the strains direction of DI the fine root length of 0-10 cm soil layer was the largest while the maximum value of the fine root length in the diagonal and row directions was 10-20 cm soil layer.In different directions under CI the fine root length of 10-20 cm soil layer was the largest.In the strains direction of DI,the difference of fine root length was very significant in 0-40 cm soil layer while the soil layers were 0-20 cm in diagonal and row direction.(3)Drip fertilization did not change the vertical distribution pattern of fine roots.The fine root length of poplar plantation were 0-10>10-20>20-30>30-40 cm in the vertical direction under different fertilization treatments,and with the increase of soil depth,the distribution of fine root decreased.Drip fertilization significantly affected the growth and accumulation of fine roots and the total length of fine roots under different fertilization treatments increased with the increase of fertilizer application.Under the condition of CK,the fine root length was 3.02 cm,and T1-T7 treatments was 1.09,1.25,1.26,1.42,1.56,1.61,and 1.65 times of CK,respectively.The fine root length at the same soil layer increased with the increase of fertilizer.The fine root length under CK in each soil layer showed the smallest and the fine root length of T1-T7 fertilization in 0-40 cm soil layer was 1.04-1.68,1.13-1.69,1.15-1.67 and 1.05-1.56 times of CK respectively.The investigation and study of soil under different fertilization treatments showed that increasing the amount of fertilizer could improve the soil fertility and improve the soil condition,the contents of available N,available P and available K in T1-T7 were significantly higher than those of CK.The soil enzyme activity under different fertilization treatments showed an increasing trend with increasing fertilizer application.Drip fertigation affects the growth and accumulation of fine roots by changing the soil conditions of the forest land,and then change the absorption ability of forest soil to soil water and fertilizer,and improve the productivity of forest land.(4)Drip fertilization could improve the net photosynthetic rate and transpiration rate of middle and upper leaves of canopy.In June,July,August and September,the net photosynthetic rate under T1-T7 treatments was 1.16-1.54,1.04-1.21,1.03-1.34 and 1.05-1.30 times of CK respectively,and the transpiration rate was 1.04-1.48,1.12-1.34,1.12-1.72,1.06-1.31 times of CK.Simultaneous determination of stomatal conductance and intercellular CO2 concentration of leaves showed that drip fertilization could increase the stomatal conductance to a certain extent,which was beneficial to photosynthesis and transpiration of trees.The physiological indices of net photosynthetic rate under different fertilization treatments in different months showed a similar increase and decrease characteristic with CK,that is,the value of each index rose in June,the largest in July,then began to decline in August,the lowest in September.(5)The cost and benefit of each stand under different fertilization treatments under drip irrigation were analyzed.The largest annual income per unit area was T6 treatment,for 23217 yuan/hm2 and 41.5% higher than of CK.Based on CK,the marginal benefit of each fertilizer treatment was T6>T5>T4>T7>T3>T2>T1,T6 treatment of the marginal revenue was the largest,6389 yuan and 1.37-3.69 times of other treatments.Under T6 treatment,the poplar plantation can get the maximum economic benefit while satisfying the growth of poplar,and the corresponding fertilizer amount(252 g/tree N + 42 g/tree P + 126 g/tree K)is the optimal fertilization level of 6 year old poplar plantation under drip irrigation.According to the principles of several times,fertilization every year from mid-May to the end of mid-August,10 times finished,the corresponding fertilization system is the optimal fertilization scheme for poplar plantation under drip irrigation,which can provide the basis for the cultivation of poplar fast-growing and high-yielding forest. |
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