Study On Key Techniques And Theory To Maintenance Site Productivity Of Triploid Populus Tomentoza Pulp Plantation

Carrying out the study on key techniques and theory to maintenance the long-term-site productivity of fast-growth pulp plantation is very important. Not only had it theoretical meanings to enrich contents of the long-term-site productivity study, to promote the development of related disciplines. But also it had practical significance to raise the pulp plantation productivity, to ensure the pulpwood sustainable production, to guarantee our country pulp and paper industry security. In order to assess the change of triploid populus tomentoza pulp plantation long-term-site productivity, The paper studied on effects of aboveground litterfall, fine root turnover and wet dust precipitation in nutrient(N,P) cycling of triploid populus tomentoza pulp plantations at different ages,namely 2a,4a,5a,6a.It studied influence of different factors on decomposition of leaf,tree bark and twig of triploid populus tomentoza to select the operations to accelerate the decomposition and nutrient release. Finally, it studied influence of different intercrops on plantation site productivity and the relationship of intercrops and triploid populus tomentoza to select suitable intercrops. The main results as follows:(1)The aboveground litterfall of triploid populus tomentoza increased along with age from 216.03±59.7gm^-2 at 3a to 482.38±101.3gm^-2 at 7a, The N returned by litterfall wasl8.38±2.46kg.hm^-2a^-1;21.63±2.25kg.hm^-2a^-1;39.51±4.61kg.hm^-2a^-1;38.89±4.89kg.hm^-2a^-1 at 3a,5a,6a,7a respectively. The P returned by litterfall was 5.80±0.62kg.hm^-2a^-1,8.16±0.94kg.hm^-2a^-1, 11.31±1.33kg.hm^-2a^-1,11.76±1.37kg.hm^-2a^-1 at 3a,5a,6a,7a respectively. The nutrient returned by fine root turnover increased along with age, too. The N returned by fine root turnover was 3.85±0.41kghm^-2a^-1,5.22±0.63kghm^-2a^-1,7.62±0.89kghm^-2a^-1,9.17±1.22kghm^-2a^-1 at 3a,5a,6a,7a respectively. The P returned by fine root turnover was 0.73±0.07kghm^-2a^-1,1.69±0.09kghm^-2 a^-1,1.92±0.31kghm^-2a^-1,1.96±0.21kghm^-2a^-1 at 3a,5a,6a,7a respectively. The leaf was the principal pathway to return nutrient(N,P) to soil among litterfall, fine root turnover and wet dust precipitation. The proportion of returned N by leaf was 74.84%,71.96%,78.58%,75.03% at 3a,5a,6a,7a respectively,The proportion of returned P by leaf was 85.93%,80.31%,83.04%,83.23% at 3a,5a,6a,7a respectively. Therefore, it is important to protect and utilize the leaf in order to maintenance and enhance the long-term-site productivity of triploid populus tomentoza pulp plantation.(2)The remained N of triploid populus tomentoza pulp plantation increased from 212.00kghm^-2 at 3a to 775.61kghm^-2 at 7a, the remained P increased from 109.61kghm^-2 at 3a to 407.15kghm^-2 at 7a. The returned N increased from 24.56kghm^-2 at 3a to 51.83kghm^-2 at 7a. The ratio of returned N to absorbed was 34.75%,45.85%,48.81%,46.78% at 3a,5a,6a,7a respectively. But the total N in soil decreased from 0.54% at 3a to 1.92% at 7a. The ratio of returned P to absorbed was 18.47%,29.66%,26.75%,24.29% at 3a,5a,6a,7a respectively, but the total P in soil decreased from 0.35% at 3a to 0.52% at 7a. The turnaround time of N was shortened from 345.6 years at 3a to 163.8 years at 7a, The turnaround time of P was shortened from 1625.0 years at 3a to 596.1 years at 7a. Thus the management of triploid populus tomentoza pulp plantation might cause soil nutrient(N,P) deficiency and threaten site productivity maintenance.(3)The influence of different factors on decomposition of leaf, twig and tree bark was defferent. Neither the circumstance between interior-intermediate of plantation belt nor the leaf brought out by different age's trees had significance difference. The decomposition of leaf of triploid populus tomentoza was accelerated by mixed with cotton leaf in 1:1 mass ratio. The time of 50% leaf decomposed was shortened 254 days compared to pure triploid populus tomentoza leaf. The time of 95% leaf decomposed was shortened 1076 days compared to pure triploid populus tomentoza leaf. The decomposition ratio at 1 year increased 15.43% compared to pure leaf. The circumstance of underground 10cm promoted decomposition of leaf,twig and tree bark significance. Compared to soilsurface, The time of 50% leaf decomposed under ground 10cm was shortened from 499 days to 291 days of 2a plantation, from 777 days to 304 days of 4a plantation, from 1036 days to 393 days of 6a plantation respectively. The time of 95% leaf decomposed was shortened from 1853 days to 1114 days of 2a plantation, from 3080 days to 1157 days of 4a plantation, from 4326 days to 1544 days of 6a plantation respectively; The time of 50% twig decomposed was shortened from 771 days to 338 days, the time of 95% twig decomposed was shortened from 3073 days to 1223 days. The time of 50% tree bark decomposed was shortened from 710 days to 304 days and the time of 95% tree bark decomposed was shortened from 2803 days to 1072 days. Thus it could accelerate decomposition of leaf,twig and tree bark if they were buried under surface soil during operations such as cultivation,weed eradication.(4)From the result of laboratory experiment, the difference of decomposition rate among different N-resource was significance. The leaf decomposition was accelerated by added ammonium nitrogen, The half leaf decomposition needed 175d by added ammonium nitrogen compared to 301d,316d or 348d by added nitrate nitrogen,mixed N or control respectively. The 95% leaf decomposition needed 781d by added ammonium nitrogen compared to 1397d,1238d or 1627d by added nitrate nitrogen,mixed N or control respectively. The decomposition ratio of one year was 75.28% by added ammonium nitrogen, compared to 55.90%, 55.14% and 51.14% by added nitrate nitrogen, mixed N or control respectively.(5)The different intercrops had different effects on soil physic-chemical characteristics. Soil bulk density,soil organic matter and soil available nitrogen were improved significance by intercropped cotton. There were no significance influence on tree height growth by different intercrops, but tree diameter at breast height was increased significance by intercropped cotton.the yield of different intercrops were not influenced by tree at first year. The RCI(relative competition index) were 0 almostly.Therefore the whole, cotton was suitable intercrop at first year.