| The aim of this work is to present the water-nitrogen coupling effects on the stand volumes and economic benefits of Populus tomentosa plantations. Field experiment with split plot design consisted of four Populus tomentosa clones (1316, BT17, B331, S86) has been conducted for five years in Weixian nursery of Hebei Province. The main results were as follows:(1) The effects of water, nitrogen and clone on leaf area of Populus tomentosa, chlorophyll, N, P, K content of leaf reached a very significant level. The effects of interaction for water and nitrogen and interaction for nitrogen and clone on leaf area of Populus tomentosa, N, K content of leaf reached a highly significant level. The effects of interaction for water, nitrogen and clone on N content of leaf reached a significant level.(2) The effect of moisture, nitrogen and clone on leaf area of Populus tomentosa, chlorophyll, N, K content of leaf were W3>W2>W1,N3>N2>N1>N0, S86>B331>BT17>1316, respectively. The effect of moisture, nitrogen and clone on P content of leaf were W3>W2>W1, N3>N2>N1>N0, S86>B331>BT17>1316, respectively.(3) The summit of the annual increment in height and DBH appeared at the furth year with an annual increment of2.28m,2.76m,2.81m,3.01m in height and1.88cm,2.33cm,2.61cm,3.06cm in DBH. The annual increment in height and DBH of BT17, B331, S86were the fastest under the treatment of W3N3with an annual increment of1.75m,1.85m,2.11m in height and1.86cm,1.95cm,2.07cm in DBH. The annual increment in height and DBH of1316were the fastest under the treatment of W3N3and W3N2with an annual increment of1.61m in height and1.51cm in DBH.(4) The coupling effects of water and nitrogen on both the stand volumes and the economic benefit of established tree of four Populus tomentosa clones were significant. Water was the main factor affecting the stand volume followed by nitrogen and then the interaction of nitrogen and water of which were positive.(5) Optimization mathematical models of four Populus tomentosa clones were established which showed that the optimal combinations of water and nitrogen for1316in2008,2009,2010,2011were67.02%,71.13%,76.92%,77.31%of field capacity respectly,210kg/ha(165g/plant),278kg/ha(219g/plant),380kg/ha(299g/plant),385kg/ha(303g/plant)of nitrogen respectly, under which, the stand volumes would achieve25.57m3/ha,45.96m3/ha,86.32m3/ha,116.87m3/ha respectly. The optimal combinations of water and nitrogen for BT17in2008,2009,2010,2011were70.60%,74.41%,80.02%,81.93%of field capacity respectly,281kg/ha(226g/plant),363kg/ha(286g/plant),457kg/ha (360g/plant),461kg/ha (363g/plant) of nitrogen respectly, under which, the stand volumes would achieve41.15m3/ha,79.54m3/ha,149.92m3/ha,177.53m3/ha respectly.The optimal combinations of water and nitrogen for B331in2008,2009,2010,2011were71.45%,73.91%,81.46%,83.29%of field capacity respectly,283kg/ha (223g/plant),350kg/ha (276g/plant),472kg/ha (372g/plant),477kg/ha (375g/plant) of nitrogen respectly, under which, the stand volumes would achieve43.61m3/ha,80.04m3/ha,163.45m3/ha,202.82m3/ha.The optimal combinations of water and nitrogen for B331in2008,2009,2010,2011were72.57%,75.60%,84.46%,84.89%of field capacity respectly,296kg/ha (223g/plant),364kg/ha (276g/plant),508kg/ha (372g/plant),514kg/ha (375g/plant) of nitrogen respectly, under which, the stand volumes would achieve49.21m3/ha,92.70m3/ha,200.28m3/ha,233.82m3ha.(6) Significant economic benefits of four Populus tomentosa clones have been achieved after5years optimization of water and nitrogen management.Under high water and nitrogen conditions S86is the best fast-growing and high-yielding clone of this region. |
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