Coupling effects of water and nitrogen on the stand volume and economic benefit of Populus tomentosa clone plantations

The aim of this work was to present the waternitrogen coupling effects on stand volume and economic benefit of Populus tomentosa clone plantations. Field experiment with split plot design consisted of four P. tomentosa clones (1316, BT17, B331, S86) had been conducted for four years in Weixian County Nursery of Hebei Province, northern China. The main results were as the followings: the coupling effects of water and nitrogen on both the stand volume and economic benefit of established trees of four P. tomentosa clones were significant.Water was main factor affecting the stand volume, followed by nitrogen, and then the interaction of nitrogen and water of which were positive. Four optimized mathematical models were established and it showed that the optimal combination of water and nitrogen for clone 1316 was 76.92% of field capacity, 380 kg/hm2（300 g/plant）of nitrogen, under which the stand volume would reach 86.33 m3/hm2; that for clone BT17 was 80.10% of field capacity, 457 kg/hm2（360 g/plant）of nitrogen, stand volume would reach 149.92 m3/hm2; that for clone B331 was 81.46% of field capacity, 472 kg/hm2（371 g/plant）of nitrogen, stand volume would reach 16345 m3/hm2, and the optimal combination for clone S86 was 84.86% of field capacity, 508 kg/hm2（400 g/plant）of nitrogen, the stand volume would reach 200.28 m3/hm2 The net profit under the optimal combinations of water and nitrogen of four P. tomentosa clones (1316, BT17, B331, S86) reached 32 866, 69 519, 77 418 and 98 630 RMB/hm2, respectively, and was 69.87%, 82.82%, 80.15%, 81.45% higher than that of control (W1N0). The stand volume per hectare of clone S86 was 2.3 times of clone 1316, 1.3 times of BT17 and 1.2 times of B331 The net profit per hectare of S86 was 2.9 times of clone 1316, 1.4 times of BT17，and 1.3 times of B331 respectively. Therefore, under high water and nitrogen conditions，clone S86 is the fastestgrowing and highest-yielding clone of this region.