Response of pulp plantation growth of Populus tomentosa S86 in short rotation period to coupling of water and fertilizer in furrow irrigation

  Objective  This paper aims to research the coupling effects of furrow irrigation and nitrogen fertigation on the growth and stand productivity of high-density and short-rotation triploid Populus tomentosa S86 pulp plantations, in order to provide scientific theoretical basis for selecting efficient furrow irrigation-fertilization technology system suitable for the local area.

  Method  The plant materials were triploid P. tomentosa S86 in Gaotang County, Shandong Province of eastern China. A completely random block experiment design was adopted to monitor three irrigation levels, i.e. irrigation started when the soil water potential reached −20 kPa (W1), −33 kPa (W2) and −45 kPa (W3), and four fertigation levels (N1, 120 kg/(ha·year); N2, 190 kg/(ha·year); N3, 260 kg/(ha·year); N4, 0 kg/(ha·year)), and the control treatment was with no irrigation and no fertigation set (CK).

  Result  It took a long time for the fast-growing period of DBH growth of triploid P. tomentosa S86. The DBH growth of different stand ages in the growing season conformed to the Logistic function (R² > 0.99), and the difference of furrow irrigation and fertilization treatments was mainly manifested in June. Nitrogen application in furrow irrigation significantly affected the DBH increment and relative growth rate of 2-year-old P. tomentosa S86 plantations (P < 0.05), but had no significant effect on 3−5-year-old P. tomentosa S86 plantations. The coupling measures of water and fertilizer had a strong promotion effect on the average volume and average productivity of 2−3-year-old trees, but had no significant promotion effect on 4−5-year-old P. tomentosa S86 plantations. The average annual productivity of triploid P. tomentosa S86 stands was 19.65−25.31 m³/(ha·year) in four years, among which, W1N1 had the highest annual productivity, which was significantly higher than CK by 28.41% (P < 0.05). Under the treatment of 5-year-old stand W1N1, the tree growth was optimal, with unit area volume and average productivity reaching 104.39 m³/ha and 27.42 m³/(ha · year), respectively, which were 28.15% and 11.74% higher than CK treatment, respectively.

  Conclusion  The furrow irrigation and fertilizer coupling measures have different degrees of improvement on the unit area storage and annual productivity of 2−3-year-old triploid P. tomentosa S86 stand, but have no significant effect on the unit area storage and annual productivity of 4−5-year-old P. tomentosa S86 plantation. Among them, W1N1 furrow irrigation and nitrogen application treatment has the best growth. Under similar climatic and soil conditions, maintaining sufficient water (irrigation threshold of −20 kPa) and a lower nitrogen application rate (120 kg/(ha · year) is most conducive to the growth of high-density short-rotation triploid P. tomentosa targeting pulp forests.