Abstract
Combined drip irrigation and fertigation significantly increased stem volume and biomass production in a poplar plantation, and showed a cumulative effect over years. The promoting effects were mainly attributable to increased nitrogen and water availability in the surface soil through the combined management. Fast-growing and high-yielding poplar plantations have been identified as major commercial forests in China. Intensive management of irrigation and fertilization can greatly increase productivity of plantations. Quantitative investigations on the cumulative effect of drip irrigation and fertigation over years are quite infrequent. We aimed to quantitatively evaluate the effects of drip irrigation and fertigation plans on tree growth and productivity in a poplar plantation, and to analyze their possible cumulative promoting effect over multiple years. Treatments including nine drip irrigation and fertigation combinations, and single furrow irrigation in spring as control, were conducted in a poplar plantation for three successive years. The combined treatments consist of three irrigation levels (WP−75, WP−50, and WP−25, in ascending order) and three levels of nitrogen addition (N60, N120, and N180, in ascending order). Soil nitrogen and water content were measured throughout the 3 years. Based on tree surveys, tree growth, volume, and biomass production were evaluated each year. Nitrogen and water availability in the surface soil increased in the drip irrigation- and fertigation-treated plots. Drip irrigation and fertigation treatments resulted in significant higher growth, stem volume, and biomass productions compared to control. Biomass increments in drip irrigation- and fertigation-treated plots were 4.8–50.0, 5.3–26.5, and 4.3–52.2% higher than control in the three experimental years, respectively, with WP−25N180 and WP−50N180 recording the highest increments. Fertigation showed cumulative effects over multiple years and the positive effects increased with the dosage. However, irrigation showed little cumulative effect and the greatest effect was obtained under medium level. Combined drip irrigation and fertigation greatly promoted the plantation productivity. The combined management effect varied with application plans and plantation ages, and showed a cumulative effect over years.
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