Poplar tree buffer strips grown in riparian zones for biomass production and nonpoint source pollution control

摘要

Research studies were conducted to test an innovative wooded buffer strip using Populus spp. (poplar) trees planted in an agricultural riparian zone. Cuttings 180 cm (6 ft) long were planted vertically in 150 cm (5 ft) deep trenches in four rows. Poplar spacing in the buffer strip was 30 cm (1 ft) apart in-row and 100 cm (40 in) between rows for an area allocation of 0.37 m$sp2$ (3.3 ft$sp2$) per tree. The initial planting density is approximately 35,600 trees per hectare (14,000 trees per acre).;The Populus spp. trees demonstrated viable root growth their entire buried length. Tree root systems and the deep-planting method very significantly (p $<$ 0.0005) reduced the average nitrate-nitrogen mass in the 150 cm (5 ft) soil profile from 25 mg N/kg dry soil to 2.3 mg N/kg dry soil. The tree roots reduced nitrate-nitrogen in near-surface groundwater. Sampled wells 6 m (20 ft) apart beneath the corn and the poplar buffer contained 92 mg nitrate-nitrogen per liter and 2 mg nitrate-nitrogen per liter respectively.;Shallow planted Populus spp. trees had a survival rate of 40%; the deep-rooted poplars had a survival rate of 99.4%. Following the second 175-day growing season, all trees averaged over 4.5 m (15 ft) tall with an average growth rate of 5.4 g biomass/tree/day (dry weight basis). At this growth rate and planting density, the poplar buffer strip will yield 46,000 kg biomass/hectare (41,000 lb biomass/acre) in two growing seasons. This mass is approximately 25% leaf and 75% stem.;The sampled poplar trees contained an average of 2.3% N in the leaf tissue and 0.4% N in the stem (dry matter basis), metabolized from inorganic nitrate-nitrogen or ammonium-nitrogen in the soil pore water. Following the second growing season, each tree contained an average of 10 g N/tree in the stem and leaf for a harvestable nitrogen mass of 330 kg N/hectare (300 lb N/acre).