Abstract
Irrigating hybrid poplars in northern Wisconsin, a cool humid temperate area, resulted in consistent growth increases. Maintaining field soil moisture tensions higher than −0·07 MPa and probably higher than −0·03 MPa resulted in the greatest biomass yields. Height growth increases ranged from 2 to 22% for 1- to 4-year-old trees, and biomass increases ranged from 27 to 33% for 3- to 5-year-old trees. Irrigation produced an added 8·0 Mg ha −1 of accumulated biomass in a 5-year-old plantation. Consumptive water use during the growing season was from 4·4 to 4·8 mm day −1. Irrigation had little effect on growth and no effect on tree survival during the establishment year. After the first year, increased number of irrigations were required to maintain the designated soil moisture tension levels. This suggests that the primary benefits of irrigation in northern Wisconsin may occur from cumulative biomass increases during the rotation rather than from improved survival during establishment.
Published Version
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