FIRST-YEAR BIOMASS PRODUCTION AND SOIL IMPROVEMENT IN <em>LEUCAENA</em> AND <em>ROBINIA</em> STANDS UNDER DIFFERENT POLLARDING SYSTEMS

Abstract

YOUKHANA, A. & IDOL, T. 2008. First-year biomass production and soil improvement in Leucaena and
Robinia stands under different pollarding systems. The study of biomass production and soil improvement
of two fast growing and multipurpose trees, Leucaena leucocephala and Robinia pseudoacacia, was carried out
in Mosul Forest, northern Iraq, to examine the impact of pollarding height (0, 15, 30 and 45 cm) and
frequency (no pollarding, pollarding every three or six months) on growth responses and soil properties.
These species are being studied as part of a larger research programme to develop novel agroforestry systems
in Iraq. Leucaena leucocephala showed the greatest response in terms of branching, shoot basal diameter,
height, biomass and nitrogen and phosphorus contents of leaves and stems with pollarding every three
months at 15 cm. For R. pseudoacacia, pollarding once after six months at 45 cm resulted in the greatest
growth response of leaves and stems. Physical soil properties such as bulk density, infiltration rate and
chemical properties such as pH, total soil organic matter and nitrogen, available potassium and phosphorus
were all improved under L. leucocephala and R. pseudoacacia. Management of these trees in Iraq for soil
improvement or in agroforestry systems with different crops such as wheat, barley, corn and cotton should
take into consideration optimal pollarding frequency and height as well as planting density to produce the
desired levels of shade, soil cover and green manure, as well as animal fodder or wood products.