Decomposition and Macronutrients Release of Roots of Millettia Thonningii Placed at three Soil Depths in the Tropics

Decomposition of Millettia thonningii (Schumach and Thonn) Bak fine roots (?2 mm) and coarse roots (2-5 mm) was conducted at IITA Ibadan, south-western Nigeria. The study investigated the effect of soil depths, root size and chemical composition of the roots on decomposition, mineralization and immobilization of nutrients. The roots were put in 2 mm mesh-bags and buried at three soil depths; 1.5, 15, and 30 cm and evaluated for 210 days. Decomposition of fine and coarse roots was significantly (pphosphorus (P)>nitrogen (N)>magnesium (Mg)>calcium (Ca), K>P>N>Mg>Ca, and K>P>N=Mg>Ca respectively. The nutrient release patterns of coarse roots at 1.5, 15 and 30 cm soil depths were: K>Mg>N>P>Ca, K>N>Mg>P>Ca and K>N>Mg>P>Ca respectively. The results therefore indicate that soil depth and root sizes have major influence on decomposition and mineralization of nutrients though polyphenol concentrations, C: N and L: N ratios also influenced these biological processes.