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

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Egbe E.A., Nwoboshi L.C., Ladipo D

Department of Botany and Plant Physiology, University of Buea, Cameroon

International Institute of Tropical Agriculture, (IITA) PMB3112 Ibadan, Nigeria

 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 (p<0.05) greater at 15 cm soil depth than at the 1.5 cm and 30 cm soil depths.  The decomposition constant at 1.5, 15 and 30 cm for fine roots were, 1* 10-2, 1.3*10-2 and 1.2*10-2 respectively while those of coarse roots were 9*10-3, 1.2 * 10-2 and 9 * 10-3 respectively. The nutrient released was greatest at the 15 cm soil depth than the other soil depths for both root sizes. Potassium was the most and easily released element while calcium was immobilized in the coarse roots. The nutrient release patterns of fine roots at 1.5, 15 and 30 cm was as follows: potassium (K)>phosphorus (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.

Keywords: Mineralization, Immobilization, Decomposition Constant, Nutrient Release Constant Rate, Half-life and Lignin:Nitrogen Ratio

 

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