The effects of decomposing albizia species leaf litter on soil nutrient status

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The rates of decomposition and nutrient release from leaf litter of Albizia adianthfolia, Albiziaferruginea and Albizia zygia were studied using the wooden box method over a period of fourteen weeks. The experimental design used was the completely randomized design (CRD) with the three species as treatments, and each replicated twenty-four (24) times. A known dried weight of leaf litter (bOg) of each species was put in the wooden box and the opened end was inverted unto the ground in the open field. Litter on the floor was removed so that the opened and inverted end of the box containing the litter of the three species got direct contact with the soil. These were fixed to the ground with wooden pegs to prevent movement of the wooden boxes. In all there were 72 wooden frame boxes (ie. each of the three species (treatments) was replicated 24 times making 72 samples) distributed randomly on the ground. At intervals of two weeks, three boxes of each species were picked from the ground. The residual litter in the boxes was removed, oven-dried and weighed. The residual litter for each species was then analysed for N, P, K, Ca, Mg and organic C concentrations. Soil samples were also taken at the beginning and end of the experiment (week zero and week 14) respectively. These were collected from 0-15cm and 15-30cm depth from the surface, subsequently air dried and the N, P, K, Ca, Mg and Organic C concentrations determined. The results showed that the rates of decomposition of the three species leaf litter were in the order: Albiziaferruginea (K= 3.5) > Albizia zygia (K= 3.7) > Albizia adianthfolia (K= 4.7). However, these observed differences were not statistically significant (P>O.05). The half-lives were also 3.5, 3.7 and 4.7 weeks for Albiziaferruginea, Albizia zygia and Albizia adianthfolia respectively. The ranking of nutrient mineralization rates were also in the order: Albiziaferruginea: K > N > C> P> Ca> Mg; Albizia zygia: K > N> C> P > Mg> Ca and Albizia adianthfolia: P > N > C > Ca> K> Mg. It was also observed that climatic conditions like temperature significantly influenced litter decomposition rate of Albizia adianthfolia (P<O.05), while the combined effects of temperature and relative humidity also significantly influenced leaf litter decomposition of Albiziaferruginea and Albizia zygia (P<O.05). It is concluded that, although there were observed variations in the rate of decomposition of the three Albizia species ( Albiziaferruginea > Albizia zygia > Albizia adianthfolia), the differences were however statistically not significant (P>O.05). It was also observed that Potassium had the highest released rates in both Albiziaferruginea and Albizia zygia whilst Phosphorus had the highest released rate in Albizia adianthfolia. Finally, it was realised that soil nutrient changes after decomposition did not follow any consistent pattern. It is recommended that the synchrony of nutrient release by decomposing litter and nutrient uptake by crops should be studied. Again, the indigenous species scope should be broadened and lastly soil invertebrates like termites and their specific roles in decomposition should be determined.
A thesis Submitted to the Board of Postgraduate Studies Kwame Nkrumah University of Science and Technology, Kumasi in Partial fulfillment of the requirements for the award of Master of Science degree in Agro forestry, 2005