s:1823:"%T Nitrogen uptake of maize (Zea mays) from isotope-labeled biomass of Paraserianthes falcataria grown under controlled conditions 
%A Chintu, R. 
%A Zaharah, A.R. 
%X Roots can be an important though poorly quantified source of nitrogen (N) in agroforestry systems. Nitrogen uptake of maize using P. falcataria below- and aboveground biomass separately and their combination as source of N was assessed in a controlled experiment using 15N isotope labeling techniques. The 15N-direct and the 15N-indirect labeling techniques were compared for discrepancies in measuring N cycling from P. falcataria tree residues. N contribution to maize production was as follows; 40–57% from below ground biomass and 10–18% from above ground biomass (P < 0.05). Residue N use efficiency (%rNE) by maize was between 99 and 106% for belowground biomass 4–4.5% for aboveground biomass. This implies that though nutrient release characteristics of aboveground biomass are commonly used as a basis for selection of agroforestry trees those of belowground biomass would be of fundamental importance as well. Combining P. falcataria below and aboveground biomass did not result in significant (P < 0.05) effects on N recovered by maize suggesting the absence of decomposition interactions between the two bio-chemically contrasting residues. There were no significant methodological differences reflected in measured N cycled by maize from leaves (Ndfr); 15% and 18% as estimated by 15N direct and indirect method respectively. The two methods compared very well (P < 0.05) as tools of estimating N cycling from surface applied leaves. However the ability of the direct method to measure N without disturbing either the tree or the soil would make it a more attractive and valuable tool in N cycling studies in agroforestry systems. 
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