An evaluation of plant-available soil nitrogen in selected sandy soils by electro-ultrafiltration, KCl, and CaCl2 extraction methods |
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| Authors: | H Dou A K Alva T Appel |
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| Institution: | (1) Florida Department of Citrus, Lake Alfred, FL 33850-2299, USA e-mail: hdou@icon.lal.ufl.edu Tel.: +1-941-956-1151, Fax: +1-941-956-4631, US;(2) University of Florida, Institute of Food and Agricultural Sciences, Citrus Research and Education Center, Lake Alfred, FL 33850-2299, USA, US;(3) Institute for Plant Nutrition, Justus Liebig University, Südanlage 6, D-35390 Giessen, Germany, DE |
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| Abstract: | Improving the precision in estimating the nitrogen (N) requirement for citrus trees on sandy soils is important for increasing
N efficiency by the trees and minimizing potential losses of N in commercial citrus production areas. In this study, representative
Florida soils were sampled from major citrus production areas and the electro-ultrafiltration (EUF) technique was used to
measure the concentrations of total EUF-extractable nitrogen (EUF-Nt), ammonium-N (EUF-NH4
+–N) and nitrate-N (EUF-NO3
––N). Available organic N (Norg) was calculated as: EUF-Nt–(NH4
+–N+NO3
––N). The N concentrations in the EUF extraction were greater than those by the KCl or CaCl2 method. The Norg fraction, estimated by the EUF method, varied from 4.4 to 40.8 mg kg–1 soil, equivalent to 10 to 91 kg N ha–1 (for the top 15 cm depth soil) and was positively correlated with the total soil N determined by the Kjeldahl method. The
presence of appreciable amounts of Norg in these soils indicates that these soils contain high proportions of the total soil N in easily mineralizable Norg forms. This study demonstrates that the EUF-extractable organic bound N must be considered in developing N fertilizer recommendations
for citrus.
Received: 13 January 1999 |
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| Keywords: | Key words Nitrate-N Ammonium-N Organic bound N N-extraction methods |
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