Submitted to: Biol Fertil Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/1999
Publication Date: 2/1/2000
Citation: DOU, H., ALVA, A.K., APPEL, T. AN EVALUATION OF PLANT-AVAILABLE SOIL NITROGEN IN SELECTED SANDY SOILS BY ELECTRO-ULTRAFILTRATION, KCI, AND CACL2 EXTRACTION METHODS. BIOL FERTIL SOILS, 30:328-332. 2000. Interpretive Summary: Nitrogen (N) in soil undergoes a series of chemical and biological transformations which influence the plant availability and leaching losses. Improving the technique of measuring various forms of N in the soil is important to improve N management to minimize various losses. Electro- ultrafiltration (EUF) is a technique which works on the principle of ionic charges. In this study, the EUF method was used to determine the concentrations of total nitrogen, ammonium and nitrate forms of N. The latter two are inorganic forms, therefore, subtraction of concentrations of these two forms from the total N provides an estimate of organic form of N which plays a major role in N availability to plants. There was a good correlation between the EUF extractable total N, and N extractable by eithe 2M KCL or 0.01 M1CaCL2 solution. However, the concentration of the former greater than that of the latter, thus suggesting that the EUF-total N also includes organic fraction.
Technical Abstract: Improving the precision in estimating the nitrogen (N) requirements 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 sused to measure the concentrations of total EUF-extractable nitrogen (EUF- N1), ammonium-N (EUF-NH4+-N) and nitrate-N (EUF-NO-3-N). Available organic (Norg) was calculated as: EUF-N1-(NH4+-N+NO-3-N). The N concentrations in the EUF extraction were greater than those by the KCI 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.