Relationship between availability indices and plant uptake of nitrogen and phosphorus from organic products |
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Authors: | GL Velthof ML van Beusichem WMF Raijmakers BH Janssen |
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Institution: | (1) Department of Environmental Sciences, sub-department Soil Science and Plant Nutrition, Wageningen Agricultural University, P.O. Box 8005, 6700 EC Wageningen, The Netherlands. Corresponding author |
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Abstract: | A better knowledge of the plant-availability of nitrogen (N) and phosphorus (P) in organic products may help to improve the efficient use of these products as fertilizers. In the present study, availability indices for N and P of nine widely differing organic products obtained by different fractionation methods were compared with the plant uptake of N and P from these products. The fractionation methods included CaCl2 extraction, thermal fractionation (heating of organic products), and pepsin extraction, for N, and extraction with diluted sulphuric acid, P-Bray-I, P-Olsen, and extraction using an iron oxide coated filter paper, for P. The results of pot experiments with ryegrass using a double-pot technique (Janssen, 1990) over 62 (N experiment) and 93 days (P experiment) were used as reference for plant-availabe N and P. The 0.01 M CaCl2 extractable inorganic N reasonably predicted plant-available N only in organic products with a high inorganic N fraction. Thermal fractionation and pepsin extraction provided a reasonable index for mineralizable N in organic products having a high fraction of mineralizable N. Of the P fractionation methods, the extraction using iron oxide coated filter paper was the best indicator of plant-available P in the products. |
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Keywords: | iron oxide coated paper organic products pepsin extraction plant-available N plant-available P thermal fractionation |
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