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it may be still worth considering a trial for a restricted number of sites such as intensive monitoring (Level II) sites. (b) The second possibility is to use surrogate measures such as near infrared (NIR) or mid infrared (MIR) spectroscopy and develop statistical models for which the data of selected samples for desorption set would be available. NIRS is a simple and cheap technique to handle a big set of samples as will be available for the BZE. There have been a number of studies reported in literature, where this technique has been tested for assessing P in the soil and plant samples. It has shown to be useful for studying retention of P by Al and Fe rich humus soils (Giesler et al 2005).It is routinely already used in some laboratories for C and N analysis. In short the suggested development of a suitable method will include the following steps: 1. Preliminary experiment on a small set of samples from BZE collective to test the suitability of different anion based extractants including anion resin exchange methods. The subset of BZE1 samples that cover the wide variation in soil conditions encountered. 2. A set of suitable soil samples will be selected from BZE collective to develop desorption procedure including the fitting of the desorption isotherm to obtain the capacity and the rate functions. The number of samples will depend upon the different types of soil matrix to be included in prediction models. 3. This set of soil samples will be used for NIRS and/or MIRS analysis and appropriate calibration and validation models will be developed to obtain parameters of desorption isotherms. 4. All soil samples in the BZE collective will be analysed with NIRS or MIRS to predict the desorption parameters. Desorption parameters will then provide soil data to assess the status and changes in the P supply of soils. 3.5 Summary of P in Forest Soils Dynamics of P in forest soils involve both the organic and inorganic fractions which are in different dynamic equilibria involving various processes of mineralization, immobilization, desorption, solubilisation, retention and uptake. It is therefore hard to 72
assess P status or any changes in P status of soils by using simple methods, rather the complex nature of interactions requires special techniques often involving a number of different methods. It was shown that P in the soil solution phase determines P uptake but it is the most dynamic component of soil P. Through solubility product diagrams it has been possible to assign the dominant inorganic forms of P which may be determining the concentrations of P in soil solutions. A conceptual framework is normally used to assign differences in the lability of different soil P fractions with respect to their availability for uptake. Sequential extraction methods are used to obtain P fractions which are differently labile. However, not the easily labile fractions undergo changes in the long term but in many cases the fractions of moderate to low turnover indicating the dynamic equilibria occurring among different forms of P. This creates a problem for selecting the suitable chemical fractions which could be extracted by appropriate methods. Consequently there are many different types of soil P tests which are used both in agriculture and forestry. Agricultural methods have been developed specifically to provide fertilizer recommendations for crops, and are thus of limited use to describe the long-term P status of forest soils. The limitations and advantages of various methods have been described. We recommend a method including repeated extractions of soil P by using an appropriate extractant. The selection of extractant(s) would require some initial studies. Such a repeated desorption of P from soils will provide a capacity factor giving the amount of labile fraction and a desorption rate function which may be related to soil characteristics. Any change in those two parameters would then indicate a change in P status of soil. The development of the method should be done on a small but representative set of soils of the BZE collective. In order to save resources, for the rest of the samples these parameters may be obtained by developing suitable models using NIRS or MIRS techniques. The proposed method will still require a high level of resource commitment to be made available in future under the BZE program. Despite the major concerns of changes in P status of forest soils, this area of research has not received sufficient attention in the past. 4. ACKNOWLEDGEMENTS A number of persons provided ideas, data evaluation and support for this document. We wish to thank for their efforts: Dr. Carl Hoecke, Dr. Jan Evers, Dr. Henning Meesenburg and Dr. Michael Mindrup. 73
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ASSESSMENT OF CHANGES IN THE PHOSPH
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RECOMMENDATIONS 1. The results of t
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EXECUTIVE SUMMARY 1. The first nati
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High N inputs and uptake by plants
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12. It is recommended that a series
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Below, these hypotheses are being d
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Douglas fir which suffered from abs
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easons of such results. Another rea
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The frequency and the amount of mas
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usually present in the leaves. In v
Page 21 and 22: level class are given in brackets.
Page 23 and 24: 2.3 Factors influencing the foliage
Page 25 and 26: example the compiled data from BZE-
Page 27 and 28: mostly during periods of active gro
Page 29 and 30: Table 3: Number of cases included f
Page 31 and 32: P % 0.1 0.2 0.3 0.4 Kiefer 4 4,5 5
Page 33 and 34: P % 0.1 0.2 0.3 0.4 0.5 Eiche 4 4,5
Page 35 and 36: 19.84 n=144 NVHU< 1228 | CMENGE< 38
Page 37 and 38: 2.6 Changes in P concentrations in
Page 39 and 40: in section 1 of this report. In sum
Page 41 and 42: Fig 8: Mixed linear model describin
Page 43 and 44: Fig 10: . Mixed linear model descri
Page 45 and 46: Table 6: Concentration of P (mg/g)
Page 47 and 48: (Nilsen and Abrahmsen 2003) reporte
Page 49 and 50: 3. PHOSPHRUS IN FOREST SOILS 3.1 In
Page 51 and 52: sequential extraction scheme of ext
Page 53 and 54: Table 8 : Sequential extraction pro
Page 55 and 56: phosphates at pH values
Page 57 and 58: 3.2.2 Inorganic forms of P - desorp
Page 59 and 60: Mineralisation of organic P does no
Page 61 and 62: enhances the dissolution of Ca-phos
Page 63 and 64: water, and sodium bicarbonate metho
Page 65 and 66: Table 10. Estimated transfers and c
Page 67 and 68: 3.3 Use of pedo-transfer functions
Page 69 and 70: the amount taken up at each site. T
Page 71: is commonly saturated with HCO3 is
Page 75 and 76: Forest Ecol. Manage. 92, 119-152. B
Page 77 and 78: Rev. Plant Physiol.Plant Mol. Biol.
Page 79 and 80: and N-free-fertilisation. Plant Soi
Page 81 and 82: Sparling GP, Hart PBS, August JA. (
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