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Book review

M. Birkás (Ed.): Environmentally-sound adaptable tillage. 2008. Akadémiai Kiadó, Budapest, Hungary. 354 pp. ISBN 978 963 05 8631 3

Acta Agronomica Hungarica
Author: K. Rajkai
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Ten pedotransfer functions (PTF) estimating soil saturated hydraulic conductivity were investigated using the HunSODA database and the SOILarium 2.0 software. The predicting efficiency of the PTFs was investigated by using statistical indicators, such as the expected value of absolute as well as relative errors. The estimated values, along with measured values of two characteristic Hungarian sites were used in a model application for simulating infiltration during a heavy rainfall event. When choosing a pedotransfer function it is most safe to choose an empirical PTF or a PTF that was developed on a large base dataset applying a not-too-simple not-too-complex formula. Considering the uncertainty related to arbitrary choosing a PTF and using its estimation in a model application, it is more safer to measure than estimate the saturated hydraulic conductivity of the soil.

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The electrical capacitance method was applied for the examination of living root systems in a pot experiment. The measured root capacitances gave an unambiguous indication of the development of root mass and length. The root capacitances measured using needle and clamp plant electrodes were closely similar when the roots of whole plants were placed in water, while increasing differences were observed with a decrease in soil water saturation. The difference in capacitance between the plant electrodes is outlined by interpreting the action mechanism of the clamp electrode. The capacitance and electrical impedance spectra (30 Hz-1 MHz) were determined for roots in soil, for pieces of roots washed free of soil, and for the soil itself. The root capacitance was smaller than that of the soil and higher than that of root pieces at 1 kHz, while the capacitance of the soil became equal to that of roots in soil at about 2 kHz. This calls attention to the importance of the measuring frequency when determining root capacitance. A capacitor model with two dielectric media is proposed besides Dalton's model in order to interpret the behaviour of root and soil capacitances. However, its validity requires further verification.

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A new method is introduced to agricultural practice for measuring the living active root of the plants. The measured root capacitance is interpreted in electro-chemical principles. In addition to the electrochemical interpretation of the measurements we aimed to find a non-wounding electrode instead of the needle plant electrode. Another reason for dealing with the tweezer plant electrode was to decrease the relatively high standard deviation of the root capacitance readings due to the relatively high uncertainty of hitting the xylem with the needle plant electrode. To improve and standardize the contact between the tweezer plant electrode and the stem a high electrical conductivity gel (UNIGEL) was applied on the stem before clipping the tweezers.   Experiments for the root capacitance measurements were made in temperature and light controlled climate chambers (Conviron, Canada) in 2 litre plastic pots filled with 4:1 soil:sand mixture and water culture. Comparison of the root capacitances of five-week old sunflower plants measured with the needle and the tweezer plant electrodes proved identical in water culture and capillary water saturated soil. However, the applicability of the tweezer plant electrode needs further study for other plants and environmental conditions. The effect of measurement frequency on root capacitance and resistance with the HP4284A impedance bridge was also studied to see the effectiveness of polarization (Figure 1).  From Figure 1 it can be seen that root capacitance decreased at frequencies above 1 kHz, while it increased up to the dielectric constant of water at lower frequencies. An interpretation of measurable root capacitance in the soil-plant system is given using separate measured plant tissue and soil capacitances. We established that root capacitance in the soil-plant system approximates the capacitance of the root tissue.  Good correlation was found between root capacitance and the calculated root surface area (RA) for sunflower plants (Figure 2).   The GW LCR-814 was found suitable for making root capacitance measurements.  Finally, further experimental work is needed to collect information for the more general and extended applicability of the method before it becomes a routine tool in ecological and agricultural practice. 

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Results of the performed preliminary particle size determination (PSD) experiments of soils show the importance of the preparation details of the laser diffractometer method (LDM). The analysis of the effect of each preparation factor on soil PSD data calls attention to the need for working out standard instructions defining the pre-treatments and settings for the LDM instrument. Further laboratory experiments involving larger soil datasets are required for the better understanding of the effects of soil pre-treatments and settings on PSD data. There is a practical reason of substituting the time-consuming pipette method with the LDM. In case of this substitution, linkages of the LDM PSD data and other soil properties are to be established. Correlation study of the LDM and conventional PSD data could make the harmonization of newly built and historical databases possible. Finally, the introduction of the LDM technique to soil physical methodology could generate the reevaluation of existing soil physical interrelations.

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According to the Hungarian Soil Information and Monitoring System's (HSIMS) database a group estimation method was developed to predict the mean soil hydrophysical properties. The estimation efficiency of the worked out prediction procedures was controlled on a test database, and on a dataset of a study area. It can be established that the water retention and the hydraulic conductivity of soils are sufficiently predictable from the category data of soil maps. The 10-digit map codes of the PWW mapping method were created by different estimation methods, and as a result the PWW map was drawn. However, it is not always possible to estimate the necessary soil hydrophysical properties from the available map information for preparing the PWW map. Sometimes the knowledge gained from the field reports is needed as well. Further studies are planned for integrating these morphological information into our estimations.

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Parameters governing the retention and movement of water and chemicals in soils are notorious for the difficulties and high labor costs involved in measuring them. Often, there is a need to resort to estimating these parameters from other, more readily available data, using pedotransfer relationships.

This work is a mini-review that focuses on trends in pedotransfer development across the World, and considers trends regarding data that are in demand, data we have, and methods to build pedotransfer relationships. Recent hot topics are addressed, including estimating the spatial variability of water contents and soil hydraulic properties, which is needed in sensitivity analysis, evaluation of the model performance, multimodel simulations, data assimilation from soil sensor networks and upscaling using Monte Carlo simulations. Ensembles of pedotransfer functions and temporal stability derived from “big data” as a source of soil parameter variability are also described.

Estimating parameter correlation is advocated as the pathway to the improvement of synthetic datasets. Upscaling of pedotransfer relationships is demonstrated for saturated hydraulic conductivity. Pedotransfer at coarse scales requires a different type of input variables as compared with fine scales. Accuracy, reliability, and utility have to be estimated independently. Persistent knowledge gaps in pedotransfer development are outlined, which are related to regional soil degradation, seasonal changes in pedotransfer inputs and outputs, spatial correlations in soil hydraulic properties, and overland flow parameter estimation.

Pedotransfer research is an integral part of addressing grand challenges of the twenty-first century, including carbon stock assessments and forecasts, climate change and related hydrological weather extreme event predictions, and deciphering and managing ecosystem services.

Overall, pedotransfer functions currently serve as an essential instrument in the science-based toolbox for diagnostics, monitoring, predictions, and management of the changing Earth and soil as a life-supporting Earth system.

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