Rolf O. Kuchenbuch

A method for determining concentration profiles at the soil-root interface by thin slicing rhizospheric soil

SummaryA method is described for the determination of concentration gradients in the vicinity of plant roots. Plants are grown in small containers in which the roots are separated from the soil by a screen of nylon cloth. Root hairs but not roots penetrate the screen into the soil. In order to investigate the rhizospheric soil, the soil is frozen by liquid nitrogen and sliced into layers about 0.06 mm thick by means of a refrigerated microtome.

Sensory analysis and instrumental measurements of short-term stored tomatoes (Lycopersicon esculentum Mill.)

Abstract The effect of short-term storage of tomatoes (air temperature 20°C, relative air humidity 55%, air velocity

Potassium availability in relation to soil moisture I. Effect of soil moisture on potassium diffusion, root growth and potassium uptake of onion plants

SummaryThe objective of this research is to evaluate the influence of soil water content on- the mobility of potassium in soil,- plant growth and- K uptake of plants. The mobility of K increased with soil moisture. Increasing the volumetric water content (θ) from the 0.1 to 0.4 resulted in a rise of the effective diffusion coefficient (De) by a factor of about 10. This is mainly due to the increase of the tortuosity or impedance factor with higher soil moisture.In order to relate K mobility in soil to the availability of K for plant uptake, onion plants were grown in special containers under constant water content in the range of 0.1 to 0.4 cm3 H2O cm−3 of soil. Results are- both K content and growth of the plants increased with soil moisture,- water content below θ=0.1 reduced root growth- K inflow per unit of root surface increased with soil moisture. Maximum rate of inflow occurred with θ=0.25 in the soil used. It is therefore concluded that soil moisture affected K availability by affecting both K mobility and root growth.ZusammenfassungDie Arbeit hat das Ziel, den Einfluss des Wassergehaltes des Bodens auf- die Mobilität der Kaliumionen im Boden,- das Pflanzenwachstum und- die K-Aufnahme Zu bestimmen. Hierzu wurden einerseits Messungen der Mobilität von Kalium im Boden durch-geführt. Sie ergaben eine Erhöhung des effektiven Diffusionskoeffizienten (De) mit ansteigendem volumetrischen Wassergehalt (θ). De nahm um mehr als das Zehnfache zu während θ von 0,1 auf 0,4 anstieg. Dies ist der Erhöhung des Tortuositäts-oder Widerstands-faktors mit steigendem Wassergehalt zuzuschreiben. Um zu prüfen, in welchem Masse die Diffusionsbedingungen im Boden die Pflanzenverfügbarkeit von Kalium beeinflussen, wurde ein Vegetationsversuch durchgeführt. Hierzu wurden Zwiebelpflanzen in speziellen Versuchsgefässen bei konstanten Wassergehalten zwischen 0,1 und 0,4 cm3 H2O/cm3 Boden kultiviert. Die Ergebnisse sind:- K-Konzentration und Ertrag der Pflanzen wurden mit zunehmedem Bodenwassergehalt erhöht.- Der Wassergehalt des Bodens beeinflusste das Wurzelwachstum; unter θ=0,1 nahm die Wurzellänge stark ab.- Die K-Aufnahmerate eines Wurzelabschnitts stieg mit dem Wassergehalt an; bei θ=0,25 war die maximale Aufnahmerate in diesem Boden erreicht. Bie niedrigem Wassergehalt des Bodens wird die Kalium-Verfügbarkeit demnach beeinträchtigt sowohl durch den Rückgang der Mobilität von Kalium im Boden als auch die Verringerung des Wurzelwachstums.

Assessment of the predictive quality of simple indicator approaches for nitrate leaching from agricultural fields

Diffuse N losses from agriculture are a major cause of excessive nitrate concentrations in surface and groundwaters. Leaching through the soil is the main pathway of nitrate loss. For environmental management, an anticipatory assessment and monitoring of nitrate leaching risk by indicator (index) approaches is increasingly being used. Although complex Nitrogen Loss Indicator (NLI) approaches may provide more information, relatively simple NLIs may have advantages in many practical situations, for instance, when data availability is restricted. In this study, we tested four simple NLIs to assess their predictive properties: 1. N balance (Nbal); 2. Exchange frequency of soil solution (EF); 3. Potential nitrate concentration in leachate (PNCL); 4. A composite NLI (balance exchange frequency product, BEP). Field data of nitrate leaching from two sites in northeast Germany along with published data from several sites in Germany, Scotland and the USA were utilized. Nbal proved to be a relatively poor indicator of Nloss for the time frame of one year, whereas its prediction accuracy improved for longterm-averaged data. Correlation between calculated EF and experimental data was high for single-year data, whereas it was lower for longterm-averaged data. PNCL gave no significant correlations with measured data and high deviations. The results for BEP were intermediate between those for Nbal and EF. The results suggest that the use of EF is appropriate for assessing N leaching loss for single-year data and specific sites with comparable N input and management practices, whereas for longterm-averaged data, Nbal is better suited. BEP is an appropriate NLI both for single year and longterm data which accounts for source and transport factors and thus is more flexible than source-based Nbal and transport-based EF. However, such simplified NLIs have limitations: 1. The N cycle is not covered completely; 2. Processes in the vadose zone and the aquifer are neglected, 3. Assessment of management factors is restricted.

Environmental indicators to assess the risk of diffuse Nitrogen losses from agriculture.

Diffuse Nitrogen (N) loss from agriculture is a major factor contributing to increased concentrations of nitrate in surface and groundwater, and of N2O and NH3 in the atmosphere. Different approaches to assess diffuse N losses from agriculture have been proposed, among other direct measurements of N loads in leachate and groundwater, and physically-based modelling. However, both these approaches have serious drawbacks and are awkward to use at a routine base. N loss indicators (NLIs) are environmental management tools for assessing the risk of diffuse N losses from agricultural fields. They range in complexity from simple proxy variables to elaborate systems of algebraic equations. Here we present an overview of NLIs developed in different parts of the world. NLIs can be categorized into source-based, transport-based, and composite approaches. Several issues demand more attention in future studies. (1) Is incorporation of leaching losses and gaseous losses into one single NLI warranted? (2) Is it sufficient to restrict the focus on the rooted soil zone without considering the vadose zone and aquifer? (3) Calibration and validation of NLIs using field data of N loss seems not sufficient. Comparisons of several different NLIs with each other needs more attention; however, the different scaling of NLIs impedes comparability. (4) Sensitivity of input parameters with regard to the final NLI output needs more attention in future studies. (5) For environmental management purposes, factors addressing management decision by farmers deserve more attention.

Image analysis for non-destructive and non-invasive quantification of root growth and soil water content in rhizotrons

Studies aiming at quantification of roots growing in soil are often constrained by the lack of suitable methods for continuous, non-destructive measurements. A system is presented in which maize (Zea mays L.) seedlings were grown in acrylic containers — rhizotrons — in a soil layer 6-mm thick. These thin-layer soil rhizotrons facilitate homogeneous soil preparation and non-destructive observation of root growth. Rhizotrons with plants were placed in a growth chamber on a rack slanted to a 45° angle to promote growth of roots along the transparent acrylic sheet. At 2- to 3-day intervals, rhizotrons were placed on a flatbed scanner to collect digital images from which root length and root diameters were measured using RMS software. Images taken during the course of the experiment were also analyzed with QUACOS software that measures average pixel color values. Color readings obtained were converted to soil water content using images of reference soils of known soil water contents. To verify that roots observed at the surface of the rhizotrons were representative of the total root system in the rhizotrons, they were compared with destructive samples of roots that were carefully washed from soil and analyzed for total root length and root diameter. A significant positive relation was found between visible and washed out roots. However, the influence of soil water content and soil bulk density was reflected on seminal roots rather than first order laterals that are responsible for more than 80 % of the total root length. Changes in soil water content during plant growth could be quantitifed in the range of 0.04 to 0.26 cm3 cm—3 if image areas of 500 x 500 pixel were analyzed and averaged. With spatial resolution of 12 x 12 pixel, however, soil water contents could only be discriminated below 0.09 cm3 cm—3 due to the spatial variation of color readings. Results show that this thin-layer soil rhizotron system allows researchers to observe and quantify simultaneously the time courses of seedling root development and soil water content without disturbance to the soil or roots. Bildanalyse zur nicht-destruktiven und nicht-invasiven Quantifizierung von Wurzelwachstum und Bodenwassergehalt in Rhizotronen Untersuchungen, die der Quantifizierung des Wurzelwachstums im Boden dienen, werden oft durch das Fehlen geeigneter Methoden zur kontinuierlichen und zerstorungsfreien Messung eingeschrankt. Daher wird ein System vorgestellt, in dem Mais (Zea mays L.) in Gefasen — Rhizotronen — aus Acrylglas in einer 6 mm dicken Bodenschicht wachst. Diese Rhizotrone ermoglichen die homogene Einbringung des Bodens und die Beobachtung des Wurzelwachstums. Die bepflanzten Kuvetten werden in einer Klimakammer auf Gestellen platziert, die durch ihre Neigung von 45� bewirken, dass vermehrt Wurzeln an der transparenten Akryl-Oberflache entlang wachsen. Im Abstand von 2—3 Tagen werden die Rhizotrone auf einen Flachbett-Scanner gelegt und digitale Bilder erzeugt. An diesen wurden mit RMS-Software Wurzellangen und -durchmesser quantifiziert. Weiterhin wurde die Bodenfarbe mittels des Programms QUACOS analysiert; die resultierenden Farbwerte wurden anhand einer separat bestimmten Beziehung zwischen Bodenwassergehalt und Bodenfarbe in Bodenwassergehalte umgerechnet. Um zu bestatigen, dass die sichtbaren Wurzeln reprasentativ fur die Wurzeln im Bodenvolumen sind, wurden sie mit Wurzellangen verglichen, die nach destruktiver Ernte und Auswaschen bestimmt wurden. Es ergab sich eine signifikante positive Beziehung zwischen sichtbarer und gesamter Wurzellange. Allerdings spiegelte die sichtbare Wurzellange verlasslich nur den Einfluss von Bodenwassergehalt und Bodendichte auf samenburtige (dicke) Wurzeln wider, nicht auf Seitenwurzeln erster Ordnung, die uber 80 % der Gesamtwurzellange ausmachen. Veranderungen des Bodenwassergehaltes wahrend des Pflanzenwachstums konnten im Bereich von 0.04 to 0.26 cm3 cm—3 quantifiziert werden, wenn Flachen von 500 x 500 Pixel analysiert und gemittelt wurden. Mit einer Auflosung von of 12 x 12 Pixel konnte der Bodenwassergehalt aufgrund der raumlichen Variabilitat der Farbwerte nur unterhalb von 0.09 cm3 cm—3 bestimmt werden. Die Ergebnisse zeigen, dass dieses Rhizotron-System mit einer dunnen Bodenschicht es erlaubt, die Entwicklung der Wurzel junger Maispflanzen und den Bodenwassergehalt in kurzen Zeitabstanden zu bestimmen, ohne Veranderungen an Boden oder Pflanzen vorzunehmen.

Root effects on soil water and hydraulic properties

Plants can affect soil moisture and the soil hydraulic properties both directly by root water uptake and indirectly by modifying the soil structure. Furthermore, water in plant roots is mostly neglected when studying soil hydraulic properties. In this contribution, we analyze effects of the moisture content inside roots as compared to bulk soil moisture contents and speculate on implications of non-capillary-bound root water for determination of soil moisture and calibration of soil hydraulic properties.In a field crop of maize (Zea mays) of 75 cm row spacing, we sampled the total soil volumes of 0.7 m × 0.4 m and 0.3 m deep plots at the time of tasseling. For each of the 84 soil cubes of 10 cm edge length, root mass and length as well as moisture content and soil bulk density were determined. Roots were separated in 3 size classes for which a mean root porosity of 0.82 was obtained from the relation between root dry mass density and root bulk density using pycnometers. The spatially distributed fractions of root water contents were compared with those of the water in capillary pores of the soil matrix.Water inside roots was mostly below 2–5% of total soil water content; however, locally near the plant rows it was up to 20%. The results suggest that soil moisture in roots should be separately considered. Upon drying, the relation between the soil and root water may change towards water remaining in roots. Relations depend especially on soil water retention properties, growth stages, and root distributions. Gravimetric soil water content measurement could be misleading and TDR probes providing an integrated signal are difficult to interpret. Root effects should be more intensively studied for improved field soil water balance calculations.

Assessment of sampling and analytical uncertainty of trace element contents in arable field soils.

Assessment of trace element contents in soils is required in Germany (and other countries) before sewage sludge application on arable soils. The reliability of measured element contents is affected by measurement uncertainty, which consists of components due to (1) sampling, (2) laboratory repeatability (intra-lab) and (3) reproducibility (between-lab). A complete characterization of average trace element contents in field soils should encompass the uncertainty of all these components. The objectives of this study were to elucidate the magnitude and relative proportions of uncertainty components for the metals As, B, Cd, Co, Cr, Mo, Ni, Pb, Tl and Zn in three arable fields of different field-scale heterogeneity, based on a collaborative trial (CT) (standardized procedure) and two sampling proficiency tests (PT) (individual sampling procedure). To obtain reference values and estimates of field-scale heterogeneity, a detailed reference sampling was conducted. Components of uncertainty (sampling person, sampling repetition, laboratory) were estimated by variance component analysis, whereas reproducibility uncertainty was estimated using results from numerous laboratory proficiency tests. Sampling uncertainty in general increased with field-scale heterogeneity; however, total uncertainty was mostly dominated by (total) laboratory uncertainty. Reproducibility analytical uncertainty was on average by a factor of about 3 higher than repeatability uncertainty. Therefore, analysis within one single laboratory and, for heterogeneous fields, a reduction of sampling uncertainty (for instance by larger numbers of sample increments and/or a denser coverage of the field area) would be most effective to reduce total uncertainty. On the other hand, when only intra-laboratory analytical uncertainty was considered, total sampling uncertainty on average prevailed over analytical uncertainty by a factor of 2. Both sampling and laboratory repeatability uncertainty were highly variable depending not only on the analyte but also on the field and the sampling trial. Comparison of PT with CT sampling suggests that standardization of sampling protocols reduces sampling uncertainty, especially for fields of low heterogeneity.

Which part of the root system of corn (Zea mays L.) is visible at transparent surfaces

Roots are growing in soil and hence are not available for direct observation. This causes quantitative root studies to be difficult and time consuming. As an alternative to washing roots from soil often root boxes, minirhizotrones and rhizotrones are used (BoHM 1979, SMIT et al. 2000). However, one prerequisite for the quantification of root traits from these methods is that the visible part of the root system is a representative part of the total root system. The research reported here compares roots of corn (Zea mays L.) visible at transparent surfaces with roots washed from soil using the method described by INGRAM and LEERS (2000). In principle, roots are grown in a soil layer that is 6…7 mm thick and allows root observations and root length measurements after scanner images are taken from the transparent acrylic surface of the container. Two experimental approaches were used for comparison: (i) soil was compacted to soil bulk densities from 1.25 to 1.8 g/cm3, and (ii) different initial soil water contents were established in soil layers prior to planting. 15 days after planting root length was measured on scanner images with available software (Quacos Software, copyright the University of Georgia), and root length was determined for two diameter classes, i.e. 0 to 0.7 and 0.7 to 1.3 mm(corresponding to seminal and secondary roots) from washed out roots using WinRhizo Software (Regent Instruments, Quebec, Canada). The comparison of both measurements showed that: There was no identical relationship between visible and total root length of the diameter class 0…0.7 mm over the range found in the containers, neither for the soil water content nor the soil bulk density experiment. Hence, the length of secondary roots could not be predicted from observations at the transparent surface. For roots with diameters 0.7…1.3 mm both, for soil differing in water content and bulk density, visible and total root length showed a strong linear correlation. However, the slope of the regression line differed between the experi ments.

Methode zur zerstörungsfreien Messung der Wurzelentwicklung

Studies aiming at quantification of roots growing in soil are often constrained by the lack of suitable methods for continuous, non-destructive measurements. A system is presented in which maize (Zea mays L.) seedlings were grown in acrylic containers — cuvettes — in a soil layer 6 mm thick. These thin-layer soil cuvettes facilitate homogeneous soil preparation and observation of root growth. Cuvettes were placed on a rack slanted to a 45° angle throughout the experiment to promote growth of roots along the transparent acrylic sheet. At two- to three-days intervals, cuvettes were placed on a flatbed scanner to collect digital images from which root length and root diameters are measured using available software. Results show that this system allows researchers to observe and quantify simultaneously the time courses of root development.