physical properties of cereal grain and rape stem

7/27/2019 Physical Properties of Cereal Grain and Rape Stem

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80 RES. AGR. ENG., 54, 2008 (2): 8090

Dedicated to the 80thAnniversary of Prof. Rado eznek

aking into consideration the jubilee character ofour article, dedicated to Prof. Rado eznek, andthe fact that the presented research works were to alarge extent inspired by Jubilee and sometimes by hiswards, the authors decided to show also the resultsof the current research, which bear witness to a closeco-operation. Tis long-term co-operation betweenthe Department of Physics of echnical Faculty ofCULS in Prague (formerly the Faculty of Mechanisa-tion CUA in Prague) and the Department of Physicaland echnological Properties of Agromaterials ofIA PAS in Lublin has lasted continuously since the

beginning of 70ties of XX century and in each yearextends the research interests of both sides. Teauthors present the results of research in two mainareas of interest: physical properties mainly of wheatgrain but also of rape stems.

Modern technology of harvesting and threshingrequires the knowledge of the mechanical propertiesof cereals, if the objective is to optimise these proc-esses and to reduce the quantitative and qualitativelosses of grain. Preliminary research in the domainof cereal grain properties covered the question ofthe origin of quantitative losses of grain in combineharvesting.

One of the factors causing these losses is thespontaneous shedding of grain in the field by hit-ting the elements of the harvesting system, anotherone is the unthreshed grain left in ears. In the firstcase, the grains are bound to the ear torus with toosmall forces, while the leaving of unthreshed grainoccurs with the varieties strongly binding grainwithin the ear, at improper regulation of workingparameters of the combine harvester (1970; et al.1978a,b; S & 1984). As a continuation of the above mentioned in-

vestigations, G and P (2004) described

some characteristics of physical properties of singlekernel in wheat heads.

wo main destructive factors of grain were takeninto consideration in our co-operation. Internalcracks originate already in the pre-harvest periodand lead to a crop reduction as the result of theweakening of the structure of endosperm. Grainbecomes softer and less resistant to dynamic loadsinflicted by the active elements of harvesting andstatic or quasi-static loads during transport or stor-age. Fragmented grain is more susceptible to theattacks by infesters and infectors in storage bins.Te second factor is storage pest activity in storage

Physical properties of cereal grain and rape stem

S. G, G. S

Bohdan Dobrzanski Institute of Agrophysics of Polish Academy of Sciences, Lublin, Poland

Abstract: Te paper presents the results of a study on the mechanical properties of cereal grain and of rape stems,conducted within the framework of the continuing long-term cooperation between the Bohdan Dobrzaski Institute ofAgrophysics, Te Polish Academy of Sciences (IA PAS) in Lublin, and the Czech University of Life Sciences (CULS) inPrague, Czech Republic. Within the scope of the mechanical properties of cereal grain, the study showed a significantrelation between the physical conditions of kernels of common wheat as determined through X-ray detection, and theirmechanical properties determined by means of standard tests used in the mechanics of structural materials and of thetests used in the technology of cereal grain processing. Te study on the mechanical properties of rape stems demon-strated inter-variety differences between plants with varied resistance to lodging. Te estimation of the variability ofthe mechanical properties along the length of rape stems showed the existence of a characteristic point located close tothe first bifurcation. Significant effects were noted of the density of the canopy expressed in the number of plants persquare meter, and of nitrogen fertilisation on the strength characteristics of rape stems obtained on the basis of testsof mechanical properties. At the same time, a relation was proved between the mechanical properties of the stems andabsorption of X-rays

Keywords: wheat grain; rape stem; physical properties; utility value


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bins. Granary weevil (Sitophilus granariusL.) is themost significant infester of storage grain in Europe.Te activity of insects leads to an increase of themoisture content and temperature of stored grainwhich is the cause of the occurrence of conditionsfavourable for the infection by fungi and subsequentreduction of quality by mycotoxins. Infested grainis hazardous for humans due to the contaminationby metabolites, body fragments, and dead bodies,strongly allergenic to human.

Te second field of investigation looked for thereason of proneness of rape stem to lodging. Rapeplants are prone to lodging, which reduces the levelof rape seed yield obtained. As it is known, the re-sistance of plants to lodging is closely related tothe mechanical properties of their stems. Tis facthas been reflected in many years of research on themechanical properties of plant stems ( etal.1978a, 1980; B et al.1983, 1984, 1985;S et al.1989; B & S 1990;

S 1982, 1991, 1998, 2001a,b; S &M 1991; S & B 1997).

In the studies, the static test was used to determinethe stem rigidity and maximum bending stress, andthe dynamic test to determine the shearing energyand shearing energy per unit of rape stem cross sec-tion area (S et al.1989; B & S1990; S 2001a,b). Also, analyses were madeof the mechanical properties of rape varieties inthe course of the plant growth and development.At the same time, the estimation was conducted of

the mechanical properties of stems of plants grownunder varied conditions in terms of plant density per

square meter and of nitrogen fertilisation applied(S 1995, 2001a,b). In the final stage of thestudy, the authors searched the relations between themechanical properties and X-ray absorption by rapestems (S & V 1994, 2000).

MATERIALS AND METHODS

Wheat grain investigations

In co-operation with Physical Dept. of CULS inPrague, a direct method based on the measurementsof the force binding particular grains with the earhas been worked out. Using the tensometric micro-picker elaborated in Prague, the investigations werecarried out in the prior period of cooperation in19731975. Te research material consists of wheat

varieties cultivated in both countries on a wide scaleand staying in the range of experiments at least overthe period of the mentioned three years. In effect,

the investigations comprised the winter wheat varie-ties Kavkaz and Mironovskaya, and the spring wheat

variety Zlatka, cultivated in the Czech Republic,and the winter wheat varieties Kavkaz, Grana, andHelenka as well as the rye Dankovskie Zlote culti-

vated in Poland. Te methodology of this investi-gation (Figure 1) is clearly described in a paper by et al.(1978b). In the paper by Gand P (2004), the experimental material con-sists of common winter wheat of the cultivar Kris.Te heads from the main and lateral stalks of this

cultivar were gathered prior to full maturity of grainat the Station of Varieties Estimation in Czeslawice

1

2

3

4

5

6

5

4

3

2

1

(a)

(b)

(c)

(mm)l

Pz

P(N)

Pw

S1

S2

Figure 1. Scheme of measurementsets: (a) diagram of the tensometricmicro-picker (CLUS-Prague): 1 ear,2 pliers, 3 body of the micro-picker,4 flexible connector, 5 tensometricring, 6 holder of the micro-picker,7 recorder; (b) diagram of themeasuring system of the Instron 1253

machine (IA PAS Lublin): 1 loadinghead, 2 pliers, 3 ear, 4 univer-sal holder, 5 base of the holder;(c) diagram from the recorder of theInstron apparatus, presenting thecourse of separating grain from ear:Pz maximum force of grain-to-eartorus binding, Pw maximum forcekeeping grains in glumes after break-ing off from torus, l total way a grainmust cover for its complete separationfrom ear to occur, S1 energy neces-sary to break grain off from ear torus,S

2- energy necessary to remove grain

from among glumes (dechaffing)


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82 RES. AGR. ENG., 54, 2008 (2): 8090


(Poland). In these investigations, two apparatuses:Single Kernel Characterization System (SKCS) andX-ray apparatus were used (Figure 2).

Te physical properties of wheat grain are describedto a great extent by the properties of endospermwhich takes 8086% of its volume. Endosperm is acomposite material consisting of thin-walled cellswhich are filled mostly with starch granules embed-ded in a strong- protein matrix. Pores constitute theremainder of the cell volume. Methodical aspectsare described in detail in a paper by H andG (1985). Endosperm density and the densitydistribution (Figure 3) were measured in specimensin the shape of rectangular prisms cut out of grains ofthree winter wheat varieties (H et al.1989).

Some problems of the measurement of the rheo-logical properties of grain endosperm by the pulse

ultrasound method (Figure 4a) were also studied(H & G 1983). he samples wererectangular in shape and were prepared from thewheat varieties Jana and Grana, and from the barley

variety Rapid.In cooperation with Hnilica (G & H

1985), an introductory study of the internal poros-ity changes in the endosperm of the wheat varietyJana was also carried out by G and H(1985). Mercury porosimetry and samples in theform of rectangular prisms were used in this study.Te samples were subjected to elastic and plasticdeformation prior to the experiments.

In the paper by G et al.(2006) some resultsof the application of ImageJ to X-ray image analysisof wheat kernels are presented. ImageJ based onX-ray technique enabled to construct rapid and

Figure 2.View of the X-ray apparatus (a), and the SKCS (b)

(a)

(b)

(c)

y

x

zx

y

z

plp

lp

p

Strain,

Strength(MPa)

0 0.04 0.08 0.12

50

40

30

20

10 Figure 3. Wheat grain spatial orienta-tion (a), endosperm section shape (b),and characteristic curve with para-

meters recorded by Instron machine(c)

(a) (b)


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accurate procedures for the estimation of grainsinternal structure and its quality. Digital ImageAnalysis (DIA) has been used in many branches ofscience. Among them, the attention should be paidto ImageJ (NIH Images). ImageJ (http://rsb.info.nih.gov/ij/) was written in JAVA and run on everycomputer platform (Linux, Mac OS 9, Mac OS X,Windows, and the Sharp Zaurus PDA). Further, theimpact of the scanning resolution on the accuracy ofautomatic detection of internal damage in X-ryayedwheat kernels was evaluated by G (2007).

Rape stem investigations

Te study on the mechanical properties of stemscomprised varieties of winter rape and included

varied cultivation conditions for the plants (sowingdensity, row spacing, and nitrogen fertilisation). Temeasurements were carried out during flowering, atthe stage of full pods, and during the technical andfull ripeness of rape seeds. A representative samplecomprised 30 stems.

he mechanical properties of rape stems wereexpressed on the basis of their mechanical param-

eters determined in static and dynamic tests. In thestatic test, an Instron strength tester was employed

to determine, in the process of bending, the stemrigidity (EI) and maximum bending stress (

max) and,

in the process of shearing shearing energy (Es).Te results were recorded by means of a computersystem, using a program specially developed for thepurpose. Maximum bending stress was expressed asa function of natural cross section area of the stemmax (S et al. 1989; S 1993). Shear-ing energyEswas obtained by integrating the areabeneath the curve recording the force of shearing.In the dynamic test, dynamic shearing energy (Ed)was measured by means of a Dynstat type apparatusoperating on the principle of a pendulum hammer,

in which the knife moved at a velocity of v= 2.1 m/s.Te values ofEsandEd through division by the areaof the stem cross section (S) were used to calculatethe equivalent value of the work performed to sheara unit of the stem cross section area (wSand wd). Te

values of the stem cross section area S and S(naturaland after the removal of the parenchyma) were de-termined by means of a area meter. o determinethe variability of the mechanical properties alongthe stem length, the measurements were taken atseveral heights of the stems (from the root to the

tip). Te estimation of the plant lodging was madeusing a 10-step scale where 10 means the absence

Figure 4. Diagram of the mechanical part of the equipment used to measure the speed of ultrasound waves in grain endosperm(a), and the values of the speed of ultrasound wave front in the endosperm of wheat and the course of its regression depend-ence on the height of sample column (b)

(a) (b)

Material: wheat grain cv. Jana

Regresion equationC = 3 214 109.1 L

Coefficient of corelation = 0.809

direct of load x direct of load z

Spee

do

fu

ltrasoun

dwave

C(m s)

Length of sample 0 5 10 15 20 25 30 l (mm)

3 400

3 200

3 000

2 800

2 600

2 400

2 200

2 000

1 800


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84 RES. AGR. ENG., 54, 2008 (2): 8090


of lodging and 1 corresponds to the most advancedlodging (stem close to the ground).

In the final stage of the study on the mechanicalproperties of rape stems the X-ray method was em-ployed (S & V 1994, 2000), wherethe densitometric method was used to determinethe value of OD which defines the degree of the

film lighting after the passage of X-rays through thestem, which is equivalent to the amount of radiationenergy absorbed by the stem.

RESULTS AND DISCUSSION

Results of wheat grain investigations

In respect to the examination of the mechanicalproperties of cereal grains, a significant relation wasconfirmed between the binding force of kernel to ear

of common wheat and rye. Te variability of this pa-rameter indicates the differentiation in the range ofthe examined cultivars of wheat and rye. Te resultsobtained in the frame of the investigations of grainbinding to ear by the tensometric micro-picker werecompared with the measurement data received fromthe apparatus Instron. Tese results indicate un-equivocally that grains are bound the most stronglyin the middle part of the ear, the most weakly in theupper part, while medium values occur in the lowerpart of the ear. Significant differences between theparticular years were also noted which undoubtedlyresults from the different atmospheric conditionsduring the development of grain and its maturity. Itwas stated that the varieties cultivated in the CzechRepublic were characterised by the decidedly higher

value of the grain-to-ear binding force in compari-son to the Polish varieties. It was established that themethods of direct measurements of the grain-to-earbinding force applied in the Czech Republic and in

Poland were sufficiently accurate and allow for anexact determination of this important property ofthe cereals investigated. Tese first investigationscarried out jointly within the frame of internationalco-operation with the application of direct methods(Figure 1c) constitute an important step forward inthe works on unifying the methods of investigating

the physical properties of cereal plants.Te research of mechanical properties of wheat

grain endosperm proved a strict relation betweendensity and the type of endosperm structure and itsmechanical characteristics. Using X-ray method andmechanical properties of wheat grain endosperm, astrict relation between density and the type of en-dosperm structure and its mechanical properties wasproved (G & H 1983, 1987; H &G 1985, 1992; B et al.1991).

For example, in Figure 4a the values of the speed of

the ultrasound wave front in the endosperm of thewheat variety Jana and the course of its regressiondependence on the height of the sample column arepresented.Te results of the study carried out byG and H (1985) may serve for solvingthe problems of technological processing of grainand for machine designing.

Te results obtained from the porosimetric studyshowed in increased internal porosity from initial0.085 to 0.225 in the samples deformed beyond thepressure strength limit. It was ascertained that theplasticity of the tested material is caused by theformation of micro-cracks the radii of which are inthe range of the starch grain dimensions. Te mi-crocrack formation is connected with the tearing ofthe protein matrix from the starch grain.

Further research proved that the intensive changesof grain moisture during the moistening of dry grainor drying of wet grain in laboratory led to an increaseof the internal damage of grain which took place in

Figure 5. Accuracy of automatic procedure of image analysis (%) for each scanning resolution of roentgenograms of cracked(a), and infested (b) kernels

75 100 200 300 dpi

100

80

60

40

20

0

100

80

60

40

20

0 75 100 200 300 dpi

y= 22.875x+ 3.1875 (R2= 0.94)

y= 15.063x+ 39.063 (R2= 0.81)

(a) (b)


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pre-harvest field conditions as well. Different sus-ceptibility of grain to this kind of damage may causeobvious losses in the yield during harvesting and adecrease of quality in storage and processing (P

et al.1992, 2001, 2002; G et al.2002, 2005;G & P 2004).

Figure 5 presents the accuracy of the automaticprocedure of image analysis for scanning resolutionof roentgenograms of cracked and infested kernels,and 95% confidence intervals according to G(2007).

In this case the application of the digital imageanalysis of wheat grain in different stages of infesta-tion is supported by a modern technique of shock(impact) load registration by a digital oscilloscope

equipped with a super sensitive impulse detector(Figure 6) which put our research in line with themost advanced measuring techniques (P etal. 2003, 2006, 2007; P 2007; G et al.2007).

Tis research is currently taken in the frame of anew scientific network gathering specialists fromscientific centers in Poland, the Czech Republic(CULS, Prague J P), and Russia (Agro-physical Research Institute of RAASin St. Petersburg M A and L V).

Results of rape stem investigations

In the study on the mechanical properties of rapestems, variability of the parameters analysed wasobserved both along the length of the stems andin the growth stages of the plants (S 1991,2001a,b). Te character of the changes is describedby a quadratic polynomial.

Te study showed that the shearing energy valuesEsandEdprovide comparable estimations of the in-ter-variety differences. High values of the correlation

coefficients were obtained for those parameters atthe level of r0.05= 0.800.90.

Te analysis of the results concerning the vari-ability of wdalong the length of rape stems showedthe existence of a characteristic point located closeto the first bifurcation of the plant stem (Figure 7)

(S et al.1989; S 2001a,b).A strong correlation was found between the vari-

ability of the mechanical properties of rape stems,stem cross section area, and the absorption of X-ray radiation by the stems (S & V1994, 2000).

rise time fall time

top

ma

gnitu

de

width

10%

10%

50%

50%

base

A ... pulse startB ... pulse stop

1

4

3

2

a

h

Figure 6. Schemeof the used apparatus (a): 1 barley kernel, 2 glass tube, 3 force transducer, 4 digital oscilloscope(DSO): and graphic presentation of the pulse parameters and their geometric sense (b)

y1= 0.000034x2 0.00022x+ 0.0044

y2= 0.00050x2 0.00247x+ 0.00868

y3= 0.00041x2 0.0024x+ 0.0091

y1 R= 0.97y2 R= 0.89y3 R= 0.87

103

7

6

5

4

Theworkrequire

dtoshear

aunito

fcrosssectionareawd

(J/m3)

1 2 3 4 5

Points of measurements along the stem

Figure 7. Distribution of the values of the shearing energy perstem cross-section area unit in dynamic test along the stem ofJupiter rape in successive phenophases (y1,y2,y3 regression

curve, y1 complete silique filling, y2 technical ripeness,y3 full ripeness)

(b)(a)


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Te analysis of variance demonstrated a significant

inter-variety variability, both on the basis of the me-chanical properties (wd) and on the basis of X-rayradiation absorption by the stems (OD) (Figure 8).Tis fact indicates also the applicability of the X-raymethod for the study of the strength properties ofthe rape varieties.

Te results of the study showed the effect of variedplant density per square meter on the variabilityof the mechanical properties of rape stems. At thesame time, it was found that the density of plants/m2differentiates the plants in terms of their resistanceto lodging. It was found that the mean values of themechanical parameters decreased with increasingdensity of plants/m2, and the degree of their lodgingintensified (S 1995, 2001a,b).

One effect of the studies on the mechanical prop-erties of rape stems is the application of a widerange of measurement methods and indication ofthe most suitable mechanical parameters that canbe used for the strength testing of rape stems, withsimultaneous consideration of varied conditions ofcultivation of the plants and their various growthand development phases.

he application of the static test permitted toobtain the mechanical parameters of stems sub-

je cted to the process of bending and shearingwith the help of a high-precision strength-testingapparatus that allowed monitoring the whole proc-ess of stem bending or shearing and an accuraterecording of the range of elastic deformations andof the moment of the occurrence of permanentdeformation. In the dynamic test, performed withthe help of an apparatus operating on the principleof a pendulum hammer, the loss of kinetic energy

was recorded, equivalent to the energy of shearinga rape stem. In both tests, thanks to the possibility

of taking precise measurements of the irregular

cross section area of rape stems using the opticalmethod, the amount of work required to shear aunit of the stem cross section area was determined.hat value undoubtedly indicates the density of themechanical tissue at particular heights of the stem.his parameter proved to be especially useful intesting the mechanical properties of rape stems,as it demonstrated the existence of an extreme onthe stems of winter rape, located close to the firstbifurcation. he study showed an extensive vari-ability of the mechanical parameters analysed, bothalong the length of the stem and in the phenologicalphases. Significant inter-variety differences werealso observed.

As a result of the methods applied it was pos-sible to determine maximum bending stress valuesthrough measurable stem cross section areas, and todemonstrate the applicability of that parameter fortesting the mechanical properties of stems of winterrape varieties. Significant inter-variety differenceswere also found.

Te comparison of rape stem strength character-istics obtained in the static and dynamic shear tests,

by means of parametersEsandEd, revealed that bothenergy values characterise the mechanical propertiesof the stems of winter rape varieties in an identicalmanner. Terefore, it is possible to use the static anddynamic tests alternatively, while in the subsequenttesting the dynamic test only was employed.

Te work required shearing a unit of stem crosssection area wS, and the wdparameter in particu-lar, demonstrated the existence of a characteristicpoint on the length of the plant stem, located closeto the first bifurcation, where a notable minimum

was observed. Tis result justified the limitation offurther studies to the test in one characteristic point

9

8

7

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4

Theworkrequ

ire

dtoshear

aunito

fcrosssecti

onareawd

(J/m3)

Bolko Ceres Leo Libravo Mar

0.30

0.28

0.26

0.24

0.22

0.20

TheparameterOD

Figure 8. Mean values and the 95% ukeyHSD intervals of wd(a), and OD (b) stemsfor the varieties of the winter rape


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on the stem height, documented by the geometricstructure of the stem.

Te results of the study concerning the variabilityof wdon the length of rape stem present the courseof variability similar to the value of S/S which attainsa minimum of its value close to the first bifurcation(S cross section area after the removal of the pa-

renchyma), performed by S et al. 1989. Tisconclusion indicates a relation between the shearenergy per unit of the stem cross section area andthe stem geometry.

Te analysis of the mechanical properties of rapestems in the course of the plant development showeda maximum of the value of the dynamic shear energyper unit of the stem cross section area (wd) in thephase of technical ripeness of seeds. Tis suggeststhe harvest time in the phase of technical ripeness asmore favourable than that in the phase of full ripe-

ness. In the phase of technical ripeness, rape stemsare characterised by the greatest resistance to shear,the unit density of the mechanical tissue in the crosssection being the highest.

Based on the analysed mechanical parameters ofwinter rape varieties, significant differences werenoted in the course of the development of plants,indicating the possibility of employing the developedmethodology in breeding cultivars. Te mechanicalparameters determined in the process of bendingand shearing are applicable for the testing of cul-tivars. Te study demonstrated the validity of themechanical parameters determined for breeders ofnew cultivars of rape while the range of stem shear-ing energy provides useful information for harvesttechnology engineers.

Variations were found in the mechanical proper-ties of rape stems, caused by the conditions of plantcultivation, and also a significant effect of the den-sity of plants per m2on both the lodging of plantsand the variability of the strength characteristicsof rape stems. he study showed that, at their lowdensity in the canopy, the plants stems have the

most favourable mechanical parameters in termsof their resistance to lodging, and are character-ised by three-fold greater rigidity (EI) and by high

values of dynamic shear energy (Ed). he resultssuggest that the density of 40 plants/m2is the mostfavourable, the plants being strong in terms of thestrength characteristics of their stems, and resist-ant to lodging.

As follows from literature concerned with thecharacterisation of winter rape varieties in termsof the quality and quantity of the yields obtained,plant density of 40 plants/m2constitutes the lowerlimit of plants/m2that can be left till spring in terms

of profitability of the expected crop yield (S2001a,b).

he X-ray method, included in the final stageof this study, permitted the determination of thestrength properties of stems of rape varieties. Si-multaneous application of the dynamic test and theX-ray method demonstrated that the value denoting

the absorption of X-rays by the stem (OD) corre-lates significantly with the energy of dynamic shear-ing (Ed), and especially strongly with the amount ofwork required to shear a unit of stem cross sectionarea (wd) which defines the density of the mechani-cal tissue (S 1996; S & V2000).

Beyond any doubt, these results were achievedthanks to the wonderful personality, competence,and coordination of the guest of honour, Prof.R , and also to the great co-authors

J B of the CULS in Prague, LV of the Agrophysical Research Institute ofthe RAAS in St. Petersburg, Z M, PhDof the University of Agriculture in Gdllo, Hungary,and to the Project Manager, Prof. B S ofthe Institute of Agrophysics of the PAS in Lublin.

CONCLUSIONS

To the wheat grain investigations

Te results obtained in the studies of grain-to earbinding and single kernel characteristics on thelength of wheat heads present a unique collec-tion of data, which can be utilised in monitoringthe process of wheat breeding.

Te results received in the porosimetric studylead to the presumption that microckracs canbe initiated on the natural discontinuities whichare the size of starch grains and develop furtherby tearing off the protein matrix from the starchgrains.

Te results obtained with ultrasound may serve

for solving the problems of the technologicalprocessing of grain and for machine designing.

Using X-ray measured set, the possibility existsto evaluate inner damage of kernels connectedwith endosperm cracking which can not be de-tected by the commonly used method.

Considering the measurement sets, it should bestated that the combination of both sets (SKCSmethod, X-ray method, and the newly proposedmethod of the impact of kernel by using the forcetransducer with the amplifier and the DSO) givesthe possibility of the evaluation of many physicalproperties of single kernels in on-line systems.


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Proposition to build this kind of combine mea-surement systems found its reflection in theestablishment of the Working Group on SingleKernel echnology by the American Associationfor Cereal Science and echnology (AACC) andcan help in further progress in this field by cerealscientists in the world.

To the rape stem investigations

Tere is a notable variability in the mechanicalparameters of winter rape stems along the lengthof the stem and in the development phases of theplants. Te study also showed inter-variety dif-ferentiation of the mechanical properties.

Te shear energy determined in the static (Es)and the dynamic (Ed) tests provides acomparableestimation of the inter-variety differences. A high

positive correlation was found between these en-ergy values. Tis conclusion suggests the possi-bility of choice between the two types of test forrape stem shearing.

Te work required to shear a unit of the stemcross section area (wd) indicated the existence ofa characteristic point on the length of the stem,close to the first bifurcation.

A significant correlation exists between theabsorption of X-ray radiation and the param-eters defining the mechanical properties of rapestems.

Te application of the X-ray method notably ex-panded the possibilities of the determination ofrape stems susceptibility to shearing.

A significant correlation was found betweenthemechanical properties of rape stems and the re-sistance of the plants to lodging.

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Received for publication January 14, 2008

Accepted after corrections February 3, 2008

Abstrakt

G S., S G. (2008): Fyzikln vlastnosti obilnho zrna a epkov lodyhy.Res. Agr. Eng., 54: 8090.

Prce uvd vsledky studia mechanickch vlastnost obilnho zrna a epkovch lodyh, kter byly provedeny v rmci

pokraujc dlouhodob spoluprce mezi stavem agrofyziky Bohdana Dobrzanskho Polsk akademie vd v Lublinu(IA PAS), Polsko a esk zemdlsk univerzity v Praze (CULS), esk Republika. V rmci mechanickch vlastnost


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obilnho zrna, studie ukzala signifikantn vztah mezi spolenmi fyziklnmi podmnkami zrn penice urenmirentgenovou detekc a mechanickmi vlastnostmi urenmi ve standardnch testech pouvanmi v mechanice struk-

turnch materil a testy pouvanmi ve zpracovatelskch technologich. Studium mechanickch vlastnost lodyhyepky demonstrovalo meziodrdov rozdly v polhavosti. Odhad variability mechanickch vlastnost podl epkov

lodyhy ukzal charakteristick bod v blzkosti prvho rozvtven. Vznamn vliv na pevnostn charakteristiky lodyhyvykazovaly hustota porostu (vyjden potem rostlin na metr tveren) a hladina hnojen duskem. Zrove byly

nalezeny zvislosti mezi mechanickmi vlastnostmi lodyhy a absorpc rentgenovch paprsk.

Klov slova: penin zrno, epkov lodyha, fyzikln vlastnosti, uitkov hodnota

Corresponding author:

Prof. S G, Bohdan Dobrzanski Institute of Agrophysics of Polish Academy of Sciences,Doswiadczalna Str.4, 20-290 Lublin, Polandtel.: + 4881 744 50 61; fax: + 4881 744 50 67; e-mail: [email protected]

physical properties of cereal grain and rape stem

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