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Revista Ciencias Técnicas Agropecuarias

versión On-line ISSN 2071-0054

Rev Cie Téc Agr vol.26 no.1 San José de las Lajas ene.-mar. 2017


Revista Ciencias Técnicas Agropecuarias, 26(1): 4-13, 2017, ISSN: 2071-0054




Evaluation the Main Physical-mechanical Properties of Cassava (Manihot esculenta Crantz) for their Mechanization


Evaluación de las principales propiedades físico-mecánicas de la yuca (Manihot esculenta Cranz) para su mecanización



Dr.C. Annia García-Pereira,I M.Sc. Ellys Petrocelly,II M.Sc. Yolanda Sabín-Rendón,I Dr.C. Antihus Hernández-Gómez,I Dr.C. Jorge García-Coronado,I

IUniversidad Agraria de La Habana (UNAH), Facultad de Ciencias Técnicas, San José de las Lajas, Mayabeque, Cuba.
IIUniversidad Politécnica Territorial “José Antonio Anzoátegui”, El Tigre, Edo. Anzoátegui, Venezuela.




The knowledge of the mechanical-physical properties in agricultural products has great importance to face mechanization and agro industrial process. The purpose of this research is addressed in determining the main physical-mechanical properties of cassava (Manihot esculenta Crantz, varieties La Reyna y Paigua Negra), for the mechanization of its cultivation. In the study are determined properties such as: the total mass of the plant (Mtp), length of maximum root (Lrm), average diameter of root (Dpr) and high-extraction strength (Re), among others. For processing and analyzing data the Plus version 5.1 STATGRAPHICS software was used, to look for significant differences by means of hypothesis testing. The results show that the sweet variety is significantly better than the bitter one in: total height of plant, number of buds, stem diameter, total weight of plant, number of root/plant, maximum length, diameter and soil resistance with values higher than 5%.

Key words: agroindustrial process, length, diameter of root and high-extraction strength of cassava.


El conocimiento de las propiedades físico-mecánicas de los productos agrícolas es de gran importancia de cara a la mecanización y manejo agroindustrial de los mismos. El objetivo del trabajo está dirigido a determinar las principales propiedades físico-mecánicas de la yuca (Manihot esculenta Crantz, variedades La Reyna y Paigua Negra), para la mecanización de su cultivo, se determinan propiedades como: el Masa total de la planta (Mtp), longitud de la raíz máxima (Lrm), Diámetro promedio de la raíz (Dpr) y la resistencia a la extracción (Re), entre otras. Para el procesamiento y análisis de los datos se utilizó el software especializado STATGRAPHICS Plus versión 5.1.buscando diferencias significativas a través de una prueba de hipótesis. Los resultados muestran que la variedad dulce supera significativamente a la amarga en: altura total de planta, número de yemas, diámetro de tallo, peso total de planta, número de raíz/planta, longitud máxima, diámetro, y resistencia al suelo con valores superiores al 5%.

Palabras clave: manejo agroindustrial, longitud, diámetro de la raíz y resistencia a la extracción de la yuca.




Cassava, native to tropical America before 1600 and taken by Portuguese explorers to Asia and Africa, is now sown in 92 countries where it feeds more than 500 million people (Alarcón & Dufour, 1998). Cassava (Manihotesculenta L., Crantz) is a staple in the diet of 17.8 million people worldwide, according to FAO (2010), as well as being an industrial crop with high potential that generates permanent income for small and medium farmers (Mojena & Bertolí, 2004), which, in addition to its value for human and animal food, has been acquiring importance for its use as raw material in the textile, carton, pharmaceutical and sausage industries, with a great perspective for the production of ethanol and biodegradable plastic materials (Henry et al., 1998; Salgado et al., 2008; Kaewtatip y Tanrattanakul, 2012; Souza et al., 2012; Vercelheze et al., 2012; Maran et al., 2014).

Studies are currently underway to obtain alcohol from cassava starch as a catalyst in unleaded gasoline. This crop is included as strategic item within the Plan of the National Economy1.

Mechanization of cassava cultivation is one of the main needs of agriculture in the southern region of Anzoátegui State, considering the projection of this crop in national and international markets and its application in the oil industry. Given the conditions explained above, the mechanization of this crop and the use of different technologies for agro-industrial processing is a phenomenon that has been worked for a little more than half a century. The use of mechanization for its extraction from the field is conditioned by the dimensions that the variety sown reaches, its depth of development and the type of soil.

Although cassava has been extensively studied worldwide, its characteristics have been shown to vary from region to region depending on climatic conditions, varieties planted, and types of soil. Even when the State of Anzoátegui is one of the largest cassava consuming areas, both fresh and as cassava bread, it does not have yet a detailed study of the physical and mechanical properties of the two main cassava varieties produced in the region. Due to the necessity of increasing the volume of production demanded by the socio-economic context of the country, the objective of this research is to determine the main physical and mechanical properties of cassava (ManihotesculentaCrantz, La Reyna and Paigua varieties Black), for the mechanization of its cultivation.



Methodology for determining physical and mechanical properties

Initially two plots of study were selected, one per variety of interest. After that, the normal grid method was applied in order to randomly select the 20 plants that will characterize the varieties under study in the respective plots. Then the determination of physical-mechanical properties, was carried out according to the methodology proposed by Ospina y Ceballos (2002), adjusted to Ruiz-Altisent y Chen (1996) and to Engels´s manuals, with some modifications (Engels, 1981).

Total mass of the plant (Mtp). The whole plant is extracted from the depths of the substrate. After removing sand particles adhered to the roots, the sample containing roots, stems and branches, including the leaves, are weighed and the unitary measurements are noted in kg per plant.

The estimation of the root set diameter (Dcr) is determined by placing the set on a grid of 1 x 1m proportions, with measurements marked in centimeters on its bars. Once the whole plant is positioned vertically, the outline is marked and the dimensions are acquired in at least three equidistant points by using a tape measure.

The maximum root length (Lrm) is measured with a meter graduated in centimeters, by placing the ruler from the basal part of the reservoir structure, immediately where the peduncle ends, and extending the folding meter over the length, ending the reading in the distal part of this organ.

The resistance to extraction (Re) is measured with a dynamometer of 240 kg capacity. The instrument is placed in a metal bar, to whose center the weight is coupled and fastened with cords in the upper part. In the lower part the rope is attached to the main stem of the plant. Two people apply a force at the ends of the lever until the root set is extracted, registering the reading in which the needle of the weighing device descends at its peak.

Coefficient of static friction. A completely clean tilting table is used, which is bolted to the side by placing a steel surface together with a level-angle conveyor using a bubble level, then each cassava sample (20 in total) is placed indistinctly on it. The table is tilted slowly until the sample starts moving downward, the movement is stopped and the reading of the rotated angle is taken. The tangent of the obtained angle is the coefficient of friction, according to the expression 1

F = tanα                    (1)


F - coefficient of static friction;

Α - static friction angle of the root.

Resistance to compression (F) and Resistance to rupture (Rr).The device used to measure GRIFFIN® brand compressibility modules, is set under load conditions expressed in kgf to distinguish them from mass units. This device is calibrated in a ratio of 50 rpm (50 crank turns = 0.1mm). The test pieces are cylindrical and 21.4 mm length and 10.8 mm diameter (Figure 1). They are previously debarked, and made with a metallic device to preserve approximate measures of each, worked at room temperature.

Each test piece is placed on one of its faces between the compression plates of two stainless steel discs, each one being compressed at a constant speed, the mechanical behavior is expressed in terms of the force required to reach the point of rupture (Rr), and the force used to compress 3% of its length (F) (Yirat et al., 2009). The readings of the upper disc descendant trajectory on the test piece are recorded by a digital dynamometer (waxed at each measurement) coupled to the apparatus. With the help of two video cameras, Samsung® brand every test is recorded. Simultaneously, the dynamometer readings and crank trajectory are projected on the computer screen through video software until the clicking sound announces the breaking point, and then the decline of the force. These videos are triggered at the same time, when recording the readings in Excel books.

Bark penetration resistance (Rc): The penetration resistance is measured with a GRIFFIN® branded Penetrometer mounted on a support to maintain consistency, performing a puncture per test piece of cassava root bark of 25 x 65 mm, previously washed, to avoid impurities minimize the degree of error in the measures. The sample is held against a disk on a stationary surface and a force is exerted on the section of the bark at a uniform speed (Figure 2). The depth of penetration must be related to the line inscribed on the tip. The value obtained is expressed in pound-force (£f) or kg-force (kgf).

Methodology for processing and analysis of data obtained

The data obtained from the experimental tests are tabulated using Excel 7.0 tool of Microsoft office 7, and they will be later processed through the specialized software STATGRAPHIC 5.1 (Statistical Graphics Crop, 2000), to compare the main statistics of each of the studied properties in both varieties. Due to the importance of studying in greater depth the information related to the yield of each variety and for the mechanization and agro-industrial processing of this crop, the physical properties that characterize phenotypically each variety a comparison of means or test of hypothesis is applied to determine significant differences between both varieties, through the tabular options within this analysis and the visual presentation of the dispersion and symmetry of the data analyzed. An analysis of standardized asymmetry and kurtosis is also performed to determine whether samples come from normal distributions provided their range is between -2 and 2.

The dependence between the variables that have the greatest impact on the mechanization of the cassava production process will also be studied by applying a simple regression analysis.



Mechanical properties

Table 1 shows the results of the mechanical properties tests performed. It is observed that there is no significant variability among the clones characterized in terms of mean values of density, with estimated of 1.07 and 1.14 g / cm3for sweet and bitter cultivars, respectively.

The coefficient of friction obtained for the cassava without bark in contact with the steel yielded similar data of 0.41 and 0.39 between the two varieties, which coincides with values reported for agricultural products that range from 0.30 to 0.65 according to different friction surfaces (Padonou et al., 2005). That indicates that during the design of machines it can be assumed that the technology can work with both varieties satisfactorily, like Abbott (1999), Yang et al. (2008), and others stated2. In general, the data of the physical-mechanical properties determine the technology of harvest, transport, packing and storage (Famá et al., 2006).

The results showed that the average resistance to bark penetration was higher in sweet (5.71 MPa) than in bitter (3.96 MPa), thus showing that the former surpasses the latter in 30%. Therefore, La Reyna has a greater possibility of not suffering mechanical damages while mechanized tasks. However, a peeling machine will demand greater energetic requirements for the sweet variety since it surpasses the bitter one in size, proportion in weight of the bark, diameter, and force of penetration and bark shear stress, in relation to the evaluations of Adetan et al. (2003).

Analyzing firmness (F) per varieties, when compressing 3% of the length of the test tube, bitter cassava with 0.29 MPa exceeds sweet (0.25 MPa) in 13.8%. In breaking strength (Rr), the behavior is reversed and the latter reaches values of 0.90 MPa, while the first only reaches 0.63. In this behavior, although both roots present a slightly fibrous tissue, it is shown that the bitter cassava responds as a more fragile structure, that it is less resistant to hits and to the cut. These results influence the manipulation of the product and its response in relation to mechanical damages, as Mohsenin (1970) expresses, about biological materials when they are under the effect of static and dynamic loads.

The resistance to extraction (Re) from the ground, necessary in La Reyna variety (0,83 kN) exceeds in 59,03% to the one of Paigua Negra (0,34 kN). There are several factors that affect this result, but since the soil is similar, Oxisol type, that one plot is 20 m from the other and then it is attributed to the difference in the diameter of the root set and its mass, the number of roots and the size of them. Taking into account the explanation before each property, obviously, it should not be in other way due to the superiority of La Reyna in terms of the variables mentioned above. This property defines power requirements of the aggregate (or machine that performs the harvest), cost of the technology and other more specific aspects that depend on them such as fuel consumption, etc. The dependence between the resistance to extraction and the properties mentioned above was evaluated statistically and the results confirm a strong dependence between them (Figures 3, 4, 3.5 and 6) for both varieties studied, predominating a dependence described by exponential and polynomial models.

Behavior of the properties studied in the varieties La Reyna and Paigua Negra

Total mass of plant (Mtp)

The analysis shows that the values of the total mass of the plant are normally distributed and the difference between the means shows that there is a statistically significant difference between the means of the two samples, for a confidence level of 95%. These results can also be corroborated taking into account the average values of total mass of the plant of 11.28 and 5.63 kg for the varieties La Reyna and Paigua Negra, respectively. On the other hand, the difference reached according to the coefficients of variation of the data analyzed is 10.7%. Figure 3a shows that there is a slightly higher dispersion in the data of this property for PaiguaNegra variety, whereas there was a greater frequency of plants with total mass between 5 and 8 kg in the PaiguaNegra variety and between 10 and 13 Kg in La Reyna (Figure 3b).

The total mass of the plant is a parameter of great importance during the extraction of the roots from the ground. It will determine the power of the machine to be used, as well as the resistance and material to be used in the organs that make the ground-root contact.

Maximum root length (Lrm)

The average values of the maximum root length reach values of 0.061 and 0.036 m for La Reyna and PaiguaNegra, respectively. Figure 4a, shows a very similar dispersion in the data of both varieties. Likewise, it can be said that there is a greater frequency of roots with length between 0.055 and 0.067 m in La Reyna, while it ranges from 0.027 to 0.040 in PaiguaNegra (Figure 4b). The coefficients of variation around the mean reached values of 13 and 23.6%,respectively, with a10.3% difference between both of them. The maximum root set length is a variable that normally distributes for both varieties and there is a statistically significant difference between the means of the two samples for a confidence level of 95.0%. The maximum root lengthand the variation,that is manifested statistically, between the lengths of the roots for each variety, is an aspect of great importance incassava extraction mechanization, and it will define the working width of the machines and of the containers to transfer the product from the field.

Mean root set diameter (Dcr)

The mean root set diameter (Dcr) reaches values of 0.918 and 0.545 m for the varieties La Reyna and PaiguaNegra, respectively. Figure 5a, shows a superior dispersion of the data of PaiguaNegra variety. It can be said that there is a higher frequency of plants with 0.8 and 1.0 m radicular diameters in La Reyna, while it ranges from 0.4 to 0.6 m in the Black Paigua (Figure 5b). The coefficients of variation around the mean reached values of 8.9 and 22.66%, respectively, with a difference between both of them of 13.7%. The root set diameter is a normally distributed variable for both varieties and there is a statistically significant difference between the means of the two samples for a 95.0% confidence level. This variable is of great significance for this tuberous root harvest mechanization due to according to the diameter it is determined the area covered by the plant below the ground and thus the working width of the extraction tool, and the power required to achieve the proper operation of the machine or the aggregate according to the technology used.

The total mass of the plant and of the stem root set are higher in La Reyna variety than inPaiguaNegra, in correspondence with that previously described for each property analyzed. Although there is no significant difference between the number of roots per plant for each variety, the dimensions (diameter and length) and therefore, the mass is higher in the variety La Reyna, which is an important indicator of productivity. Both properties mentioned are of great importance to any attempt to mechanize the extraction of this important root and it is manifested in a marked dependence between the mass of the plant and the roots, with respect to the resistance to extraction that both offer, with values of R2 above 0.73, (Figures 6 and 7).

The greatest dependence was found between the mass of the stem root set and the resistance to extraction inPaiguaNegra variety with R2 value of 0.83, in all cases according to the models obtained, it describes an exponential dependence of a variable with respect to the other.

Similarly, the mass of the root set is higher in the La Reyna clonedue to the same reasons above mentioned. This property in both clones shows a strong dependence on the resistance to the extraction whose determination coefficients are higher than 0, 70.

In this variety, a linear dependence is manifested between the mass of the root set and the resistance that it offers to be extracted from the field, given by the equation that characterizes the linear model with an R2 of 0.72, while for the clone Paigua Black it is modified by changing the other and accordingly to a model described by an exponential equation with R2 of 0.77.



The PaiguaNegra variety possesses slightly superior properties compared to La Reyna variety for the mechanization and / or processing of its cultivation with a minor total weight of the plant, diameter of the root set and resistance to the extraction from the ground, however La Reyna Has greater resistance to compression and rupture of the bark with values higher by 30%.

The comparison of means shows significant differences in properties such as the Total mass of the plant (Mtp) of 11.28 and 5.63 kg; Maximum root length (Lrm) of 0.061 and 0.036 m; Diameter of the root set (Dcr) of 0.918 and 0.545 m, for La Reyna and PaiguaNegra varieties, respectively.

The values of resistance to the extraction show a high dependenceon the plantmass and on the greatest root length,with values of R2 higher than 0,70 for both varieties.



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Received: 22/12/2015
Approved: 14/11/2016



Annia García-Pereira, Universidad Agraria de La Habana (UNAH), Facultad de Ciencias Técnicas. Email:

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