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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): 32-39, 2017, ISSN: 2071-0054

 

ORIGINAL ARTICLE

 

Geometric and Kinematic Parameters of Sensing Tips for the Soil Strength Recording

 

Parámetros geométricos y cinemáticos de sondas para el registro de la resistencia del suelo

 

 

Dr.C. Ernesto Ramos-Carbajal, Dr.Cs. Arturo Martínez-Rodríguez, M.Sc. Alexander Laffita-Leyva, Ing. Julio Cesar Ayala-López

Universidad Agraria de La Habana, Facultad de Ciencias Técnicas, Centro de Mecanización Agropecuaria, San José de las Lajas, Mayabeque, Cuba.

 

 


ABSTRACT

A research in order to evaluate the influence of several geometrical and operational parameters of sensing tips on the quality of on-the-go soil strength recording, was carried out in a Cuban typical Red Ferralitic soil. The considered parameters were the geometric characteristic of the sensing tip, the sensing speed and the protrude of the tip in front of the leading edge of the supporter shank. The experiments were carried out under controlled conditions in a Soil Chanel Laboratory of the Agricultural Mechanization Center of Havana Agrarian University. As a result was obtained that the tip with 30o wedge prismatic form and 520 mm2 base area, advancing horizontally to a speed non highest to 0,7 m.s-1 and protruded 110 mm or more in front of the leading edge of the supporter shank, constitutes the best alternative for “on- the –go” soil strength registration. Also it was determined that the sensing operation should be made when this type of soil presents a moisture near to 28%.

Key words: precision agriculture; cone index; sensors; soil compaction.


RESUMEN

En el Centro de Mecanización Agropecuaria (CEMA) de la Facultad de Ciencias Técnicas de la Universidad Agraria de La Habana, se llevó a cabo una investigación dirigida a evaluar la influencia de diferentes parámetros geométricos y cinemáticos de sondas para el sensoramiento continuo de la resistencia a la penetración del suelo, sobre la calidad del registro de este indicador en un suelo Ferralítico Rojo típico de Cuba. Los parámetros objeto de evaluación fueron: la forma geométrica de la sonda, la distancia de separación entre la sonda y la barra que la soporta, así como la velocidad de marcha. Los experimentos fueron realizados en condiciones controladas en el Laboratorio Canal de Suelos del Centro de Mecanización Agropecuaria. Como variables de control fueron tomadas muestras del índice de cono, la densidad aparente y la humedad del suelo. Como resultado de los experimentos se obtuvo que la sonda en forma de cuña prismática con ángulo de 30o y área de la base de 520 mm2, avanzando horizontalmente a una velocidad no superior a 0,7 m∙s-1, separada de la barra soporte de la sonda una distancia igual o mayor a 110 mm, constituye la mejor alternativa, entre las variantes experimentadas, para la estimación del estado de compactación del suelo en grandes extensiones. Asimismo se determinó que la operación de sondeo debe efectuarse cuando este tipo de suelo presenta una humedad cercana al 28%.

Palabras clave: agricultura de precisión; índice de cono; sensores; compactación del suelo.


 

 

INTRODUCTION      

The soils of Red Ferrallitic type are characterized to be highly productive; they occupy the second place in extension and agricultural yields in Cuba. The intensive and continuous exploitation of these soils, affected by the irrational application of chemical fertilizers, excessive laboring with heavy machinery and inefficient use of water; has driven at present time to a severe process of physical degradation. It is manifested in high compaction levels that, together with other objective factors; have caused the decrease of the crop production (Hernández et al., 2013).

The tillage operations directed to the soil decompaction are expensive, since they lead to penetration with devices to relatively big depths, for what it is of supreme interest in the agricultural practice, the most accurate determination of the soil compaction state and the distribution of the compaction profiles to different depths. (Hall et al., 2000; Khalilian et al., 2002; Raper et al., 2007).

At present time in the international field, the application of methods of Precision Agriculture, based on the application of treatments in “specific places”, constitutes one of the fundamental tendencies of modern agriculture. It is directed towards the economy of costs, fuel and time, so as to the decrease the undesirable impacts on the environment (Martínez et al., 2011).

Different procedures and means have been object of development since the decade of the 90s directed to the sensing on the flight (on-the-fly) or on the operating (on-the-go) of parameters of the soil indicators of the compaction level (Alihamsyah et al., 1990; Glancey et al., 1996; Adamchuk et al., 2001, 2006; Mouazen et al., 2004; Chukwu y Bowers, 2005; Hall y Raper, 2005; Andrade-Sánchez et al., 2007; Hemmat et al., 2009; Herrera et al., 2011).

A great part of the developed devices uses as a sensor of the soil strength a wedge with an angle of 30o, with dimensions more or less in order of those of the standardized cones for the measurement of the cone index by means of penetrometers, introducing the concept of “wedge index” with a similar definition to that of the standard cone index.

Wedges with different dimensions have been experienced, determining the correlation of the wedge index with indicative parameters of the soil compaction, such as the bulk density of the soil and the own cone index (Alihamsyah et al., 1990; Chukwu y Bowers, 2005; Raper et al., 2005; Hemmat et al., 2009).

The obtained results, although diverse, are acceptable; nevertheless, convincing design and operation approaches have not been elaborated for the wedges or other types of sensing tips that can support the convenience of using one or other geometry. Therefore, the present investigation has as objective to sustain the design parameters and operation of the probes for the continuous sensing of the soil compaction state.

 

METHODS

The experimental investigations were carried out in the laboratory Bin of Soils belonging to the Center of Agricultural Mechanization (CEMA) from the Faculty of Technical Sciences at the Agrarian University of Havana (UNAH), located in the municipality of San José de las Lajas, Mayabeque province during the period 2014-2015.

The object of study is a Lixiviated Red Ferrallitic soil according to the last effective classification in the country (Hernández et al., 1999)), coming from the agricultural area of San José de las Lajas, in Mayabeque province, Cuba, with a plasticity index of 30,4%, behaving as a plastic soil (González et al., 2008).

The used installation (Figure 1) consists of a bin of soil (1), on which a carrying tools car moves (4), to which a structure is joined (2) to couple the sensor device (3). The carrying tools car is pulled by the flexible cable (5) which is rolled by the drum (6) and receives the movement of the reducer motor (7).

The sensor device transmits an electric sign (proportional to the penetration strength force) in the order of millivolts to a dynamic extensometer amplifier (8) KYOWA-YA-520 with DPM-602B type amplification modules. The amplified sign to volt levels is processed in an A/D converter card (9) which introduces the data in a computer (10), creating a database with a sampling frequency of 96 000 recordings per second.

The sensor device is shown in Figure 2 and it consists of a supporter shank (1) to which a load cell is linked (2), this one is pushed by the rod (3) that supports the probe (4) that can be conical or prismatic type and which constitutes the primary sensor element of the measure system.

To determine the displacement speed of the probe, an inductive type sensor of revolutions was used. It was placed in one of the wheels of the carrying tools car. It emits a voltage sign of pulse type for each wheel revolution, allowing the indirect determination of the displacement and the probe advance speed. The electric exit of the sensor of revolution was connected to one of the A/D converter card, obtaining its recording on the computer.

During the investigation, two experiments were carried out. A first experiment was directed to evaluate the influence of the protruded distance between the probe and the supporter shank, as well as of the on-the-go speed, on the strength to the penetration captured by the probe.

In this experiment, the protruded distance (b) between the probe and the supporter shank (exit of the probe) (Figure 2), with three levels (5; 50 and 110 mm) and the on-the-go speed, with two levels (0,7 and 0,8 m∙s-1) were taken as independent variables. It resulted in a 2x3 factorial design, which generated six combinations of procedures during the experimental process runs. For the delimitation of the speed levels and the protruding of the probe from the supporter shank, the results of the reported tests in the consulted literature were taken into account (Chung et al., 2004).

The type of probe used in all the process runs consisted on a prismatic probe of 30o x 520 mm2. The operating depth was marked at 0,20 m (half of the depth of the soil in the bin). As control variables, samples of the cone index (ASAE y ASABE, 1999; ASAE, 1999), in vertical direction and samples of the bulk density to an average depth equal to that of the continuous horizontal recordings (0,20 m) were taken.

The second experiment was intended to evaluate the behavior of probes in different geometric shapes during the horizontal and continuous recording of the strength force to penetration of the soil studied.

For that test, three geometric shapes of the probe were taken: one corresponding to the standard cone (ASABE) and two corresponding to the probes, which showed best statistical correlation with the cone index and the bulk density (cone of 30o x 520 mm2 and wedge of 30o x 520 mm2)1. The on-the-go speed and the protruding of the probe to the supporter shank were determined according to the results of the first test. The moisture and the bulk density were established at similar levels to those of the previous test. In total, there were three procedures. The control variables considered were equal to the first test.

The moisture content and the soil bulk density were determined according to the standard NC 67: 2000. The determination of standard soil cone index (ASAE) was made with a digital penetrometer FIELDSCOUT Model: SC 900 SN: 328.

 

RESULTS AND DISCUSSION    

Recording results of the penetration strength force obtained in the first test are exposed in figures 3 and 4, using two levels of average speed of displacement of the probe (0,686 and 0,867 m∙s-1), moisture between 26 and 29% and dry bulk density between 0,95 and 1,01 g∙cm-3.

In Figure 3, it is appreciated that, in spite of using the same probe, the recordings of the soil strength obtained with the probe farther from the supporter shank (b = 110 mm), reached significant values superior in 52% to those obtained with the nearest probes to the supporter shank. That evidences that, during the interaction with the soil, the supporter shank causes a removal area preceding the probe and disturbing the correct recording of the soil strength penetration. This result indicates the necessity that the probe should be placed at a prudential distance of the supporter shank. This disturbing effect was also reported by Hemmat et al. (2009), during rehearsals made with a prismatic probe of base area of 324 mm2 and angle of 30º, protruded 40 mm in front of the advancing shank. In a similar way, Raper et al. (2005) obtain, among other results that, the dimensions of the probe, so as the placement position of this with regard to the front face of the supporter shank are decisive in the measurements accuracy.

In Figure 4, it is observed that the three recordings, made to the higher speed of the probe, were affected by the disturbance of the soil removed by the supporter shank, including the recording of the most protruded probe. This result contrasts with those obtained by Chung et al. (2004) who reported the existence of a critical speed for the sensing of 1,5 m∙s-1, although Chukwu y Bowers (2005) reported to obtain results with a level of significance of 5%, when they used low speeds for a prismatic probe of 0,33 m∙s-1.

From that, it is evidenced that a high speed of the movement of the probe would imply to adopt a higher longitude b of the rod, in order to avoid the interference of the supporter shank in the recording.

Of course, the excessive longitude of the rod conspires against its mechanical strength, as well as against its stiffness and stability, so it would be more convenient to limit the on-the-go speed of the probe. On the other hand, to increase the diameter of the rod is an inconvenience, because it causes an increment of the friction force between the rod and the soil, which introduces errors in the recording of the soil strength penetration.

Then, based on the obtained results in these experiments; it is inferred that during the selection of rational parameters for the design and operation of probes for the horizontal and continuous recording of the soil strength penetration in Red Ferrallitic soils, a minimum distance should be guaranteed between the base of the probe and the supporter shank of at least 110 mm. Also, a forward speed of 0,7 m∙s-1 should not be surpassed. That maximum speed was inferior to the one recommended (1,5 m∙s-1) by Chung et al. (2004).

In Figure 5, the results of the second experiment are shown. The recording of the soil strength penetration with three probes of different geometry is compared, but maintaining in the three cases the rod longitude to the level that avoids the interference of the shank (110 mm), the same diameter of the rod (10 mm) and the lower level of speed (0,686 m∙s-1), with levels of moisture and bulk density in the same range of the previous experiment. As control variable in the experiment, samples were taken from the index cone to the same depth of the horizontal probes (20 cm), in vertical direction and quasi-static, according to ASAE (1999), y ASAE y ASABE (1999).

From the recordings it is appreciated, that the values of the soil strength penetration, in horizontal, are significantly superior (average value of 0,74 MPa) with the cone of dimensions smaller than the base area (130 mm2), compared to those obtained with the wedge and the cone of dimensions 30o x 520 mm2. That confirms the effect referred to the influence of the friction in the rod and the effect this force causes in the recording of the soil strength when cones or wedges are used with area of small base in relation to the diameter of the rod.

It can also be appreciated in Figure 5, the obtaining of higher values of the soil strength penetration obtained with the wedge, in relation to the one obtained with identical angle cone and base area.

When comparing (Figure 5) the result of the recordings of the soil strength penetration (average value of 0,74 MPa), obtained with continuous horizontal movement of the probe of 30o x 130 mm2 (ASABE cone) to a speed of 0,686 m∙s-1, with the results of the measurements of sampling of the index cone(with an average value of 1,48 MPa) taken in vertical direction and to very low speed (quasi-static movement), it is obtained a decrease close to 50% of the continuous horizontal recording in relation to the vertical measurements, made at the same depth (200 mm), what coincides with the report made by Hall y Raper (2005) during the continuous horizontal measurement to 100 mm deep, with a prismatic probe of 625 mm2 of base area in a sandy loam soil with 11% of clay.

 

CONCLUSIONS

It was evidenced a noticeable influence of the disturbing of the supporter shank on the soil, so as it affected the result of the measurements. For the conditions on which the tests were carried out, it was determined to avoid this disturbing effect: the protruding between the base of the probe and the supporter shank should be superior to 110 mm. As well as the sensing speed should not exceed the 0,7 m∙s -1.

Also it was determined that to this on-the-go speed of the sensing system, the horizontal and continuous recording of the index cone (30o x 130 mm2) was inferior to the control measurements made in vertical direction, in manual form and at the same level of depth, with a standard ASABE cone. The decreasing percent reached values close to 50%.

As a result of the comparison of the behaviour of different geometry probes, it was determined that the use of a standard ASABE cone during the horizontal and continuous recording of the soil strength, presents the inconvenience of being more susceptible to the effect of the rod friction, due to the small difference between the base area of the cone and the diameter of the rod.

 

NOTES

RAMOS, E.: Fundamentación de parámetros para el diseño y operación de sondas destinadas al sensoramiento continuo de la resistencia a la penetración del suelo, Universidad Agraria de La Habana, Tesis de Doctorado, Mayabeque, Cuba, 116 p., 2015.

*The mention of commercial equipment marks; instruments or specific materials obey identification purposes, not existing any promotional commitment with relationship to them, neither for the authors nor for the editor.

 

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Received: 12/03/2016
Approved: 14/11/2016

 

 

Ernesto Ramos-Carbajal, Investigador y Profesor, Universidad Agraria de La Habana, Facultad de Ciencias Técnicas, Centro de Mecanización Agropecuaria, San José de las Lajas, Mayabeque, Cuba. Email: carbajales@unah.edu.cu

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