RESEARCH WORK

Penetration resistance in a Chromic Vertisol with different uses, managements and sampling sites

J. A. Villazón¹, G. Martín², Y. Rodríguez² and Yakelín Cobo²

¹Universidad de Holguín (UHO), Ave. XX Aniversario, vía Guardalavaca, Piedra Blanca, Holguín, Cuba
² Estación Provincial de Investigaciones de la Caña de Azúcar (EPICA), Mayarí, Holguín, Cuba
E-mail: villazon@facing.uho.edu.cu

ABSTRACT

A study was conducted in order to determine the influence of the land use, tillage system and sampling site on the penetration resistance in a Chromic Vertisol soil. The land uses were: silvopastoral system, natural pasture, food crops and sugarcane; the last one with traditional tillage and localized tillage. The two agricultural uses were sampled in the ridge and the furrow, and the depths were 0-10, 10-20, 20-30 and 30-40 cm. The highest penetration resistance (p < 0,001) was found in the areas with livestock production purposes (8,64 and 7,71 impacts/dm³ in natural pasture and silvopastoral system, respectively). The lowest penetration resistance was found, in decreasing order, in the sugarcane furrow with localized tillage, the ridge in food crops and the sugarcane furrow with traditional tillage. This variable increased as the sampling went deeper into the soil profile. In the livestock production uses a layer closer to the surface, in which compaction increased, was observed. It is concluded that most depths were classified as little and moderately compacted; the former appeared in the surface, with variations regarding thickness. Only one compacted layer was found in the 30-40 cm depth, in natural pasture.

Key words: Physical and chemical properties of the soil, soil compaction.

Since the first decades of the 20^th century, for the first time, the importance of the anthropic influence as a factor of soil formation was explained, because the utilization of soils in agriculture influences their cultural formation and properties (Cairo and Fundora, 2005). In this sense, the different land uses (Blanco et al., 2005) and management systems (Imhoff et al., 2009; Gaitán et al., 2009; Parra et al., 2011; Álvarez et al., 2012) used by man cause the occurrence of changes in some of the original edaphic characteristics.

The change of soil use modifies its properties (Soane, 1990). The agricultural works that are carried out for the land clearing and preparation for diverse crops can cause degradation and also the decrease of productivity in the plantations (Buol and Stokes, 1997). The soils which in natural status maintain autochthonous vegetation show adequate physical characteristics for normal plant growth (Andreola et al., 2000). When the land use changes to agricultural exploitation, the drastic modification of its physical properties occur, which unfavorably alter plant growth (Spera et al., 2004).

It is also possible that the physical, chemical and biological properties are transformed because of the influence of management systems (Parra et al., 2011; Devine et al., 2014). These systems, by acting directly on the structure, exert a higher influence on the physical performance of the soil (Vieira and Klein, 2007).

The inadequate use and management of the soil accelerate its physical degradation (Jaramillo, 2002). In this sense, compaction causes the increase of soil density and mechanical resistance, and decreases porosity (Villamil et al., 2000; Taboada and Micucci, 2009). The compaction status can be established with the aid of tools that measure the penetration resistance (Cuéllar et al., 2002), known as penetrometers (Jaramillo, 2002).

Vertisols have properties that are derived from the interaction of different edaphogenic factors, such as relief and climate, which guarantee the occurrence of contraction and dilation processes. These dynamic processes are associated to the predominance of illitic or smectic clayey minerals in the parent material. Such soils are formed in regions in which a plain-depression relief prevails, with marked hydromorphic processes (Imbellone and Mormeneo, 2011). In addition, they show a structure in which aggregates are vertically oriented (Hernández et al., 2010).

Taking into consideration these antecedents, the objective of this research was to determine the influence of land use, tillage systems and sampling site on the penetration resistance in a Chromic Vertisol soil.

MATERIALS AND METHODS

Characteristics of the zone. The study was conducted on two calcic Chromic Vertisol soils, in the Guaro experimental block and in the experimental area Kilómetro 27, both belonging to the Provincial Sugarcane Research Station (EPICA), in Holguín, Cuba. The soil polygons of the areas were similar; they were only different in the salinity degree and the effective depth (63 and 60 cm, respectively).

The areas are found in the eastern part of the Alto Cedro plain, which shows a water balance with two dry periods in the year and intermediate and intermediate-dry regime. In addition, it has a range that oscillates between 219 and 292 days per year of water stress and an Aw climate (savanna). From the paleogeographic point of view, in the region there were periodically flooded plains during the lower Pliocene-Pleistocene and higher Pleistocene, and relatively low emerged lands, in the late higher Pleistocene.

Selection and sampling of the areas. In sugarcane, the penetration resistance was determined in the area belonging to a tillage experiment, in which three replicates were sampled (in the furrow and in the ridge) with traditional tillage (TT) and three with localized tillage (LT). For the selection of the other sampling spots, the areas were stratified according to the soil type and land use (silvopastoral system, natural pasture and food crops), through the soil map 1:25 000, the satellite images IKONOS (1 m of resolution) and the software Mapinfo Professional 10.0.

The areas occupied by the different land uses were divided into 5, 15 and 11 plots of 1 566 m² (silvopastoral system, natural pasture and food crops, respectively). The plot of 43,5 x 36 m (1 566 m²) was chosen as minimum study unit, because it is in correspondence with the lowest surface occupied by one of the land uses (sugarcane). Each plot (cell) was divided into twelve 48-m² subplots.

This operation was repeated to choose three subplots within the selected plot. Then the penetrometry study was conducted, at the center of each subplot. Three samplings were carried out in each treatment, at four depths: 0-10, 10-20, 20-30 and 30-40 cm.

Description of the treatments. Four land uses, two tillage systems and two sampling sites were evaluated (table 1). The samplings were made according to the land use: silvopastoral system: area with more than 15 years established as forest and, at least, the last 10 years dedicated to silvopastoral system; natural pasture: area with around 10 years of exploitation and previously planted with sugarcane; food crops: banana as main crop in the area and cassava as associated crop, with approximately two years with that use, and previously planted with sugarcane; and sugarcane, two years after being planted. The first three were located in the experimental block, and the last one, in the experimental area Kilómetro 27, with a split-plot experimental design. Two tillage systems were used which constituted the treatments: TT: plowing up with disc plow, two harrowings and furrowing; and LT: plowing up and furrowing with C-101. In both systems the weed control was manually performed.

For the evaluation of the sampling sites, the soil penetration resistance in the ridge and furrow, in the uses food crops and sugarcane, was determined. In the latter the tillage system was taken into consideration.

Evaluation of the penetration resistance. To evaluate the penetration resistance an impact penetrometer, model IAA/Planalsucar-Stolf (Stolf et al., 1983), with the impacting mass regulated at 0,40 m, was used. The compaction degree was classified according to the following categories: friable, little compacted, moderately compacted, compacted and highly compacted; which are correlated with different density ranges of the soil (Ds). The samplings were carried out with the soil at field capacity.

Statistical analysis. A simple classification variance analysis, through Duncan's multiple range test, at 95 % of probability, was made, and Pearson's correlation coefficient among the values was determined, according to the sampling site. For the data processing the software Statistica 7 was used.

RESULTS AND DISCUSSION

The highest soil penetration resistance (fig. 1) was found in natural pasture (8,64 impacts/dm³ = imp/dm³), followed by silvopastoral system (7,71 imp/dm³). Both highly significantly differed from the other uses, tillage systems and sampling sites. The treatments with livestock production purposes were followed by the ridge of the LT in sugarcane, the furrow in varied crops and the ridge of the TT in sugarcane (5,85; 5,80 and 4,50 imp dm^-3, respectively), without significant differences among them.

The results in the ridge of the TT in sugarcane did not differ either from the ones obtained when sampling the furrow in sugarcane managed through LT (3,96 imp dm^-3), the ridge in food crops (3,65 imp dm^-3) and the furrow in sugarcane by TT (3,52 imp dm^-3).

The highest compaction in the areas with livestock production purposes caused an increase in soil density, and a decrease in total porosity and aeration, which can influence the reduction of water infiltration rate. In addition, the hydromorphy, risks increase with the subsequent increase of the pseudogleyzation process to which Vertisol soils are prone (characterized by their impermeability and deficient drainage). Besides, the adequate root growth of the plants becomes difficult.

Álvarez et al. (2012) stated that in the areas with pasturelands, the soil density shows differences related to the management system, and that this physical property increases in the sites in which there are stress and cattle trampling conditions. Likewise, Cabrera et al. (2011) stated that the soil density increased due to the influence of the stocking rate and the cattle trampling; with regards to the soil humidity conditions, this increase was higher in wet soil than in dry soil.

On the other hand, the penetration resistance increased as the soil profile was further sampled (fig. 2), because values of 3,03; 5,46; 6,48 and 6,85 imp/dm³ were found at the depths 0-10, 10-20, 20-30 and 30-40 cm, respectively. There were highly significant differences in all the layers. The increase of compaction could have been related to the decrease of organic matter (OM) in the lower horizons.

The increase of compaction as the depth is higher which can be related to the contraction of the OM content and the formation of a B horizon with predominance of clayey minerals causes the reduction of the volume of gravitational water within the Vertisols. The decrease of the water movement in the soil prevents the correct washing and this causes a high carbonation level. In addition, the risk of salinization to which Vertisols are prone increases.

Ponce (2003) stated that the decrease of the OM content affects the soil structure and, thus, the soil density. This effect is much more noticeable in sub-surface horizons, in which compaction cannot be ascribed to the transit of agricultural machinery because it only has incidence on the first centimeters of depth, where it causes the mechanical compaction of the soil.

In a typical Pellic Vertisol of the central region of Cuba, subject to different managements, Cabrera et al. (2001) observed that the decrease of the OM as the depth increased (0-20 and 20-40 cm) coincided with the reduction of the aggregation degree, structure coefficient, stable aggregates, filtration coefficient and aeration volume. In addition, they reported that the physical deterioration of the soil was less stressed when organic fertilization (sugarcane filtercake, at a rate of 50 t ha^-1) was included. In the treatment in which sugarcane filtercake was applied and a subsoiling was also made with a mole plow, the differences between the two depths were less appreciable. These authors stated that there is a simple, strong and direct linear relation between the first three physical indicators and the OM of the soil.

Likewise, González et al. (2009) reported about the importance of OM in the improvement of the soil structure, by favoring the formation and stability of the aggregates; as well as in the decrease of compaction and the increase of the humidity interval in which the soil can be tilled.

The performance in the natural pasture was similar to that of the silvopastoral system (fig. 3), because the penetration resistance suddenly increased up to 20 cm of depth, which indicated the formation of a compacted sub-surface layer. This was also very stressed in the ridge in sugarcane, where the land preparation was carried out in a localized way. In this case, the quantity of impacts per cubic decimeter did not equal the one determined in the livestock production areas, and although the highest compaction was found in the 15-20 cm horizon, the thickness of this compacted layer was lower than in the above-mentioned uses.

It is remarkable that the highest compaction in food crops was found in the furrow and not in the ridge, as occurred in the sugarcane use, in its two tillage systems. This performance is due to the inadequate use of agricultural implements with animal draught. Although from the agrotechnical point of view the damaging effects are lower, the use of the American mouldboard plow and the Creole plow (for plowing up and furrowing, respectively), at a same depth, has caused the appearance of a compacted layer with similar characteristics as the existing one in sugarcane in the ridge with localized tillage.

In the other treatments, the soil penetration resistance also tended to rise with the increase of depth, which was more remarkable in the TT in sugarcane, as well as in the furrow of that same use, when localized tillage was performed.

In the silvopastoral system a moderately compacted layer was found (table 2), in all the depth; while in the natural pasture the soil layer with equal category was overlaid on a compacted horizon at 30-40 cm.

On the other hand, the soil in food crops, in the ridge, was classified as little compacted at the 0-10 cm depth, and as moderately compacted at 10-40 cm; while the furrow was moderately compacted at all depths. The lower compaction in the surface (0-10 cm) of the ridge with regards to the furrow could have been due to the frequent cultivation made with animal draught in these strips of the plantation.

In sugarcane with TT a little compacted surface layer, overlying on the next 30 cm classified as moderately compacted, was found in the ridge. In the furrow, the little compacted surface layer was prolonged up to 20 cm. Below this depth, there was an increase of compaction.

Likewise, when preparing the soil with LT a little compacted surface layer was not found in the ridge. The divergence in equal sampling site, in the same land use with different management, was due to the fact that the mechanical resistance of the soil was little disturbed during the LT.

According to the report by Jaramillo (2002), when the LT is made the soil should be friable and have an optimum humidity degree for the maximum efficiency in the tillage to be obtained. The first condition was not fulfilled in the case of Chromic Vertisols, because the high content of montmorillonitic clays throughout the soil profile confers to it great plasticity and a low infiltration and aeration capacity, which causes its consistency to be firm when it is in wet status and compact, when it is dry. Pulido et al. (2009) stated that the high clay content of Vertisols confers them high structural stability when wet.

In the sugarcane furrow with a localized tillage, the compaction of the different depths was similar to the one observed in this same sampling site, but with TT.

The different compaction categories are correlated with a specific soil density range for each case. Blanco (2009) obtained a regression equation that explains 60 % of the variability of the soil density, from the mechanical resistance and plasticity, at field capacity.

The increase of compaction causes deterioration of the soil physical status, and brings about a rise of density and a decrease of total porosity and aeration porosity, from which the decrease of the volume of macropores is derived. In addition, this phenomenom increases impermeability and this causes the decrease of the water infiltration rate, for which different stages of pseudogleization can be manifested, with aeration problems and changes in the redox properties of the soil. The salinization risk also increases.

On the other hand, there was a simple and direct correlation between penetration resistance in the ridge and in the furrow (fig. 4), which was appreciated through the positive value of the coefficient in the uses food crops and sugarcane with TT. The highest probability that the dependent variable increases when the independent increases existed in the latter (85,97 %). In the case of the LT in sugarcane, the r value showed that there was no relation among the variables, because its value was lower than 0,5.

In this sense, a much more uniform land preparation could have been the cause of the higher correlation coefficient in sugarcane with TT and in food crops. On the other hand, the lower incidence of agricultural implements on the ridge explains, in the case of sugarcane with LT, the inexistence of relation among the variables.

CONCLUSIONS

The highest soil penetration resistance was found in natural pasture and in silvopastoral system, which was related to the use with livestock production purposes and waterlogging.

The penetration resistance increased as the soil was sampled deeper.

Most of the depths were categorized as little compacted and moderately compacted; the former appeared in the surface, with variations regarding their thickness. Only one compacted layer was found in the 30-40 cm depth in natural pasture.

Received: November 20, 2014
Accepted: February 3, 2015