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INTRODUCTION
In Cuba there are around 257,700 ha with heavy clay soils and poor drainage problems dedicated to the cultivation of sugarcane (37%). Within these soils are those that have specific edaphoclimatic characteristics, very susceptible to the over-dampening, created by the rainy periods which require the phytotechnical attention of the cane, through a differentiated management in the process of its harvest. Areas with these characteristics have been called high humidity conditions (Cid et al., 2011).The harvest is one of the most important stages in the production of sugarcane. Because of that, it requires a high degree of organization and coordination of all the factors involved on it, from the field to the industry (Rodríguez y Valencia, 2012; Aguilera Esteban et al., 2019).
There are several basic principles for a good harvest, among them: harvesting the cane at maximum level of maturity, achieving good rates of efficiency, minimum fuel consumption, high productivity of the harvesting and minimum damage in the stump (Rodrígues et al., 2002; Matos et al., 2014; Guimarães Júnnyor et al., 2019).
Soil compaction is one of the factors that increases soil degradation, being the most worrying of global environmental problems. Compaction is one of the causes of the fall in agricultural yields, mainly for the reduction of the sprouts, for this reason it is considered one of the main problems to be faced in sugarcane agriculture. The wet soil is much more susceptible to compaction than dry soil. Between factors that affect the degree of soil compaction, moisture is considered the most important (García Ruiz et al., 2010; Guimarães Júnnyor et al., 2019; Emmet-Booth et al., 2020).
Compaction in agricultural soils is a problem that leads to the high use of energy in field labors, consumption in machines parts and land degradation, causing the loss of their properties as well as low rates of production yield (Colombi & Keller, 2019; Awe et al., 2020). Soil compaction takes place when pressure is applied to the surface, as a result of trampling by animals and people and the inadequate use of equipment as tractors, especially when the soil is wet. Compaction causes changes in the physical properties of the soil, increasing resistance to penetration, dry bulk density and a reduction in porosity (González et al., 2013; Mesa et al., 2016).
Considering the high importance of sugarcane production in the economy of the northern area of Villa Clara Province, both, in yield and in cultivated areas, which are characterized by heavy soils with poor drainage and adverse harvest conditions due to high moisture, the objective of this research is to determine the effects of traffic of machinery during sugarcane harvesting on the soils of the north coast of Villa Clara.
MATERIALS AND METHODS
The study was carried out in “Héctor Rodríguez” Base Enterprise Unit, in three sugarcane production units called: Carlos Perera, Antonio Bacallao and Monte Lucas, located in the sugar cane massif in north coast of Villa Clara Sugar Enterprise. The study was performed in sugarcane plantations in rainfed land conditions. The area under study is characterized by predominant Oxisol soils with slopes less than 2% and little effective depth (less than 20 cm), also with compact consistency, poor drainage, not stoniness and no-rocky scarce concretions (Cid et al., 2011).
Due to these characteristics this soils are prone to maintain high humidity in rainy stages that makes harvesting difficult and predisposes to structural damage as well as variation of profile of the furrows. The machinery that took part in the sugarcane harvest were the CASE IH 8 800 harvester and the self-dumping car pulled by the Maxxum Case IH 150 Tractor (Figure 1).
The moisture based on dry soil (hbss)%, was determined by the gravimetric method. Soil samples with a depth of 10, 20 and 30 cm were taken in the center of the furrow and in the ridge before harvest. The treatment of the samples in the laboratory was carried out in accordance with Cuban Standard NC 3447:2003.
The variation of soil profile was determined before and after the transit of the machinery, using a spirit level and a soil profilometer with divisions in the horizontal plane every 5 cm and appreciation in the measurement in the vertical plane of 1 mm. The evaluations were made in a total width of 3.20 m, from the center of the ridge. Five profilometry measurements were made per field to 20 m from the edges, to avoid the areas with the greatest effects caused by the turn and the traffic of the machinery during the harvest. In addition, damages related to the transit of trucks and trailers within the field were evaluated based on the landslide and skidding.
The Chamfer Cylinder method was used to determine the soil dray bulk density. Soil samples were taken in the center of the furrow and in the center of the ridge before and after the passage of the machinery, at depths of 10, 20 and 30 cm using a 5 cm high and 5 cm diameter cylinder. Samples were dried by oven at a constant temperature of 105° C, their mass was determined using a balance with a division value of not more than 0.1 g until constant values of the soil masses were obtained. The calculation procedure was performed according to Cuban Standard NC 3447:2003.
RESULTS AND DISCUSION
Variations in the Soil Profile
The profiling of the soil in the fields under studied showed variations due to the traffic of the different equipment involved in the harvest and transport of sugarcane. As shown in Figure 2, in the microrelief measurements before harvesting, height variations are defined between the furrow and ridge with an average value of 8.13 cm, in the same way the width of the furrow is defined with an average of 59.6 cm. These values are partially adjusted to the agrotechnical demands of the crop and allow drainage during the rainy season, which is especially important in the study area. As shown in profile B of Figure 2, the pass of the harvester does not produce significant deformations in the geometry of the ridge, while the machinery passes over the furrows, showing average sinking of 2.8 cm which does not affects its structure. In this sense, the harvester was able to move satisfactorily in all the conditions studied without jam, showing low values of pressures over the soil.
Finally, as a result of intermediate transport within the sugarcane field, the height of the ridge is reduced in the soil profile with an average value of 3.8 cm from the initial value and the depth of the furrow is maintained at constant values. This is justified before the increase in the contact area between the tire and the sides of the ridge which reduces the specific pressure, effect similar to those obtained by other authors (Gutiérrez-Rodríguez et al., 2012; Rodríguez & Valencia, 2012; Mesa et al., 2016).
Variations in soil profiling demonstrate the process of soil compaction and of modification of the furrow geometry of the plantation. In this process, the machinery for cutting and for intermediate transport of the sugarcane take part. However, the greatest incidence is by the tractor with the self-dumping car as a result of the dimensions of its trail that do not adjust to the furrow width, passing over part of the planted area. This fact affects the germination of the cane shoots mainly by the high pressures which are subjected the roots, according to studies of Aguilera Esteban et al. (2019).
Damages were also found in the headwaters of the furrows due to the turning and parking of the different equipment involved in the mechanized harvest. When this procedure is reiterative during harvest, it causes total local destruction of the entire structure of the furrows.
Variations in Soil Moisture
The soil moisture of the different UBPC (Figure 3) shows an increase in depth for the three cases under study, all were below 65% at three levels of depth; considering this value as the upper limit of moisture for clay soils (Rodríguez, 2015), and for these conditions, machinery for harvesting and sugarcane transportation must be able to traffic into the field, according to the traffic requirements.
Under the three conditions evaluated, the CASE IH 8800 harvester was able to move satisfactorily, due to the running mats system, which generates low pressures on the ground. However, this was not the case for the aggregate formed by the Maxxum CASE tractors with the self-damping car due to the increase of the moisture present in some areas of the field, resulting in jam situation (Figure 4). This phenomenon took place interchangeably in all the fields studied with major intensity in the fields with greater soil moisture.
The prints produced by the tires caused serious deformations in the soil profile and, as a consequence, in the development of the sugarcane plant. For recovery, the field needs additional tasks that increase costs reducing productivity.
Variations in the Soil Dry Bulk Density
Variations regarding soil dry bulk density before and after the transit of the machinery used in the sugarcane harvest showed values between 0.8 and 1.38 (g/cm3), where highest values of soil densification were found at the UBPC Monte Lucas (Figure 5). The UBPC Carlos Perera and J.A Bacallao showed a slight increase with respect to the depth in the first 20 cm before the harvest, both in the ridge and in the furrow. The UBPC Monte Lucas, on the other hand, showed a considerable increase of 1.33 (g/cm3) up to 20 cm deep and this value is maintained up to 30 cm, this same pattern is shown in the ridge where it reaches densities of up to 1, 38 (g/cm3). The cause of this bulk density behavior in this unit may be linked to the work related to the cultivation in the furrow during the growth of the sugarcane.
For the three case studies an increase in bulk density is verified after the passage of the harvester and the intermediate transport, which affects all three agricultural layers of the soil, mainly the superficial layer.
CONCLUSIONS
Variations in soil profiling was caused by traffic of harvester, tractor and the self-balancing car, as well as the parking and turning of the auxiliary machinery in the headwaters of the furrows. However, the tractor coupling with the self-balancing car introduce a major modification because it does not adjust to the used planting frame.
Soil moisture did not exceed the maximum values for traffic established for this soil, with values between 24.1% and 64% of moisture, however, only the harvester was able to move smoothly under such conditions. The tractor with the self-balancing car experienced jams related to high moisture in soil depressions.
The dry bulk density of the soil before harvest showed averages between 0.90 and 1.32 g/cm3, in the three units studied. An increase was observed after the passage of the harvesting machine system in the furrow and the ridge, with values between 0.98 and 1.37 g/cm3.
