INTRODUCTION

Soil is an essential resource for food and climate security around the world, and its main threat since the beginning of agriculture has been erosion (^{Amundson et al., 2015}), which represents the most visible effect of soil degradation (^{Lugo-Morin & Rey, 2009}; ^{Sampietro-Vattuone et al., 2019}). Erosion consists of the accelerated removal of the upper layer of the same through water influence and wind or farming practices (^{FAO & ITPS, 2015a}). Annually, it represents between 25 to 40 billion kg of the lost soil resource, which in projections towards 2050 will mean losses close to 1.5 million km² (^{FAO, 2015b}). Additionally, this phenomenon generates average losses of 0.3% of annual crop yield globally (^{FAO & ITPS, 2015a}).

On the other hand, approximately 48% of soils in Colombia have been degraded (^{IDEAM & U.D.C.A, 2015}). As an illustration, anthropic erosion have been reported in different production systems, such as potato crops in the municipality of Pasto, with losses of 6.12t ha^-1year^-1 (^{Alvarado et al., 2011}); conventional coffee (1.14 t ha^-1year^-1) and blackberry in the region of Huila (0.99t ha^-1year^-1) (^{Agudelo et al., 2015}), coffee in municipalities such as Buenavista, Calarca, Cordoba, Genova, and Pijao (26 - 100t ha^-1year^-1) (^{Castro et al., 2017}), and coffee (1.4 - 2.4kg/ha) and bean (1.9 - 3.1kg/ha) in Dagua (^{Alarcon & Reyes, 2013}).

However, soil loss varies according to developed agricultural systems, such as crop cover, which reduces soil erosion, especially on steep slopes (^{Loch, 2000}; ^{Huerta et al., 2018}). Management practices and climatic and edaphic conditions also contribute to this purpose.

The hillside soils of the western region of Valle del Cauca are susceptible to erosion (^{Tafur, 2006}; ^{Alarcón & Reyes, 2013}), where processes are favored not only by topographical and climatic conditions but also by the scarce vegetation cover during the first months of pineapple growth, and the incorrect agricultural practices applied.

In this regard, this review aims to address this agricultural culture by showing and analyzing the crucial factors that bring on the erosion of soils in the major pineapple-producing municipalities in the region of Valle del Cauca.

Generalities, importance, and distribution of pineapple (Ananas comosus L. Merr). Pineapple, whose scientific name is Ananas comosus L. Merr is an essential contribution of pre-Colombian culture to agriculture (^{Delgado & Arango, 2015}), as it is one of the most prominent tropical fruits worldwide (^{Zhang et al., 2014}). It is grown and consumed on all continents, named after the queen of colonial fruits due to its pleasant characteristics of smell, taste, and appearance (^{Crestani et al., 2010}).

Such characteristic components have led to the growth of this fruit in the market, increasing its demand and generating competitive prices (^{Martínez et al., 2012}; ^{Abu Bakar et al., 2013}). On the other hand, this growth in recent years has been associated with a customer increase in income and a change in consumer preferences towards a healthy life based on an adequate diet and nutrition (^{Altendorf, 2017}). Therefore, it is expected that the scenario will continue to increase in terms of production in the coming years (^{PTP et al., 2013}).

It has been noted that this crop ranks third place among the most produced tropical fruits worldwide, after bananas and citrus fruits (^{Hassan & Othman, 2011}; ^{El-Ramady et al., 2015}; ^{Oculi et al., 2020}). In this regard, the major pineapple-producing countries are Costa Rica (3056.45mt), Philippines (2671.71mt), Brazil (2253.90mt), Thailand (2153.18mt), and India (1891.00mt) (^{FAO, 2022}). In terms of representation, Costa Rica contributes 10.62% of total production worldwide, while in second and third place are the Philippines and Brazil with 9.4% and 9.3%, respectively (^{FAO, 2019}).

Production is mainly associated with tropical countries; however, it is widely cultivated in South America and consumed fresh or processed in various food products, as shown in Figure 1.

Figure 1 Main pineapple-producing countries. Source: ^{Uriza et al. (2018)}. 

However, Belgium, Netherlands, Germany, Japan, the United Kingdom, Italy, Spain, and the United States are reported as the primary consumers of this fruit, which demand about a quarter of the total production (^{PTP et al., 2013}), also used in different presentations, such as fresh fruit, canned pineapple or pineapple juice.

In Colombia, during the period 2014 to 2018, production increased at an annual rate of 12%, where Santander, Valle del Cauca, and Meta recorded the highest participation. In this sense, Santander ranked first with a production of 455.701t and Valle second with 145.162t, values representing 43% and 14% participation of each of the two regions, respectively (^{ASOHOFRUCOL, 2018}; Figure 2).

At the level of Valle del Cauca, the leading pineapple producer in hillside areas during 2018 was the municipality of Dagua, which yielded 46.680t in 1.270ha. Next, Restrepo with 35.700 t in 650ha, Vijes with 14.400t in 421ha, and La Cumbre with 14.179t in 178ha (^{AGRONET, 2019}).

Figure 2 Main pineapple-producing areas in Colombia. Source: (^{ASOHOFRUCOL, 2018}). 

Factors influencing soil loss in pineapple cultivation. A starting point for addressing the factors that influence soil loss dedicated to pineapple cultivation is to consider the Universal Soil Loss Equation factors, known by its acronym in English as the USLE. This equation was proposed by ^{Wischmeier & Smith (1978)} and represents one of the most widely used approaches during an 80-year history of erosion modeling and has been widely accepted and employed in different researches conducted in 109 countries (^{Alewell et al., 2019}).

The equation proposes that annual soil losses are influenced by the erosion or aggressiveness of rain (R), soil erodibility or susceptibility to detachment (K), topographic factor (LS), coverage factor (C), and soil conservation practices (P).

Although this equation has been applied in a large number of researches in different crops at an international level, the information on erosive processes in pineapple cultivation is still very scarce, especially at the planting level; therefore, the results reported in this regard are diverse for the different regions that have been studied (^{Afandi & Novpriansyah, 2020}).

The following are the primarily reported researches on the erosion of pineapple cultivation, which have been carried out over the past four decades, and are presented chronologically.

^{Valentin & Roose (1980)} developed research on the erosion of the soil cultivated with pineapple in the humid tropical area of Ivory Coast; they pointed out that the value of farming practices (P) was scant (0.002-0.070) in that area. In addition, they concluded that the main conservation problem did not come initially from pineapple fields but the drainage of roads and access roads.

^{El-Swaify et al. (1993)}, in the study "Problems of erosion and conservation needs in pineapple culture", highlight that the loss of soil in the Hawaiian pineapple lands reached 35t/ha/year and that this value was more significant than that presented in sugarcane fields. Such a problem may respond to the conditions of the access roads to the field since they are unpaved and the soil exposed during the tillage and the early growth stage of the crop.

^{Ciesiolka et al. (1995)}, in their study "Erosion and hydrology of the slopes under commercial production of pineapple", found that soil erosion of pineapples that are grown on steep slopes (up to 40%) in southeastern Queensland, Australia, was very high, reaching 178t ha^-1; however, soil erosion and runoff decreased in the second and third year after planting.

^{Wan & El-Swaify (1999)} analyzed the effects of the plastic mulch on erosion and runoff in a Hawaiian pineapple field. They reported that, for all simulated storms, the plastic plot showed the highest runoff and soil erosion rates, while those values were lower on the plastic plot with pineapple crowns. Therefore, it can also be considered a variable within crop management practices, an issue that should be further evaluated.

^{Hernández & Florentino (2004)} evaluated two types of coverage in pineapple-grown soils (A. comosus) in Lara state under simulated rain. They found out that the scarce soil cover and the high slopes are crucial aspects that favor water loss from runoff and soil from erosion, mainly in the early stages of pineapple cultivation. Likewise, the authors also note a beneficial effect of coverage on the decrease in water erosion and runoff on the erosion trays assessed and the increase of water infiltration into the soil.

In this regard, ^{Ingwersen (2012)} developed a study called "Costa Rica's Fresh Pineapple Life Cycle Assessment," where, among other aspects, it assessed the impact on soil erosion. The sensitivity analysis results showed that the slope was the factor that most influenced the erosion response and found that an increase in the slope of only 2.5 to 30% caused an increase in erosion in kg/ha/harvest of 2100%. Likewise, it also reported that the sensitivity of the soil texture, about the percentage change in average erosion (58 to 33%), together with the degree of contouring of the rows (44 to 0%), yield (43 to 96%), use of plastic mulch (78%) and the use of double harvest systems (32%) showed significant influences on soil erosion in pineapple-grown farms.

^{Alvarez & Peña (2013)} estimated erosive levels in soils with pineapple cultivation in Sarapiquí, reported values of up to 142t/ha/year, which are framed in the category of severe erosion. They concluded that the levels of erosion recorded could be associated with the parameters of water capacity and apparent density. An inadequate condition of these parameters would affect the soil structure, and the soil system would be more fragile, increasing the erodibility processes and the effects of erosivity. Therefore, these factors must also be analyzed.

^{Afandi & Novpriansyah (2020)} studied soil erosion in pineapple plantations in Indonesia under climate change analysis and used the USLE as an evaluation methodology. They concluded that erosion values at various research sites were low, and although the erosivity value found was high, other erosion factors in the equation were low, so soil erosion tends to be low.

Agroclimatic effects on erosion in pineapple. The hillside area where pineapple is grown in Valle del Cauca has the following location: in flat coordinates (Magna sirgas Colombia west) 1046866.83 (centroid x) and 898276.9324 (centroid y) and in geographic coordinates of the centroid 3-40'34.324"N and 76-39'20.266"W. That zone has an approximate area of 138800.885 ha and a perimeter of 229.587512 km (Figure 3).

Figure 3 Main pineapple-producing municipalities in the Valle del Cauca region. 

Dagua, Restrepo, La Cumbre, and Vijes municipalities are circumscribed to the Dagua River basin, being of great importance to Colombia, for its responsibility in more than half of foreign trade and for communicating the country with the Pacific Basin. Nevertheless, the inappropriate use of productive activities, represented mainly by pineapple farming (^{Loaiza et al., 2012}), has caused severe damage to the ecosystem (^{Daza et al., 2012}; ^{Cardona et al., 2014}); soil erosion processes stand out where more than 50% of the area has been degraded (^{Loaiza et al., 2012}).

In climate terms, the Dagua River watershed is connected to one of the highest precipitation centers in the world. In this way, in its upper part, it presents precipitation levels in the range of 900 to 1600mm/year, and in its lower part, it ranges from 6000 to 8000mm year^-1 (^{Aguirre et al., 2017}).

On the other hand, studies carried out in areas near this region by ^{Ramírez et al. (2009)} and ^{Castro et al. (2017)} indicate values of erosivity that are between the high and very high categories. Likewise, a study developed by ^{Pacheco et al. (2019)} reports erosivity values framed between 3162.12 and 12683.72MJ.mm.ha^-1 for an Ecuadorian tropical region, and more recently, ^{Yue et al. (2020)} report values for the last two decades for South America up to 10273.67MJ.mm.ha^-1.

Although information regarding soil erodibility (k factor) is scarce, ^{Alarcón & Reyes (2013)} found K values of up to 0.003254t.ha.h/MJ.mm.ha of typic dystrudepts, typic hapludands, and andic dystrudepts by rain simulator in La Centella micro-basin (Dagua, Valle del Cauca), which mean that the susceptibility of these soils to erosion is high.

According to the basic plan of territorial ordering, the soils of Dagua have adequate drainage, but they show a high tendency to landslides, ranging from superficial to moderately deep (^{Alcaldía Municipal de Dagua, 2001}). On the other hand, the main orders of soil present correspond to Inceptisoles, followed to a lesser extent by Alfisols, Mollisols, Andisols, and Entisols, many of them susceptible to erosion (^{Tafur, 2006}; ^{CVC, 2013}; ^{CVC, 2014}).

In Dagua, the crops are located in hillside areas from the subxerophytic zone belonging to the canyon of the Dagua River at 1500 meters above sea level, where slopes exceed 20% (^{Chaparro et al., 2012}). The municipality of Restrepo also establishes this crop in hillside areas, and the municipalities of Vijes and La Cumbre are not the exceptions, as they show more significant environmental effects at the regional level.

A recent study developed by ^{Martínez et al. (2021)} indicates that the highest values of the topographic index in the Dagua River basin extend from the northwest to the southwest, mainly covering the municipality of Dagua. This finding coincides with the upper part of the basin, where the slopes that can reach 81 degrees are located. In this sense, it is essential to consider this factor as one of the most critical factors contributing to soil erosion in pineapple cultivated areas around this region.

Regarding the plant coverage factor (C), in the USLE, this represents the relationship between the soil losses generated in a plot subject to fallow and those that occur for the same plot, under conditions of specific coverage of a given crop (^{Wischmeier & Smith, 1978}).

According to ^{Afandi & Novpriansyah (2020)} using USLE to calculate soil erosion cultivated with pineapple plants is complex, mainly to estimate the factor (C) of the crop. Pineapple has a long-life cycle and is harvested between 15 and 18 months after planting; then, it could be continued as a ratoon crop for about 15 months.

Pineapple canopy coverage increases as age increases. Six months after planting, the pineapple canopy would completely cover the soil surface to affect soil erosion significantly. Furthermore, soil erosion would be affected by the number of canopies covering the soil surface. Soil losses in the field cultivated with pineapple will vary during pineapple growth. Thus, values ranging from 0.1 to 1 have been found, depending on the crop's phenological stage (^{Afandi et al., 2020}).

^{Abbasi & Jamal (1999)} indicated that soil loss and runoff are more substantial during the first four months of pineapple crop establishment, and then it is gradually reduced due to the development of plan cover. Nevertheless, ^{Sugahara et al. (2001)} state that pineapple growth is so slow that, for at least one year, the fields do not have sufficient plant cover that could lead to severe erosion problems. In any case, this index must be calculated because it is one of the essential aspects in determining soil erosion.

In the case of the pineapple regions of Valle del Cauca, it must be known that this agricultural culture has to be managed as a clean crop, as it is a very demanding plant in weed control (^{Gómez et al., 2006}). Therefore, farmers do not allow the establishment of weeds, which increase the percentage of uncovered area, maximizing the area exposed to the impact of the falling raindrop that causes soil detachment.

Pineapple management and influence on erosion. Regarding the management practices, developed by AGROSAVIA (formerly CORPOICA) in "simple practices for planting pineapple on the hillside," the basic principle for hillside planting is through the slope, being also indispensable to be established in areas with slopes below 30%, using soil conservation practices; However, is possible to find soils without plant cover associated with intensive livestock farming and overgrazing. In addition, no conservation practice is applied, burning is carried out before planting, and activities such as weeding leave the soil entirely uncovered and exposed to favor the processes of erosion (^{Gómez et al., 2006}).

Likewise, crops are established in favor of the slope. In many cases, plastic mulch is used, causing effects on soil erosion, and the environmental effects of productive activity in terms of loss of soil quantity are unknown.

Currently, drip irrigation continues to be the most recommended system in terms of conservation of water and soil resources, whose application has intensified in recent years due to greater efficiency and savings (^{Cubero & Sandí, 2013}). This method consists of localized, low flow, low pressure, and high-frequency water application, allowing significant savings in energy consumption (^{Cruz, 2015}).

The factors mentioned above added to aspects such as the inadequate selection of the land to be sown, limited plant coverage, and its management as a clean crop can lead to the loss of soil in a few decades. In this sense, when crops are located in areas of high rainfall, their productive potential can fall in less than twenty years, and if it also has a level of slope, the problem is even more significant, leading to a total loss of soil in a short time (^{Quijandria et al., 1997}).

Relevant Results. Finally, as relevant results, although there is not enough research on erosion in soils dedicated to pineapple cultivation, the available studies indicate losses that range between 35 and 178t/ha/year, values that can be classified in the category of severe erosion.

Regarding pineapple-producing municipalities in Valle del Cauca, erodibility, erosivity, and topographic factors can reach high values, taking into account the predominant soil orders, heavy rains that reach 10273.67Mj.mm.ha^-1 (very high erosivities), and considering that in this sector, the slopes are usually higher than 20%. On the other hand, the coverage is almost nil during the first months of the plant's life and lacks conservation practices.

CONCLUSIONS

It was possible to address the agricultural culture of pineapple and present and analyze the leading factors that bring on the erosion of soil in the main pineapple-producing municipalities in the region of Valle del Cauca.

According to this study, it is highlighted that one of the most important factors that favor soil erosion is given by the topography, mainly the inclination of the slopes. The conditions of access roads, unpaved roads, practices such as the use of plastic mulch also show an influence; besides, apparent density, texture, structure, and water capacity are correlated with erodibility. Furthermore, concerning pineapple-producing municipalities in Valle del Cauca, erodibility, erosivity, and topographic factors can reach high values, considering the predominant soil orders and heavy rains.

Although Pineapple (A. comosus) is a fruit of great importance; inadequate soil management may contribute to the loss of natural capital in a few decades. It is recommended to carry out future studies in which the erodibility and erosivity of these areas are determined to know the potential degradation rate. This aspect is essential and will function as a valuable tool for identifying vulnerable areas, decision-making, generating management, and conservation practices on these soils.