Original Article

Main soils and its particularities of the Carrizal-Chone system, Manabí, Ecuador

M.Cs Leonardo Ramón Vera-Macías^{1  *}  , Dr.C Alberto Hernández-Jiménez²  , M.Cs Freddy Wilberto Mesías-Gallo¹  , M.Cs Ángel Frowen Cedeño-Sacón¹  , Dr.C Ángel Monserrate Guzmán-Cedeño^{1  3}  , M.Cs Katty Paola Ormaza-Cedeño¹  , Ing Geoconda Aracely López-Alava¹ 

¹Facultad de Ingeniería Agrícola, Escuela Superior Politécnica Agropecuaria de Manabí. (ESPAM MFL). Campus Politécnico El Limón, km 2,7 vía Calceta - Morro - El Limón Sector La Pastora. Manabí, Ecuador

²Instituto Nacional de Ciencias Agrícolas (INCA), carretera San José-Tapaste, km 3½, Gaveta Postal 1, San José de las Lajas, Mayabeque, Cuba. CP 32 700

³Facultad Ciencias Agropecuarias, Universidad Laica Eloy Alfaro de Manabí, vía San Mateo, km 11/2 Manta-Ecuador

ABSTRACT

One of the most important premise to arise the suitablemanagement of soils in a region is the study of the distribution and characteristics of soils. For this reason, the main objective in this paper was to elaborate a soil map in scale 1:25 000 for the Carrizal-Chone System (7 233 ha) in Manabí, Ecuador. At the same time to know, the chemical, physical and morphological soil characteristics, based on 145 soil profiles that were taking in different soil separated in the map. Among the results is the diagnosis and classification of four Referential Soil Groups, Fluvisols (53 % de of the total area), Feozems (29 %), Cambisols (14 %) and Gleysols (4 % only), by the World Reference Base soil classification system. In this paper are included the study of Soil Units in each Referential Soil Group. Is determined that the natural soil formation in this region is Feozem and Fluvisol, the Cambisol appears because the degradation of the cambicFeozem for the cultivation during many years.In the results are present also, the analytical data of the Referential Soil Groups studied.

Key words: World Reference Base; Fluvisol; Feozems; Cambisol; Gleysol

INTRODUCTION

Food production is becoming increasingly difficult in the world, problems such as climate change, desertification and above all the degradation of soils influence this task worldwide, bringing as consequence that Food Security becomes today one of the largest concerns at the government level.

To achieve food Security, it is necessary to take into account the situation of natural, human and infrastructure resources available. Within the natural resources the knowledge of the soils, their properties and diagnosis of the change of the same by the anthropogenic influence, is essential, reason why it is necessary to carry out studies in this regard.

According to studies carried out, it is suggested that soils are essential to achieve food security and nutrition and have the potential to help mitigate the negative effects of climate change ¹, in addition that the pressure on soil resources is reaching limits critics

The soil resource is the most important pillar to face the challenge of food security, since about 95 % of food is produced directly or indirectly in soils ². On the other hand, it is of vital importance for biodiversity, as it is one of nature's most complex ecosystems and one of the most diverse habitats on the planet, as it houses an infinity of organisms that interact with each other and contribute to the cycles global that make life possible. It is estimated that a quarter of the biodiversity of our planet is found in soils ³.

In Manabí province, Ecuador, for the Carrizal and Chone rivers basin, there are few edaphological studies, including about 10 soil pits studied in the mountain region of the Membrillo Parish, whose results are published in scientific journals ^4,5 and about 14 soil pits that were the result of a Master's thesis, Vera 2013 ⁶ in the 60 ha study, of the Campus of the Superior Polytechnic Agricultural School of Manabí (ESPAM).

Taking into account the above in the Carrizal - Chone river plain system, a project is underway for the first time to study the soils in an area of 7 233 ha. The main objective of this project is to prepare a 1:25 000 scale soil map and perform their morphological, chemical and physical characterization in order to determine their current status, after tens of years that have been cultivated.

The preparation of large-scale maps is the main tool to know the current properties of its soils ⁷. On the basis of the map and the profiles studied, its characteristics and their agro-productive status are determined, culminating in a classification in classes of use capacities.

MATERIALS AND METHODS

The study was conducted in an area that has a cultivable area of 7233 ha, with crops such as corn, beans, cocoa, plantain and grassland for livestock. The cartographic base were orthophotos taken from Google and cartographic sheets. The geographical genetic method for the selection of points with augers and profile taking was followed, it is based on the variations of the soils according to their formation factors (relief, source material, climate, vegetation and weather) and by the activity of man; which constitutes the basis of the classification of soils based on genetic principles ⁸.

After separating the different soil contours, for their characterization the 145 profiles were taken, following the mapping standards for the 1:25 000 scale of 1 profile every 50 ha. The following properties were determined for each profile:

• Description of soil profiles, following the Manual of Description of Soil Profiles prepared by Vera and collaborators ⁹; adapted to the characteristics of the soils of the study region.

• pH by potentiometry in H₂O, in soil: water 1: 2 ratio.

• Total soluble salts by conductimetry.

• Organic matter by the method of Walkley & Black (1934) ¹⁰

• Organic carbon by dividing the percentage of organic matter by a factor (1,724).

• Volume density by the cylinder method (100 cc volume) in the field.

• Soil color by the Munsell Table, (Munsell Soil Color Chart, 2009) ¹¹.

• The mechanical composition by the Bouyoucos method using sodium pyrophosphate for the extraction of organic matter and breaking the soil microaggregates and sodium hexametaphosphate as dispersant.

• The textural class of the soil according to the percentages of the mechanical particles, using the textural triangle.

• Exchangeable bases (Ca, Mg and K) by extraction with normal ammonium acetate pH 7.

• Match assimilable by Olsen.

• Assimilable potassium calculated from the exchangeable K content.

• Organic carbon reserves (in tons of carbon per hectare) of the 0-20 cm layer of each of the profiles studied by the international formula:

$RCO = DV x CO x Layer Depth$

where:

• RCO: organic carbon reserves in tons of carbon per hectare

• Dv: volume density in Mg m^-3

Depth of the layer, in this case 20 cm from the top of the shale (soil profile).

The soil classification system that was applied is the World Reference Base (WRB), version 2014 ¹².

The soil classification system of the World Reference Base was recently applied in the Soil Atlas of Latin America ¹³ and has two classification units; The Soil Reference Group (GRS) and the Soil Unit (US) which is the GRS with qualifiers according to their properties.

RESULTS AND DISCUSSION

Natural conditions of the region

The study region is located 50 km from the Portoviejo city, capital of Manabí province, involving territory of the cantons Bolívar, Tosagua, Junín and Chone, covering an area of 13 268 hectares, of which 7233 hectares are studied of arable area. The project area is located between the geographic coordinates 0^o35´ and 0^o´55´ South latitude and 80^o 20´ West longitude and between the 2 and 45 m a.s.l.

The topography of the area has mostly slopes between 0 and 2 %, flat or almost flat relief and between 2 and 6 % slope, gently wavy relief.

Climate characteristics

According to the weather stations that exist in Chone and Tosagua (La Estancilla), for a period of 30 years and the one located in Calceta (ESPAM MFL), 21 years old, the cantons involved in the area present the annual average data shown in Table 1.

Table 1 Some climatic characteristics of the study region 

Cantons	Altitude m a.s.l.	Medium temperature in ^oC	Precipitation(mm year^-1)	Relative humidity Annual mean (%)
Chone	40	25.9	1228.6	90.0
Bolívar	10	25.0	952.0	80.0
Tosagua	45	25.1	825.4	79.0
Junín	15	24.0	1200	77.0

According to data from Meteorological Stations of La Estancilla and Chone of 30 years and of Calceta of 21 years

The climatic factor has variations, if analyzed from Membrillo rural parish of the Bolívar canton (located to the east in the premountain region) where they fall 1600-1800 mm per year, passing through Calceta (Bolívar), until Tosagua there is a facial distribution of the climate, from tropical humid in Membrillo, through a subhumid tropical climate in Calceta and to a tropical dry in Tosagua.

The climatic variations presented are of great importance because, according to this, the initial natural vegetation that existed in these regions behaves, which were: broadleaf forests in Membrillo, deciduous forest in the area of Calceta with mesophilic trees and dry forest with microphilic trees and thorny bushes towards Tosagua.

These differences are important for the biological cycle of substances, which is much greater in Quince, intermediate in Calceta (Bolívar) and lower in Tosagua. Depending on the intensity of the biological cycle of the substances, they will be the contributions in organic matter to the soil and the degree of humification that may occur. Thus, at the heights of the Membrillo Parish, it has been possible to find soil profiles under primary and secondary forest that reach about 100 t C ha^-1 in the thickness of 0-30 cm of the upper layer of the soil profile ⁴.

The source material throughout this plain is formed from the southeast and north of Calceta to La Estancilla, as a result of the influence of the Carrizal and Canuto rivers of river sediments (alluvial). Towards Tosagua, these rivers deviate from the region and there is some alluvial influence, but with deluvial influence of the geological formation that occurs in the heights of Tosagua-Bachillero called Onzole. These heights were formed before the alluvial plain and the deludes influence decisively, in the characteristics of the soils

The Onzole formation is described as a geological formation of the Upper Miocene formed by terrigenic material and the shales apparently developed under flysch conditions; which are low-bottom sedimentary formations, so shales usually have a relatively high sodium content.

The time of formation of the soils is relatively young, since they are formed by alluvial and alluvial-delluvial materials of the Quaternary. Even in them the sedimentation of texturally differentiated materials is observed (of frank texture, sand or clay loam).

In these conditions, the main soils that form are Feozems (Mollisols) and Fluvisols (Fluvents) and in some low parts, Gleyols may occur, although not very frequently.

Cambisols (Inceptisols) also appear, but they are presented not as a natural formation but by degradation of Feozems due to the influence of continued cultivation for more than 50 years, due to the action of man in agricultural production.

In this sense, it should be considered that this entire area was influenced by the activity of man by agriculture, both for cotton crops (in the driest area towards Tosagua), and for cocoa, bananas, corn and rice. In addition, it should be borne in mind that rice cultivation is one of the fastest degrading the soil ^14,15. Therefore, in many cases the initial formation of the Feozems has been transformed due to the mineralization of the organic matter by the crop, losing the dark color that characterizes them (molic horizon) becoming Cambisol in the case that they are Cambrian Feozems or Fluvisols in the case that they are fluovic Feozems. Losses of organic carbon in ecosystems due to anthropic action have been widely studied in recent years, as highlighted by various investigations ^16-19.

With the field trips and taking of points with augers and the taking of the profiles, the soil map is conformed and the presence of four Referential Soil Groups and 16 Soil Units is confirmed. (Figure 1).

Figure 1 Soil map of the area of influence of the Carrizal-Chone system 

In Table 2 is shown area distribution that GRS and US occupy.

Table 2 Distribution and area that occupy the different Referencial Groups and the Soil Units of Carrizal-Chone system, Manabí, Ecuador 

Soil referencial group	Area in ha	Soil unit	Area in ha	% of GRS
Feozems	2107.6(29 % of the total area)	Feozem fluvic	1098.5	52
		Feozem fluvic. cambic	848.2	40
		Feozem fluvic. gleyic	160.9	8
Fluvisols	3787.8(53 % of the total area)	Fluvisol eutric	2506.5	66
		Fluvisol eutric. ocric	792.9	21
		Fluvisol eutric. protovertic	192.6	5
		Fluvisol gleyic. eutric	21.1	1
		Fluvisol gleyic. eutric. ocric	191.9	5
		Fluvisol gleyic. eutric. protovertic	82.8	3
Cambisols	1036.9(14 % of the total area)	Cambisol fluvic. eutric	42.1	4
		Cambisol fluvic. vertic. eutric	261.8	25
		Cambisol fluvic. vértico. eutric. ocric	139.2	13
		Cambisol fluvic. gleyic. eutric	31.2	3
		Cambisol fluvic. gleyic. vertic. eutric	234.6	23
		Cambisol fluvic. estagnic. vértico. eutric	328.0	32
Gleysols	301.4(4 % of the total area)	Gleysol fluvic. eutric	301.4	100
TOTAL	7233.7		7233.7	100

Soil characteristics

For the characterization of soils it is very important to study the profiles due to the classification adopted, World Reference Base ¹². The morphology of the profiles is necessary, since this classification is based on the genesis of the soils and on horizons and diagnostic characteristics. This is very important for any soil classification system that is based on horizons and diagnostic characteristics in relation to the genesis of soils, such as the classification of soils of Russia ²⁰ and that of Cuba ⁽⁸; Therefore, the following has been expressed in recent studies, in recent soil classification systems, based on horizons and their diagnostic characteristics in relation to soil genesis, the priority of morphological studies is obvious , while soil formation factors and analytical data, are weakly included in soil identification ²¹.

According to the classification adopted in this work, of the World Reference Base, version 2014 ¹², Fluvisols and Feozems are diagnosed by:

Feozems

They are dark colored soils, comprising an extension of 2107.6 ha (29 % of the total). These soils do not have the characteristics of Fluvisols and are diagnosed by having a surface mollic horizon, which is present when the soil has a good structure; they are usually nuciform and granular or of subangular blocks that crumble into nuciform and granular, dark color with value and dry chroma not greater than 5 and wet not greater than 2.5 and also a thickness of at least 18 cm and a degree of saturation greater than 50 %, therefore all are Eutric ones which is not among the GRS qualifiers.

The data of a Feozem soil are presented in Table 3, 4 and 55.

Table 3 Mechanical composition and soil texture of the Feozems of the Carrizal-Chone System, Manabí, Ecuador 

Horizons	Depth cm	Sand%	Slime%	Clay%	Texture
IA	0-70	31.20	8.00	60.80	clay
IIC	70-110	77.60	19.20	3.20	sand-loam
IIIC	110-150	40.00	44.00	16.00	Sand-frank

Table 4 Some chemical properties of the Feozems soil of the Carrizal-Chone System, Manabí, Ecuador 

Horizons	Depthcm	pHH2O	M.O.(%)	CE dS/m
IA	0-70	5.93	2.3	0.223
IIC	70-110	6.27	0.5	0.001
IIIC	110-150	6.44	1.5	0.002

Table 5 Content in organic matter and reserves of CO from soil of Feozems of Carrizal-Chone system, Manabí, Ecuador 

Horizons	Depthcm	MO%	C%	DvMg m^3	RCOMg ha^-1	RCO Mg ha^-10-30 0-50 0-100
IA	0-70	2.3	1.33	1.14	106.46	46 76 118
IIC	70-110	0.5	0.29	1.24	14.38
IIIC	110-150	1.5	0.87	1.29	44.89

The GRS of the Feozems, presents the following Soil Units (the Soil Unit is formed by the GRS with the qualifiers or properties that they may have). The following Soil Units are presented on the soil map (Figure 1):

Feozem fluvic

This Feozem is characterized by having a mollic A profile, generally with a frank texture, on mollic materials with a sandy texture; that is to say, it is a profile of type A-C. They occupy an area of 1098.5 ha; 52 % of the Feozems area.

The fluvial material is of river, marine or lake origin and is identified by the stratification of mineral particles, or the irregular distribution of organic matter or both by profile, in the first 50 cm of the upper soil thickness.

Cambic fluvic Feozem

It is a Feozem soil also formed of fluvic materials, but with a Cambic B horizon. It is a soil that has a mollic A horizon, with a Cambic B, formed of river materials. It has an area of 848 hectares (40 % of the Feozems area).

The cambic qualifier is when the Feozem has a horizon B; that is, the profile is not A-C; but A-B-C.

Gleyic fluvic Feozem

Feozem formed of fluvial materials, but which has a presence of gleyic properties below 50 m deep, often with a water table present 100-120 cm deep. Within the GRS it is the most bad drainage, and has an extension of 161 ha; 8 % of the Fluvisols area.

The gleyic properties correspond to the gleyzation process:

1. 90 percent or more reductimorphic colors comprising white to black, or bluish to greenish, or

2. 5 percent or more mottled redoximorphic colors (yellow, red, and gray).

Fluvisols

They are soils formed by river sediments, which are diagnosed by having materials differentiated by mechanical particles (sand, silt and clay) or by presenting differences in organic matter content at a depth of less than 25 cm measured from the surface. They are AC profile without a mollic A horizon, nor a cambic B horizon. They have an area of 3787.7 hectares; which represents 53 % of the total. The characteristics of a Fluvisol profile are presented in Tables 6, Tables 7 and Tables 8.

Table 6 Mechanical composition and soil texture of the Fluvisol of the Carrizal-Chone System, Manabí, Ecuador 

Horizons	Depth cm	Sand%	Slime%	Clay%	Texture
IA	0-40	41.60	36.00	22.40	frank
IIC11	40-68	68.00	28.00	4.00	sandy loam
IIC12	68-108	68.80	28.00	3.20	sandy loam
IIIC	108-150	52.00	34.40	13.60	frank

Table 7 Some chemical properties of the Fluvisol soil of the Carrizal-Chone System, Manabí, Ecuador 

Horizons	Depthcm	pHH2O	M.O.(%)	P2O5AssimMg 100 g^-1	K2OAssimMg 100 g^-1	Ca Mg K Na Sum Cmol (+) kg^-1	CE Ds m^-1
IA	0-40	6.98	2.1	10.8	45.4	16.0 5.4 0.97 Nd 22.37	0.04
IIC11	40-68	7.57	0.5	5.3	35.1	16.0 5.3 0.75 Nd 22.05	0.05
IIC12	68-108	6.98	0.2	4.1	26.7	17.0 4.7 0.57 Nd 22.27	0.08
IIIC	108-150	6.79	0.5	4.1	27.1	17.0 4.9 0.58 Nd 22.48	0.11

Table 8 Content in organic matter and CO reserves from Fluvisol soil of Carrizal-Chone system, Manabí, Ecuador 

Horizon	Depthcm	MO%	C%	DvMg m^3	RCOMg ha^-1	RCO Mg ha^-10-30 0-50 0-100
IA	0-40	2.1	1.22	1.38	67.24	50 71 82
IIC11	40-68	0.5	0.29	1.19	9.66
IIC12	68-108	0.2	0.12	1.32	6.13
IIIC	108-150	0.5	0.29	1.03	12.55

The soil Units present are the following:

Eutric fluvisol

They are Fuvisols that have more than 50 % base saturation at a thickness of 1 meter, measured from the surface. The area it occupies is 2506 hectares; 66 % of the Fluvisols. The éutrico character is given when the soil has a degree of saturation by bases of 50 % or more.

Eutric and ocric fluvisol

Fluvisols that have more than 50 base saturation, but have a very low organic matter content (equal to or less than 1 %). They have an extension of 793 ha, 21 % of the Fluvisols. The qualifier is placed when the soil has a mineral surface horizon that is ≥ 10 cm thick, with ≥ 0.2 and <0.6 % organic carbon (on average). Actually these values correspond to equal or less than 1% of organic matter.

Eutric and protovertic fluvisol

These are eutronic fluvisols that have thick aggregates at the top of the profile, they are an initial stage of formation of Vertisols from the Fluvisols. They are clayey and with poor drainage inside the Fluvisols. They have an extension of 193 ha; 5 % only of Fluvisols. The qualifier proto-desert in the Fluvisols is set when the soil has a horizon that has the same properties as the vertic horizon but has very few slickensides or is absent and the prismatic blocks are equal to or less than 15 cm in size.

Fluvisol gleyic and eutric

This is eutrophic Fluvisol that has glyphic properties below 50 cm, usually with a water table between 80 and 120 cm deep measured from the surface. It has an area of 21 hectares; only 1 % of the Fluvisol area.

Fluvisol gleyic, eutric and ocric

It is a gleyic and eutric Fluvisol, but it has an organic matter content on horizon A, which most often corresponds to a content equal to or less than 1 %, this Soil Unit within the study area has an extension of 191, 9 hectares. Profile 97 is representative of this soil.

Fluvisol gleyic, eutric and protovertic

They are Fluvisols that have even worse drainage than the Gleyic Fluvisols and the Protovertic ones, since they combine the presence of a water table around the depth meter and also clay texture with thick aggregates, with a large and medium block structure on the surface It has an extension of only 83 ha.

Cambisols

Their formation is not natural within the study region, they are formed by the degradation of the Cambic Feozems. For this reason they are lighter colored soils than the Feozems and presence of a cambic B horizon. In Tables 9, 10 and 11, there are the data that characterize this GRS.

Table 9 Mechanical composition and soil texture of Cambisol from the Carrizal-Chone System, Manabí, Ecuador 

Horizons	Depthcm	Sand%	Slime%	Clay%	Texture
IA	0-32	44.00	45.60	10.40	frank
IB	32-68	42.00	47.60	10.40	frank
IIC11	68-100	45.60	49.60	4.80	sandy loam
IIC12	100-130	46.40	49.60	4.00	sandy loam

Table 10 Some chemical properties of the Cambisol soil of the Carrizal-Chone System, Manabí, Ecuador 

Horizons	Depthcm	pHH2O	M.O.(%)	CE dS/m
IA	0-32	6.90	2.7	0.278
IB	32-68	6.68	0.5	0.097
IIC11	68-100	6.32	0.2	0.334
IIC12	100-130	6.43	0.5	0.115

Table 11 Organic matter content and CO reserves of the Cambisol soil of the Carrizal-Chone System, Manabí, Ecuador 

Horizon	Depthcm	MO%	CO%	DvMg m^3	RCOMg ha^-1	RCO Mg ha^-10-30 0-50 0-100
IA	0-32	2.7	1.57	1.28	64.15	60 71 82
IB	32-68	0.5	0.29	1.28	13.36
IIC11	68-100	0.2	0.12	1.22	4.53
IIC12	100-130	0.5	0.29	1.23	10.70

The Soil Units presented are very varied, among them we have:

Fluvic and eutric Cambisol

They are Cambisols that have fluvial materials and more than 50 % base saturation up to one meter of depth measured from the surface. It has an extension of only 42 ha.

Fluvic, vertical, and eutric Cambisol

This Unit of Soil is classified when the fluvial Cambisols soils have vertic characteristics and also have more than 50 % base saturation. They occupy an area of 262 ha.

Fluvic, vertic, eutric and ocric Cambisol

It is the soil of the previous US, but it has a content equal to or less than 1 % of organic matter. It has an extension of 139 ha.

Fluvic, gleyic, vertic and eutric Cambisol

Cambisols result in worse drainage within the Soil Reference Group, it is formed of fluvial materials, has 50 % or more base saturation, but has vertic and glyceic properties, usually with a water table between 1-1.20 depth meter They have an extension of 235 ha.

Fluvic, gleyic and eutric Cambisol

They are Cambisols that also have glyphic properties, therefore with poor drainage, but without the vertic properties. They comprise an extension of 31 ha only.

Stagnic, fluvic, vertical and eutric Cambisol

They are stagnic, fluvic and eutric Cambisols of clayey texture, which have a thick structure in the form of prismatic aggregates that can be up to 15-20 cm in size, usually in the first 50 m of the upper part of the profile. Pressure cutanes or slickensides are absent or very small, so that the soil can be classified as Vertisol. They have an extension of 328 ha.

Gleysols

In addition to the previous GRS, in some depressive parts a water table can develop, which causes oxidation-reduction phenomena according to the oscillation of the mantle in relation to the periods of rain and drought, giving rise to the soil formation process called gleyzation. When this mantle is at a depth of 50 cm or closer to the soil surface, the soil is classified as Gleysol. Only the fluvic and eutric Gleysol is separated from the soil map, which results in a Gleysol that has a base saturation percentage equal to or greater than 50 % and formed from fluvial materials. It occupies an area of 300 ha.

Tables 12, Tables 13 and Tables 14 show the characteristics of a profile of this GRS that has a water freactic 40 cm from the ground surface

Table 12 Mechanical composition and soil texture of Gleysol from the Carrizal-Chone System, Manabí, Ecuador 

Horizons	Depthcm.	Sand%	Slime%	Clay%	Texture
A	0-40	20.00	46.40	33.60	franko-limo-arcillosa

Table 13 Some chemical properties of the Gleysol soil of the Carrizal-Chone System, Manabí, Ecuador 

Horizon	Depth cm.	pHH2O	M.O (%)	CE dS/m
A	0-40	7.58	2.3	0.08

Table 14 Organic matter content and CO reserves of the Gleysol soil of the Carrizal-Chone System, Manabí, Ecuador 

Horizon	Depthcm	M.O.%	C%	DvMg/m^3	RCOMg/ha	RCO Mg ha^-10-30 0-50 0-100
A	0-40	2.3	1.33	0.94	50.16	38 63 125

With the completion of the elaboration of the soil map, valuable information is obtained on the soils, the distribution laws, the surface they occupy, their limiting factors, the response to their characteristics, including the anthropogenic factor, which is a current aspect. Based on these results, important recommendations for soil management are developed.

However, considering the current problem of degradation of soil properties, its possible improvement through the application of organic enhancers and biofertilizers, with or without fertilizers, which allow obtaining good yields but improving or at least preventing soil deterioration; it is necessary, as mentioned above, to create Sectors and Reference Plots.

Sectors and Reference Plots are technologies that combine the study of the characteristics and evolution of soil properties and their management, based on advanced techniques such as the implementation of Geographic Information Systems ²².

These technologies are known from studies conducted by French edaphologists ^23,24 applied in relatively shallow areas (less than 1000 ha) and that represent a small unit of a representative landscape (geographic region), based on a Large-scale soil map (1:25,000; 1:50,000), to search for sustainable management technologies.

In the chosen sector, it is necessary to carry out a topographic survey and this plan is taken as the basis for mapping soils on a detailed scale (1:10 000 or more detailed, in relation to the selected area).

The cartographic survey of the soils must be done walking, with the help of a compass or a theodolite, with fixed transept, separated from each other according to the selected scale. Surveys are carried out with the soil auger and with the implementation of previously prepared forms, the soils are classified and the agroproductive limiting factors are predetermined, as well as the characteristics of the area, climate, relief, vegetation, etc. are recorded.

For the Carrizal-Chone System, two Reference Sectors (SR) and a Reference Plot (PR) are selected. The SR must be one for the area of Calceta and another entity Estancilla and Tosagua; the PR must be established in the part between Calceta and La Estancilla.

The contours of separate soils in the different SRs, serve as a basis to look for sustainable management technologies, for degraded soils, mainly Cambisols, with the test of organic and biological improvers, with and without mineral fertilizers.

With the corresponding monitoring of crop yields and soil properties, sustainable management technologies will come out for this region for degraded soils and better soils.

Furthermore, on the basis of the results obtained in the carbon stock map, the carbon gain or loss in t C ha^-1 year^-1 begins to be established through soil monitoring. For example, how much contribute per year in carbon reserves does the teak grove or the combination of grove with guava and coffee, plantation of cocoa, bananas. This always taking into account the climatic conditions and the soil.

These results really exist today in developed countries of temperate climate, which are those that have resources to carry out these investigations. They would be the first obtained in Manabí and possibly throughout Ecuador. The results obtained will serve to propose a carbon sequestration and carbon sequestration policy in the region, which can serve the regional and provincial authorities for climate change mitigation policy.

CONCLUSIONS

• The study of the cartography and classification of the soils of the Carrizal-Chone System is carried out, with the preparation of the soil map. In addition, it is confirmed that there are four Reference Groups (Feozems, Fluvisols, Cambisols and Gleysols) with 16 Soil Units.

• The most extensive soil is Fluvisol, while the best agro-productive characteristics are Feozems.

• Cambisol is a soil formed by degradation of Feozems.

• On the basis of the work carried out, the establishment of two Reference Sectors and a Reference Plot is selected, for the search of sustainable soil management with food production

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Received: November 29, 2017; Accepted: January 31, 2019

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