Abstract
Few studies have comprehensively evaluated the effect of changing land use on the soil quality in Ecuadorian amazon region that subject to continued deforestation processes. This study evaluated the influence of different types of land use on soil quality using an integrated soil quality index (SQI) with minimum set of indicators, based on 140 soil samples from 7 land use types, in seven productive distinct landscapes in the Pastaza province, Ecuador. The land use type evaluated were: Chakra_A, Chakra_B, Chakra_C, Cattle_A, Cattle_B, Cattle_C and Forest. Land use type had significant effects on soil properties and thus on soil quality. Soil quality index was developed by using, AP, Zn, TOC, BD and LL; AP and Zn had highest weighting values (0.38), which indicated that these indicators contributed the most to final SQI. In general, the SQI decreased as soil depth increased and for each type of land use, in the surface layer (0-10cm) the uses of Chakra_A (0.46) and forest (0.44) showed the highest SQI, while for the second depth (10-30cm), Chakra_A (0.45) and Chakra_B (0.43) presented significantly higher SQIs than the other land uses. The applied SQI can be used to assess the effect of changes on land use on soil quality in other landscapes of the Ecuadorian Amazon Region.
Keywords: Land use, soil quality index, indicators, soil properties, Ecuadorian Amazon Region.
INTRODUCTION
Soils are an integral part of natural ecosystem and agroforestry systems, within which their physical and chemical composition shape the quality of ecosystem services (McBratney et al., 2014). Land use change is a global threat to soil quality and related ecosystem services, however, agroforestry systems (AFS) have been introduced as a sustainable alternative for soil reclamation and increasing land productivity (Nair et al., 2009; Shibu & Dollinger, 2019). Agroforestry system is defined as a dynamic and ecologic system of managing natural resources by integrating trees on arable land and pasture; which are diversified and permit the production of little exploitations leading to important social, economic and ecologic advantages (Shibu & Dollinger, 2019). In this context, several soil quality definitions have been proposed (Doran & Parkin, 1997; Karlen et al., 1997). One of the most widely used is defined as the capacity of a soil to function within ecosystem and land use boundaries, to sustain productivity, maintain environmental quality, and promote plant and animal health (Doran & Parkin, 1997; Karlen et al., 2003; Karlen et al., 2006). Soil quality is determined by extrinsic factors such as parent material, climate, topography and hydrology may influence potential values of soil properties to such an extent that it is impossible to establish universal target values, at least not in absolute terms (Bünemann et al., 2018; Carter et al., 1997; Shukla et al., 2006). Soil quality index (SQI) is often used to quantitatively gauge the effect crop management practice on overall soil health (Andrews et al., 2002; Bünemann et al., 2018). Therefore, an important component of soil quality assessment is the identification of a set of sensitive soil attributes that reflect a soil’s ability to function and can be used as indicators of soil quality (Cantú et al., 2007; de la Paz Jimenez et al., 2002; Doran & Parkin, 1997; Karlen et al., 1997; Viana et al., 2014).
Soil quality has suffered a remarkable degradation worldwide as a consequence of anthropogenic and natural disturbances (Peng et al., 2013; Pla, 2010; Zhang et al., 2019). The Ecuadorian Amazon Region is particularly susceptible to severe soil degradation due to its special geological conditions and fragile ecosystems (Bravo, Marín, et al., 2017; Custode & Sourdat, 1986; Espinosa et al., 2018; Nieto & Caicedo, 2012). In this region, large areas have been subjected to deforestation process and a change in land use towards agricultural and livestock systems that have greatly deteriorated its resources (soil, water, vegetation and biodiversity), affecting its productive potential and capacity (Bravo et al., 2015; Torres et al., 2019).This situation is magnified by the area’s characteristics with unfavourable soil chemical parameters coupled with harsh climatic conditions (abundant, high-intensity rainfall), an irregularly topographical agricultural landscape and high slopes (Espinosa et al., 2018).
Physical and chemical properties have been commonly used to characterise soil quality in areas that are subject to changes in land use (Cantú et al., 2007; Masto et al., 2008; Ngo-Mbogba et al., 2015; Vallejo-Quintero, 2013) and experience various states of restoration (Peng et al., 2013; Viana et al., 2014; Zhang et al., 2019). In the Argentinian Pampas, it was found that the soil quality index obtained by a minimum set of indicators was strongly influenced by soil organic carbon (SOC), which was the property most affected by land use change (Cantú et al., 2007). For soils in the Brazil’s central Amazon Region, subjected to several level of restoration, the most sensitive parameters to differentiate restored and degraded areas with respect to the reference soil (in a forest) were bulk density, total nitrogen, exchangeable potassium (K+) and available phosphorus (P), which were (≥ 0.70) (Viana et al., 2014). In the Ecuadorian Amazon Region, progress has been made in characterising soil quality based on morphological indicators (Bravo, Marín, et al., 2017) and factors associated with fertility, which has allowed for a comprehensive diagnosis of the state of the resource, as well as the influence of land use change (Bravo, Torres, et al., 2017). The results showed that the physical indicators of soil, measured as bulk density (BD), saturated hydraulic conductivity (Ksat), total porosity (TP) and aeration porosity (AP) in uses such as forest, agroforestry, livestock and chakra systems were strongly influenced by variation in organic matter content. Although the effect of change use land on soil quality has been studied in different countries (de Lima et al., 2008; Quintero, 2020; Viana et al., 2014; Zhang et al., 2019) few studies were conducted to evaluate the influence of different land use types in Ecuadorian amazon.
The objectives of this study were (1) to examine how land use types affect the physical and chemical properties of soil, (2) to establish a quality index based on a Minimum Data Set (MDS) to evaluate the effect of land use types on soil quality, and (3) to identify the factors that influenced soil quality. In this investigation, the quality of the soil physical and chemical properties was hypothesized to be directly affected by the change in land use.
  1. MATERIALS AND METHODS
  2. Study Area
The study was carried out in the Boayacu community, which belongs to the Teniente Hugo Ortiz parish. The parish measures 97 km2and is found in Pastaza canton, Ecuador (Figure 1). This area is characterised by a climate that is typical of an evergreen tropical rainforest (MAE, 2013), with an altitude ranging between 823 and 1086 metres above sea level. The predominant bioclimatic conditions vary between pluvial humid and hyper humid (MAE, 2013), with an average annual rainfall of 3481.7 mm, evapotranspiration of 150 mm, average temperatures of between 23.4 and 25.4°C and a relative humidity of 87%. The lowest precipitation occurs from January to April, whilst the highest occurs from May to July and the temperature varies all year around (Torres et al., 2019). The soils belong to the Andisols order (Soil Survey Staff, 2006), meaning they have a clay loam texture and a granular and blocky structure. They are generally acidic and have low natural fertility (low P, K+, Ca2+and Mg2+ contents) and have saturation percentages with bases<35%, high Fe and Al3+ contents (Nieto & Caicedo, 2012). With a plant cover of 90%, the biological resources of this region are abundant and the biodiversity quality is high (Estupiñan et al., 2007).
Figure 1 .