The Global Assessment of HumanInduced Soil Degradation (GLASOD) methodology provide insight in the assessmentof soil degradation process. It is expert based assessment to develop map onsoil degradation is the GLASOD map, which used indicators of soil degradationto assess the cause, severity, extent and trend in soil degradation through aquestionnaire (Oldeman et al., 1990).
The experimental methodology frequentlyused in soil degradation assessment based on soil quality parameters (Swanepoel et al.,2014; Nezomba et al., 2015). The soil quality conceptinvolves measuring a set of soil properties which influenced by the soil managementpractices (Karlen et al.,1997).Participatory approaches which based on the farmers’ local knowledge such asperceptions of local peoples on the soil degradation processes and propertiesalso used to assess soil degradation (Lima et al.
, 2011). ParticipatoryRural Appraisal (PRA) and household surveys using a house hold questionnairewere also used as the research tools to assess soil degradation with theintegration of scientific evident (Malley et al., 2006).2.
1.3. Expert-based laboratory assessment of soil quality Identification of soil qualityindicatorsIdentification of appropriatesoil quality indicators is a first step in the assessment and evaluation of thecontribution of soils in the delivery of ecosystem goods and services (Robinsonet al., 2012). Thus, the need is to develop indicators for on-site assessmentof soil quality by farmers, researchers and extension personnel (Doran , 1994).Soil structure is considered a key physical soil factor in thefunctioning of soil, as its ability to support plant and animal life,control other soil functions (porosity,water and air movement and retention in soil) and moderate environmentalquality (Bronick& Lal, 2005).
The soil structure assessment is dividedin to direct and indirect methods. Indirect characterization of soil structureincludes its estimation from soil properties such as infiltration rate, hydraulicconductivity, soil aggregation, bulkdensity (BD) ), available water content and pore-size distribution (Pagliaiet al., 2004). Direct methods involve observation ofmorphological structural features by microscopy, analysis of images like city scans for quantification of spatial poresarrangement, measuring soil aggregation and aggregate stability underlaboratory conditions, and visual field description of structural form (Pagliaiet al., 2004). Thesoil chemical properties (indicators of soil quality) are cation exchangecapacity (CEC) (García-Ruiz et al.
, 2008), available K, soil organic matter (SOM)(Qi et al., 2009), Total organic carbon (Rojaset al., 2016), soil pH (Zornoza et al.
, 2007) andtotal nitrogen content are frequently used. Theseproperties are easy to measure in the laboratory, avoiding expensive andtime-consuming methods required to analyses other rather more complexbiochemical properties, such as microbial biomass or enzyme activity,among others. Besides, SOM is the most used indicator and important in soilquality assessment (Zornoza et al., 2015).
Evaluation of soilquality indicatorsThe evaluation and identification of soil variablesthat use some level of control or impact over numerous soil properties can providethe best return on management in a soil monitoring program. Multivariate analysis is use to evaluate the relationshipsbetween indicators, detecting main scopes of indicators and targeting on linearrelationships between variables (Husson et al., 2011).It is used to determine minimum indicator set (MDS) through principal componentanalysis (PCA) for different soils indicators (Qi et al., 2009).