Land management and its impact on the fertility status of southern Al Jabal al Akhdar, Libya

INTRODUCTION

In drylands, characterized by severe climatic conditions and water scarcity, it is especially difficult to earn benefits from the land without degrading resources. Disturbance of dryland ecosystems can quickly lead to severe land degradation and thus desertification. Desertification is defined as ‘‘land degradation in arid, semi-arid, and dry subsumed areas resulting from various factors, including climatic fluctuations and human activities’’ (unccd, 2008). Combating desertification is complex and usually requires changing the very land management that contributed to desertification in the first place (wwap, 2012).

Attention to land management to increase production capacity is an important aspect, and the best production rate can be achieved when conditions and factors improve soil fertility. The quickest acceptable aspect of management is to address the problems of soil fertility that may result from poor management of these lands, such as incorrectly adding fertilizer or implementing service operations that exacerbate the loss of their conditions. Land assessment is an assessment of its effectiveness and performance when used for a particular purpose. The continuous increase in population requires an increase in world food production and the preservation of land resources from degradation to make their use sustainable (fao, 1985). The lack of sound management leading to land degradation can be observed and measured by indicators of decreasing soil fertility and reduced productive capacity (yousuf, 2017). Thus, some of the indicators used to assess land degradation can also be used to assess the adverse state of the land. In other words, the soil is the medium that reflects many changes in the appearance of the earth's surface and is a measure of land fertility (stocking and murnaghan, 2001). According to the above, it is possible to use indicators showing soil fertility because of its relative ease of measurement and its direct link to soil productivity reduction and management (stocking and murnaghan 2001). The assessment of the soil fertility conditions is carried out through field measurements as well as laboratory measurements to determine the extent to which the land can supply nutrients to the plant. Hence, the result is the realization of a fertility status while applying the management systems (bear, 1953).

The soil of dry and semi-dry territory as fragile and vulnerable will be a priority in pursuing management that increases its productive capacity or maintains its fertility. Ben mahmoud (1995) has shown that attention to managing the soil, reducing its loss through loss factors such as erosion, and improving its characteristics will contribute to improving its fertility. Protecting soil, especially those that are said to lose their testicles, such as aridisols, is considered a priority in pursuing sound management that contributes to maintaining their fertility. The libyan soil, which is capable of agricultural production if water is available, is only 10% and varies in characteristics from region to region as well as within region (alkhubuliu et al., 2014). Considering that aridisols are most prevalent in the territory of south al jabal alkhdar and are subject to rapid and alarming degradation, the most important causes of this accelerated degradation are unrivaled human activity such as overgrazing, tillage of marginal land, and inappropriate exploitation of a fragile and resource-limited environment (aburas, 2009).

Therefore, the management methods that have been adopted for the aridisols of south al jabal alkhdar and their effects on the adversarial state will be evaluated by measuring some of the field and laboratory indicators.

MATERIALS AND METHODS

The study area:

An assessment of the adversarial status of the study area was carried out along a longitude (°21.334581-°21.326403), latitude (°32.464413 – °32.453215), in which a comparison was established between the cultivated land against the bare land to achieve the study objectives, map (1):

Map (1). Map showing the location of the study area in the southern Al Jabal Al Akhdar, Libya

The climate of the study area, in general, is the Mediterranean climate, which is characterized by warm and rainy winters, and hot and dry summers, and the prevailing winds are from north to northwest in Winter, while northeast, and sometimes southern at summer. The data were obtained from the NASA website (NASA, 2021) issued by the Shahat weather station from1985 to 2019 as shown in Table (1).

The soil type was determined by a map prepared by Selkhoz Prom Express (1980). Two areas of the study (cultivated and bare) were identified for each of 29 ha. For cultivated areas, some management regulations were applied in 2004, such as contour tillage, protection against grazing, and human activities.

Fieldwork:

Primary selection of 10 profile points representing each profile point was identified in the Google Earth Map of the study area and determined with GPS value in study areas A (cultivated soil) as well as study area B (bare soil), Map (2). At the field scale, the profiles were carefully chosen based on the different physiographic landforms (Map 2) that existed in the study area in 2020. The selected profile points were selected from google earth maps and correction was applied if necessary and were excavated, the layers for each profile were identified, the morphological properties were determined according to a proposal of FAO (1990). The samples were then collected from each layer of the profile, air-dried, sieved with a 2 mm sieve diameter, and preserved for chemical and physical analysis.

Laboratory soil analysis:

Electrical conductivity (EC) of soil: water extract, 1:1 (w/v) was ‎measured using ‎a conductivity meter according to Jackson (1973).‎

Soil pH was determined in the 1:1, soil: water suspension using a pH meter (Jackson, 1973).‎

Organic carbon (OC) was determined using the modified Walkley-Blacks ‎titration method (Carter and Gregorich, 2008). The organic matter content ‎‎(OM) was calculated using the suitable ‎constant (‎1.724‎).‎

Total carbonates content: was estimated using the calcimeter and calculated as calcium carbonate ‎percentage according to Richards (1972).

Particle-size distribution (sand, silt, and clay %) was determined by the hydrometer method according to Carter and ‎Gregorich (2008).‎

The soil bulk density of each soil sample was measured using the soil core method according to the weight of soil and the ‎volume of packed cores (Evans et al., 1996).

Cation exchange capacity was determined using the method described by Gillman and Sumpter (1986).

Map (2).Map showing the locations of soil profiles in the southern Al Jabal Al Akhdar, Libya (scale 1:50000)

Available nitrogen in the soil was extracted using 0.5 N NaHCO₃ solution (pH 8.5) and was determined using spectrophotometer by Nessler's solution at a wavelength of 420 nm, extraction ratio 1:20 soil: NaHCO₃ (Carter and Gregorich, 2008)

Available phosphorus was extracted using 0.5 N NaHCO₃ solution (pH 8.5) and was determined using a spectrophotometer by ascorbic acid at a wavelength of 772 nm, extraction ratio 1:20 soil: NaHCO₃‎ (Carter and Gregorich, 2008)‎.

Available potassium in the soil was extracted using 0.5 N NaHCO₃ solution (pH 8.5) and was determined by a Flame photometer, extraction ratio 1:20 soil: NaHCO₃ (Carter and Gregorich, 2008)‎.

GIS maps

The following maps and programs were done:

-          Climatic information from NASA(2021).

-          Reports of inventory and classification of lands for the southern Al Jabal al Akhdar area from the Selkhoze Prom(1980).

-          ArcGIS 10.5 (Esri, 2016): The ArcGIS desktop 10.5 program was used through several steps, including converting the collected data into digital images by entering spatial data and converting it into digital maps, then processing and analyzing the data by the tools attached to the program by signing geographical coordinates, rearranging data and layer boundaries to calculate the total area and produce a map for each property.

Statistical analysis

All obtained data of the present study were statistically analyzed according to the design used by the Statistix (2019) computer software program and were tested by analysis of variance. The revised least significant difference test at 0.05 level of probability was used to compare the differences among the means of the various parameter combinations as illustrated by Duncan (1955) and Gomez and Gomez (1984).

           Table (1). Climatic parameter of the study area during the period of 1985-2019.

RESULTS AND DISCUSSION

Physiographic properties

The physiographic characterization of the cultivated and bare soil areas was illustrated in Tables (2 and 3).

The slop degree ranged between 2 and 6 for the cultivated area with shapes as flat and convex, while for bare soil area, the slope ranged between 1 and 6 with the shape of flat and convex. Soil profile depth ranged between 9 and 52 cm for cultivated, while for bare soil area ranged between 18 and 48 cm

Table (2). Profile locations and physiographic properties of cultivated soil area

Table (3). Profile locations and physiographic properties of bare soil area

Photo(1). Picture of the bare soil area           Photo (2). Picture of the cultivated soil area

Soil physical properties

The soil physical properties of the cultivated and bare soil areas were illustrated in Tables (4and 5).

For cultivated soil profiles (Table 6), the clay content ranged between 12.83 and 36.49% with an average of 26.91%, the silt content ranged between 15.81 and 39.38% with an average of 28.17%, while the sand content ranged between 33.70 and 57.96% with an average of 44.90%., in addition, soil bulk density ranged from 1.19 to 1.57 g/cm³ with an average of 1.40 g/cm³

Table (4). Some physical properties of cultivated soil profiles

For the bare soil profiles (Table 5), the clay content ranged between 10.13 and 33.61% with an average of 25.43%, the silt content ranged between 15.85 and 46.58% with an average of 28.19%, while the sand content ranged between 38.67 and 58.39% with an average of 46.07% and the soil bulk density was ranged from 1.31 to 1.57 g/cm³ with an average of 1.45 g/cm³. The relative decrease in bulk density in the cultivated soils could suggest the positive effect of plowing and contour farming on the semi-arid slopes south of Al-Jabal Alkhdar, while several studies on the Libyan Red Mediterranean soils showed the negative impact of overgrazing and unsustainable land uses on the physical soil properties and particularly bulk density (Aburas, 2015).

Table (5). Some physical properties of bare soil profiles

Soil chemical properties

Soil chemical properties of cultivated and bare soil areas were illustrated in Tables (6 and 7).

For cultivated soil profiles (Table 6), the electrical conductivity of soil paste extracts ranged between 0.51 and 2.50 dS/m with an average of 1.34 dS/m, the values of soil pH was ranged between 7.8 and 8.6 with an average of 8.11, while organic matter content (OM) ranged between 0.29 and 2.75% with an average of 1.25% and soil calcium carbonates were ranged between 11.28 to 37.0% with an average of 24.24%.

Table (6). Soil chemical properties of cultivated soil profiles

For bare soil profiles (Table 7), the electrical conductivity of soil paste extract ranged between 0.60 and 6.75 dS/m with an average of 1.67 dS/m, soil pH values were ranged between 7.8 and 8.8 with an average of 8.28, soil content of organic matter (OM) was ranged between 0.10 and 2.06% with an average of 0.83%, and soil calcium carbonates were ranged from 15.0 to 48.0% with an average of 32.39%. Soils under cultivation showed a relative decrease in soil PH which could indicate the positive effect of plant roots and organic material additions to the soils.

Table (7). Soil chemical properties of bare soil profiles

Cultivated soil has a higher value of OM than bare soil due to land management by the cultivation of plowed lines with broad-leaved forest trees (eucalyptus tereticornis) and (Pinus halepensis). The decomposition of dead leaves enriched the soil with organic matter. Contour plowing resulted in a decrease in calcium carbonates.

Soil fertility status

The soil fertility status of cultivated and bare soil areas was illustrated in Tables (8 and 9).

For the cultivated soil profiles (Table 8), the available soil nitrogen content (N) ranged from 4.80 to 16.28 mg/kg with an average of 9.02 mg/kg, while the available phosphorus content ranged between 2.09 and 10.87 mg/kg with an average of 5.78 mg/kg, and the available potassium content (K) ranged from 350 to 800 mg/kg with an average of 529.50 mg/kg. The CEC for the soils under cultivation were ranged between 8.6 and 31.50 meq/100 g soil with an average of 15.02 meq/100 g soil.

Table (8).Soil fertility status of cultivated soil profiles

For the bare soil profiles (Table 9), the available soil nitrogen content (N) ranged from 6.73 to 14.74 mg/kg with an average of 8.96 mg/kg, while the available phosphorus content ranged between 1.08 and 13.13 mg/kg with an average of 7.43 mg/kg, and the available potassium content (K) ranged from 150 to 950 mg/kg with an average of 417.82 mg/kg. The CEC for bare soils were ranged between 5.29 and 16.46 meq/100 g soil with an average of 8.89 meq/100 g soil.

Table (9). Soil fertility status of bare soil profiles

Both cultivated and bare soil profiles have poor N and P contents, the low N and P content of cultivated soils could be due to the more extraction that might take place by the trees cultivated in.  Both soils have a high level of available K, which may be due to the soil composition.  The management practices that have been applied on the cultivated soils, and the effect of decomposition of dead leaves from trees could have contributed to the relative increase of some nutrients in the soil. Under cultivation, the significant improvement in the CEC parameter in those semi-arid slopes could confirm the positive consequences of applying suitable and sustainable land practices.

The multiple linear regression between soil fertility status (N, P, and K) and some chemical properties (ECe, OM, CaCO_3, and CE) is illustrated in Table (11).The equation in the form of:

Where:

Y is the required property (N, P, and K)

a1, a2, a3, and a4 are the regression parameters

Table (10). Multiple linear regression between soil fertility status and some chemical properties

‘

The soil content of N, P, and K showed a highly significant correlation with ECe, OM, CaCO₃, and CEC parameters, which means that soil fertility status is highly dependent on chemical properties with R² ranging from 0.6785 to 0.9489.

GIS map of soil characters

The GIS maps of soil fertility parameters and some related chemical characters are illustrated in Maps (3 – 9).

Map (3). The distribution of available N in the cultivated and bare soils of the study area

Map (4). The distribution of available P in the cultivated and bare soils of the study area

Map (5). The distribution of available K in the cultivated and bare soils of the study area

Map (6). The distribution of OM in the cultivated and bare soils of the study area

                Map (7). The distribution of ECe in the cultivated and bare soils of the study area

Map (8). The distribution of CEC in the cultivated and bare soils of the study area.

Map (9). The distribution of CaCO₃ in the cultivated and bare soils of the study area

The area distribution of each soil character is illustrated in Tables (11 to 14) for bare and cultivated areas.

Both bare and cultivated soil profiles have a low content of available N, P, and K content. For bare soil, 83.89% of the total area has 4 to 12 mg/kg available N content, but for cultivated soil, 73.11% of the total area has 4 to 8 mg/kg available N content. The available K content has adequate values ranging between 350- 550 mg/kg representing 79.83 and 79.17% of the total area for bare and cultivated soil, respectively.  The available P content represents 73.20 and 94.17% of the total area in the range of 2 to 8 mg/kg for bare and cultivated soil, respectively.

Table (11).  Area distribution of soil fertility for the bare soil

Table (12). Area distribution of soil fertility for the cultivated soil

The organic matter content represents 69.8% in the range of 0.5 to 1.5 % OM content for bare soil, but for cultivated soil, it represents 80.62% in the range of 0.5 to 2.5 % OM. The total soluble salts (ECe)  has a high value of about 70% of the total area in the range of 2 to 3 dS/m for bare soil, but it distributed overall the area in the range of 1 to 5 dS/m for cultivated soil. The management of bare soil by cultivation decreased the ECe in all cultivated areas. The cation exchange capacity (CEC) represents 85% of the bare soil in the range of 8 to 10 meq/100g soil for bare soil, but it represents  96.87% of the cultivated soil in the range of 10 to 14 meq/100g soil. The CaCO₃ content in the range of 30 to 40% represents about 71% of bare soil, but it represents about 17.72% of cultivated soil. The distribution of soil characters indicated that the bare soil improved through the cultivation and the soil become more suitable for use.

Table (13). Area distribution of some chemical characters for the bare soil

Table (14). Area distribution of some chemical characters for the cultivated soil

Table (15).  Comparison between cultivated and bare soil for allstudied soil properties