evaluation of gully erosion impact on soil quality

Evaluation of gully erosion impact on soil quality development in Fagoji, Kargo and Zai villages of Dutse, Jigawa State Nigeria

Usman, S., Mahmu, and Adinoyi, S.S.Department of Soil Science, Faculty of Agriculture, Federal University, Dutse, Jigawa State, Nigeria

ABSTRACT

The impact of gully erosion on soil quality development in three villages in Dutse was undertaken applying the USDA methodology to calculate the soil loss impact. The objective of the study was to evaluate the impact of gully erosion on soil quality development andto draw comparisons regardingits consequencesin the study sites for possible solutions. Concept of visual soil assessment (VSA) adapted by FAO was used for sites selection, and the physical conditions of the surface soil were classified based on texture, structure, vegetation, soil management practices, cropping systems, soil type and drainage function according to the guidelines in USDA-NRCS field manual. Four parameters namely: length, depth, width at top and width at bottom were measured to guide soil loss calculation and interpretation. The results showed that eroded soil

3 volumes of 11591.52 m recorded at Fagoji is reasonably high than the soil volumes recorded at Kargo 3 3(5907.33m ) and Zai (3342.72m ). Correlation analysis indicates that there is a positive relationship

between the soil conditions affected by gully erosion at Fagoji-Zai (0.774633*),and was negative between NS NSZai-Kargo (-0.34556 ) and Kargo-Fagoji (-0.49436 )accordingly. It is concluded that the affected sites

required immediate managements for the control of gully erosion. The state government should provide a sustainable gully rehabilitation scheme for a regular identification of the affected villages for inclusion in the management plan.

Keyword: Evaluation, Gully erosion, Correlation Analysis, Impact, Dutse.

A. T.

Nig. J. Soil & Env. Res. Vol. 17: 2018, 92 - 102@ Department of Soil Science,Faculty of Agriculture,Ahmadu Bello University, Zaria, Nigeria

Nigerian

Journal of Soil andEnvironmental Research

dry land area (Usman, 2007). However, if erosion processes occur, the descriptions of how intensive they are, depends largely on soil properties (e.g. texture, structure), topography and vegetation cover of the affect sites (Poesenet al., 2003). According to Maiangwa et al. (2007) erosion affects areas which have been subjected to bush burning, continuous cultivation and mining on hill side slopes in north-west zone of Nigeria. Under these circumstances, it is obvious that soil particles can be moved by raindrops or flowing water, and created erosion channels of varying size, shapes and length (Usman, 2012; Evans, 2013). Factors such as rainfall and runoff (commonly referred to water erosion processes) caused severe problems including filling of reservoirs, reduction in water quality and loss of surface soil cover (Kukal et al., 1991). These impacts are both on-site (at the place where the soil is detached) and off-site (wherever the eroded soil

INTRODUCTION

Soil erosion is the detachment of soil particles and their transport by wind, water, winnowing and mass-movement of surface soil particles (0-15 cm depth) (Usman, 2016).It is one of the surface land degradation processes that affect some parts of West African's dry land areas (Warren et al., 2001; Usman et al., 2017), and perhaps the most serious land mechanism in the tropics (Fortet al., 2010).It is the common forms of land degradation that affect significant part of dry land area in northern Nigeria (Usman, 2007). The energy required for soil particle detachment and its transport is provided by increase in precipitation intensities (Michael et al., 2005). This occurs as a result of complex factors such as poor vegetation cover, lack of surface soil management and poor environmental policy execution in the aspect government in northern Nigerian

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considerable soil damage under agricultural soil (Prasuhn et al., 2007). It accounts for the damage of several hectares of farmlands, annually (FAO, 1993). This willaffects almost all the components of soil including soil particles, organic matter, soil profile, drainage potentials, biomass and microorganisms (Lal, 1984; Usman et al., 2017). Nonetheless, available data on soil erosion in the affect sites is very limited, and the information is needed to improve the quality of soil and minimize the impact of gullies occurrence. Therefore, the aim of this study was to evaluate the impact of gully erosion in three (3) areas of Dutse namely: Kargo, Zai and Fagoji and measure the soil loss of the sites.

MATERIALS AND METHODS

Description of the study areaKargo, Zai and Fagoji are located in Dutse, the

capital headquarters of Jigawa State which is geographically located in the north-west zone of Nigeria bordering the states of Kano, Bauchi and Gombe (Figure 1).

The area is within the latitude 11°76N and longitude 9°34E in Nigeria (Figure 1). The average monthly temperature around the three study sites is

o obetween 30 C and 45 C with an annual average rainfall of 743 mm. The total population of citizenship has been estimated according to National Population Census of

gets deposited) (Poesen et al., 2003; Usman, 2007). It caused disruptions on many engineering projects because of increased sediment in the watershed areas of sub-Saharan Africa (Usman et al., 2017). It affects the surface soil quality, soil structural development, infrastructures such as houses, roads, buildings and vegetation areas (Hurtrez et. al., 2008). This might also directly affects the soil productivity by moving the topsoil (humus layer), resulting in a rearrangement of soil particles and soil profile development (Thomas, 1997; Usman et al., 2017).

Basically, water erosion has many dimensional forms, which include sheet, rill and gullies (Evans, 2013). The detachment and subsequent transport of soil particles by sheet erosion has direct repercussions in terms of reduced soil depth, diminishing fertility and declining crop productivity (García-Ruiz, 2010). However, gully is visually the most impressive of all types of soil erosion in northern Nigeria (Usman, 2007). It was considered as the well-defined water damaged channel (Van Dijk et al., 2005), and an extended drainage waterway that transmits ephemeral flow, steep side, steeply sloping or vertical head scarf with a width greater than 0.3 m and a depth greater than 0.6 m (Boix-Fayos et al., 2006). Gully erosion was reported to have a great impact on the faster depletion of soil moisture and ground water in arid and semiarid regions (Nyssen et al., 2007). It was reported to have caused severe damage to agricultural lands and construction sites such as bridges, roads, and settlements (Poesen et al., 2003).It was noted to have caused

Figure 1: Map of Dutse, Jigawa State Nigeria


erosion in the study area as typically revealed in Figure 2. Also, the physical conditions of the surface soil were classified based on texture, structure, vegetation, soil management practices, cropping systems, soil type and drainage function according to the guidelines in USDA-NRCS (2002) field manual.

Method used for the assessment of gully erosion impact

This study adapts the concept of direct measurement of soil erosion at in situ level introduced by United State Department of Agriculture (USDA, 2012). This measurement take place in the field to covers 6 different measurement transects or points on each advancing gully erosion of the study sites (Figure 3). Selection of these measurement points was base on random sampling within the affected area. It covers the width at lips (W ), width at bottom (W ), depth (d) and 1 2

length (L).The overall results were used to determine the

volume of soil loss at each study site. This was calculated base on the following formula (USDA, 2012):

Nigeria to be equal to 246,143 (NPCN-JG, 2007). Agricultural activities are the key sources of income for many people in the area. The common crops grown are pearl millet, groundnut, sorghum, cowpea, sesame and date palm. The vegetation is mainly trees such as Acacia, Baobab, Neem and Palm (Dabino). The geomorphologic information of the study sites includes the elevation, UTM and the 32p and geophysical features (Table 1).

Site selection Site selection is important primarily because of the

fact that this study is only limited to gully erosion, therefore, only areas where gully channels occurred were considered. This selection was made according to the basic principles of visual soil assessment (VSA) described by Food and Agricultural Organization of the United Nation (FAO, 2008). These principles entails that a given site can be assessed based on direct evaluations of soil properties (including soil erosion: rills or gullies), which are visible by the naked eye and which can be evaluated directly in the field. It also includes the depiction of physical impact of soil erosion in term of soil loss, forms and shapes of a given site (Soil Survey Staff, 2010). These notions were used to identify the affected sites of gully

94Usman,S., Mahmud, and Adinoyi, S.S.A. T.

Table 1: Elevation, GPS and coordinates at Kargo, Zai and Fagoji

Site Elevation from sea level (m)

No. of set light (GPS)

Coordinates Geographical Feature

Kargo 462 4 0540998N 1297341E Rocks, Mountains, Land Zai 349 5 0538534N 1295709E Rocks, Land Fagoji 353 3 0541062N 1297011E Rocks, Mountains, Land

Figure 2: Depiction of gully erosion in the study area: (a) Kargo, (b) Fagoji and (c) Zai

(W1 + W2V = Lx 2xd

L was measured in the field from all the 3 sites as constant i.e. 12 m with an interval of 2 m extent from one point to another.

Where: V = volume of soil lossL = length W = the average top width measured from the gully 1

channel and W = the average bottom width measured in the gully 2

channeld = the average depth of gully erosion

Soil sampling and statistical AnalysisSoil samples were collected from the study sites

using soil auger to evaluate the textural classes. At each site, 1 sample was collected (1+1+1 = 3) and packaged in a plastic container for lab analysis. The percentage textural particles (%sand, %silt and %clay) were recorded using USAD-NRCS (2002) guidelines for textural analysis. Also, soil structural classes were evaluated according to the guidelines of visual soil assessment explained in USDA-NRCS (2002) manual.

However, soil management practices, cropping systems, soil type and drainage functions were further evaluated according to the principles of visual soil assessment in the field. The data were subjected to simple statistical analysis using excel to compute the sums, average mean, minimum and maximum values of depths,

width at top and width at bottom between the three (3) study sites. Similarly, the same excel was used for correlation analysis to know how these 3 sites are associated with each other in terms of gulley erosion occurrence.

RESULTS

Tables 2: Presented the overall results of the measurement conducted at the gully site sat the same length of 2m.

Physically, there were high scores of depth at Zai and Fagoji and range between 1.1m and 1.8mwhich contrast the scores at Kargo (0.46m and 1.3m). Correspondingly, highest scores of width at the top were recorded at Fagoji varied between 16.6m and 22.3m compared to those recorded at Kargo between 11.5mand 17m andwere very low at Zai between 1.6 m and 3.1m. There were also lowest scores of bottom width at Zai which is between 2.2m and 5.2mcompared with those recorded at Fagoji between 15.7m and 21.5m and Kargo between 12m and 17.4m, accordingly. There-evaluation of these parameters were presented in Table 3, and provided information on sum, average, maximum and minimum scores at each site.

The sum of depth was high at Fagoji (8.2m) and Zai (8m) compared to Kargo (5.6m) and on average indicated

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Figure 3: Example of the field layout for measurement exercise of gully affected area


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1.1m) and Zai (1.5m and 1.1m) when compared to those recorded at Kargo (1.3m and 0.5m) respectively (Figure 4).

These accounted for the crest and base areas of the soil that was removed at each site and confirm that the

3volume of soil loss at Fagoji (11591.52 m ) is high 3 3compared to Kargo (5907.33m ) and Zai (3342.72m ),

accordingly (Table 4). This means that the dimensions of how gully erosion affected the soil quality in these three sites varied considerably in term of width, depth and soil loss, (Figure 5). This variation shows that the size of the area eroded at Fagoji is wider than the area eroded at Kargo followed by Zai site (Figure 5).

Table 4 shows the relationship between the measured parameters and the study sites and indicated that there is a positive relationship between the soil conditions affected by gully erosion at both Fagoji and Zai sites, respectively. However, this relationship was found to be negative between Zai-Kargo and Kargo-Fagoji, correspondingly. This disparity may be probably due to the condition of soil and vegetation of these sites, which were evaluated in terms of soil texture, soil structure and present/absent of plant biomass around each site (Table 5).This indicated that there were sandy-loam textures at Fagoji and Zai which seem to be different from sand texture recorded at Kargo. Similarly, soil structure was visualized as structure-less at Kargo but weak at both Fagoji and Zai. Vegetation cover was also visualized as poor at Zai and Fagoji but looked to be good at Kargo site. This could means that an enlargement of gully erosion dimension in terms of depth and widths at Kargo site may probably not affect the Zai site due to variation in vegetation cover (Table 5). Similarly, an increase of this erosion at Fagoji may vary from its increase at Kargo site. Conversely, there could be a possibility whereby an increase of gully erosion damage at Fagoji site may also differs from the Zai site. These hypotheses depend on

that the gully erosion impact at former sites (1.4m and 1.3m) is high than the later site (0.9m). This explained that the distance downward and the penetration of water movement that had removed the soil particles at Fagoji and Zai is more severe and hazardous than at Kargo site. This can be recognized further by reading the maximum and minimum scores recorded at both Fagoji (1.8m and

Table 3: Summary table of the measured field parameters at Kargo, Zai and Fagoji

Evaluation of parameters measured Kargo Zai Fagoji

1. Depth (m) Sum of depth 5.6 8.0 8.2 Average depth 0.9 1.3 1.4 Maximum depth 1.3 1.5 1.8 Minimum depth 0.5 1.1 1.1

2. Width at top (m) Sum of width at top 86.6 13.1 121.4 Average width at top 14.4 2.2 20.2 Maximum width at top 17 3.1 23.0 Minimum width at top 11.5 1.6 16.6

3.

Width at bottom (m) Sum of width at bottom

89.1

21.8

114.9

Average width at bottom

14.9

3.6

19.2

Maximum width at bottom

17.4

5.2

21.5

Minimum width at bottom

12

2.2

15.7

4.

Soil loss (m3)

Volume of soil loss

5907.33

3342.72

11591.52

Transects Depth (m) Width at top (m)

Width at bottom (m)

Kargo site 1 0.75 12.3 12.12 0.8 11.5 123 1.1 14.2 15.54 1.2 15.2 15.95 1.3 16.4 16.26 0.46 17 17.4Zai site 1 1.2 1.9 5.22 1.3 3.1 4.83 1.5 2.7 4.24 1.4 1.65 2.95 1.1 2.12 2.26 1.5 1.6 2.45Fagoji site 1 1.1 23 21.52 1.35 22.3 20.73 1.3 21.5 204 1.55 19.6 19.15 1.1 18.4 17.96 1.8 16.6 15.7

Table 2: Depth, width and length at Kargo, Zai and Fagoji sites

Usman,S., Mahmud, A. T. and Adinoyi, S.S.

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Figure 4: Depiction of depths and widths at Fagoji, Zai and Kargo Figure 5: Depiction of soil quality damage at Fagoji, Zai and Kargo

Table 4: Correlation analysis of the parameters in the study sites

Parameter (m) Zai-Kargo Fagoji-Zai Kargo-Fagoji

Depth -0.34556NS

0.774633* -0.49436NS

Width at top -0.63822NS

0.582979* -0.94417NS

Width at bottom

-0.90146NS

0.886242*

-0.87803NS

NS

signifies not significant at P = 5%

* signifies significant at P < 5%

Table 5:

Soil texture, structure and vegetation condition of the study sites

Site %Sand %Silt %Clay Textural class Soil structural class Vegetation

Kargo 76 4 20 Sand Structure-less Reasonable Zai 70 8 22 Sandy loam Weak Poor Fagoji 74 6 20 Sandy loam Weak Poor

Table 6: Average annual rainfall, soil management practices, cropping systems, soil type and drainage function at Fagoji, Kargo and Zai sites

1Local meteorological record(Ministry of Agriculture, Jigawa State)2 3Farmers experiences, Widely used by local farmers (Field assessment 2018)4According to USDA classification (USDA-NRCS, 2002)5Visual Soil Assessment (Field assessment 2018)

Site Average Annual Rainfall1

Soil management practices2

Cropping system3 Soil type4 Drainage function5

Fagoji 743mm –

845mm

Organic manure

Inorganic fertilizer Mono-cropping

Inter-cropping Entisols Absent

Kargo 743mm – 845mm Composting

Inorganic fertilizer Inter-cropping Entisols Absent

Zai

743mm – 845mm

Organic manure

Inorganic fertilizer

Mono-cropping

Inter-cropping

Entisols

Absent


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many factors including annual rainfall intensity, soil management practices, cropping systems, soil type and drainage function, which were assessed to be similar at Fagoji-Zai sites and dissimilar at Zai-Kargo and Kargo-Fagoji (Table 6).

DISCUSSION

This study followed other studies in Nigeria and Africa which have examined the impact of soil erosion on agricultural soils (Dunne, 1985; Thomas, 1997; Nyssen et al., 2007; Kimaro et al., 2008; Usman et al., 2017; Onyelowe et al., 2018). It is also tallied with other similar studies (e.g. Stott, 1997; Shi et al., 2011) that measured soil losses and made comparisons between the affected

3 3sites. Eroded soil volumes of 5907 m and 3343 m recorded at Kargo and Zai accordingly interpreted within

3the same range with the soil volumes of 2147 m and 2545 3m recorded at Star cross and Kenton districts of England

and Wales (Chambers et al., 1992). Although, these studies differed in terms of their geographical locations and soil types, however, the impact was described as annual hazards, which blocked a public highway and created wider channels that conveyed water into the River areas (Chambers et al., 1992). This impact leaves the surface soil features and soil properties damaged and had destroyed the functional services in soil medium (Lal, 1998). The excavation was considered to create deep channels that crossing is impossible with agricultural machines such as tractors (Evans, 2013). The formation of these channels is believed to have been increased with a coarse soil texture characterized by poor structural arrangement (Atkinson, 1993). This had probably gives direction for gully erosion to enlarge by progressive head cutting collapsed and damaged the surface soil of the study sites (Figure 5). The large volume of soil loss and deep cut of gully erosion in the affected sites (Table 2) can be linked to the overall surface soil conditions, which were visualized as poor vegetation cover, loose soil particles, poor soil management application and lack of good drainage system (Usman, 2016). This also might have caused considerable amount of surface soil damage and nutrients lost as noted by Zhang and Zhang (2005) in China as well as rapid production of drainage networking as noted by Oostwoud Wijdenes and Bryan (2001) in Kenya. Obviously, the three (3) sites have natural slopes (Figure 2), which can be explained as instable due to the nature and condition of the surfaces that appeared to be more homogeneous in nature (Atkinson, 1993). Usually, soils with this slope type may probably experience very slow erosion which over time may create deep-cut and wider channels leading to surface damage and land sliding as visualized in the study sites (Atkinson, 1993; Figure 2).

Gully erosion has an advance soil impact over rill erosion as it has complex effects on all components of surface soil including soil profile development, soil

fertility and soil quality reservation (Evans, 2013). Low-income farmers who owned small lands (1ha or >1ha size)typically in the study area are affected more by gully erosion as its kinetic energy and occurrences cannot be possibly control by them. Eroded soil volumes of

3 11591.52 m recorded at Fagoji is typically high compared to the other two sites, which could be probably due to the variation in soil textural classes and vertical homogeneity within soil profiles (Vásquez-Méndez et al., 2010). On average, sandy or very poor coarse soils have low capacity to withstand the force of rains, which move lighted to very-lighted soil particles due to reduced bind agents/cemented particles (Usman et al., 2017). This might have caused high soil loss impact at Fagoji compared to Kargo and Zai accordingly (Table 2).This can be evaluated further from the aerial photographs taken at Fagoji site (Figure 6). These aerial photographs were used to monitor soil erosion in the field and evidently recorded important information on how soil erosion occurred and the variations exist between one areas of land to another (Paudel and Andersen, 2010; Evans, 2013).Typically, there was a wider surface soil damages at Fagoji and Kargo compared to Zai (Figure 6), which signified reduced agricultural activities and low quality vegetation in the former two sites than the later site. Perhaps, this had destroyed the functional services that played important roles in transforming and maintaining soil quality, soil fertility and soil biodiversity (Usman et al., 2017), and yielded serious sediments due to irregularly shaped of the gullies (Maaoui et al., 2012).

Correlation was used to show the relationship of the study sites in terms of depth, width at top and width at bottom (Table 4). This confirmed that the sites have a strong relationship because the value fall within the established statistical range of ±1 and the P-value is less than 5%. This tallied with what has been noted by Supriyadi et al. (2018) and hence factors such as soil type, vegetation cover and anthropogenic activities might have influence the occurrence of gully erosion in the study sites. A positive correlation confirmed that there was a close relationship between Zai and Kargo site which probably explained the fact that an increase of gully erosion at Kargo may also means an increased of the same problem at Zai (Table 4). The soil of these sites is weak, fragile and light-textured used by farmers for the millet-sorghum cultivation (Usman, 2007). According to Morgan et al. (1987) erosion on light-textured soils under cereals cropping accounted high impact of up to 5–11% of soil loss. This might be probably one of the reasons by which Fagoji site recorded high soil loss impact and perhaps shows positive relation with Zai site (Figure 7).However, a negative correlations found between Zai and Kargo as well as Kargo and Fagoji explained how expanding of gully erosion in each site differs from one another (Figure 7). This is probably due to variation in soil texture, vegetation cover, management practices, cropping systems and level of poverty leading to


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Figure 6: Aerial photographs of gully erosion at Fagoji

Figure 7: Correlation chart between Fagoji, Kargo and Zai


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CONCLUSION

Degradation of soil through gully erosion had caused soil loss and surface soil damage in Dutse villages of Fagoji, Kargo and Zai. High eroded soil loss volumes are likely to be influenced by the weakly developed soil texture, weak soil structure and poor vegetation covers, which favour movement of soil particles by water at high storms. The affected sites are vulnerable to very serious gully channels, which can significantly influence the total deterioration of surface soil fertility and soil quality, and putting the entire area at risk of landslide, agriculturally null and village relocations. Field observation of gully erosion appears to be an important tool for recording data that can be used to deduce the soil condition and problems that affect it for immediate solutions and/ advises. Soil erosion impact can be estimated from field examination of the affected sites and offers opportunities to develop a management plan. Monitoring of gully affected areas is an incredibly important exercise worth to be emphasized. Therefore, it is recommended that the following should be put into considerations:

a. The state government should provide a sustainable gully rehabilitation scheme for identification of gully affected sites or villages and the developments of proper management plans.

b. Treated gullies should be checked regularly and the healed process monitored closely.

c. Structures built in the gully for stabilization purpose should be observed for damage especially during rainy seasons and/ after heavy storms.

d. Villagers mining in eroded sites should be provided with awareness on the deformities impact and the affected areas ought to be restricted by the government if they persist on mining the sites.

ACKNOWLEDGMENT

This work was supported by the Department of Soil Science, Faculty of Agriculture, Federal University Dutse, Jigawa State Nigeria as part of Rural Research and Developments around the University environment.


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evaluation of gully erosion impact on soil quality

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