**9. Identification of gullies and erosion sites**

Soil erosion sites in southeastern Nigeria have been identified through various methods. In the 1960s and 1970s gullies were enumerated through natural resource surveys but this method proved to be very cumbersome and often do not actually represent the actual situa‐ tion on ground. This led to the use of aerial photo interpretation (API) in the generation of information for soil erosion studies. Niger Techno & Technital Spa [28] employed API in the documentation and publication of soil erosion problems in eastern Nigeria. The other meth‐ ods in this category is remotely acquired data from satellites, radar imageries and from geo‐ graphic information systems GIS. The advantages of API and other remotely acquired information is that the information they show are real and exact and sometimes in real time. However, acquiring information through this source is very expensive and most often unaf‐ fordable by some governments and establishments in Nigeria.

Soils Soil Classification DR CDI RUSLE K CFI MWD GMD Overall\*

Gully Erosion in Southeastern Nigeria: Role of Soil Properties and Environmental Factors

\*1- most erodible; 25- least erodible; DR- Dispersion ratio; CDI- clay dispersion index; RUSLE K- Wischmeier erodibility factor (K); CFI- clay flocculation index; MWD- mean-weight diameter of soil aggregates; GMD- geometric mean-

In other parts of the world the use of some soil parameters such as the water-dispersible clay (WDC) has been adopted as a major parameter in soil erosion models as in the Water Ero‐ sion Prediction Project (WEPP) [29]. This method has been widely used in the development of soil erosion models for some parts of eastern Nigeria [22]. Soils with high WDC have high soil erosion potential and therefore WDC constitutes a great problem to the soil and the en‐ tire environment. The negative influence of high clay dispersion on soil erosion results in detachment, transportation and deposition of sediments with essential plant nutrient ele‐ ments down stream. This clay associated sediments constitute high environmental menace to man, livestock and agricultural fields. The streams and rivers are silted, while the aquatic life suffers serious problems due to high concentration of nitrates, organic matter and phos‐ phorus in clay suspension down stream. These information have served as basic information

The state of soil erosion problem in southeastern Nigeria calls for a comprehensive soil con‐ servation programme so as to check catastrophic erosion hazard. The soil conservation measures should be those farming system practises which ensure sustainable soil productiv‐ ity while maintaining equilibrium between the ecosystem and regular anthropogenic influ‐ ence. In the design of soil conservation strategies, the permissible soil loss tolerance so as to avoid catastrophe in the event of failures of such strategies. In the United States of America, the permissible soil erosion loss is between 2.5 and 12.5 t ha-1 y-1 [7], while in Czech Repub‐ lic, Holy [30] noted that the permissible soil loss was between 1.0 to 16 t ha-1 y-1 in very deep soil of 120 cm thickness. Obi [31] observed that for a highly weathered, porous and deep ul‐

weight diameter of soil aggregates (Source: Igwe et al [21]).

for soil conservation processes

**10. Control and Remediation**

**Table 1.** Ranking of soils in order of significant erosion predictability

Awka Acrisols 2 1 5 1 13 16 2 Idodo Acrisols 20 24 20 24 14 14 22 Ukehe Acrisols 7 4 8 4 19 22 8 Abor Acrisols 4 4 2 4 9 18 3 Nachi Acrisols 6 11 4 11 25 24 14 Nanka Acrisols 7 14 2 14 11 1 6 Nawfija Acrisols 1 3 1 3 5 11 1

Ranking

167

http://dx.doi.org/10.5772/51020

Of late modelling soil erosion hazard in southeastern Nigeria has been very useful not only for erosion hazard prediction but for conservation purposes. Ofomata [3] used multiple re‐ gression equation with the environmental factors of climate, vegetation, soil and anthropo‐ genic factors being the variables to predict the soil erosion hazard in southern Nigeria. Again, Igwe et al. [21, 8] employed two different models in predicting soil erosion hazard in some parts of southeastern Nigeria. The predictive abilities of these models with some mod‐ ifications were satisfactory and approximated data obtained from the field. Table 1 presents the predictive ability of some soil parameters in 25 selected soils in the region.



\*1- most erodible; 25- least erodible; DR- Dispersion ratio; CDI- clay dispersion index; RUSLE K- Wischmeier erodibility factor (K); CFI- clay flocculation index; MWD- mean-weight diameter of soil aggregates; GMD- geometric meanweight diameter of soil aggregates (Source: Igwe et al [21]).

**Table 1.** Ranking of soils in order of significant erosion predictability

tion on ground. This led to the use of aerial photo interpretation (API) in the generation of information for soil erosion studies. Niger Techno & Technital Spa [28] employed API in the documentation and publication of soil erosion problems in eastern Nigeria. The other meth‐ ods in this category is remotely acquired data from satellites, radar imageries and from geo‐ graphic information systems GIS. The advantages of API and other remotely acquired information is that the information they show are real and exact and sometimes in real time. However, acquiring information through this source is very expensive and most often unaf‐

Of late modelling soil erosion hazard in southeastern Nigeria has been very useful not only for erosion hazard prediction but for conservation purposes. Ofomata [3] used multiple re‐ gression equation with the environmental factors of climate, vegetation, soil and anthropo‐ genic factors being the variables to predict the soil erosion hazard in southern Nigeria. Again, Igwe et al. [21, 8] employed two different models in predicting soil erosion hazard in some parts of southeastern Nigeria. The predictive abilities of these models with some mod‐ ifications were satisfactory and approximated data obtained from the field. Table 1 presents

the predictive ability of some soil parameters in 25 selected soils in the region.

Soils Soil Classification DR CDI RUSLE K CFI MWD GMD Overall\*

Oseakwa Gleysols 5 10 24 10 10 13 11 Akili ozizor Fluvisols 21 22 22 22 18 16 24 Osamala Cambisols 17 13 22 13 1 4 10 Oroma etiti Gleysols 15 25 21 25 2 5 20 Umuewelu Cambisols 21 20 19 20 3 6 18 Ezillo Acrisols 16 12 13 12 17 12 17 Abakaliki Acrisols 10 16 13 16 7 2 8 Okija Ferralsols 9 8 8 8 4 9 4 Ogurugu Fluvisols 11 17 11 17 15 8 13 Nenwe Cambisols 14 19 25 19 5 9 19 Ifite ogwari Cambisols 18 18 16 18 21 25 21 Umueje Cambisols 18 7 16 7 23 7 12 Umumbo Cambisols 24 15 16 15 8 3 14 Omasi Acrisols 25 21 8 21 22 19 22 Adani Acrisols 23 23 15 23 24 23 25 Nsukka Acrisols 12 8 12 8 20 21 14 Obollo afor Acrisols 12 2 5 2 12 15 5 Nteje Ferralsols 3 6 5 6 15 20 7

Ranking

fordable by some governments and establishments in Nigeria.

166 Research on Soil Erosion Soil Erosion

In other parts of the world the use of some soil parameters such as the water-dispersible clay (WDC) has been adopted as a major parameter in soil erosion models as in the Water Ero‐ sion Prediction Project (WEPP) [29]. This method has been widely used in the development of soil erosion models for some parts of eastern Nigeria [22]. Soils with high WDC have high soil erosion potential and therefore WDC constitutes a great problem to the soil and the en‐ tire environment. The negative influence of high clay dispersion on soil erosion results in detachment, transportation and deposition of sediments with essential plant nutrient ele‐ ments down stream. This clay associated sediments constitute high environmental menace to man, livestock and agricultural fields. The streams and rivers are silted, while the aquatic life suffers serious problems due to high concentration of nitrates, organic matter and phos‐ phorus in clay suspension down stream. These information have served as basic information for soil conservation processes

### **10. Control and Remediation**

The state of soil erosion problem in southeastern Nigeria calls for a comprehensive soil con‐ servation programme so as to check catastrophic erosion hazard. The soil conservation measures should be those farming system practises which ensure sustainable soil productiv‐ ity while maintaining equilibrium between the ecosystem and regular anthropogenic influ‐ ence. In the design of soil conservation strategies, the permissible soil loss tolerance so as to avoid catastrophe in the event of failures of such strategies. In the United States of America, the permissible soil erosion loss is between 2.5 and 12.5 t ha-1 y-1 [7], while in Czech Repub‐ lic, Holy [30] noted that the permissible soil loss was between 1.0 to 16 t ha-1 y-1 in very deep soil of 120 cm thickness. Obi [31] observed that for a highly weathered, porous and deep ul‐ tisol in southeastern Nigeria, the tolerable soil loss was about 10 t ha-1 y-1 under maize pro‐ duction, with appreciable loss in the production capacity of the soils.

soil conservation with respect to soil erosion should include a more comprehensive soil conser‐ vation method which will involve the application of certain hydrological or bioenvironmental

Gully Erosion in Southeastern Nigeria: Role of Soil Properties and Environmental Factors

http://dx.doi.org/10.5772/51020

169

[1] Ofomata, G.E.K. (1981). Acrtual and Potential erosion in Nigeria and measures for

[2] Ofomata, G. E. K. (1975). Soil erosion. *Nigeria in maps, Eastern States*, Ethiope Publish‐

[3] Ofomata, G. E. K. Soil erosion. Southeastern Nigeria: the view of a geomorphologist,

[4] Igwe, C. A. (1999). Land use and soil conservation strategies for potentially highly erodible soils of central-eastern Nigeria. *Land Degradation Development* [10], 425-434. [5] Igwe, C.A. (1994). The applicability of SLEMSA and USLE erosion models on soils of

[6] Giordano, A., Bonfils, P., & Briggs, D. J. (1991). Menezes de Sequeira E., Roquero D.L.C., Yassoglou A. the methodological approach to soil erosion and important land

[7] Renard, K. G., Foster, G. R., Weesies, G. A., Mc Cool, D. K., & Yoder, D. C. (1997). Predicting Soil Erosion by Water: A Guide to Conservation Planning with the Re‐ vised Universal Soil Loss Equation. *U.S. Department of Agriculture, Agriculture Hand‐*

[8] Igwe, C. A., Akamigbo, F. O. R., & Mbagwu, J. S. C. (1999). Chemical and mineralogi‐ cal properties of soils in southeastern Nigeria in relation to aggregate stability. *Geo‐*

[10] Lal, R. (1976a). Soil erosion on alfisols in Western Nigeria. I. Effects of slope, crop ro‐

[9] Hudson, N.W. (1981). *Soil conservation*, Cornell University Press, New York.

tation and residue management. *Geoderma*, 16, 363-373.

resources evaluation of the European community. *Soil Technology* [4], 65-77.

control. *Soil Science Society of Nigeria Special Monograph 1*, 151-165.

Inaugural lecture series University of Nigeria Nsukka (1985).

southeastern Nigeria,. *PhD Thesis*, University of Nigeria, Nsukka.

processes so as to control the overland flow and excessive runoff.

Address all correspondence to: charigwe1@hotmail.com

ing House, Benin City Nigeria.

*book*, 703, 384pp.

*derma* [92], 111-123.

Department of Soil Science, University of Nigeria, Nsukka, Nigeria

**Author details**

C.A. Igwe

**References**

Therefore, the suggested soil conservation measures based on the agricultural land use is recommended for the entire agro-ecological system. The land use option suitable to the area should be that based on integrated watershed management with arable farming, agrofores‐ try and intensive afforestation. These practises are considered cheap option which can be af‐ forded by the rural poor farmer. The methods are also very sustainable and not destructive to the agricultural land. This is aimed at reducing the annual soil loss rate and prevents the development of fresh gullies in the area. Agricultural land use should be based on topo‐ graphic variations, major soil distribution, soil potential erosion hazard, hydrology and oth‐ er geomorphological variables. Igwe [4] recommended that the entire region should be partitioned into 4 broad sections based on their location on the landscape. The lowlands and valley floors which also contain sediments should be put to rainfed and irrigated farming of arable crops. The main soil conservation strategies should be those that improve plant nu‐ trient availability, land levelling in case of irrigation and drainage. On the land areas that are on 5% slope and below, the regular recommended cultural practises of organic matter appli‐ cation to the soil is suggested while mulching, crop rotation and well managed agro-forestry are some of the ways of keeping the soil uneroded. Crop residues in association with tillage systems contribute immensely in the conservation of the soil or other wise. The other re‐ maining 2 land units are those that vary between 5-30 % slope and mostly the sites of cata‐ strophic gullies in the area. They should be permanently forested and may be used for wildlife conservation. The kind of forestation should be that which produces intimate multistoreyed association of woody species, grasses and creeping legumes. This will ensure steady cover for the bare soil and offer some kind of protection to the soil against the high intensive and aggressive rainfall. The major soil conservation strategies are broad-based ter‐ races and cover cropping of bare soils. A more comprehensive soil conservation method will involve the application of certain hydrological or bioenvironmental processes so as to con‐ trol the overland flow and excessive runoff.

### **11. Conclusion**

Soil erosion in the form of gullies is very common in southeastern Nigeria. This review has shown the influence of geology, climate, geomorphology (slope), vegetation, man and soil it‐ self on gully development and soil erosion in general. Typical empirical examples are cited from previous works from other researchers in other parts of the world and locally. Past works on estimation of potential soil erosion hazard in the region indicate that more than 1.6% of the entire land area has been devastated by gullies. The inherent characteristics of the local soils to a large extent promote the spread of soil erosion especially the gully type in the region. The roles of anthropogenic factors with regards to land use and its influence on the vegetation are considered. The serious deforestation of the vegetation and poor revegetation or afforestation programmes have all contributed to the catastrophic erosion hazards. General strategies for soil conservation with respect to soil erosion should include a more comprehensive soil conser‐ vation method which will involve the application of certain hydrological or bioenvironmental processes so as to control the overland flow and excessive runoff.
