ABSTRACT

Soil survey and land evaluation for selected crops in Ibiono Ibom Local Government Area of Akwa Ibom State (LGA), Nigeria were carried out. The objectives were to survey, characterize, classify and evaluate the suitability of the soils for the cultivation of four arable crops (cassava, maize, plantain/banana, wetland rice) and three permanent crops (cocoa, oil palm and rubber). Topographic map of the study area at the scale of 1:50,000 was acquired from the office of the Surveyor General of Akwa Ibom State. A digital elevation model (DEM) of the study area was also acquired from United State Geological Survey (USGS) at 30m resolution. Elevation map was generated from both the topographic map and digital elevation model and superimposed on each other to generate the final base map of the study. The base map was made up of three mapping units based on elevation gradient of 0-50 masl (soil mapping unit 1), 51-100 masl (soil mapping unit 2) and 101 masl and above (soil mapping unit 3). with the help of Hand held Global Positioning System (GPS), the latitudes, longitudes and   elevation on the base map were cross-checked in the field (ground truthing). Profile pits were sunk in representative locations within each soil mapping unit.  A total of nine profile pits were sunk with three in each mapping unit. Each pit was described in accordance with FAO guidelines for soil profile description. Soil samples were collected based on genetic horizons for laboratory analysis. Undisturbed bulk soil samples were also collected using core ring for bulk density and saturated hydraulic conductivity determinations. The results showed that soil mapping unit 1 is located in the poorly drained, nearly level to level topography with elevation gradient of 0 – 50 masl.  Soil texture was sand in the Ap-horizon and sandy clay loam in the B-horizon. Soil pH was moderately acid in both Ap and B-horizon.  Organic carbon was high in the Ap -horizon and moderate in the B-horizon. Total N was low in both Ap and B -horizon. Available P was moderate in both Ap and B -horizon. Exchangeable Ca was moderate in the Ap- horizon and low in the B -horizon. Exchangeable Mg was moderate in both Ap and B-horizon. Exchangeable K was very high in the Ap- horizon and high in the B-horizon. The ECEC was moderate in the Ap- horizon and low in the B-horizon. Soil mapping unit 2 is located partly within the imperfectly drained and partly within somewhat well-drained with gently sloping topography. The elevation varied from 51 to 100 masl. Soil texture was sand in the Ap-horizon and sandy clay loam in the B-horizon. Soil pH was moderately acid in the Ap-horizon and strongly acid in the B-horizon.  Organic carbon was high in the Ap -horizon and moderate in the B-horizon. Total N was moderately low in both Ap and B -horizon. Available P was moderate in the Ap-horizon and low in the B -horizon. Exchangeable Ca was low in the Ap- horizon and moderate in the B -horizon. Exchangeable Mg was moderate in both Ap and B-horizon. Exchangeable K was very low in both the Ap and B- horizon.  Effective Cation Exchange Capacity (ECEC) was low in both the Ap and the B- horizon. Soil mapping Unit 3 is located within the well-drained, gently sloping topography. The elevation varied from 101 masl and above. Soil texture was sand in the Ap-horizon and sandy clay loam in the B-horizon. Soil pH was strongly acid in both Ap and B-horizon. Organic carbon was moderate in the Ap -horizon and low in the B-horizon. Total N was low in both Ap and B -horizon. Available P was moderate in both Ap and B -horizon. Exchangeable Ca was low in both the Ap and B -horizon. Exchangeable Mg was moderate in both Ap and B-horizon. Exchangeable K was very high in   the Ap- horizon and low in the B-horizon. The Effective Cation Exchange Capacity (ECEC) was moderate in   the Ap- horizon and low in the B-horizon. Soil mapping unit 1 was classified as Typic Epiaquept or Gleyic Cambisol.  In soil mapping unit 2, the imperfectly drained area was classified as Aeric Epiaquept or Gleyic Cambisol.  Soil mapping unit 3 was classified as Typic Hapludult or Haplic Acrisol. The results of land suitability evaluation showed that, soil mapping unit 1 (Ibom 1) .was marginally suitable (S3) for maize cultivation, moderately suitable (S2) for wetland rice, marginally suitable (S3) for cassava, marginally suitable (S3) for plantain/banana cultivation, not suitable (N1) for cocoa cultivation, not suitable (N1) for rubber cultivation but marginally suitable (S3) for oil palm cultivation, Soil mapping unit 2 was moderately suitable (S2) for maize cultivation, marginally suitable (S3) for wetland rice, marginally suitable (S3) for cassava cultivation, marginally suitable (S3) for plantain/banana cultivation, not suitable (N1) for cocoa cultivation, not suitable (N1) for rubber cultivation but marginally suitable (S3) for oil palm cultivation. Soil mapping unit 3, was. Highly suitable (S1) for maize cultivation, not suitable (N1) for wetland rice, moderately suitable (S2) for cassava cultivation, marginally suitable (S3) for plantain/banana cultivation., not suitable (N1) for cocoa cultivation and marginally suitable (S3) for rubber and oil palm cultivations. Major limitations for all the crops in the three mapping units were fertility, soil physical characteristics and wetness. Climatic variables were optimum or suboptimal for most of the crops under consideration in all the mapping units.