ABSTRACT
The research determined properties of soils from sixteen locations (Agaie, Papiri, New Busa, FUTMinna, Enagi, Izom, Lemu, Badeggi, Kontagora, Lapai, Gaba-Lavun, Beri, Nasarawa-Kainji, Sarkin-Pawa, Paiko and Wushishi) within Niger State, Nigeria with emphases on distribution of iron and aluminium oxides, zinc and iron, taking into cognizance the geology of the state.
Soil samples were collected from horizons identified within 100 cm mini profile pit dug at each experimental site, prepared and taken to the laboratory for analysis. Standard procedures for soil analysis were employed to deteremine soil chemical and physical properties. The oxides were extracted by sodium dithionite-sodium citrate and acid ammonium oxalate extraction methods. The locations of mini-profiles, at latitudes of between 9.010 and 10.800 N and longitudes of between 4.510 and 7.010 E confirmed the geographical situation of the state.
Three to seven horizons were identified within 100 cm depth of the soils with colours varying mainly from typical black through strong brown to red. Low organic matter content with mean values of 0.46 and 0.34 g/kg; pH, 7.77 and 7.41, Eh, 41.97 and 28.23 mV; total N, 0.06 and 0.07 %; available P, 1.99 and 0.91 mg/kg; exchangeable acidity, 1.46 and 1.49 cmol/kg; exchangeable Ca, 6.38 and 7.26 cmol/kg; exchangeable Mg, 2.24 and 1.93 cmol/kg; exchangeable Na, 0.16 and 0.15 cmol/kg; exchangeable K, 0.29 and 0.28 cmol/kg; ECEC, 10.38 and 11.49 cmol/kg; base saturation (BS), 85.71 and 81.21 %; sand content, 74.31 and 64.23 %; silt content, 15.44 and 21.60 %; clay content, 10.92 and 14.37 %; electrical conductivity (EC), 0.16 and 0.18 dS/m were recorded for the soils formed on the sedimentary deposits and basement complex respectively. Findings showed that geology from which soils of Niger state formed had no significant effect on most chemical and physical properties but Eh, total-N, pH, OM, EC and sand contents were significantly affected. The result also indicated that the total Al content was 13.45 to 21.23 mg/kg and 14.45 to 19.75 mg/kg; oxalate Al content was 4.00 to 8.20 mg/kg and 5.00 to 9.00 mg/kg; dithionite Al content was 6.80 to 12.80 mg/kg and 7.00 to 12.00 mg/kg; total Fe content was 345.98 to 505.44 mg/kg and 256.02 to 758.52 mg/kg; oxalate Fe content was 20.0 to 240.0 mg/kg and 90.00 to 270.00 mg/kg; dithionite Fe content was 30.00 to 560.00 mg/kg and 140.00 to 430.00 mg/kg; crystalline Fe content was 10.00 to 320.00 mg/kg and 50.00 to 200.00 mg/kg; iron weathering index (IWI) was 0.19 to 0.82 and 0.48 to 0.60; iron activity index (IAI) was 0.43 to 0.91 and 0.33 to 0.72; iron crystallization index (ICI) was 0.05 to 0.33 and 0.13 to 0.39; Zn content was 12.10 to 31.00 mg/kg and 12.08 to 33.22 mg/kg; dithionite Fe/clay co-migration was 0.05 to 0.70 and 0.07 to 0.56; dithionite Fe/OM co-migration was 1.04 to 19.40 and 1.06 to 57.14; dithionite Fe/Zn co-migration was 2.48 to 29.95 and 4.49 to 27.97 for the soils formed on sedimentary deposits and basement complex respectively. Correlation results pointed out that pH had effects on metallic ions availability and of course on nutrients such as P, strong association of Zn and oxides, interaction between pH and Eh which influenced soil behaviours, amongst others. Soils within the landscape of Niger state developed at nearly the same rate, although, the development of the upper horizons were hampered by anthropogenic activities. The exhibition of reducing conditions by the soils accelerated nutrient loss in addition to being non-saline, with the ones formed on the basement complex being relatively older than the soils formed on the sedimentary deposits. It was therefore supposed that the sedimentary deposits have reasonable materials originating from the basement complex.
