ABSTRACT

This study was conducted to determine the physical, chemical and mineralogical properties of soils as well as the distribution of phosphorus (P) forms in soils supporting rice production in Abia State, Nigeria. A total of 54 composite soil samples were collected from the depths of 0-20cm, 20 — 40cm and 40 — 60cm respectively from 18 different farms, located at Amaeke-Abam, Ahaba-Imenyi, Bende, Urbanu-Ibeku and Uzuakoli in Abia State. The soil samples were subjected to routine physical and chemical analysis in the laboratory. Results obtained showed that the soils varied in texture from sandy clay loam at the surface (0-20cm) to sandy clay at lowest depth (below 40cm-60cm).The soils were very acidic (pH 4.74-5.00) and the pH increased insignificantly with increase in soil depth, drganic matter level was moderate (ranging from 36.60g/kg to 24.00 g/kg) and decreased with increase in depth. ECEC was low all through the three depths (ranging from 19.40 cmol/kg to 20.40cmol/kg).Total exchangeable acidity decreased down the depth, with mean values of 3.09cmol/kg, 2.85cmol/kg and 2.47cmol/kg and these were rated above the critical value of 2.00cmol/kg Al toxicity. Apart from exchangeable Ca and magnesium, values of Na and K were low, with values increasing with profile depths. Exchangeable calcium had a range of 6.09cmol/kg to 6.44cmol/kg in the 0-20cm depth and 40-60cm depth respectively. Exchangeable K was low in the top soil (0.16cmol/kg) and increased above the critical value of 0.2cmol/kg in the sub soils. Exchangeable Mg and Na contents were in the ranges of 9.96cmol/kg (top soil) to 11.61 cmol/kg (sub soil) and 0.08cmol/kg (top soil) to 0.09cmol/kg (sub soil) respectively. The available phosphorus was low (<15.0mg/kg) and increased along the profile. Total nitrogen was low (1.57g/kg) at 0-20cm with values decreasing with depth. The mineralogy ofsand sized fractions was predominantly quartz with little quantity of kaolinite. Silt fraction mineralogy showed the presence of quartzj (23.82% - 62.07%), microcline (1.13% - 2.65%), kaolinite (0.21% - 0.26%) and some traces ofthe other minerals. Mineralogy of the clay particles showed that the soils studied had mixed mineralogy dominated by quartz (12.13% — 83.22%), little quantity of kaolinite (3.12% — 5.67%) and microcline (1.97% - 4.84%). The abundance ofthe P fractions was in this order Ca-P > Fe-P > AlP > Org.P > Ca-P. It was observed that only Al-P significantly varied between depths. The correlation study showed that Al-P had a positive significant (P<0.01) correlation with total nitrogen, but slightly and positively correlated with exchangeable magnesium, total exchangeable bases, base saturation and effective cation exchange capacity. Fe-P significantly (P<0.05) and positively correlated with organic matter, organic carbon, exchangeable H and TEA, Ca-P had a significant (P<0.05) and positive correlation with exchangeable Al and silt. Organic P correlated positively and significantly (P<0 05) with exchangeable Mg and Ca, TEB and ECEC. These soils supporting rice production in Abia State will require good application of organic manure and mineral fertilizers to enhance their fertility for sustainable rice production.