Physical Properties And Maize Production In A Spent Oil-Contaminated Soil Bioremediated With Legumes And Organic Nutrients

Information on the use of plant species and organic nutrients to improve the physical properties of oil-contaminated soil, with a view to making it conducive for crop production, is very important. Three legumes (Gliricidia sepium, Leucenae leucocephala and Calapogonium caeruleam) combined or not with poultry manure were tested for their ability to improve the physical properties of a sandy soil, contaminated with 5% (w/w) spent lubricating oil, each for two years, and its effects on the growth and yield of maize in south eastern Nigeria. Aggregate stability (MWD), saturated hydraulic conductivity, and macro-to micro-porosity ratio improved with time in all the treatments over the 5% oil contamination (A5) and control. At 12 and 18 months, the use of Gliricidia sepium with 0.5% (w/w) poultry manure (A5+Gl+PM) gave the highest improvement of 58% and 94% in MWD, corresponding to 136% and 187% improvement in saturated hydraulic conductivity, respectively over the A5. The A5+Gl+PM also enhanced soil aggregate sizes > 0.25 mm by 63.6% and showed a 3-fold positive modification in soil macro-porosity. Positive relationships, significant at 0.01 level of probability, were observed between crusting hazard (R) and soil organic matter (r = 0.814), micro-porosity (r = 0.686) and saturated hydraulic conductivity (r = 0.787). The A5+Le+PM also increased maize growth and grain yield. Gliricidia sepium and Leucenae leucocephala combined with.0.5% (w/w) poultry manure is recommended for follow-up investigation, as it may offer a viable choice for remediation of oil-contaminated soil.Agro-Science Vol. 7 (1) 2008: pp. 33-4

Effects of sewage sludge application on selected soil properties and yield of maize and bambara groundnut

Several studies in the temperate region have indicated that sewage wastes have the potential to improve soil properties but may also cause drastic reductions in soil productivity. We studied the effects of long-term application of dehydrated sewage wastes on soil properties and yield of maize (Zea mays L.) and bambara groundnut (Vigna subterranea) on a sandy Ultisol (Arenic Kandiustult) at Nsukka, Nigeria. The sewage sludge was applied at the rate of about 36 t/year for 40 years before this study was carried out. We sited two profile pits on the site that received the sewage (S/NSK/1 and S/NSK/2) and one pit on the site that did not (NS/NSK) and described them before collecting soil samples from the genetic hori­zons of each pit for analysis of soil properties. Soil organic carbon (OC), microbial respiration, electri­cal conductivity (EC), sodium adsorption ratio (SAR) exchangeable sodium percentage (ESP), total N, exchangeable Na and Ca, cation exchange capacity (CEC) and maize performance were significantly (P < 0.05) enhanced in the sewage treated soil compared to the non-sewage treated soil. The growth of salt-sensitive bambara groundnut was very poor on the former until the sludge was leached of excess salts with distilled water, after which its yield was identical with that from the control soil. Maize height and dry matter yield after 6 weeks were significantly improved (P = 0.05) on the sewage treated soil than the control. These results indicate that the application of sewage sludge on agricultural soils should be done with caution because of its negative effects on soils and crops when used at high rates. Key words: Sewage sludge disposal; exchangeable bases; electrical conductivity; microbial respiration; salinity levels; sodium adsorption ratio. Agro-Science Vol.2(2) 2001: 37-4