COMPARISON OF THE PHYSICOCHEMICAL POTENTIAL OF BOILER ASH, POULTRY DROPPINGS AND INORGANIC FERTILIZER AND THEIR EFFECTS ON ULTISOL AND MAIZE PERFORMANCE IN SOUTH EASTERN NIGERIA
The power boiler ashes (BA) from burnt oil- palm mill wastes at Solive Vegetable Oil Mills Ltd, Nsukka has not been assessed for its crop-use potentials before, and its disposal could pose environmental challenge in future. Several studies have shown that recycling such ash through agronomic production system could alleviate the risks associated with its disposal and make it a value-added input in crop production with the potentials of solving the challenges posed by high cost of mineral fertilizers and low fertility status of soils. The use of this BA can only be sustained if soil quality improvement and increased crop productivity effects can be demonstrated. The extent to which it can improve an Ultisol and increase maize performance relative to commonly used organic manure (poultry droppings) and inorganic fertilizer (N P K fertilizer) is not known. This study compared the crop-use potentials of BA with that of poultry droppings (PM), inorganic fertilizer and their combinations as well as their effects on an Ultisol and maize performance. It also compared the effectiveness of the different levels of BA, PM, and NPK fertilizer and their combinations on soil boron, cadmium and zinc loadings and uptake by maize plant. The study was conducted on an Ultisol at the Research Farm of the Department of Soil Science, University of Nigeria, Nsukka. The experiment was laid out in a randomized complete block design with three replications. The treatments were a control (no amendment), and a sole application of three levels of BA (10, 50, and 100 t ha-1) designated BA10, BA50 and BA100, respectively; three levels of PM (5, 10, and 20 t ha-1) designated PM5, PM10 and PM20 , respectively; three levels of NPK 20-10-10 fertilizer (75, 150, 300kg ha-1) designated NPK75, NPK150 and NPK300, respectively. In addition, combinations of different levels of BA with different levels of each of PM and NPK fertilizer (BA100+PM5, BA50+PM10, BA10+PM20, BA100 +NPK75, BA50 +NPK150 and BA10 +NPK300) were studied. The plots were planted with Oba Super II maize variety and changes in the physicochemical properties of the soil and crop-use potentials of the amendments were monitored for two consecutive years and compared. The physcico-chemical properties of the BA, PM and soil were determined pre and post experiment. Maize grain yield parameters were measured. Data collected were subjected to one-way analysis of variance and significant treatment means were separated by Fisher’s least significant difference at 5% level of probability. The BA consisted mostly of sand-sized particles (741 g kg-1), and had low bulk density (0.37 Mgm-3), high saturation moisture content (77%), high pH (8.9) and high electrical conductivity (441 d S cm-1). The contents of organic carbon was high (12.5 mg kg-1), nitrogen very low (0.24 mg kg-1) content, phosphorus high (298.5 mg kg-1) and K high (9.58 cmolkg-1) while, Fe, B, Cd and Pb values were relatively low. The PM had a higher bulk density (0.49 Mg m-3), N (4.15 mg kg-1) and Fe (167.0 mg kg-1) but lower in P (8.32 mg kg-1) than BA. The NPK plant nutrient ratios of the BA, PM and NPK mineral fertilizer were 1-147-5, 25-5-1, 20-10-10, respectively. Application of ≥ 50 t ha-1 BA increased significantly the sand–sized particles resulting in pseudo-change of soil texture from sandy clay loam to sandy loam. The bulk density of the control soil (1.92 Mg m-3) was significantly reduced to 1.76, 1.03 and 0.88 Mgm-3 in NPK300, BA100 and BA100+PM5 treated plots, respectively. Total porosity (61%) and water holding capacity (54%) were highest in the BA100 treated plots. The BA50 + NPK150 treated plots had the highest mean weight diameter of 0.69 and 0.76 at first and second cropping seasons respectively. The BA100 + NPK75 treated plots had the highest saturated hydraulic conductivity (141cm-3 hr-1) at the second cropping season. The highest soil pH value (7.7) was obtained in plots treated with BA50 and BA10+PM20. The BA100 + PM5 plots had the highest soil N (0.16 mg kg-1 ) and residual available P (124.6 mg kg-1). The highest soil exchangeable K (0.56 cmolkg-1) and Mg (17.8 cmolkg-1) were obtained from BA100+NPK75 treated plots. The NPK300 treated soil had the highest concentration of boron (4.56 mg kg-1) and sodium adsorption ratio (0.37) whereas Cd concentration (0.8mg kg-1) was highest in BA50 treated plots. The BA100 treated plots had the highest Mn concentration of 11.6 mg kg-1 and Zn (12.04 mg kg -1). Application of BA100 impeded maize germination (21%) but its residual effect on germination was highest (83%). The dry shoot biomass at 12 weeks after planting (WAP) was highest (421 g plant-1) in BA50 + PM10 treated plots. Application of BA10 + PM20 produced tallest maize plants (89.5 cm plant-1), highest leaf area index (7.32) and had the maximum maize grain yield of 5.43 tha-1 at the first cropping season; while, PM20 produced the highest residual effect (2.56 tha-1). The nitrogen (2.3 mg kg-1) and potassium (96.1 mg kg-1) concentrations in maize grain from plots treated with BA100 and BA100 + NPK75, respectively, were the highest. Residual effect of PM5 produced grains with the highest P content (0.82 mg kg-1). The boron (14.5 mg kg-1) and Cd (4.53 mg kg-1) concentrations were highest in maize grains grown in BA100 + NPK75 and BA50 + PM10 treated plots, respectively. The bio – concentration factor of the heavy metals in maize grains as affected by the amendments were in the order B > Zn > Cd while their residual effects were Cd > Zn > B. The result revealed that BA when compared with other alternatives (PM and NPK fertilizer) was superior in sroil conditioning but poor as a source of plant nutrient. Therefore, BA should not be applied alone without supplementary nutrient source especially when used for crop production. It is also preferable to blend it with organic manures like poultry droppings rather than inorganic manure such as NPK.