ABSTRACT
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 soil 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.
CHAPTER ONE
INTRODUCTION
The use of biomass wastes as fuel for power boilers to produce steam or electricity is important for reducing dependence on fossil fuel and cutting greenhouse emissions and other pollutants. Such practice generates a residue known as boiler ash which contains the bulk of the mineral fraction of the original biomass (Khan and Quasim, 2008; James et al., 2012). Given the global focus on waste recycling and bioenergy development, the use of biomass wastes in energy generation has been on the increase and as a result, the production of boiler ash has continued to increase.
The disposal of the ash represents an emergent environmental challenge in many developing countries as these wastes are deposited on soil surfaces without any criteria supported by scientific and environmental concern. Such practice covers several hectares of valuable land and pollutes the soil, air and water, which ultimately affect human health (Pathak et al. 1996; Finkelman et al. 2000; Borm, 1997; Pujari and Dash, 2006). According to Singh and Gupta (2014), a suitable and sustainable solution for the disposal of boiler ash is required to be done to minimize the threat to the environment. An agricultural utilization of these ashes could alleviate the risks associated with its disposal and make it a value-added product of agriculture with the potentials of solving the challenges posed by high cost of mineral fertilizers and low fertility status of soils. However, there are many restrictions to agricultural utilization of these materials. Non- judicious application of boiler ash to soil can deteriorate soil quality as well as crop growth (Shukla et al. 2003; Sharma and Kalra, 2006). The heavy metals in boiler ash may be toxic to plants and animals; the high salt content may induce salt stress in plants; the pH value in soil may affect the mobility of elements and the leaching of heavy metals into ground water could be of environmental concern (Glardano et al. 1983). It also leads to deterioration of soil structure, water intake capacity of the soil and alteration of electrical conductivity and chemical properties such as pH, C.E.C. etc. These changes in the soil can affect the moisture availability, seedling emergence and crop establishment, root and shoot growth and consequently crop yield.
Boiler ash from sugarcane bagasse has been used as soil amendment in China, India, Pakistan, America etc. to improve crop yield and soil physico-chemical characteristics in an environmentally friendly manner (Khan and Qasim, 2008). So far, published data on the physical, chemical and agronomic properties of boiler ash from Nigerian bio-energy plants are somewhat limited. Most reported works have dealt with ashes generated at low temperatures as farm sanitation measures and applied at low rates (Ayeni et al., 2008; Onwuka, 2009; Ojeniyi et al., 2010). The results of these studies may not accurately predict, the potential uses and safety of boiler ash from burnt oil palm mill wastes and applied to an Ultisol for maize production in southeastern Nigeria.
The use of boiler ash from oil palm mill wastes in agronomic production system can only be sustained if soil quality improvement and increased crop productivity effects can be demonstrated. Most local farmers are unaware of the nutrient imbalance of boiler ash (Heraldsen et al.; 2011) and equate it with commonly used poultry manure or NPK fertilizer while, most researchers on boiler ash use in agriculture recognized the nutrient imbalance. They corrected the imbalance either by applying basal doses of NPK fertilizer (Khan and Qasim. 2008), or integrating it with other nutrient sources (Karmakar et al., 2009, Mohammadi and Rokhzadi. 2012); the results of which may not be used to accurately predict the potentials and safety of boiler ash applied without blending with other nutrient sources. Therefore, there is a research gap between farmers practice and the research focus especially with respect to boiler ash (BA) from oil palm mill wastes. The extent to which this BA can improve soil quality and increase maize performance relative to commonly used organic manure (poultry droppings) and inorganic fertilizer (N P K fertilizer) is not well known. This study compared the crop-use potentials of BA, poultry droppings (PM), inorganic fertilizer (NPK, 20-10-10) and their combinations as well as their effects on the properties of an Ultisol and maize performance in order to identify possible constraints associated with BA use for crop production. This is for developing a utilization strategy for boiler ash that would maximize their beneficial effects while minimizing any potential for negative effect on soil and environmental quality.
The specific objectives were to:
(i) compare crop-use potentials of BA derived from burning oil palm mill wastes with that of PM and NPK fertilizer,
(ii) determine the BA application rate that would have minimal environmental impact while still providing benefit to soil health and maize performance,
(iii) evaluate and compare the effects of different levels of BA, PM and NPK fertilizer in an Ultisol, growth and yield of maize, and
(iv) assess the comparative 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.
This material content is developed to serve as a GUIDE for students to conduct academic research
COMPARISON OF THE PHYSICOCHEMIAL POTENTIAL OF BOILER ASH POULTRY DROPPINGS AND INORGANIC FERTILIZER AND THEIR EFFECTS ON ULTISOL AND MAIZE PERFORMANCE IN SOUTH EASTERN NIGERIA
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