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

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.

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