Blaise Pascal Bougnom, Brigitte Amalia Knapp, Francois-Xavier Etoa, and Heribert Insam

Abstract Infertility of acid soils is a major limitation to crop production on highly weathered and leached soils throughout the world. The main characteristics of these soils are their low pH, low levels of organic matter, Ca, Mg, P, or Mo deficiency, Al or Mn toxicity, or both, and very low mineralization and nitrification rates. Lime is generally recommended to correct soil acidity, but lime is unaffordable for resource-poor farmers in the tropics. Many alternatives have been proposed, and among them products from organic waste materials, e. g., composts, have proven to be an efficient alternative to the use of lime. Wood ash is a potential source of trace elements, nutrients, and lime. Wood ash could be used as an additive to fertilizer, and wood ash admixture to organic wastes prior to composting is known to improve compost quality and may reduce the amount of compost required to raise the pH to suitable levels. Wood ash compost as a liming agent as a replacement for lime could potentially aid in remediating acidity and base deficiency as well as boosting the soil microbial pool in tropical agricultural soils.

7.1 Introduction

Agricultural primary production is essential for maintaining human life. Sustaining the productivity of soils is important for future generations, but the way to maintain productivity is often disputed. Intensive agriculture is based on the use of large quantities of pesticides and other chemical substances aiming at increasing yields, but the price to pay is the deterioration of soil quality and the environment, water pollution, the emergence of new pathogens that are more and more resistant to pesti­cides, and the threat to human health from the consumption of pesticide residues

B. P. Bougnom (H) and F.-X. Etoa

Laboratory of Microbiology, Department of Biochemistry, University of Yaounde I, P. O. Box 812,

Yaounde;, Cameroon

e-mail: bpbougnom@uy1.uninet. cm

B. A. Knapp and H. Insam

Institute of Microbiology, University of Innsbruck, TechnikerstraBe 25 d, 6020 Innsbruck, Austria

H. Insam and B. A. Knapp (eds.), Recycling of Biomass Ashes,

DOI 10.1007/978-3-642-19354-5_7, © Springer-Verlag Berlin Heidelberg 2011

entering the food chain as well as inhalation of toxic gases. These practices, however, are beyond the reach of resource-poor farmers in the tropics, because of their high cost. On the other hand, agricultural and forestry products are exported from tropical to western countries; together with nutrients like nitrogen, phosphorus and potassium, present in this biomass. Sustainability issues are thus becoming more important, reflecting the need for long-term fertility and environmental protection. A sustained agricultural system is one in which the sum of income extracted every year is sustained over years without altering the natural resource levels (Yunlong and Smit 1994). Organic farming principles and objectives are achieving good crop yields by using techniques which minimize the human impact on the environment (Rigby and Caceres 2001). Organic farming can allow resolution of the problem of disposal of organic wastes that human beings have to get rid of and which are a valuable source of nutrients for plants, and serve the purpose of soil conditioners. That allows the carbon cycle to be closed and thus greenhouse gas emissions to be reduced.

Besides organic wastes, ashes from biomass incineration are also worth consid­ering for agricultural recycling. Wood energy production is classified as a form of green energy production because it is both carbon neutral and renewable (Kumar 2009). In many African regions, fuel wood constitutes 61-86% of primary energy consumption and generates large amounts of wood ash, which are just discarded to the natural environment without any control, causing serious environmental pro­blems (Samir Amous 1999). On the other hand, in Europe and North America, the increased use of wood to produce bioenergy generates huge quantities of wood ash that are currently deposited at high cost. That ash, known to be rich in nutrients and lime, could be returned to depleted soils as a supplement to organic fertilizers by suitable management practices (Bougnom et al. 2009). Addition of wood ash to compost is among the available possibilities, and the compost produced could be used for forest fertilization as well as for agricultural purposes such as replenishing depleted and/or acid soils (Bougnom et al. 2009, 2010; Kuba et al. 2008). In this chapter, we explore the possibility of using both compost and wood ash as an addi­tive to remediate tropical acid soils. The problem of soil acidity is also explained to inform the reader about the origin of this phenomenon and its consequence for soil fertility as well as the mechanisms by which organic wastes could alleviate soil acidity.