International Journal of Engineering and Applied Sciences (IJEAS) ISSN: 2394-3661, Volume-8, Issue-8, August 2021 8 www.ijeas.org Challenges Facing Effective use of Bat Guano as Organic Fertilizer in Crop Production: A Review Ernest Melkiory Marwa 1* , Twisege Andrew 2 , Asha Ally Hatibu 3 ABSTRACT - Bat guano is excrements of bats and it is commonly used in agriculture as a soil amendment and sometimes as a pesticide in organic farming. Small-scale farmers nearby guano deposits use it for indoor and outdoor plants as well as for hydroponic crop production. Guano in soils acts as a source of carbon (C) and energy to drive microbial activities as well as a precursor to soil organic matter fractions. With all these benefits, bat guano should be used in crop production with some precautions. Chemical composition and properties of bat guano are not fixed and are changing with time depending on the maturity, reaction with the country rock and bat diet. The pH of guano changes from alkaline to strongly acid with maturity. Similarly, guano loses some essential plant nutrients on decomposition and sometimes acquires potentially toxic elements as it reacts with the host rocks. Amounts added to the soil also vary with maturity and composition of guano. Thus, utilization of bat guano as organic fertilizer requires a thorough and regular characterization at the time of using it as soil amendment for crop production. Keywords: Bat guano, nitrogen, phosphorus, organic fertilizer INTRODUCTION Bat guano is excrements of bats and is commonly found in isolated islands and in caves [1]. Many studies indicate that bat guano is enriched with both macro-and micronutrients that are required by plants in natural form [1], [2]. In soil, guano acts as a source of carbon (C) and energy to drive microbial activities as well as a precursor to soil organic matter fractions. On decomposition, it releases a number of essential plant nutrients and also it controls the net mineralization-immobilization patterns in the soil [2]. However, its chemistry is highly variable. It contains a varying amount of nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg), potassium (K), aluminium (Al), iron (Fe) and sulphur (S) [3]. Other elements such as fluorine (F), chlorine (Cl), copper (Cu), manganese (Mn), molybdenum (Mo), nickel (Ni), zinc (Zn) and cadmium (Cd) occur in low concentrations. Presence of these elements in guano is associated with the reaction between the surrounding rocks (cave wall) and guano solutions. Most of these elements exist in guano as compounds [4], [5]. Guano tends to generate secondary minerals that are beneficial to plant on decomposition. Formation of secondary minerals such as gypsum and phosphate rocks help in a long-term availability of nutrients to plants as these minerals decompose and release nutrients slowly, hence are of high residual value. Harmful materials such as urea, which are due to high concentration of urine, can be volatilized and toxic bases such as sodium and aluminium can be leached with time. Immature (fresh) guano has little variations in nutrients concentration due to poor formation of secondary minerals as a result of low decomposition [6]. In agriculture, guano is reported to be useful in a number of ways, such as fertilizer material due to high content of nitrogen and phosphorous [5], [7]. It is reported to contain 2-6% total nitrogen, 1.5-10% available phosphoric acid and 1.5-10% soluble potassium [8]. The concentrations of N, P and K in bat guano meet the 5% N P K composition set as criteria for any material to qualify as a fertilizer [4]. It can act as a soil building material, fungicide (when foliar fed to plants), control of nematodes through attracting decomposers which work as biological control agents against nematodes, as well as a compost inoculants/activator [9], [10]. Microbes found in guano act as soil cleansers (bioremediation microbes) that help to clear up toxic residues, control root pathogens such as nematodes; and some microbal species such as Aspergillus and Penicillium spp are known to produce strong mycotoxins (biochemicals) [11] that repel other microorganisms such as bacteria, protists, nematodes and dangerous pathogens in the soil [12]. That is why guano can be used as pesticide in crop production system. With respect to all benefits listed above, guano remains a key resource of nutrients for organic farmers, especially small-scale farmers nearby guano deposits where it can be used for indoor and outdoor plants as well as for hydroponic crop production. Although guano can be used as organic fertilizer, it requires characterization to assess its suitability for agricultural uses at the time of application to ascertain its physic-chemical properties and whether or not they contain potentially toxic elements (PTEs), which could be of health and environmental concern. SOME CHALLENGES WITH BAT GUANO Variation in Chemical Composition There are different factors that determine the composition of bat guano. These factors are nutritional habit of the bat, age of guano in the cave (guano maturation), amount of water in the guano, the intrusion of other materials from outside the cave, and the composition of the bedrock forming the floor and the surrounding host rocks of the cave. Thus, chemical composition of bat guano is not fixed, it varies with time and surrounding environment of the cave.