Journal of Environment and Earth Science www.iiste.org ISSN 2224-3216 (Paper) ISSN 2225-0948 (Online) Vol.5, No.13, 2015 152 Spatial Variation in Some Physical Properties of Vertisols of Kerau in Guyuk area of Adamawa State Jinga CLEMENT JAHKNWA (Corresponding author) Department of Disaster Management, Adamawa State Polytechnic, P.M.B. 2146, Yola 640001, Nigeria Helen Humuo RAY Department of Geography, Modibbo Adama University of Technology, Yola, 640001, Nigeria Abstract This study assessed the spatial variation of some physical properties of vertisols of Kerau in Guyuk local government area of Adamawa State, Nigeria. The objective of this study was to examine the physical properties of vertisols and assess their micro-scale variation at the study site. Physical properties measured are %sand, silt and clay and available water capacity. Soil samples were collected at two depths of 0-15cm and 15-30cm with an auger. A total of 100 soil samples were collected and analyzed using standard analytical methods. Soil properties measured exhibited low coefficient of variability and strong spatial autocorrelations. The spherical and Gaussian models provided the best fit for soil properties of the study site at the scale of measurement. Kriged maps show no relations between surface depth distribution of properties and subsurface depths. Accordingly, Soil conservation measures that would improve soil structure are recommended for vertisols. Keywords: vertisols, microscale, variation, semivariograms, kriging, kerau, range 1. Introduction Soil physical properties play a very strategic role in defining the characteristics of vertisols of any area (Lin et al,, 2005; Enger and Smith, 2004; Wilding and Drees, 1983). This, from the fertility point of view is hinged on the knowledge that they are products of the interplay of factors of soil formation and anthropogenic activities (Khan et al, 2007; Jung et. al., 2006; Ayoubi et al 2006; Lin et. al., 2005; Corwin, 2003; Warrick and Nielson, 1980). Vertisols physical properties are however known to be very variable and this variability at any given time is scale dependent more because of the mulching ability of the soil, the gilgai morphology and varying temporal moisture regimes of the soil (Kovda, et al, 2010; Garten Jr. et al, 2007; Wilding, et al., 2002; Yang et al 2002; Webster, 1997). This has most often been the major source of soil management problems to many a farmer especially in tropical Africa. Today, the focus is on precision farming for optimal crop production which requires knowledge of within-field variability comprising that over short distances of a few centimeters (short range variation) and that over longer distances of tens of meters (Garten Jr., et al, 2007; Lin et al, 2005; Oliver and Carrol, 2004). Many studies have focused on studying variability at large and medium scales (Heuvelink and Webster, 2001). For instance, studies on soil texture by Adhikari et al, (nda), Warrick and Gardner, (1983) and Tanji, (1996) found that soil texture variability has a significant influence on the availability of nutrient, moisture and yield potential of any soil of any site. Similarly, Zhang et al (2010) assessed variability of surface soil moisture in karst regions using a 20m interval grid sampling technique and found that variability was explained by the exponential and Gaussian models with a weak to moderate spatial dependence and a mosaic pattern exhibited in the kriged maps. Wang et al (2001) observed that soil moisture exhibits changing spatial dependence with depth. Soil moisture is also known to exhibit moderate variability spatially at a field scale (She et al, 2010; Yang et al 2002). These studies are in tandem with the farming systems in the developed world. Information from such studies does not however relate with the small scale or small holder farming systems that exist in countries like Nigeria. Very little has also been done on variability in vertisols at micro-scales in the sudano- sahelian region of Nigeria where they present both structural and soil moisture problems to local farmers. It is based on the foregoing that this study investigated the variability in the physical properties of vertisols in Sudano-sahelian Nigeria at a micro-scale. This study assessed the spatial structure of physical properties of vertisols. 2. Methods 2.1 Study site The study site is a 2.2ha Sorghum bicolor farm located on latitude 9 0 38.613N - 9 0 38.595N and longitude 11 0 54.623E-11 0 54.571E, with an elevation of approximately 200m above sea level and a near flat slope with a northeast to southwest trending of 0.02% in Kerau village of Guyuk local government area in Adamawa State. The area has a wet-dry savannah climate with mean annual rainfall of 978mm. The wet season spans between April and October with average temperatures as high as 35 0 C in March and relative humidity that reaches 70% in