ABSTRACT
The conventional soil sample pretreatment often involved soil air-drying, crushing, sieving, extracting and filtering. The process of soil air-drying might be replaced with the measurement of soil water content by using moisture detection technology, for example, photoelectrical method (Chen Xiaomin et al , 1995), Time Domain Reflectance (Pang Chunhao et al, 1994; Sun Yurui et al, 2004; David R. Lapen and Clarke Topp et al, 2004), capacitance method (Xiao Huirong, 1997), dielectric constant method (Wu Yingcai, 1996), resistance method (Zhao Xiuzhen et al, 2004), heat pulse technique(Ma Daokun, 2003) and ground-based sensing (Minzan Li, 2004). The process of crushing and sieving could be automatically handled by mechanical operations. Various extracting methods for extracting the nutrients from soil sample had been worldwide investigated. Some soil extractants, such as distilled water, 2 M KC1 solution and 0.01 M CuS04 solution solution, were used to extract the nitrates from the soils (Dahnke, 1971; Van Lierop W, 1986; Yu and Ji, 1993). Many extractants for simultaneously extracting multi macronutrients from soil had been successfully developed and used for soil analysis, such as Mehlich-3 extractant for P and cations (A. Mehlich, 1984), Olsen extractant for N, P and K (Olsen et al,1954), AB-DTPA extractant for N03"-N, P and K (Lucena and Bascones, 1993), CaCi2 extractant for total soluble nitrogen, nitrates, ammonium, P and K (Simonis and Setatou, 1996) and Kelcwna extractant for nitrates, P and K(Van LieropW, 1988; 1989), 1 M NH4OAc and Bray P-l for available potassium and phosphorus (Bray and Kurtz, 1945), etc. So far, most sample extraction was manually conducted by shaking and filtering processes. Magnetic stirring and heating could accelerate the dissolving of soil sample and shorten the extraction time. Several fluidic control systems, involving FIA, MEMS and Microchip technology, were investigated for soil sample solution transportation and interface with soil sensor (Lereto A. B. et al, 1996; Adsett J. F. et al, 1999; Birrell S. J. and Hummel J. W. et al, 2001; Yildirim S. et al, 2003).
