A soil analysis device and a method are disclosed for measuring characteristics of a soil sample. A mixing chamber combines a soil sample and an extractant into a liquid mixture. A filtration system receives and filters the liquid mixture. The filtered liquid mixture is transmitted through a pipe with a slope to a measurement cell. The measurement cell is coupled to a light source so that light propagating from the light source is attenuated by the liquid mixture and is measured by an optical detector that is also coupled to the measurement cell. The optical detector generates an attenuation spectrum indicating light received by the detector at different wavelengths. The attenuation spectrum is used to determine the characteristics of the soil sample.