Fast measurement of soil properties is of great value for farmland fertilizer management with the purpose of reducing environmental pollution caused by over-fertilizing and improving yield/cost ratio of land. In the study, an optical fiber sensing system was introduced. It consisted of a topsoil opener, a portable spectrophotometer (350-2500nm) and an optical fiber. Prediction models of total nitrogen (N), phosphorous (P), moisture content (MC), pH and organic matter (OM) were created in laboratory and validated by field testing. Soil samples were collected from 30 farmland blocks covering north of Zhejiang Province and south of Jiangsu Province, P.R. China. Partial least squares (PLS) regression with full cross-validation was used for calibration models building. The correlation coefficient of R2 between on-line and laboratory measurements of N, P, MC, pH and OM are 0.92, 0.78, 0.85, 0.83 and 0.76, respectively. The study shows the potential of using the optical fiber soil sensing system for next generation of precision farming.