Due to the rapidity of near infrared (NIR) spectroscopy, the information about several soil properties in NIR-spectra and the possibility to build robust field instruments, NIR has gained much interest for quantitative on-line soil analysis. As the NIR region mainly consists of broad and overlapping peaks, the spectra have to be evaluated in relation to known reference samples. Especially in on-line analysis, it could be a problem to standardize conditions as sample presentation is automatic and the operator has little control over the sample presentation. In this project, we tested a prototype of a probe with a fibre optic NIR sensor and an inbuilt light source. One spectrum averaged from 50 was saved every seven meters. The spectra showed a large variation in total reflectance and spectral features. The cause for this variation and how it could be handled is discussed.