At the on-line mode of differentiated mineral fertilization the availability of nutrients is determined by scanner (sensors). The programme of researches contained the study of the effect of the number of scanners placed across the machine operating width on the quality of nutrients providing of plants. One of the indicators of the quality of the technological process of mineral fertilization is the distribution of fertilizer across the machine working width. For the precise distribution is necessary to ensure minimal irregularity of the actual dose relative to addition ones. The equation allowing to define the inaccurate distribution of fertilizers across the machine working width caused by impossibility of measurement and, afterwards, providing of application of a required dose in each point of the selected section is received. The factors influencing inaccurate distribution are revealed. Numerical evaluation of irregularity for different conditions of mineral fertilization is executed. Even in case of absolutely precise distribution of fertilizers across the machine working width the deviations of the actual doses of application of fertilizers in comparison with required can exceed the value allowed by agrotechnical requirements considerably. Additional scanners allow to lower in proportion coefficient of irregularity of distribution of fertilizers across the machine working width.