The development of root system is extremely sensitive to the supplies of various nutrients, the effects of different levels of NH4+ supplying on plant growth were studied in Solanum lycopersicum by using an agar-based whole-plant or root localized contact culture. The results showed that when the concentration of whole-plant supplied NH4+ was higher than 0.5 mmol/L, primary root length, lateral root numbers and plant height were decreased with further increase of the concentrations of NH4+ in the agar, and the development of lateral roots was almost completely inhibited by 10 mmol/L NH4+. Compared with the influence of corresponding NH4+ supplied only to the roots, the inhibitory effect of NH4+ on growth was greater when whole plant exposed to NH4+. Lower concentrations of NH4+ (10-100 μmol/L) supplied to the roots can significantly increase the lateral root numbers without evident influence on primary root length. Thus, depending on the concentration and distribution, NH4+ has either negative or positive effects on the development and growth of Solanum lycopersicum especially for the lateral roots.