Abstract
Comparison of NO_3-N and NH_4-N as the nitrogen sources to tomato plant was investigated by the constant renewal water culture method. In general, NO_3-N was better nitrogen source to tomato than NH_4-N, but its degree varied with conditions such as pH and other ion-concentrations of culture solution. When NO_3-N was used, optimum pH was and tomato was relatively insensible to k-mangel, but NH_4-N was used, optimum pH was near 8.0 and very sensible to k-mangel.
