The future of hydroponics as a research and plant production method 1

Although most plants can use ammonium (NH₄) or nitrate (NO₃) as a source of N, the degree of effectiveness of these two N forms on tomato growth was found to be dependent on the NH₄: NO₃ ratio. The addition of small amounts of NH₄ to NO₃ solutions, up to 14 ppm, improved plant growth but did not significantly change the uptake of K, Ca, and Mg as compared to NO₃ alone. However, with 28 ppm NH₄‐N and above, dry weights and cation accumulations decreased in amounts of about 35 to 50% and in a 12‐day period. The decreased dry weight and cation uptake with 77: 77 ppm NH₄: NO₃ ratio was comparable to that obtained with a O N treatment for the same interval.