Experiments were performed to compare the influence of ammonium nitrogen supplied in various growth stages, on the growth of turnip and cabbage in the sand culture outdoors. The growth period from the sowing time middle in April to the harvesting time middle in June was divided into four periods about two weeks each, and ammonium nitrogen was supplied in any one of the four periods, respectively, nitrate nitrogen being supplied for the remaining periods. The control treatment was supplied with nitrate nitrogen throughout all stages of growth.
When ammonium nitrogen was supplied in the stage from the sowing time to immediately after emergence, many seedlings with cotyledons exhibiting abnormal appearance were produced, and considerable number of these seedlings died. In any subsequent growth stage also, ammonium nitogen supplied lowered growth rate as compared with the control, though not so severer as in the emergence stage. In the leaves of plants supplied with ammonium nitrogen, the concentration of nitrate lowered rapidly, while, ammonium and soluble organic nitrogen accumulated. When nitrate was given again to these ammonium seedlings, their growth rates were restored rapidly, however, they could not catch up with the control. In the leaves of these plants, the concentration of nitrate increased quickly, and ammonium concentration decreased considerably.
When ammonium nitrogen was supplied at the emergence stage of tomato and cucumber, their growth rates were lowered, and at higher concentrations of ammonium, even germination percentage decreased, and further, seedlings with cotyledons exhibiting abnormal appearance increased.