Nitrate tests as a diagnostic method of nutritional status of vegetable crops

Abstract

Ample storage of nitrates was found in the lea-ves and stems of most kinds of vegetable crop tested, except Allium, in the leaves of which nitrates were scarecely found. Experimental results revealed that nitrate content of the leaves and stems was affected by various factors such as age of plant, nitrogen supply, as well as their position on the plant. High-er nitrate content was found in the mature leaves, especially in the petioles, and lower portion of the stems, while nitrate content decreased as age of the leaf became younger, or as the portion of the stem approached to the tip. As to the age of the plant, it was found that nitrate content started low in young age, reached its maximum in the middle stage, then decreased as the plant grew older, in the plants grown in sand culture with the constant levels of nitrate.
Diurnal change and change during storage up to for three days in room temperature in darkness or in difused light were not significant in nitrate content in the petioles of the turnip leaves.
Effects of the amount of nitrogen fertilizer on the nitrate content in the leaves of several kinds of vegetable tested were significant.
Nitrates could not be detected in the plants sup-plied with ammonium nitrogen only. In the early stage of growth of radish and chinese cabbage, nitrate content was low in the plants applied with:, higher amount of ammonium sulfate in the field. Nitrification of ammonium ion should be proceeded in the soil, before positive correlation between the amount of nitrogen applied and nitrate content in, the plants was established.
Changes in the nitrate concentration in the cul-tural solution were rapidly reflected in the nitrate content in the leaves of komatsuna in the sand cul-ture.
Nitrate reduction process in the plants was dis-cussed in relation to the diagnosis of nutritional status of nitrogen.
Rapid tissue tests by the BRAY's reagent methods and the diphenylamine method are simple and con-venient for diagnosing nitrogen deficiency of vege-table crops in the field, if the portion of the plant: to be tested are properly selected.
Tissue analysis method using phenyldisulphonic acid is more accurate and reliable for diagnosing: nitrogenous nutrition, if the portion of the plant and time of sampling are adequatly selected and definate standards for critical levels were provided. by fertilizer experiments.