Nitrogen nutritional studies with flower-bulb crops

I. Growth, bulb yield and nutrient absorption of Dutch iris as influenced by the time of nitrogen supply in sand culture

Abstract

Studies have carried out for the effect of nitrogen nutrient on some flower-bulb crops which are important in the Tottori region.
This paper presents the effect of nitrogen supply and omission at the various stages of growth on the absorption of nutrient, the growth and the yield of Dutch iris by using 5.5±0.2g bulbs of cv.‘Wedg-Wood’in sand culture. Growth period was divided into the following four stages; I, Stage of advance growth (Oct.-Nov.); II, Stage of retardative growth (Dec.-Jan.); III, Stage of later growth (Feb.-Mar.); and IV, Stage of bulb weight increase and maturity (Apr.-mid Jun.). Secondary adventitious roots grew up at the beginning of February. Blooming time was mid-April. Treatments were designed as Fig. 1.
1. Fresh weight, dry weight and dry weight rate of foliage were the highest in nitrogen omission group (C and J) at the end of March when the foliage weight was maximum of the entire growth period of normal plants.
2. Nitrogen supply or omission at stage III dominates the nitrogen level at the end of March when the nitrogen level in the foliage was maximum of the entire growth period of normal plants, in spite of the plants have had nitrogen supply or omission at stage I and II.
3. Nitrogen supply was necessary till the end of stage II for the muximum nitrogen level in the roots at the end of January when nitrogen level of roots was maximum in the entire growth period of normal plants. The nitrogen level of roots increased after stage II if nitrogen supply was not done till stage II but was done at the following stages.
4. Nitrogen omission at stage I and II resulted the decrease of much amount of nitrogen level in the mother bulb. In this case, there was high negative correlation between the nitrogen level and the weight of mother bulb at the end of January. (Correlation coefficient r=-0.979). It was suggested that absorbed nitrogen has close relation with consumption of reserve substance in the mother bulb.
5. Absorbed nitrogen content (Table 12) was little at stage II and paticulary abundant at stage IV. Nitrogen absorption was synergistic with potassium absorption (Table 11).
6. The correlation coefficient of nitrogen concentration among foliage, roots and mother bulb varied largely each other depending upon the stage of growth (Table 4). Its value was especially small between foliage and roots at the end of January (Stage II). It was guessed that absorbed nitrogen content of foliage was so little at stage II that nitrogen removed from top to roots in this stage.
7. The effects of absorbed nitrogen of each stages on the production of the bulbs were shown in Tables 5 and 6, i.e., stage I, non-effective or rather decrease the yield; stage II, the greatest increase in the yield with an ideal quality of either main or lateral bulbs; stage III, decrease the main bulb yield, but tend to increase the lateral bulbs yield. If nitrogen was applied at stage IV, omission in this stage causes maximum yield (J), and stage IV, decrease the main bulb yield, but tend to increase the lateral bulbs yield. (At this period moisture content sensitively increased in connection with the absorbed nitrogen.)
8. The moisture content in the produced bulbs had close relation with the nitrogen concentration (Fig. 5).
9. Relation between the nitrogen concentration in the foliage and the bulbs became higher after stage III (Table 10).
10. From the above investigation it was considered that suitable nitrogen supply for an ideal bulbs production are as follows: 1) Supply it at stages II and III, and omission it at stages I and IV, or 2) supply it at stages I, II and till mid-May of stage IV, and omission it at stage III and after mid-May of stage IV (Table 13).