Utilization of Reserve Nitrogen, Especially, Autumn Nitrogen, by Satsuma Mandarin Trees during the Development of Spring Shoots (I)

Abstract

To clarify the role of nitrogen applied in the previous autumn and stored in the tissues which would be utilized in the development of organs or tissues in the following spring, calcium nitrate containing 11.4g N labelled with 9.64 excess % of ¹⁵N was added to the soil in each pot carrying an eleven-year-old satsuma mandarin tree on Nov. 18, 1974 (as an autumn nitrogen), or Mar. 1, 1975 (as a spring nitrogen).
The results obtained were as follows:
1. The proportion of autumn nitrogen supplied 21 days before harvest to the total nitrogen were 11, 5, 11.3, 2.6 and 3.3% in the leaves on bearing shoots and non-bearing shoots, peel, and pulp, respectively. The results indicated that the amount of autumn nitrogen incorporated into fruits was far lower than that into leaves.
2. The utilization rate of nitrogen supplied in autumn and spring during the period from the time of labelled nitrogen application until the sampling time of mid-June were 41.4 and 25.1%, respectively.
3. Breaking up the tree, the total nitrogen in the newly developed tissues such as spring leaves, spring shoots and young fruits was 28% originated in autumn nitrogen, and 17% in spring nitrogen.
4. The amount of nitrogen in one-year-old leaves decreased through the stage before spring flush and through the period of spring shoot formation was corresponding to about 30% of total nitrogen in spring flush organs.
5. It was concluded that the increase of the ¹⁵N level in one-year-old leaves from Feb. 26 to May 15 resulted from the outflow of nitrogen from stems, roots and others to spring flush organs via one-year-old leaves, because the total nitrogen in one-year-old leaves did not increase. This amount corresponded to about 25% of total nitrogen content in the developing spring flush.