The effects of time of nitrogen supply on the tree growth, fruit quality and leaf nitrogen of Satsuma orange

Abstract

In order to clarify the effect of time of nitrogen supply on Satsuma orange trees, the gravel culture experiment was carried out for 3 years. Four years old trees were grown under non-bearing conditon in the first year and under bearing condition in the succeeding 2 years.
1. The N supply in culture solution was maintained in three levels such as 40-50, 80-100 and 140 -160 N ppm for 6 months from May to October. Vigorous tree growth and high N content in leaves were found in higher N levels. With increasing supply of N, following changes in fruit quality were observed: (a) Fruit size increased. (b) Rate of flesh weight in a fruit reduced. (c) Break of green rind color delayed. (d) Percentage of soluble solids in juice reduced. (e) Juice acidity increased. (f) Ratio of solids to acid decreased.
2. Trees grown under low N level of 40-50ppm were received high N level of 200-250ppm temporally in each period from May to June (early N raising), from July to August (middle) and from September to October (late). The effect of high N level on tree growth was dominant in the early N raising and not so apparent in the late N raising. The marked tendency was observed in trees that all the flowers were removed in the first year. That is, the early N raising resulted vigorous growth of spring and summer shoots. The growth of summer and autumn shoots was remarkably great in the middle N raising.
3. In the middle N raising, incraese of fruit size and reduction of flesh rate in a fruit were observed. Break of green rind color considerably delayed in late N raising. Juice acidity increased in the order of late, middle and early N raising, while the ratio of solids to acid was reverse. Soluble solids in juice was less in the late N raising, but this tendency was observed in only one year. The raising of N level in culture solution also resulted the increase of N content in spring leaves. The degree of increase was higher in the early N raising than in the middle and late N raising.
4. From the above experimental results, it was indicated that different N status in the period from late April to early August has strong effect on the tree growth of Satsuma orange, and that excess supply of N after late summer may exert unfavorable effect on fruit quality.