Effects of Light Intensity, Nitrogen Concentration and Soil Moisture on the Leaf Color and Fruit Quality of Young Satsuma Mandarin Trees

Abstract

Experiments were carried out to clarify the combined effects of shading, nitrogen supply and watering on leaf color and fruit quality in relation to the changes in chlorophyll, nitrogen and water contents in the leaves of young satsuma mandarin (cv. Miyagawa-wase) trees during the summer and autumn seasons.
1. Water content in the leaves of the wet plot was definitely higher than that of the dry plot, and it was slightly greater for the shaded trees than for the non-shaded ones. Chlorophyll content in the leaves of the shaded trees was greater than that of the non-shaded ones. It was higher for the plot where a high level of nitrogen was supplied than for that plot supplied with a low level of nitrogen, and also higher for trees grown under wet conditions than for those grown under dry conditions. Among those, the chlorophyll content of the shaded trees was distinctly high. Nitrogen content in the leaves of the non-shaded trees was markedly higher in the plot supplied with high level of nitrogen than that supplied with low level. On the contrary, in the leaves of shaded trees the difference was hardly observed. Potassium content in the leaves was slightly higher for the shaded trees.
2. The index of leaf color was definitely higher for shaded trees than for non-shaded trees, and the leaves of shaded trees showed a dark green color. Of the non-shaded trees, the index was higher for the plot supplied with a high level of nitrogen than for the plot supplied with a low level, and also it was higher for wet soil than for dry soil. Leaf color was most affected by light intensity, followed by nitrogen supply and then by soil moisture.
3. Growth of fruits was greater for non-shaded trees than for shaded, greater for the low level of nitrogen than for the high level, and also greater for wet soil than for dry soil. In particular shading brought about an increase in droping of young fruit and distinctly inhibited growth of the fruit. The index of fruit shape was low in the shaded trees, showing a decrease in the ratio of the transverse to longitudinal diameter, and this trend was also shown on fruits grown in the dry soil. The index of fruit color was higher for non-shaded trees than for shaded, and also higher for wet soil than for dry soil. Fruit coloring was markedly delayed for shaded trees. The proportion of rind to fruit was larger for non-shaded trees than for shaded, and also larger for the plot with the high level of nitrogen than for the one with the low level. The soluble solids content in fruit juice was higher for the non-shaded than for the shaded plot and for the plot with the high level of nitrogen than for the one with the low level. The dry soil plot displayed a little higher content than the wet soil plot. The citric acid content was higher for the shaded trees than for the non-shaded, and also for the plot with the high level of nitrogen than for the low level. Such a trend was also observed for the soil moisture variable; that is, the acid content was higher for dry soil than for wet soil.