Effect of soil moisture on the tree growth, yield and fruit quality of Jonathan apples. I

Abstract

1. Tree growth, yield and fruit quality of Jonathan apples cultured in the large size pots were observed under four different conditions of soil moisture, such as“High”80-75%, “Medium”70-70%, “Low”45% and“Very low”30% of water holding capacity. And further observations were made on the morphological charactors of leaves and fruits, apparent photosynthesis, transpiration, and nutrient content of leaves with changing soil moisture.2. Tree growth, especially top growth was markedly inferior with decreasing soil moisture, and yield and fruit size were also proportional to soil moisture.3. Skin color of fruits in the“High”plot was inferior considerably to that of the others, and sugar content of fruits decreased with increasing soil moisture. In the“Very low”plot, fruits had no crispness. From these points, it seems that dessert quality of fruits was most superior in the“Low” plot.4. Daily changes of fruit size and trunkgirth were checked in summer. Both of the fruits and the trunks shrunk during daytime and swelled again at night. The difference of fruit size between day and night became greater with increasing soil moisture, because the number of leaves per fruit increased conspicuously with increasing soil moisture.5. Leaves in the lower soil moisture plot were inferior in area, thickness, cell size and the extent of intercellular spaces, however, they were superior in the thickness of cuticle layer and the density of stomata to those in the higher one. Fruits in the lower soil moisture plot had a thick skin and a firm flesh filled compactly with small cells, which had a thick wall as compared with those in the higher one. There is no significant difference in the number of cells in flesh in each plot.6. In the“Very low”plot, many of the older leaves became yellow and abscised in summer.7. In the“Very low”plot, almost half of the fruits produced corky core owing to boron deficiency, and also, internal breakdown occurred in some fruits after the storage for two months.8. There was no significant difference in the rate of apparent photosynthesis between the“High”and “Medium”plots, but in the lower plots, it decreased apparently with decreasing soil moisture. The rate of transpiration is also proportional to soil moisture.9. As the result of leaf analysis for N, P, K, Ca, Mg and B, the contents of P and B in leaves decreased considerably with decreasing soil moisture.