1963 Volume 32 Issue 4 Pages 256-264
1. Potassium fertilization experiment was carried out with 35-year-old Satsuma oranges on trifoliate-orange rootstock over a five year period since 1959. Treatment consisted of two plots: One was K-plot where 300g of K2O (potassium sulphate) was applied every year to each tree, and another was non-K-plot where potash was not given. The trees were growing on diluvial terraced soil, in the 30-40cm depth of which there was clayey layer. The soil surface was mulched every year in early June with 15kg of wheat straw per tree. 6kg of dolomite per tree was applied each year for the two years just before the start of the experiment and only in the first year of it.
2. Even at the end of experiment, no marked differences were found between the two plots concerning the tree appearance and the fruit yields. However, fruit size became smaller, peel color developed somewhat earlier and fruit juice contained more sugar after the third or fourth year, in the non-K-plot as compared in the K-plot.
3. Throughout the five years, no remarkable difference of N, P, K, Ca and Mg contents of the peel and flesh existed between the fruits of the two plots. Leaf analysis in August showed also nosignificant difference of the K content. The average content of exchangeable K in the soil of 0 to 30cm depth was 1.05me per 100g of dry soil at the start of the experiment, while at the end of the experiment it was generally as low as 0.6me in the K-plot, and 0.4me in the non-K-plot.
4. The total amount of potassium taken in a tree for five years was calculated considering the removal by fruiting, leaf fall and pruning, as well as the absorption in the newly developed portions of a tree. On the other hand, the total amount of potassium applied to a tree was also accounted, referring to the potash fertilization, straw mulching and decreased amount of exchangeable K in the soil of 0 to 30cm depth. Thus, in the non-K-plot the total amount of potassium taken exceeded that applied. In this case, 0.2me of non exchangeable K per 100g of dry soil seemed to be utilized by a tree. In the K-plot, the result was reverse; the total amount of potassium taken was less than that applied. However, when the availability of potash applied was estimated to be 30 percent, the both amounts became nearly the same.