Effect of the phosphate fertilization during ten years on the content of inorganic macroelements of Satsuma orange leaves, and on the phosphorus content of the soil

Abstract

1. For ten years of 1953-62, the trial of phosphate fertilization was carried on with Satsuma orange trees grown singly in the concrete frames. Each tree was planted in 1952 with uncultivated upland soil derived from the sand stone, and was applied with N 380g, P2O5 230g and K2O 300g each year. In June nearly 10kg of mowed grasses was mulched on the surface of soil. The experiment consisted of the following three plots; phosphate plot-1 (lime superphosphate), phosphate plot-2(fused magnesium phosphate) and non-phosphate plot.2. Throughout all the experimental years, no significant difference was found among the three plots concerning the trunk diameter of a tree, yields and fruit quality as determined by sugar and acid content of the juice as well as the color development of the peel. However, the tree size in the phosphate plot-1 became smallest among the three plots after the eighth year of the trial. The total amount of fibrous roots distributed in the soils of 0 to 30cm depth was also most inferior in the same plot when observed in 1962 This suggests us that the continuous application of lime superphosphate will not be good for the growth of Satsuma orange trees.3. The analysis of foliage made in every month from May to November of 1962 showed no significant difference of the phosphorus content among the three plots. Besides, no certain trend of monthly variation of N, P, K, Ca and Mg content was observed in each plot. However, when examined precisely, the content of those inorganic elements was very variable even in the trees which belonged to the same plot. So, it seems necessary to study more on this subject.4. The soil analysis in 1962 indicated a decrease of soil pH during ten years probably on account of no liming, its value in each plot being less than 4. In the soils of 0 to 30cm depth, the both phosphate plots contained aluminum P, iron P and total amount of P more abundantly than the non-phosphate plot. The vertical distribution of those kinds of pl sphorus showed distinctly the movement of pl sphorus in the soil after its application. Even in the soils of the non-phosphate plot, those kinds of soil phosphorus were also found similarly, which might originated from the mulched materials. However, when observed with NH4Cl soluble P and calcium P, there existed no marked difference among the three plots. Even with aluminum P and iron P, no quantitative difference could be found among the three plots when observed in the soils of more than 30cm depth.5. Thus, so long as the result of this experiment is concerned, no favorable effect of ten years' phosphate fertilization was recognized on the growth, yields and fruit quality of Satsuma orange trees. This fact shows us also that an application of phosphate to Satsuma orange trees which are growing at least in the field, is still open to further study.