Abstract
A soil survey was performed in the Nishiwaga and Ishidoriya areas, which are principal Gentian production areas located in the central and southern part of Iwate Prefecture. The survey traced changes in soil chemistry from 1988. In addition, the survey investigated the physical features of cut flowers of the early-blooming Gentian variety (Mashirii) grown in the soil survey fields in the Ishidoriya area in order to analyze the relationship between the physical features of cut flowers and soil chemistry and soil hardness. Furthermore, we examined how the use of various liming materials improved productivity at three Gentian fields where the percentage of lime saturation in the soil was less than 40%. The survey revealed the following. 1) After the 1990s, in both areas soil pH and the saturation percentage of lime and magnesium fell significantly, and conversely the saturation percentage of potassium rose. As a result, both the ratio of lime to potassium and the ratio of magnesium to potassium decreased. 2) The lower the lime-saturation percentage, or the lower the ratio of lime to potassium and magnesium in soil, the lighter the fresh weight, and the fewer the number of flower steps of cut flowers. A fall in soil pH and a rise in y_1 also had a negative impact on the quality of cut flowers, but these factors were considered secondary because lack of lime in soil was the key factor in the loss of quality. 3) The fresh weight and the number of flower steps of cut flowers fell in proportion to increasing hardness of the soil layer 30-40 cm below the surface. This suggests that the physical properties of soil also directly influence the physical features of cut flowers. 4) Exacerbated leaf tip burn was associated with a decline in the calcium content of cut flowers and a rise in the ratios of phosphorus, potassium and magnesium to calcium, although this was not directly related to the chemistry and hardness of soil. This suggests that the leaf tip burn is related to the degree of mobility of calcium and other nutrients inside the plant body. 5) In an experiment on productivity improvement, we found the following. Regardless of whether the soil was fertilized with calcium carbonate, magnesium-calcium carbonate, or gypsum, the lime-saturation percentage of topsoil rose. In fact, in the 0-5 cm layer, it reached 40%. This caused the calcium content of cut flowers to rise, and improved the fresh weight, the number of flower steps, and the shipment quality standard.
