Effect of phosphogypsum application on the chemical properties of Andosols, and the growth and Ca uptake of melon seedlings

Allophanic Andosols are widely used as a major material in commercial nursery media for fruit vegetables in Japan because of their remarkable physical properties, such as a high water-holding capacity. In the present study, our objectives were: (1) to examine the effect of phosphogypsum (PG) on the chemical properties of Andosols, (2) to investigate the effect of PG on the growth and Ca uptake of melon seedlings. The effect of PG on chemical properties of Andosols was studied using five Andosols with different inorganic and organic colloidal components. The change in soil pH (H₂O) was dependent on the soil samples; an increase was observed in the case of Kawatabi 3Bw soil; a sharp decrease in Kawatabi A2 soil; and almost no change or a slight decrease in Kameoka A1, A2 and Bw soils. The water-soluble Ca content was examined as an index of Ca availability in Andosols treated with PG. The increment in water-soluble Ca by PG application was depressed by allophane. The effect of PG application to the nursery media prepared from Andosols on growth and Ca uptake of melon (Cucumis melo L.) was examined in 2002. Three different varieties, Amusu, Earl's and Midorishima, were used in this experiment. The pH value of nursery media was stable at 6.4 ± 0.1 regardless of PG application rate. In contrast, electrical conductivity was clearly increased by PG application, and was reached at 1.2 dS m⁻¹ in 4.0 g L⁻¹ application. The application of PG increased water soluble Ca of nursery media from 1.7 to 5.2 cmolc L⁻¹. Both top and root growth of melon seedlings were enhanced regardless of varieties, dry matter weights were maximized at 4 g L⁻¹ PG application. The Ca uptake of melon seedlings was promoted by PG application in all the varieties. It was suggested that the relative root growth rate of melon seedlings was closely related to the Ca uptake of melon seedlings.